multiphase exposure exists, the insulating protective equipment used to
remove multiphase exposure must be rated for the phase-to-phase voltage
at a minimum.\194\ In addition, the preamble to the 1994 Sec.  1910.269
rulemaking noted that ``until the multiphase exposure has actually been
removed, the phase-to-phase voltage remains the maximum use voltage''
(59 FR 4328). After the insulating protective equipment covering the
conductors not being worked on is in place, the rubber insulating
gloves and sleeves need only be rated for the phase-to-ground voltage.
This is current OSHA policy under existing Sec. Sec.  1910.137 and
1910.269 and will continue to be the policy of the Agency under this
final rule.
---------------------------------------------------------------------------

    \194\ It should be noted that the insulating values of two
insulating materials in series are not additive (Exs. 0041, 0532;
269-Ex. 60). At least one layer of insulation must be rated for the
maximum voltage for the exposure.
---------------------------------------------------------------------------

    The electrical component of MAD--general. The differences between
the minimum approach distances under existing Sec.  1910.269 and the
minimum approach distances under this final rule are the result of
changes in the way the Agency is calculating the electrical components
of the minimum approach distances. As described previously, this final
rule adopts the ergonomic components of the minimum approach distances
used in existing Sec.  1910.269. In addition, as explained later in
this section of the preamble, the number of variables (such as
elevation, maximum transient overvoltage, type of exposure, and type of
insulating medium) involved in determining the appropriate minimum
approach distance in any particular set of circumstances makes setting
minimum approach distances exclusively by means of tables unmanageable.
This approach would require one set of tables for each potential set of
variables. Consequently, the final rule requires the employer to
establish an appropriate minimum approach distance based on equations
that OSHA is adopting in Table V-2. The final rule also contains a
table, Table V-5, that specifies alternative minimum approach distances
for work done at elevations not exceeding 900 meters (3,000 feet) for
system voltages of 72.5 kilovolts and less. Finally, Appendix B to
final subpart V contains tables of minimum approach distances, for
varying maximum transient overvoltages for system voltages above 72.5
kilovolts, that employers may use for work done at elevations not
exceeding 900 meters.
    Some rulemaking participants questioned the need for any changes to
the minimum approach distances in existing Sec.  1910.269. (See, for
example, Exs. 0227, 0545.1, 0551.1, 0552.1; Tr2. 71.) For instance, Mr.
Charles Kelly with EEI testified:

    [U]nder Sections 3(8) and 6(b) of the Occupational Safety and
Health Act, as long interpreted by the Supreme Court, OSHA [is]
required to show that the change[s] in the clearance distances are,
as a matter of substantial evidence, reasonably necessary to protect
employees, and that they would reduce or eliminate a significant
risk for employees.
    As several people have stated previous to our testimony, we are
not aware that the existing MAD distances, even though they may have
been mathematically incorrect for decades, have shown to be unsafe
in that they have contributed to accidents or placed employees at
substantial risk of harm. We doubt seriously that a desire to make a
technical mathematical correction is enough to satisfy this
requirement. [Tr2. 71-72]

IBEW also maintained that the minimum approach distances in existing
Sec.  1910.269 are adequate:

    It is important to look at how the use [of] MAD values,
regardless of the origin and year of publication, have protected
workers performing tasks in the vicinity of energized power lines.
The IBEW regularly reviews accidents occurring in the electric
utility industry. We cannot remember a single accident caused by
inadequate MAD values. OSHA 1910.269 MAD values have proven to
protect workers as they were intended to do. The obvious question
then is why change successful MAD values? Based on industry
performance, we do not see why changes are necessary. [Ex. 0551.1]

    As OSHA explained in Section II.D, Significant Risk and Reduction
in Risk, earlier in this preamble, the Agency need not make hazard-
specific or provision-specific risk findings. In any event, the Agency
concludes that the electric-shock hazards faced by employees performing
electric power generation, transmission, and distribution work are
serious and significant and that the changes to the minimum approach-
distance provisions in this final rule are reasonably necessary and
appropriate to reduce a significant risk to employees.
    OSHA finds that employees are being injured by the dielectric
failure of air (that is, sparkover) between them (or a conductive
object they are handling) and conductive objects at a different
potential. It is widely recognized that electric current can arc over
distances and that it is necessary only to come too close to, rather
than contact, an energized object to sustain an electric shock. In
fact, some of the accidents in the record occurred when an employee
brought a conductive object or himself or herself too close to an
energized part and electric current arced to the object or employee
(Exs. 0002,\195\ 0003 \196\).
---------------------------------------------------------------------------

    \195\ See, for example, the five accidents described at http://www.osha.gov/pls/imis/accidentsearch.accident_detail?id=908012&id=170220602&id=564740&id=14496384&id=14418321.
    \196\ See, for example, the three accidents described at http://www.osha.gov/pls/imis/accidentsearch.accident_detail?id=200000453&id=201350485&id=596304.
---------------------------------------------------------------------------

    The Agency does not believe that it is necessary to show that the
specific minimum approach distances in the existing standards have led
to accidents. Instead, it is only necessary to show that the
probability of sparkover at the worksite, given the existing minimum
approach distances, is significant. The sparkover voltage between two
objects at different potentials is recognized as following a normal
distribution (Ex. 0532). The withstand voltage for an air gap between
two objects at different potentials is three standard deviations below
the statistical mean sparkover voltage. This represents approximately a
1 in 1,000 probability that the air gap will fail dielectrically and
spark over.\197\ The withstand distance is the distance between two
objects corresponding to a given withstand voltage. (In other words,
the withstand distance is the shortest distance between two objects
that will spark over at a given voltage approximately one time in
1,000.) Consensus standards have based the electrical component of the
minimum approach distance on the withstand distance corresponding to
the maximum voltage that can occur at the worksite. (See, for example,
Exs. 0076, 0077, 0532, 0533.) When the electrical component of the
minimum approach distance is less than the withstand distance for the
maximum voltage at the worksite, the probability of sparkover is
greater than 1 in 1,000. OSHA, therefore, concludes that employees are
at significant risk of injury whenever the electrical component of the
minimum approach distance is less than the withstand distance for the
maximum voltage that can occur at the worksite. As explained in detail
later in this section of the preamble, several of the minimum approach
distances contained in the existing OSHA standards and in the proposed
rule represent a significant risk of injury under this criterion.
---------------------------------------------------------------------------

    \197\ The probability of sparkover at the withstand voltage is
0.14 percent or 1.4 in 1,000.
---------------------------------------------------------------------------

    The electrical component of MAD--tools and conductive objects in
the air gap. The methodology used to develop the proposed minimum
approach distances, which were based on the 2002 NESC, did not account
for tools in the air gap. As noted in the 2009 reopening notice, the
presence of an insulated tool in the air gap reduces the air gap's
dielectric strength (74 FR 46961). IEEE Std 516-2009 (Ex. 0532)
generally provides two values for the electrical component of the
minimum approach distance: One in air (called MAID \198\) and one with
a tool in the air gap (called MTID \199\). However, that consensus
standard does not provide minimum tool-insulation distances for either:
(1) Any exposures (phase-to-ground or phase-to-phase) at voltages of
72.5 kilovolts or less or (2) phase-to-phase exposures at voltages of
more than 72.5 kilovolts. In the 2009 reopening notice, the Agency
requested comments on whether any of the minimum approach distances in
the final rule should be based on minimum tool-insulation distances
rather than minimum air-insulation distances. A similar question was
raised in the 2008 reopening notice.
---------------------------------------------------------------------------

    \198\ MAID is the minimum air-insulation distance.
    \199\ MTID is the minimum tool-insulation distance.
---------------------------------------------------------------------------

    Scenario 1--exposures at 72.5 kilovolts and less. Rulemaking
participants generally opposed basing minimum approach distances for
voltages of 72.5 kilovolts and less on minimum tool distances. (See,
for example, Exs. 0543.1, 0545.1, 0548.1, 0550.1; Tr2. 88.) For
instance, Pike Electric commented, ``Pike utilizes proper rubber
protective cover-up at . . . voltages [of 72.5 kilovolts and lower].
This technique would eliminate the hazard of employee exposure to
energized lines and equipment, so there is no need to utilize a MAD
approach using tool insulation distances'' (Ex. 0543.1). EEI and
Southern Company argued that only one set of minimum approach distances
is necessary for work on systems operating at voltages of 72.5
kilovolts and less because, based on IEEE Std 516-2009, minimum tool
distances and minimum air distances are the same at those voltages
(Exs. 0545.1, 0548.1). American Electric Power maintained that, for
voltages at or less than 72.5 kilovolts, MAD has not been based on
minimum tool distances in the past, so doing so now could potentially
confuse workers (Ex. 0550.1).
    IEEE Std 516-2009 defines MTID as ``the required undisturbed air
insulation distance that is needed to prevent a tool flashover at the
worksite during a system event that results in the maximum anticipated
TOV'' (Ex. 0532). Although the specified minimum tool distances in IEEE
Std 516-2009 are the same as the corresponding minimum air-insulation
distances for voltages of 72.5 kilovolts and less, the consensus
standard includes the following disclaimer in Section <IP_ADDRESS>: ``The
MTID for ac and dc line-to-line voltages at and below 72.5 kV has not
been determined. Industry practices normally use an MTID that is the
same as or greater than the MAID'' (id.; emphasis added). Thus, IEEE
Std 516-2009 does not indicate that the minimum air- and tool-
insulation distances are the same, nor does it contain tables with
minimum tool-insulation distances for voltages of 72.5 kilovolts and
less. According to IEEE Std 516-2009, electrical testing at higher
voltages indicates that the dielectric strength of an air gap is lower
when an insulating tool is present across the gap or when a conductive
object is present within the gap (id.). OSHA concludes that minimum
approach distances for voltages of 72.5 kilovolts and less should be
conservative enough so that the gap will withstand the electric
potential across it even if a tool bridges the gap or a conductive
object is present within it. As explained later in this section of the
preamble, the final rule specifies minimum approach distances that meet
this criterion. Because the final rule does not adopt separate minimum
approach distances for exposures with and without tools at 72.5
kilovolts and less, the concerns about confusion at these voltages are
unfounded.
    Scenario 2--phase-to-ground exposures at more than 72.5 kilovolts.
Some commenters maintained that the final rule should follow the
practice of

the 2007 NESC and base minimum approach distances for phase-to-ground
exposures at voltages of 72.6 kilovolts and higher on the minimum tool
distance. (See, for example, Exs. 0519, 0521, 0528, 0543.1.) For
instance, Mr. Brian Erga with ESCI commented:

    The MAD for voltages above 72.6 kV should be based on the
minimum tool distance as published in the 2007 NESC. Live line work
is conducted with tools, workers and equipment within the electrical
field of energized lines and equipment[,] and the minimum tool
distance is correct information to be provided to the industry. [Ex.
0521]

    Others suggested that the final rule include two sets of minimum
approach distances for phase-to-ground exposures at voltages exceeding
72.5 kilovolts: One each for work performed with and without tools in
the air gap. (See, for example, Exs. 0545.1, 0548.1, 0575.1; Tr2. 88.)
For instance, Mr. Charles Shaw with Southern Company commented:

    In the proposed rule, OSHA is using minimum air insulation
distances when a line worker is using a tool in the air gap.
Allowing the minimum air insulation distance plus an inadvertent
movement factor to be used as the live-line tool distance is an
incorrect interpretation of the science behind the IEEE method. At a
minimum, the note in the [Subpart] V and [Sec.  1910.269] tables
that states that the referenced distances are for ``live-line tool
distances'' should be removed since they are not.
    However, we recommend that OSHA include two sets of minimum
approach distances for phase to ground work on voltages above 72.5
kV, one for work performed without tools in the air-gap and one for
work performed with tools in the air gap. These distances should be
based on MAID and MTID respectively using the method shown in IEEE
516-2009. [Ex. 0548.1]

    Some commenters suggested that separate sets of air and tool
minimum approach distances might be necessary for phase-to-ground
exposures above 72.5 kilovolts because basing minimum approach
distances solely on minimum tool distances could prevent employees from
performing activities such as climbing and inspection with lines or
equipment energized. (See, for example, Ex. 0549.1, 0573.1; Tr2. 54-
55.)
    EEI submitted evidence that approximately 23 percent of the
insulators installed on transmission systems, and 25 percent of
insulators installed on systems operating at 345 kilovolts and more,
would be too short to accommodate the IEEE standard's minimum approach
distances for tools (Ex. 0575.1). EEI noted that ``there have been no
reported safety events or flashovers with the current insulator
lengths'' \200\ and maintained that using MAD for tools would force
employers to perform routine inspections under deenergized conditions
(id.).
---------------------------------------------------------------------------

    \200\ OSHA is unsure what EEI meant by ``safety event,'' but
assumes that it means accident or near miss.
---------------------------------------------------------------------------

    Minimum approach distances in the 2007 NESC and IEEE Std 516-2009
are generally based on a substantial body of electrical tests run on
air gaps with and without objects in them (Ex. 0532; Tr2. 38).\201\ A
1968 IEEE Committee Report entitled ``Recommendations for Safety in
Live Line Maintenance,'' and a 1973 IEEE Committee Report entitled
``Live-Line Maintenance Methods,'' presented a formula, based on that
testing, for calculating minimum safe distances for energized power
line work (Exs. 0556, 0558). This formula, which is given later in this
section of the preamble, generally provides for a 10-percent increase
in distance to account for the presence of tools across the air gap.
\202\
---------------------------------------------------------------------------

    \201\ As noted later in this section of the preamble, the 2012
NESC distances are identical to corresponding minimum approach
distances in IEEE Std 516-2009.
    \202\ The equation included a factor, C2, equal to
``1.1, composed of 1.06 for live-line tool-to-air withstand distance
ratio plus intangibles'' (Ex. 0556).
---------------------------------------------------------------------------

    IEEE Std 516-2009, in Section <IP_ADDRESS>, recognizes the effect that a
large floating object has on minimum approach distances:

    When a large floating object, not at ground or the conductor
potential, is in the air gap, additional compensation may be needed
to provide for the size and location of the floating object in the
air gap. [Ex. 0532]

IEEE Std 516-2009 accounts for this effect by reducing the withstand
voltage by 10 percent for phase-to-phase exposures on systems operating
at more than 72.5 kilovolts (id.). This approach effectively increases
the minimum approach distance by at least 10 percent. Although IEEE Std
516-2009 applies a floating-object correction factor only to phase-to-
phase exposures, the effect (as noted in the quoted passage) also
applies to phase-to-ground exposures.
    In light of the comments received and the other information in the
record, OSHA concludes that, for phase-to-ground exposures at voltages
of more than 72.5 kilovolts, basing minimum approach distances on
minimum air-insulation distances will not provide sufficient protection
for employees when insulated tools or large conductive objects are in
the air gap. Minimum air-insulation distances are based on testing air
gaps with only air between the electrodes, which does not account
adequately for the presence of tools (Ex. 0532). Therefore, the
provisions adopted in the final rule ensure that minimum air-insulation
distances are applied only when air alone serves as the insulating
medium protecting the worker. For phase-to-ground exposures at voltages
of more than 72.5 kilovolts, Table V-2 requires employers to establish
minimum approach distances that are based on the minimum air-insulation
distance ``for phase-to-ground exposures that the employer can
demonstrate consist only of air across the approach distance.''
Otherwise, the minimum approach distances for these exposures must be
based on the minimum tool-insulation distance.
    Scenario 3--phase-to-phase exposures at more than 72.5 kilovolts.
The third and final scenario the Agency has to address is the presence
of tools or other insulation across a phase-to-phase air gap at
voltages of more than 72.5 kilovolts. Rulemaking participants
maintained that, for voltages of more than 72.5 kilovolts, minimum
approach distances based on minimum tool-insulation distances are
unnecessary because the phase-to-phase air gap is rarely, if ever,
bridged by an insulated tool. (See, for example, Exs. 0545.1, 0548.1,
0550.1, 0551.1; Tr2. 89, 157). For instance, Dr. Randy Horton,
testifying on behalf of EEI, stated:

    [EEI is] unaware of any live-line working scenario situations
above 72.5 kV where the phase-to-phase air gap is bridged by live-
line tool. Most work practices are developed to work on only one
phase at a time per structure, phase to ground. [Tr2. 89]

    Thus, the rulemaking record indicates that, for voltages over 72.5
kilovolts, tools or other objects infrequently, if ever, bridge the gap
between two phases. Considering how rare the practice of spanning the
air gap is, OSHA decided against adopting generally applicable minimum
approach distances that account for tools in the gap for phase-to-phase
exposures at these voltages. However, there is still a need to account
for conductive bodies in the air gap in the limited circumstances in
which they are present, for example, when an employee is moving between
phases in an aerial lift. Therefore, OSHA is including provisions in
the final rule ensuring that the phase-to-phase minimum approach
distance for voltages over 72.5 kilovolts takes account of any objects
that will be present in the air gap. Table V-2 requires the employer to
establish minimum approach distances that are based on the minimum air-
insulation distance as long as ``the employer can demonstrate that no
insulated tool spans

the gap and that no large conductive object is in the gap.''\203\
---------------------------------------------------------------------------

    \203\ Two variables in the equation for minimum approach
distances account for tools or large conductive bodies in the air
gap. The variable C is 0.01 for exposures that the employer can
demonstrate are with air only between the employee and the energized
part if the employee is at ground potential or between the employee
and ground if the employee is at the potential of the energized
part, or 0.011 otherwise. Because it is rare that tools or large
conductive bodies are in the air gap between phases, employers
should not have difficulty making this demonstration for phase-to-
phase exposures. The second variable, the saturation factor, a, is
calculated differently when an insulated tool spans the gap or a
large conductive object is in the gap. For phase-to-phase exposures,
the final rule requires this factor generally to be based on air
only in the gap.
---------------------------------------------------------------------------

    The electrical component of MAD--maximum transient overvoltages.
Existing Sec.  1910.269 and OSHA's 2005 proposal specified maximum
transient overvoltages of 3.0 per unit for voltages up to 362
kilovolts, 2.4 per unit for voltages in the 550-kilovolt range (500 to
550 kilovolts, nominal\204\), and 2.0 per unit for voltages in the 800-
kilovolt range (765 to 800 kilovolts, nominal). These are known as
``industry-accepted values'' of maximum per-unit overvoltage (Ex.
0532). The IEEE committee and the electric utility industry, as
evidenced by the 1993 through 2002 NESC and pre-2003 editions of IEEE
Std 516, believed that these were the highest transient overvoltages
possible. However, the 2007 NESC and IEEE Std 516-2009 recognize that
even higher maximum per-unit transient overvoltages can exist (Exs.
0532, 0533).\205\ Therefore, OSHA requested comments on how, if at all,
the final rule should address the possibility of higher maximum
transient overvoltages.
---------------------------------------------------------------------------

    \204\ Table R-7 and Table R-8 in existing Sec.  1910.269 and
Table V-1 and Table V-2 in existing subpart V list the upper bound
of this voltage range as 552 kilovolts. Table R-6 in existing Sec.
1910.269 lists the upper bound of this voltage range as 550
kilovolts, which is the correct value (Ex. 0532). The final rule
uses 550 kilovolts as the upper bound of this voltage range.
    \205\ Table 441-2 of the 2007 NESC contains minimum approach
distances with maximum transient overvoltages higher than the
industry-accepted values, though the higher values do not apply when
certain conditions are met (Ex. 0533). Section <IP_ADDRESS> of IEEE Std
516-2009 lists the industry-accepted values for maximum transient
overvoltages. However, it also states that, if certain assumptions
about the operation of the system are not met, ``the values listed
in the table may not be valid, and an engineering evaluation should
be performed to determine [the maximum per-unit transient
overvoltage]'' (Ex. 0532).
---------------------------------------------------------------------------

    No rulemaking participants disputed that overvoltages beyond those
accounted for in the proposed standard were possible. Pike Electric
recommended that minimum approach distances be calculated for the
highest possible transient overvoltage (Ex. 0543.1). IBEW suggested
that, if the higher per-unit overvoltage factors are included, specific
instructions for using those higher factors also should be included in
the final rule (Ex. 0551.1; Tr2. 158).
    Electric utility representatives argued that, even though higher
overvoltages are possible, their industry does not widely recognize
that higher overvoltages exist. (See, for example, Exs. 0545.1, 0548.1,
0549.1, 0550.1; Tr2. 90-93.) These rulemaking participants urged OSHA
to base the final standard on the existing industry-accepted values
upon which the proposal was based (id.). For example, Southern Company
stated, ``Although IEEE 516-2003 and IEEE 516-2009 recognize the
possibility of higher surge values, the concept that such surges exist
is not widely accepted in the Industry'' (Ex. 0548.1).
    Dr. Randy Horton, testifying on behalf of EEI, explained this
position as follows:

    Over the years, none of the field-measured over-voltages on
actual operating systems has produced results which exceed the
industry accepted T values (transient overvoltage values). The
documentation of these measurements and of numerous simulations,
encompassing all current transmission operating voltages, and the
results have consistently supported the accepted T values. [Tr2. 90]

    However, Dr. Horton acknowledged that one utility (Bonneville Power
Administration, or BPA) measured overvoltages above 3.0 per unit on one
of its 230-kilovolt circuits (id.). As he noted, BPA tested that
circuit in response to sparkovers on rod gaps placed on the circuit to
protect it from lightning strikes (Tr2. 90-91). Dr. Horton argued that
the measured overvoltages on that circuit were unrealistic because: (1)
The gaps on the circuit flashed over at overvoltages less than 3.0 per
unit during testing; (2) the circuit breaker characteristics and
performance, including pole-closing spans and breaker current, were
unrealistic; and (3) monitoring inaccuracies could have occurred,
leading to measurements that were too high. (See, for example, Exs.
0546.1, 0575.1; Tr2. 90-92.) EEI recommended adhering to the industry-
accepted overvoltage values. However, it noted that, if OSHA elected to
account for the values of maximum per-unit overvoltage from the BPA
measurements, the final rule should just include a footnote similar to
that contained in IEEE Std 516-2009, noting: ``At 242 kV, it is assumed
that automatic instantaneous reclosing is disabled. If not, the values
shown in the table may not be valid, and an engineering evaluation
should be performed to determine `T' '' (Ex. 0545.1; Tr2. 93).
    In its posthearing submission, EEI offered evidence suggesting that
the industry-accepted values of maximum per-unit transient overvoltage
are reasonable (Ex. 0575.1). In this submission, EEI reported results
of testing on several other systems of varying voltages, none of which
exceeded the industry-accepted values. EEI explained:

    The field tests were conducted for energization, reclosings and
with or without shunt reactors. Attempts were made to obtain the
worst possible overvoltages during the field tests. For all cases,
listed above, the expected overvoltages, now, would be lower since
the system has matured and at each bus, the source strength has
increased considerably. . . .
    The IEEE Transactions Papers on the aforementioned information
are provided below. Additional IEEE Transactions Papers references
are attached for switching overvoltage field tests on system voltage
levels of 220 kV, 345 kV and 500 kV by various power companies,
including American Electric Power. All papers show that:
     Without breaker closing resistors, the maximum
switching overvoltages do not exceed 3.0 pu.
     With closing resistor, the maximum switching
overvoltages are near 2.0 pu. And, with control closings the maximum
switching overvoltages do not exceed 1.6 pu.
     Calculated overvoltages are generally much higher than
those by the field measured values . . . [Id.]

    EEI also pointed to an excerpt from International Electrotechnical
Commission (IEC) Standard 61472 as evidence that higher maximum
transient overvoltages are possible, but unlikely (id.). This IEC
excerpt reads as follows:

    B.2.2 Overvoltages under abnormal conditions.
    Among the possible abnormal conditions which can lead to very
high overvoltages, restrikes between the contacts of circuit
breakers during opening is considered, and in particular the
following conditions may be of concern:
    -single or three-phase opening of no load lines;
    -three-phase clearing of line-to-earth fault.
    Such abnormal behaviour may lead to overvoltage amplitudes of
the same order or even higher than those under three-phase
reclosing.
    However, the restrike probability of circuit breakers is
normally low, and is very low for the modern circuit breaker. So the
low probability of these events is not such as to influence the
probability distribution of the family considered (opening or fault
clearing) and thus the relevant Ue2 value. [Id.]

    OSHA understands that the information in the record pertaining to
maximum transient overvoltages applies basically to voltages over 72.5
kilovolts.

IEEE Std 516-2009 does not include separate overvoltage factors for
voltages of 72.5 kilovolts and less (Ex. 0532). For voltages of 72.5
kilovolts and less, IEEE Std 516-2009 relies on a maximum transient
overvoltage of 3.0 per unit and does not recognize the possibility of
higher values. Section 4.8.1d of IEEE Std 516-2009 states, ``Shunt-
connected devices, such as transformers, and reactors will tend to
reduce the trapped charge on the line and, therefore, limit the
overvoltages due to reenergization'' (id.). Such shunt-connected
devices are not only pervasive on systems of 72.5 kilovolts and less,
but are a necessary part of the distribution systems that form the
overwhelmingly predominant portion of these systems (see, for example,
269-Ex. 8-13). Even for the 45- and 69-kilovolt systems that are
sometimes used in transmission circuits, there is no evidence in the
record that maximum transient overvoltages exceed 3.0 per unit.
Consequently, the final rule adheres to a maximum transient overvoltage
of 3.0 per unit for systems with a nominal phase-to-phase voltage of
72.5 kilovolts or less. OSHA calculated the values in Table V-3, which
are the electrical components of the minimum approach distances, using
a maximum transient overvoltage of 3.0 per unit.
    For voltages of more than 72.5 kilovolts, no rulemaking participant
disputed the fact that maximum transient overvoltages based on
engineering calculations can exceed those on which the proposed rule
was based. (See, for example, Exs. 0532, 0575.1.) It also is clear that
maximum transient overvoltages exceeding industry-accepted values are
possible as IEEE Std 516-2009, IEC Standard 61472, and the BPA report
show. (id.) The evidence in the record indicates that most systems do
not, however, exceed the industry-accepted values on which the proposal
was based. (See, for example, Exs. 0545.1, 0549.1, 0575.1; Tr2. 90-93.)
This is the major argument relied on by the commenters that urged OSHA
to base the final rule on industry-accepted values of maximum transient
overvoltage (id.).
    The Agency considered all of the comments and record evidence on
this issue and concluded that the arguments against relying on BPA's
report are not strong enough to justify ignoring it for purposes of
this final rule. First, EEI argued that, in the BPA scenario, during
testing the gaps on the circuit flashed over at overvoltages less than
3.0 per unit (see, for example, Tr2. 91). The magnitude of the
overvoltage during these gap sparkovers is irrelevant. In one series of
tests, the measured overvoltages for two of the tests in which three
gaps arced over were lass than 3.0 per unit. However, measured
overvoltages on at least one phase exceeded 3.0 per unit during 10 of
the tests, including both tests involving sparkovers.\206\ For this
circuit, the testing found overvoltages as high as 3.3 per unit. The
BPA report explained:
---------------------------------------------------------------------------

    \206\ The measured overvoltages on the phases with gap
sparkovers were under 3.0 per unit, but the measured overvoltages on
the phases without gap sparkovers during the same tests exceeded 3.0
per unit. For example, during test 5-25, the overvoltage on the
phase with the gap sparkover was 2.83 per unit, and the overvoltage
on one of the other two phases was 3.30 per unit.

    Rod gap flashovers occurred . . . during the last two tests of
[one test series]. . . . [S]ignificantly higher overvoltages were
measured on [the] phases [with flashovers] during other tests in the
series, but the gaps did not flash over. This demonstrates the
highly statistical nature of . . . gap flashover . . . . [Ex.
---------------------------------------------------------------------------
0575.1]

Thus, that the measured overvoltages for the sparkovers were less than
3.0 per unit has no bearing on whether overvoltages exceeding 3.0 per
unit are possible.

    Second, EEI's argument that the circuit breaker characteristics
were unrealistic are unpersuasive. EEI argued that, because ``[t]he
field tests were conducted with individual phase breaker pole
control,'' the pole-closing span \207\ was exceedingly large and
unrealistic (id.). Although BPA controlled the opening and closing of
the circuit breakers during testing to ``measure overvoltage levels
that can occur on a long transmission line during high speed
reclosing,'' there is no indication in the BPA report that it varied
the closing spans for the individual poles on the circuit breakers
(id.). The report states:
---------------------------------------------------------------------------

    \207\ The circuit-breaker pole-closing span is the maximum
closing time difference between the phases.

    [The relevant test series] involved three-phase reclosing into
trapped charge on the Big Eddy-Chemewa 230-kV line. Breaker opening
was controlled and synchronized to generate the same polarity and
magnitude trapped charge on each phase for each test shot. Testing
began by switching from the Big Eddy end, varying the closing time
of the breaker uniformly over a complete 60 Hz cycle by increments
of 18 electrical degrees (\1/20\ cycle). After these 20 tests, 4
additional tests were performed in an attempt to generate a maximum
possible overvoltage. This same procedure was then repeated from the
---------------------------------------------------------------------------
Chemewa end of the line. [Id.]

Thus, it appears that BPA took measures to synchronize the switching of
the poles in each circuit breaker. The report mentioned that the
circuit breaker at the Big Eddy end was ``constructed with each phase
in its own tank'' (id.). The pole-closing span for this circuit breaker
was 3.7 milliseconds. The circuit breaker at Chemewa was ``constructed
with all three contacts in a single tank'' (id.). The pole-closing span
for this circuit breaker was 0.24 milliseconds, significantly shorter
than the pole-closing span for the Big Eddy circuit breaker. Measured
overvoltages exceeded 3.0 per unit during tests with switching
performed at both locations. Thus, OSHA concludes that pole-closing
spans did not contribute to measured overvoltages exceeding 3.0 per
unit during BPA testing. BPA did not indicate that the pole-closing
span for either circuit breaker was unusual, and EEI did not submit any
evidence that would demonstrate that circuit breakers of any type of
construction generally have shorter pole-closing spans. Consequently,
the Agency concludes that, even if the pole-closing span did contribute
to the measured overvoltages in BPA's testing, circuit breakers in
other installations could have similarly long pole-closing spans with
correspondingly high maximum transient overvoltages.

    Furthermore, although the difference in time taken for each pole to
close might affect the phase-to-phase overvoltage, that value was not
measured during the BPA tests. Because pole-closing spans only affect
the offset between phases and should have no substantial effect on the
behavior of the transient voltage on a single phase, long pole-closing
spans should have little effect on phase-to-ground overvoltages (that
is, the overvoltage on a single phase). As explained later, the report
clearly states that the main cause of the unexpectedly high maximum
transient overvoltages was ``prestrike.'' OSHA, therefore, concludes
that prestrike, not pole-closing spans, were the primary cause of the
high maximum transient overvoltages.
    EEI, through Dr. Horton, also expressed concern about the
performance of the circuit breakers in the BPA report, because the
circuit breaker current showed evidence of prestrikes (Tr2. 91).
Restrike and prestrike may occur during the opening of circuit
breakers. The current and voltage across the contacts of a circuit
breaker vary with time. When the contacts are closed, the voltage
across them is very close to zero, and the current oscillates at 60
cycles per second. When the contacts are open, the voltage oscillates,
and the current is zero. As the contacts of a circuit breaker open or
close, current can arc across them. When the current drops to zero,

the arcing stops. However, if the voltage across the contacts from
reflected traveling waves exceeds the dielectric strength of the gap
between the contacts, arcing can recur. Arcing that occurs after the
initial arc is extinguished as the circuit breaker is opening is called
``restrike.'' Arcing that occurs as the contacts close, but before they
are touching, is called ``prestrike.''
    Whether a circuit breaker is subject to restrikes or prestrikes is
dependent on the design of the circuit breaker, maintenance of the
circuit breaker, and the characteristics of the circuit to which the
breaker is connected. Prestrikes and restrikes can lead to high
transient overvoltages that can damage equipment. Therefore,
manufacturers design circuit breakers to resist restrikes and
prestrikes. However, the probability that these events will occur can
be affected by maintenance and circuit design. Poor circuit breaker
maintenance can lead to longer pole-opening times and can increase the
probability that prestrike or restrike will occur. Similarly, circuit
designs can shorten the time in which traveling waves reach the breaker
contacts, which also can increase the probability of prestrikes or
restrikes.
    The circuit breakers that were the subject of BPA's testing
exhibited prestrikes during testing (Ex. 0575.1). Commenting on this,
Dr. Horton stated:

    The line breaker performance appears suspicious. The breaker
current shows pre-strikes with abrupt interruptions and subsequent
re-ignitions [Tr2. 91]

However, the BPA report explained why the prestrikes occurred:

    During Test Series V, it was found that the sending end can
experience significant overvoltages that were previously assumed to
occur only out on the line or at the receiving end. During breaker
prestrike, a current wave (initiated by arcing across the contacts)
travels down the line to the receiving (open) end where it is
reflected. As the reflected wave travels back toward the sending end
of the line, it reduces the current to near zero along the line.
When the reflected current wave reaches the sending end of the line,
it creates a current zero and allows the prestrike arc between the
breaker contacts to extinguish, isolating the line voltage from the
bus voltage. After the arc extinguishes, the line voltage often
increases due to traveling voltage waves that continue to be
reflected from the receiving end. The voltage across the breaker
then builds up until another prestrike occurs. The next prestrike
occurs at a lower breaker cross voltage because the breaker contacts
are closer together. In Test Series V, the majority of breaker
closings resulted in only a single prestrike. However, in a few
tests, up to four prestrikes occurred on one phase during a single
closing operation. [Ex. 0575.1]

BPA found this information useful, explaining:

    This field test has also provided a considerable amount of data
on 230-kV SF6 breaker prestrikes. Typical characteristics
of the dielectric strength across the breaker contacts have now been
developed and can be used for statistical switching surge studies.
Additional information has also been obtained about another property
of 230-kV SF6 breakers--where the prestrike arc is
extinguished by the traveling current wave during line switching.
The test results show that when the prestrike arc extinguishes, the
voltage at the sending end of a line reaches values that are much
higher than were previously expected. [Id.]

    In light of this explanation in the BPA report itself, OSHA
concludes that the existence of prestrikes does not invalidate the BPA
report's findings. In fact, the prestrikes were the cause of the
unexpectedly high maximum transient overvoltages. The Agency
anticipates that any workplace where prestrikes occur during switching
operations, particularly during reclosing, can experience similarly
high maximum transient overvoltages.
    EEI's third and final concern about the BPA report was that
``inaccuracies in the monitoring system and in the waveform calibration
[could have resulted] in unrealistic over-voltage readings'' (Tr2. 91).
However, there is no evidence in either BPA's report or in OSHA's
rulemaking record that such inaccuracies existed during the BPA tests.
    For the foregoing reasons, OSHA does not accept EEI's criticism of
the BPA report and finds that it provides substantial evidence of the
existence of maximum transient overvoltages higher than industry-
accepted values.
    IEEE Std 516-2009 does not account for the possibility of circuit-
breaker restrikes. In Section <IP_ADDRESS>, IEEE Std 516-2009 explains its
approach for addressing maximum transient overvoltages, as follows:

    (a) At all voltage levels, it is assumed that circuit breakers
are being used to switch the subject line while live work is being
performed. This further assumes that the restrike probability of a
circuit breaker is low and consequently extremely low while a worker
is near the MAD and that it can, therefore, be ignored in the
calculation of T. If devices other than circuit breakers are being
utilized to switch the subject line while live work is being
performed, then the values listed in the table may not be valid, and
an engineering evaluation should be performed to determine T.
    (b) At 242 kV, it is assumed that automatic instantaneous
reclosing is disabled. If not, the values shown in the table may not
be valid, and an engineering evaluation should be performed to
determine T. [Ex. 0532]

    OSHA has serious concerns about the validity of the assumptions on
which this IEEE standard relies to support its general application of
the industry-accepted values for maximum transient overvoltages.
Indeed, with all the caveats in these paragraphs of the IEEE standard,
it is clear that even the drafters of that standard did not believe in
the universal applicability of its key assumptions. IEEE Std 516-2009
recognizes that switching can be performed using devices other than
circuit breakers and recommends an engineering analysis if such devices
are used. The Agency concludes that the prestrike experience reported
by BPA demonstrates that the occurrence of prestrikes is likely to be a
consequence of the design of the circuit breaker and the circuit
involved, rather than a low probability event for each circuit breaker
on every circuit. The BPA report explained that the occurrence of
prestrikes was influenced heavily by the magnitude of the trapped
charge on the line and the speed of the initial and repeated reflected
traveling wavefronts (Ex. 0575.1). Because the cause of prestrikes and
restrikes are the same, the Agency believes that restrikes are
similarly influenced. In this regard, prestrikes and restrikes are the
same type of event, with prestrikes occurring during circuit breaker
opening and restrikes occurring during circuit breaker closing. Thus,
although the overall probability that circuit breakers in general will
restrike or prestrike may be low, OSHA concludes that the probability
that a particular circuit breaker will restrike or prestrike may be
high enough that it cannot be ignored.
    Additionally, neither the IEEE standard nor Dr. Horton explained
why the IEEE committee chose to base maximum transient overvoltage on
the 2-percent statistical switching overvoltage expected at the
worksite, which is a probability-based assessment, while ignoring the
probability of restrikes (Ex. 0532).\208\ After all, if the probability
is low enough, then the potential for restrikes will not have a
significant effect on the 2-percent statistical switching overvoltage.
On the other hand, if it is high enough, then the 2-percent statistical
switching overvoltage will increase.
---------------------------------------------------------------------------

    \208\ Section <IP_ADDRESS> of IEEE Std 516-2009 reads, in part, ``The
line-to-ground maximum anticipated per-unit TOV (T) for live work is
defined as the ratio of the 2% statistical switching overvoltage
expected at the worksite to the nominal peak line-to-ground voltage
of the system.''
---------------------------------------------------------------------------

    In response to EEI's recommendation to permit employers to use
industry-accepted values in accordance with IEEE Std 516-2009, OSHA
concludes

that this alternative does not adequately account for higher maximum
transient overvoltages. Section <IP_ADDRESS>b of IEEE Std 516-2009 indicates
that the industry-accepted values are valid only when reclosing is
blocked at 242 kilovolts (Ex 0532). Although the BPA testing was
performed on a 242-kilovolt circuit, there is no evidence in the record
indicating that maximum transient overvoltages higher than the
industry-accepted values are limited only to this voltage. In addition,
---------------------------------------------------------------------------
the IEEE standard, in Section E.2 of Appendix E, notes:

    If restriking of the switching device is included [in the
determination of maximum transient overvoltage], then the resulting
overvoltages are essentially the same as those of reclosing into a
trapped charge. The only difference is the probability of
occurrence. [Id.]

Consequently, even if reclosing is blocked, the maximum transient
overvoltage may still exceed industry-accepted values.

    OSHA concludes that it is not in the interest of worker safety to
adopt minimum approach-distance provisions based on the conditions
expected to be present in the workplaces of most, but not all,
employers covered by this final rule. Basing the rule on industry-
accepted values of maximum transient overvoltage, as EEI and other
commenters recommended, would result in some employees not receiving
adequate protection. In the extreme case, in which the maximum
transient overvoltage is 3.5 instead of the industry-accepted value of
3.0, the electrical component of the minimum approach distance would
sparkover nearly 50 percent of the time, rather than 0.1 percent of the
time, at the maximum overvoltage. OSHA designed the minimum approach-
distance provisions in this final rule to protect employees from the
conditions that are present in their specific workplaces. Under the
final rule, employers must select and adhere to minimum approach
distances based on the maximum transient overvoltages present at their
workplaces or base minimum approach distances on the highest maximum
transient overvoltage.
    EEI and other commenters noted that IEEE recently established a
working group to examine maximum transient overvoltages and recommended
that OSHA rely on industry-accepted values for these overvoltages until
the committee reports its findings. (See, for example, Exs. 0545.1,
0548.1; Tr2. 92-93.) For instance, Dr. Horton, testifying on behalf of
EEI, stated:

    In order to address the possibility of higher surge values, the
General Systems Subcommittee of the IEEE Transmission and
Distribution Committee has recently created a working group entitled
``Field Measured Over-Voltages and Their Analysis'' to determine if
higher surge values actually exist, and if so, what is their upper
limits. This working group is chaired by myself (Dr. Randy Horton of
Southern Company) and is co-chaired by Dr. Albert Keri of American
Electric Power. Numerous experts and utilities from around the world
are involved in this work, and initial findings of the working group
will likely be available in the next 3 to 4 years. Until such time,
it is recommended that the industry accepted values (in other words
T equal to 3 per unit, 2.4 per unit, and 2.0 per unit, corresponding
to 362 kV and below, 363 kV to 550 kV, and 551 kV to 800 kV
respectively) be used as the maximum per unit transient over-voltage
values. [Tr2. 92-93]

    The Agency concludes that it is not necessary to wait for the
findings of the new IEEE working group before proceeding with new
minimum approach-distance provisions. The Agency does not believe that
it is necessary to delay action on minimum approach distances until the
IEEE or any other standard-setting organization produces additional
information on this subject. OSHA believes that there is sufficient
information in the record, described earlier in this discussion of
maximum transient overvoltages, to form the basis of a final rule on
minimum approach distances that accurately accounts for the presence,
magnitude, and effect of maximum transient overvoltages. The Agency
concludes that BPA's experience proves the existence of maximum
transient overvoltages higher than the industry-accepted values; and,
although the consensus standards do not fully account for potentially
higher values in their minimum approach distances, the 2007 NESC and
the 2003 and 2009 editions of IEEE Std 516 recognize the existence of
such overvoltages (Exs. 0041, 0532, 0533, 0575.1). Consequently, for
purposes of Table V-6, and Table 7 through Table 14 in Appendix B to
subpart V, the Agency is adopting maximum per-unit transient
overvoltages of 3.5 for systems operating at 72.6 to 420 kilovolts, 3.0
for systems operating at 420.1 to 550.0 kilovolts, and 2.5 for systems
operating at 550.1 to 800 kilovolts. These values are the same values
as the highest maximum transient overvoltages recognized in the 2007
NESC and IEEE Std 516-2009 (Exs. 0532, 0533).
    The electrical component of MAD--calculation methods for voltages
up to 72.5 kilovolts. OSHA based the minimum approach distances in
existing Sec.  1910.269 for voltages up to 72.5 kilovolts on ANSI/IEEE
Std 4 (59 FR 4383). Existing Sec.  1910.269 specifies ``avoid contact''
as the minimum approach distance for voltages between 51 and 1,000
volts. To make the revised standards consistent with the 2002 NESC,
OSHA proposed in the 2005 proposal to adopt minimum approach distances
of 0.31 meters (1 foot) for voltages between 301 volts and 750 volts
and 0.65 meters (2 feet, 2 inches) for voltages between 751 volts and
15 kilovolts. The proposal specified ``avoid contact'' as the minimum
approach distance for 51 to 300 volts.
    Two commenters objected to the requirement for employees to ``avoid
contact'' with lines energized at 50 to 300 volts (Exs. 0169, 0171).
Mr. Brooke Stauffer with NECA commented, ``The `avoid contact'
requirement on lines energized at 50 to 300 volts is infeasible for
line construction and maintenance, because linemen must contact these
energized lines on a routine basis while doing their work'' (Ex. 0171).
Quanta Services similarly asserted, ``The `avoid contact' requirement
on lines energized at 50 to 300 volts presents a problem because
linemen will contact those lines on a routine basis while doing their
work'' (Ex. 0169).

    These comments do not indicate how employees are contacting
electric conductors and other circuit parts energized up to 300
volts.\209\ It is well recognized that these voltages are potentially
lethal. Exhibit 0002 alone describes at least 25 accidents in which
employees were killed because of contact with circuit parts energized
at 120 volts to ground.\210\ OSHA believes that, in the past, the
practice was for power line workers to use leather gloves rather than
rubber insulating gloves to handle these voltages, and it is possible
that these commenters are recommending that the standard permit that
practice. However, leather gloves do not insulate workers from
energized parts (Ex. 0002).\211\ Perspiration can saturate these gloves
during use, making them conductive. One of the accidents in the record
involved an employee handling a 120-volt conductor with leather gloves
(id.). Therefore, the final rule requires employees to avoid contact
with circuit parts energized at 50 to 300 volts.\212\ If it is
necessary for employees to handle exposed parts energized at these
voltages, they must do so in accordance with final Sec.
1926.960(c)(1)(iii)(A), (c)(1)(iii)(B), or (c)(1)(iii)(C); and any
insulating equipment used must meet the electrical protective equipment
requirements in final Sec.  1926.97.
---------------------------------------------------------------------------

    \209\ In the proposed rule, the lowest voltage in the avoid-
contact range was 51 volts, not 50 volts as indicated by the two
commenters.
    \210\ See the 25 accidents described at http://www.osha.gov/pls/imis/accidentsearch.accident_detail?id=660118&id=817114&id=14307003&id=14311666&id=982645&id=14327944&id=894584&id=14351076&id=14525430&id=201360062&id=601468&id=14251771&id=14251987&id=14257034&id=14371751&id=14523591&id=14383376&id=695437&id=514547&id=170080238&id=14400782&id=14219851&id=764365&id=14505366&id=778332.
    \211\ See, for example, the two accidents described at http://www.osha.gov/pls/imis/accidentsearch.accident_detail?id=14371751&id=660118.
    \212\ OSHA proposed 51 volts as the low end of the avoid-contact
range. The final rule adopts 50 volts as the low end for consistency
with Table R-6 in existing Sec.  1910.269 and IEEE Std 516-2009.
---------------------------------------------------------------------------

    There were few comments on the minimum approach distances proposed
in 2005 for voltages of 301 volts to 72.5 kilovolts. Some commenters
objected to the small changes in minimum approach distances from
existing Sec.  1910.269 that were specified in the 2005 proposal. (See,
for example, Exs. 0227, 0543.1.) EEI maintained that the safety benefit
of slight changes was outweighed by the practical implications of
implementing revised minimum approach distances:

    For the sake of an inch or two, OSHA ought not to change the
existing MAD tables. Such changes could require revising every
safety rule book and training curriculum in the industry, including
among line contractors, as well as related retraining of line
workers. The established clearance distances are well-known to
employees in the transmission and distribution industry, and
changing them for the sake of an additional inch or two can only
lead to confusion, with no significant safety benefit. As a
practical matter, it is not clear that such a small change will make
a significant difference in the safety of line workers. [Ex. 0227]

    OSHA understands that changing minimum approach distances, even
slightly, may require employers to adjust their safety rules and
training. The Agency accounted for the cost of changing these safety
rules and training because of differences between existing Sec.
1910.269 and the final rule, including the revised minimum approach
distances (see Section VI, Final Economic Analysis and Regulatory
Flexibility Analysis, later in this preamble).
    Ignoring evidence that small increases in the electrical component
of the minimum approach distances are necessary would result in
shrinking the ergonomic component of the minimum approach distance,
thereby making work less safe for employees than if the ergonomic
component remained constant. As explained previously, OSHA designed
this final rule to ensure that the ergonomic component of the minimum
approach distance remains at least 0.31 meters (1 foot) or 0.61 meters
(2 feet), depending on the voltage.
    OSHA proposed a minimum approach distance of 0.31 meters (1 foot)
for voltages of 301 through 750 volts. Although there were no comments
on this minimum approach distance, the Agency is adopting a slightly
larger distance. In Section <IP_ADDRESS>, IEEE Std 516-2009 explained its
approach to setting the electrical component of the minimum approach
distance, as follows:

    For ac and dc line-to-line and line-to-ground work between 300 V
and 5.0 kV, sufficient test data are not available to calculate the
MAID,\[213]\ which is less than 2 cm or 0.07 ft. For this voltage
range, it is assumed that MAID is 0.02 m or 0.07 ft . . . . [Ex.
0532]
---------------------------------------------------------------------------

    \213\ IEEE Std 516-2009 assumes that MAID and MTID have the same
value in this voltage range. Using this approach, the electrical
component of the minimum approach distance would be the same in air
or along the length of an insulated tool.

Using this approach for voltages of 301 to 750 volts, OSHA added the
0.31-meter (1-foot) ergonomic component of the minimum approach
distance to the 0.02-meter (0.07-foot) electrical component, for a
total minimum approach distance of 0.33 meters (1.07 feet) in the final
rule.
    As noted earlier, OSHA based the methodology for calculating the
electrical component of the minimum approach distance for voltages from
751 volts to 72.5 kilovolts in the 2005 proposal on IEEE Std 4. Table 6
lists the critical sparkover distances from that standard as listed in
IEEE Std 516-2009.

             Table 6--Sparkover Distance for Rod-to-Rod Gap
------------------------------------------------------------------------
                                                       Gap spacing from
        60 Hz Rod-to-rod sparkover (kV peak)            IEEE Std 4-1995
                                                             (cm)
------------------------------------------------------------------------
25..................................................                   2
36..................................................                   3
46..................................................                   4
53..................................................                   5
60..................................................                   6
70..................................................                   8
79..................................................                  10
86..................................................                  12
95..................................................                  14
104.................................................                  16
112.................................................                  18
120.................................................                  20
143.................................................                  25
167.................................................                  30
192.................................................                  35
218.................................................                  40
243.................................................                  45
270.................................................                  50
322.................................................                  60
------------------------------------------------------------------------
Source: IEEE Std 516-2009 (Ex. 0532).

    To use the table to determine the electrical component of the
minimum approach distance, the employer would determine the peak phase-
to-ground transient overvoltage and select a gap from the table that
corresponds to that voltage as a withstand voltage rather than a
critical sparkover voltage. For voltages between 5 and 72.5 kilovolts,
the process for using Table 6 to calculate the electrical component of
the minimum approach distance, starting with the phase-to-phase system
voltage, was described generally as follows in Draft 9 of the 2009
revision to IEEE Std 516 (Ex. 0524):
    1. Divide the phase-to-phase voltage by the square root of 3 to
convert it to a phase-to-ground voltage.
    2. Multiply the phase-to-ground voltage by the square root of 2 to
convert the rms value of the voltage to the peak phase-to-ground
voltage.
    3. Multiply the peak phase-to-ground voltage by the maximum per-
unit transient overvoltage, which, for this voltage range, is 3.0, as
discussed earlier in this section of the preamble. This is the maximum
phase-to-ground transient overvoltage, which corresponds to the
withstand voltage for the relevant exposure.\214\
---------------------------------------------------------------------------

    \214\ The withstand voltage is the voltage at which sparkover is
not likely to occur across a specified distance. It is the voltage
taken at the 3[sigma] point below the sparkover voltage, assuming
that the sparkover curve follows a normal distribution.

---------------------------------------------------------------------------

    4. Divide the maximum phase-to-ground transient overvoltage by 0.85
to determine the corresponding critical sparkover voltage. (The
critical sparkover voltage is 3 standard deviations (or 15 percent)
greater than the withstand voltage.)
    5. Determine the electrical component of the minimum approach
distance from the table through interpolation.\215\
---------------------------------------------------------------------------

    \215\ Draft 9 of IEEE Std 516 used curve-fitted equations rather
than interpolation to determine the distance. The two methods result
in nearly equivalent distances.
---------------------------------------------------------------------------

    These steps are illustrated in Table 7.

                      Table 7--Calculating the Electrical Component of MAD 751 V to 72.5 kV
----------------------------------------------------------------------------------------------------------------
                                                   Maximum system phase-to-phase voltage (kV)
             Step             ----------------------------------------------------------------------------------
                                        15                   36                   46                 72.5
----------------------------------------------------------------------------------------------------------------
1. Divide by [radic]3........  8.7................  20.8...............  26.6...............  41.9
2. Multiply by [radic]2......  12.2...............  29.4...............  37.6...............  59.2
3. Multiply by 3.0...........  36.7...............  88.2...............  112.7..............  177.6
4. Divide by 0.85............  43.2...............  103.7..............  132.6..............  208.9
5. Interpolate from Table 6..  3+(7.2/10)*1.......  14+(8.7/9)*2.......  20+(12.6/23)*5.....  35+(16.9/26)*5
Electrical component of MAD    3.72...............  15.93..............  22.74..............  38.25
 (cm).
----------------------------------------------------------------------------------------------------------------

    This method is consistent with the method OSHA used to develop the
minimum approach distances for voltages of 751 volts to 72.5 kilovolts
in the 2005 proposal. Although OSHA received no comments on this
approach, the methodology contained in final IEEE Std 516-2009 added
one additional step (Ex. 0532). The distances in IEEE Std 4-1995 result
from 60-Hz impulse rod-to-rod tests. The extra step in IEEE Std 516-
2009 divides the phase-to-ground maximum transient overvoltage by 1.3
to account for the difference between the strength of an air gap under
60-hertz voltages and the strength under transient voltages.\216\ The
IEEE committee relied on two papers that are not in the current OSHA
record to develop the 1.3 factor.\217\
---------------------------------------------------------------------------

    \216\ A 60-hertz voltage cycles through its maximum, or peak,
voltage 60 times each second, and the value of the voltage forms a
sine wave. A transient overvoltage does not cycle, but generally
increases quickly as a single pulse.
    \217\ These documents are (1) CIGR[Eacute]/SC 33, ``Phase-to-
Phase Insulation Coordination,'' ELECTRA, no. 64, 1979; and (2)
Esmeraldo, P. C. V., and Fonseca, C. S., ``Evaluation of the Phase-
to-Phase Overvoltage Characteristics due to Switching Surges for
Application on Risk of Failure Statistical Methods in Non-
Conventional Power Design,'' Paper 34.01, 6th ISH, New Orleans,
1989.
---------------------------------------------------------------------------

    OSHA is not adopting this part of the method that IEEE Std 516-2009
uses to calculate the electrical components of the minimum approach
distances for voltages from 751 volts to 72.5 kilovolts. First, the
Agency does not believe that there is sufficient information in this
record to support the 1.3 conversion factor, which was not used in
earlier editions of IEEE Std 516 and was not used in any version of the
NESC through the 2007 edition.\218\ Second, although OSHA raised this
issue in its September 2009 reopening notice, no commenters voiced
support for such a change in the OSHA rule. Finally, as previously
noted, for voltages of 72.5 kilovolts and lower, IEEE Std 516-2009
assumes that the electrical component of the minimum approach distance
is the same with tools in the air gap as it is for air alone. The
dielectric strength of an air gap is less with a tool in the gap than
it is when the gap is air, however (see, for example, Exs. 0556, 0558).
Thus, an increase in the electrical component of the minimum approach
distance is necessary to account for tools. OSHA does not believe that
a 60-hertz-to-transient conversion factor (which reduces MAD values) is
appropriate when no counterbalancing distance is added to account for
tools in the air gap. For these reasons, the Agency is adopting the
proposed methodology for determining the electrical component of the
minimum approach distance for voltages of 751 volts to 72.5 kilovolts.
As noted earlier, OSHA also is adopting the proposed ergonomic
component for this voltage range. Thus, the final rule incorporates
minimum approach distances for these voltages generally as proposed.
However, Table V-5 in the final rule breaks the proposed voltage range
of 751 volts to 15 kilovolts into two ranges--751 to 5,000 volts and
5.1 kilovolts to 15 kilovolts.
---------------------------------------------------------------------------

    \218\ The 2012 NESC adopts minimum approach distances from IEEE
Std 516-2009, which, as noted, uses the 1.3 conversion factor.
---------------------------------------------------------------------------

    For the reasons described earlier under the discussion of the 301-
to 750-volt range, IEEE Std 516-2009 sets the electrical component of
the minimum approach distance at 0.02 meters for voltages of 301 to
5,000 volts.\219\ As can be seen from Table 6, this is the sparkover
distance for the smallest transient overvoltage listed in the table.
There is no evidence in the record that lower voltages will produce
larger sparkover distances. Consequently, there is no reason to believe
that the electrical component of the minimum approach distance will be
greater for voltages of 5,000 volts or less. In addition, rounding the
electrical component of the minimum approach distance to the nearest 25
millimeters (1.0 inch) results in a minimum distance of 25 millimeters.
As explained earlier, OSHA concludes that this value is reasonable and,
therefore, adopts 0.02 meter (1 inch) as the electrical component of
the minimum approach distance for this voltage range.
---------------------------------------------------------------------------

    \219\ The electrical component of MAD is 0.02 meters (1 inch)
for all voltages from 301 volts to 5.0 kilovolts. However, the
ergonomic component of MAD is 0.305 meters (1 foot) for voltages up
to 750 volts and 0.61 meters for higher voltages as explained
earlier.
---------------------------------------------------------------------------

    The electrical component of MAD--calculation methods for voltages
over 72.5 kilovolts. As noted earlier, OSHA based its proposed minimum
approach distances on criteria adopted by NESC Subcommittee 8 in 1993.
The NESC based its criteria, at least in part, on IEEE Std 516-1987. As
noted in Appendix B to proposed Subpart V, OSHA used the following
equation, which was based on IEEE Std 516-1987, to calculate the
electrical component of the minimum approach distance for voltages of
72.6 to 800 kilovolts in the proposed rule:

[GRAPHIC] [TIFF OMITTED] TR11AP14.003

Where:

D = Electrical component of the minimum approach distance in air in
feet
C = 0.01 to account for correction factors associated with the
variation of gap sparkover with voltage
a = A factor relating to the saturation of air at voltages \220\ of
345 kilovolts or higher
---------------------------------------------------------------------------

    \220\ This voltage is the maximum transient overvoltage.
---------------------------------------------------------------------------

pu = Maximum anticipated transient overvoltage, in per unit (p.u.)
Vmax = Maximum rms system line-to-ground voltage in kilovolts--this
value is the true maximum, that is, the normal highest voltage for
the range (for example, 10 percent above the nominal voltage).

    Phase-to-ground exposures. For phase-to-ground exposures,
rulemaking participants agreed that the proposal's methodology for
calculating minimum approach distances was generally appropriate unless
insulated tools were present across the air gap. (See, for example,
Exs. 0521, 0527.1, 0529, 0575.1.) For instance, EEI commented, ``The
existing MAID formula, based on rod-to-rod gap data, is acceptable for
all line-to-ground applications [through 800 kilovolts with a maximum
per-unit overvoltage of 2.44 per unit]'' (Ex. 0527.1).
    Therefore, the final rule requires employers to set minimum
approach distances based on Equation 1 for phase-to-ground exposures at
voltages of more than 72.5 kilovolts. Here is the full equation
contained in Table V-2, with the part that is equivalent to Equation 1
highlighted:

MAD = 0.3048(C + a)VL-GTA + M

The equation in Table V-2 is identical to Equation 1 except that it:
(1) Incorporates an altitude correction factor, A, as described later
in this section of the preamble, (2) converts the result to meters
through multiplication by 0.3048, and (3) adds the ergonomic component
of MAD, M to the electrical component of MAD given in Equation 1. In
addition, the table uses slightly different variable designations: VL-G
for Vmax and T for pu.
    As explained earlier in this section of the preamble, OSHA decided
to specify minimum approach distances that account for the presence of
tools in the air gap unless the employer can demonstrate that there is
only air between the employee and the energized part or between the
employee and ground, as appropriate. (The air gap would be between the
employee and the energized part if the employee is at ground potential,
or at the potential of another energized part, or between the employee
and ground if the employee is at the potential of the energized part
during live-line barehand work.) Consequently, in the equation for
phase-to-phase system voltages of more than 72.5 kilovolts in Table V-
2, the term C must be adjusted depending on whether the minimum tool-
insulation distance or the minimum air-insulation distance will be used
as the electrical component of the minimum approach distance. According
to IEEE Std 516-2009, C is 0.01 for the minimum air-insulation distance
and 0.011 for the minimum tool-insulation distance. OSHA concludes that
these values of C are reasonable because they are supported by
scientific evidence (Exs. 0556, 0558) and because there were no other
values recommended in the rulemaking record for the proposal.
Therefore, these values are incorporated in Table V-2 in the final
rule.
    There is one other minor issue that requires resolution before the
electrical components of the minimum approach distances for phase-to-
ground exposures can be calculated--that is, the determination of the
saturation factor, a. The proposed rule and IEEE Std 516-1987, which
formed the original basis for the calculation of phase-to-ground
minimum approach distances in existing Sec.  1910.269, relied on Figure
2 in ``Recommendations for Safety in Live Line Maintenance'' to
determine the saturation factor (269-Ex. 60; Ex. 0558). That figure
plotted the saturation factor against crest voltage. In preparing IEEE
Std 516-2009, the IEEE committee decided to use equations to represent
the saturation factor rather than reading it from the figure (Ex.
0532). The committee used a curve-fitting program to develop the
following equations for the saturation factor for calculating the
electrical components of the minimum approach distances for phase-to-
ground exposures: \221\
---------------------------------------------------------------------------

    \221\ These equations calculate the saturation factor, a, for
any exposure for which Equation 1 is used to calculate the
electrical components of the minimum approach distances. However, as
explained later in this section of the preamble, the committee chose
to apply Equation 1 only to phase-to-ground exposures.

---------------------------------------------------------------------------

[GRAPHIC] [TIFF OMITTED] TR11AP14.004

    OSHA concludes that adopting IEEE's method of calculating the
saturation factor is reasonable because that method will lead to more
accurate and consistent determinations of minimum approach distances
for phase-to-ground exposures on system voltages of more than 72.5
kilovolts than approximating the saturation factor by reading it
directly from the graph, as was done to calculate the minimum approach
distances in existing Sec.  1910.269.\223\ Consequently, the Agency is
adopting these equations for calculating the saturation factor in Table
V-2 in the final rule for phase-to-ground exposures, except for the
1,600-kilovolt limitation for the last voltage range. As explained
later in this section of the preamble, the Agency concluded that
extrapolating the saturation factor beyond the 1,600-kilovolt maximum
switching impulse used during the experimental testing used to support
the IEEE method is reasonable and will better protect employees than
alternative approaches. For phase-to-ground exposures, this limit would
have no practical effect as the Agency anticipates that few, if any,
systems will have maximum phase-to-ground transient overvoltages
(VPeak) as high as 1,600 kilovolts.
---------------------------------------------------------------------------

    \222\ Through an apparent oversight, the IEEE equations for a
fail to cover 635.0 kilovolts.
    \223\ The quality of the graph is poor, and the underlying data
is no longer available (Ex. 0532).
---------------------------------------------------------------------------

    Phase-to-phase exposures. For phase-to-phase exposures, OSHA based
the proposal on the 2002 NESC approach, which used the maximum phase-
to-phase transient overvoltage in Equation 1 for calculating the
electrical components of minimum approach distances for phase-to-phase
exposures. As noted in Appendix B to proposed Subpart V, OSHA used the
following equation to determine the phase-to-phase maximum transient
overvoltage based on a system's per-unit nominal voltage phase-to-
ground crest:
[GRAPHIC] [TIFF OMITTED] TR11AP14.005

Where:

pup = p.u. phase-to-phase maximum transient overvoltage, and
pug = p.u. phase-to-ground maximum transient overvoltage.

    The value for pup was to be used for pu in Equation (1) for
calculating the phase-to-phase MADs.
    Until approximately 2007, the technical committees responsible for
IEEE Std 516 and the NESC calculated minimum approach distances based
on these equations. Because OSHA was using the same methodology, the
Agency relied on the technical committees' calculations as they
appeared in IEEE Std 516-2003 and the 2002 NESC and proposed to include
those distances in Sec.  1910.269 and subpart V.
    During the revision cycle for IEEE Std 516-2009, the IEEE technical
committee responsible for revising that standard identified what, in
the committee's view, was an error in the calculations of phase-to-
phase minimum approach distances for nominal voltages 230 kilovolts and
higher. At these voltages, the saturation factor, a, which appears in
Equation (1), varies depending on the voltage; that is, the value of a
increases with increasing voltage. The NESC subcommittee calculated the
phase-to-phase minimum approach distances for the 1993 NESC using a
value for the saturation factor, a, corresponding to the maximum phase-
to-ground transient overvoltage, rather than the maximum phase-to-phase
transient overvoltage.\224\
---------------------------------------------------------------------------

    \224\ ANSI/IEEE Std 516-1987 did not contain distances for
phase-to-phase exposures. The NESC subcommittee derived them by
applying the IEEE equation, Equation (1), to the phase-to-phase
temporary overvoltages calculated using Equation (2).
---------------------------------------------------------------------------

    Because, in its proposal, OSHA borrowed the minimum approach
distances from IEEE Std 516-2003 and the 2002 NESC, the Agency twice
solicited comments on whether changes to its rule were necessary in
light of the

errors identified by the IEEE committee (73 FR 62942, 74 FR 46958).
    The consensus among rulemaking participants was that the proposed
rule's minimum approach distances for phase-to-phase exposures at
maximum transient overvoltages exceeding approximately 630 kilovolts
involved a mathematical error. (See, for example, Exs. 0521, 0524,
0526.1, 0528, 548.1; Tr2. 122-123, 139.) Draft 9 of the 2009 revision
of IEEE Std 516 derived formulas for the saturation factor, a, using a
curve-fitting program (Ex. 0524). When maximum phase-to-phase transient
overvoltages are less than 630 kilovolts, a is 0.0, and the
mathematical error is not present (id.). For higher maximum transient
overvoltages, a is a function of the peak voltage, which is higher for
phase-to-phase exposures than it is for phase-to-ground exposures (id.)
    Because the proposed rule used an approach for calculating phase-
to-phase minimum approach distances that commenters generally agreed
was in error, OSHA decided to make changes in this final rule to
account for that mistake.
    To determine the increased risk to employees, OSHA compared the
probability of sparkover for the electrical component of the largest
proposed minimum approach distance with the probability of sparkover
for the electrical component of the corrected minimum approach
distance.\225\ For systems operating at 800 kilovolts, the probability
of sparkover with the maximum phase-to-phase transient overvoltage at
the corrected electrical component of the minimum approach distance is
approximately 1 in 1,000. The probability of sparkover at the proposed
electrical component of the minimum approach distance is 64 in 100.
Clearly, the proposed minimum approach distance poses significant risk
to employees when the phase-to-phase transient overvoltage is at its
maximum. Because, for systems operating at 800 kilovolts, the minimum
approach distance in the existing standard is the same as the distance
in the proposed rule, the existing standard also poses a substantial
risk to employees.
---------------------------------------------------------------------------

    \225\ The corrected minimum approach distance is the minimum
approach distance calculated with an extrapolated saturation factor
for the maximum phase-to-phase transient overvoltage in place of the
maximum phase-to-ground transient overvoltage. This is the method
used in IEEE Std 516 Draft 9 (Ex. 0524).
---------------------------------------------------------------------------

    OSHA calculated the probabilities of sparkover at the proposed
electrical component of the minimum approach distance and the corrected
minimum approach distance in the following manner. The minimum approach
distance proposed in Table V-2 for this exposure was 7.91 meters, and
the electrical component of this distance was 7.60 meters (7.91 meters
- 0.31 meters). The phase-to-phase maximum transient overvoltage at 800
kilovolts is 2,352 kilovolts.\226\ Draft 9 of the 2009 revision of IEEE
Std 516 derived formulas for the saturation factor, a, using a curve-
fitting program. Equation 59 in that draft standard provided the
following equation for a for maximum transient overvoltages of more
than 1,485 kilovolts:
---------------------------------------------------------------------------

    \226\ Using Equation 2, the phase-to-phase maximum per-unit
transient overvoltage is 2.0 + 1.6, or 3.6, times the peak phase-to-
ground voltage. The peak phase-to-ground voltage is the maximum
system phase-to-phase voltage times [radic]2 divided by [radic]3.
Thus, the maximum transient overvoltage for a phase-to-phase
exposure for a maximum system voltage of 800 kilovolts (the highest
system voltage) is 3.6 x 800 x [radic]2 / [radic]3, or 2,352,
kilovolts.

---------------------------------------------------------------------------
a = (TOV - 1,485) x 0.00000491 + 0.0055704,

where TOV is the maximum transient overvoltage (Ex. 0524).

    This equation extrapolates a beyond the 1,600-kilovolt upper limit
on available rod-gap test data. Using this equation to determine a and
using that value in Equation 1, the withstand voltage corresponding to
7.60 meters is 1,966 kilovolts. The critical sparkover voltage for a
7.60-meter gap is 1,966 / 0.85, or 2,312, kilovolts. (See Step 4 in the
explanation of how to use Table 6 to determine the electrical component
of clearance earlier in this section of the preamble.) The probability
of sparkover for this distance at the maximum transient overvoltage of
2,352 kilovolts is 64 percent.\227\ This percentage means that the
electrical component of the proposed minimum approach distance at 800
kilovolts has a probability of 64 percent of sparking over at the
industry-accepted maximum per-unit transient overvoltage of 2.0.
---------------------------------------------------------------------------

    \227\ The probability of sparkover is determined by normalizing
the mean (average) sparkover voltage and the standard deviation and
looking up those two normalized parameters in standard distribution
tables. The critical sparkover voltage (that is, the mean voltage
that will spark over) is 2,312 kilovolts. The standard deviation is
5 percent of this value, or 115.6 kilovolts. The maximum transient
overvoltage corresponding to the industry-accepted value of 2.0 per
unit at 800 kilovolts is 2,352 kilovolts, or 0.346 standard
deviations above the mean voltage at sparkover. The probability of
sparkover can be determined from normal distribution tables for a Z
of 0.346.
---------------------------------------------------------------------------

    There were three basic methods submitted to the record for
calculating minimum approach distances for phase-to-phase exposures.
The first method was the one OSHA used in developing the proposed rule.
As described earlier in this section of the preamble, that method used
Equation (1) and Equation (2) to determine the minimum approach
distance, but without adjusting the saturation factor, a, in Equation
(1) to account for the increase between the phase-to-ground and phase-
to-phase maximum transient overvoltage. For the reasons already
explained, OSHA concludes that this method is invalid and would expose
employees to an unreasonable increase in risk for phase-to-phase
exposures at maximum transient overvoltages higher than 630 kilovolts.
Consequently, the Agency decided against adopting this method in the
final rule.
    The second method, adopted by IEEE Std 516-2009, uses equations
based on the paper by Vaisman,\228\ and two papers by Gallet,\229\ to
determine minimum approach distances (Ex. 0532). OSHA refers to this
method as the ``IEEE method'' in the following discussion.
---------------------------------------------------------------------------

    \228\ Vaisman, op cit.
    \229\ Gallet, G., Leroy, G., Lacey, R., and Kromer, I.,
``General expression for positive switching impulse strength valid
up to extra line air gaps,'' IEEE Transaction on Power Apparatus and
Systems, vol. PAS-94, pp. 1989-1993, Nov./Dec. 1975 (Ex. 0560); and
Gallet, G., Hutzler, B., and Riu, J-P., ``Analysis of the switching
impulse strength of phase-to-phase air gaps,'' IEEE Transactions on
Power Delivery, vol. PAS-97, no. 2, Mar./Apr. 1978 (Ex. 0553).
---------------------------------------------------------------------------

    The formula used in IEEE Std 516-2009 for calculating phase-to-
phase minimum approach distances for voltages of 72.6 kilovolts and
higher is derived from testing that replicates line configurations
rather than live-line work. Accordingly, the underlying formula in IEEE
Std 516-2009 originally was intended for determining appropriate
conductor spacing rather than for determining minimum approach
distances appropriate for employees performing live-line work. To
account for the presence of an employee working in an aerial lift
bucket within the air gap between the two phase conductors, the IEEE
committee incorporated the concept of a floating electrode in the air
gap. The committee's approach to determining the electrical component
of the minimum approach distance can be summarized as follows:
    1. Start with a formula to calculate the critical sparkover voltage
for the distance between two conductors.
    2. Modify the formula to account for a 3.3-meter floating electrode
representing an employee working within an aerial lift bucket between
the phase conductors.
    3. Modify the formula to convert the critical sparkover voltage to
a withstand voltage.

    4. Determine the maximum transient overvoltage on the line, and
substitute that value for the withstand voltage.
    5. Rearrange the equation to solve for distance.
    In more technical detail, this approach is described as follows:
    1. The equation for calculating the critical sparkover voltage for
a given distance between two conductors includes a gap factor, k. This
factor depends on several variables:

alpha = the proportion of the negative switching impulse voltage to the
total phase-to-phase impulse voltage,
Ddesign L-L = the design phase-to-phase clearance, and
H = the average height of the phase above the ground.
    Table 8 shows the values recommended by IEEE Std 516-2009 for these
variables and the resultant gap factors.

                                   Table 8--IEEE Std 516-2009 Gap Factors (k)
----------------------------------------------------------------------------------------------------------------
               Phase-to-phase voltage                        alpha           Ddesign L-L/H             k
----------------------------------------------------------------------------------------------------------------
<= 242 kV...........................................                0.33                 0.8               1.451
> 242 kV............................................                0.41                 0.8               1.530
----------------------------------------------------------------------------------------------------------------

    IEEE Std 516-2009 uses the following equation to calculate the
critical sparkover voltage for the designed gap between two phase
conductors:
[GRAPHIC] [TIFF OMITTED] TR11AP14.006

Where:

V50 = the critical sparkover voltage in kilovolts,
k = the gap factor from Table 8, and
Dl-l = the sparkover distance in meters.

    2. When an employee performs live-line barehand work, the employee
typically is positioned between two or more phase conductors. The
employee could be working, for example, from an aerial lift platform or
a conductor cart. These devices and the worker are both conductive. The
presence of a conductive object in the air gap between the two
electrodes (which, in this case, are the two conductors) reduces its
dielectric strength. IEEE Std 516-2009 introduces a constant,
KF, to account for the presence of the employee and other
conductive objects in the air gap. In that consensus standard,
KF equals 0.9 to accommodate a 3.3-meter conductive object
in the air gap. This value is equivalent to a 10-percent reduction in
the dielectric strength of the gap.
    With this factor included, the equation for the critical sparkover
voltage is:
[GRAPHIC] [TIFF OMITTED] TR11AP14.007

    3. IEEE sets the withstand voltage at a level that is 3[sigma]
lower than the critical sparkover voltage, as indicated in the
following equation:
VW = (1-3[sigma])V50

Where:

VW = the withstand voltage,
V50 = the critical sparkover voltage, and
[sigma] = 5 percent for a normal distribution.

    4. To solve for the electrical component of the clearance, the
maximum transient overvoltage is substituted for the withstand voltage.
The IEEE committee used the following equation to calculate the maximum
transient overvoltage on the line:
[GRAPHIC] [TIFF OMITTED] TR11AP14.047

Where:

TL-L = the phase-to-phase maximum transient overvoltage in per unit,
and
TL-G = the phase-to-ground maximum transient overvoltage in per
unit.

    5. Substituting the values of the various constants and solving
these equations for distance, IEEE Std 516-2009 uses the following
equations to calculate the minimum air-insulation distance:
[GRAPHIC] [TIFF OMITTED] TR11AP14.008

Where:

DL-L = the minimum air-insulation distance (the minimum distance
needed to prevent sparkover with air alone as the insulating
medium),
TL-G = the phase-to-ground maximum transient overvoltage in per
unit, and
VL-L = the rms phase-to-phase system voltage.

    Testifying on behalf of EEI, Dr. Horton explained the IEEE method
as follows:It is well recognized that the dielectric strength of a
given electrode geometry is different for line-to-ground surges than
for line-to-line surges. A phase-to-phase surge between two phases is
the voltage difference between the phase-to-ground surges which may be
of opposite polarity and displaced in time, (and many times are)
whereas a maximum phase-to-ground surge is considered uni-polar.
* * * * *
[The surges from the two phases] are displaced by some amount of
time. . . .

    The resulting line-to-line surge . . . will stress a given air
gap geometry differently than either of the line-to-ground surges
that the resulting waveform is comprised of. Unlike line-to-ground
insulation characteristics of a given electrode geometry, which
depend primarily on the gap spacing, line-to-line insulation
characteristics . . . are more complex because one of the surges has
a positive polarity with respect to ground while the other has a
negative polarity with respect to ground.
    The resulting insulation strength is a function of alpha, which
again, is the ratio of the negative surge to the sum of the negative
and positive surge.
    The IEEE recently tried to address this limitation [in IEEE Std
516-2009] by developing a method based on a modified version of the
Gallet equation. The upper voltage limit of the resulting equation
is 3500 kV peak or air gap distances of up to 15 meters. This
limitation is well within the typical range of live-line working
scenarios in the United States.
    Historically, IEEE Standard 516 has used rod-to-rod electrode
geometry data for determining line-to-ground MAID. One reason for
this is that the test data that the method is based on represents a
rod-to-rod electrode configuration.
    In addition, the line-to ground [testing] that was performed
showed that the rod-to-rod results were in the middle range for a
wide range of conductor configurations. The rod-to-rod data
presented neither the worst case nor the best. Thus, it was chosen
as a reasonable representation of all the possible gap
configurations to which a line worker might be exposed while
performing tasks, which are characterized as line-to-ground.
    When considering line-to-line minimum air insulation distances,
a rod-to-rod gap may not be the most appropriate. Typically, the
worker will bond onto one phase and will not need to bridge the gap
to the other phase. Since the shape of the adjacent electrode
remains unchanged during the task, (in other words it remains a
conductor) the resulting air gap geometry more closely resembles
that of a conductor-to-conductor. The effect of the change in
geometry of the phase to which the worker is bonded is dealt with in
the new IEEE method by introducing an additional factor that
accounts for the effect of large conductive objects floating in the
air gap. [Tr2. 83-86]

    No rulemaking participant recommended that OSHA adopt the IEEE
method for calculating minimum air-insulation distances for phase-to-
phase exposures at more than 72.5 kilovolts. In addition, the Agency
has several concerns with the approach taken in that consensus
standard. First, the IEEE method relies on test data for an electrode
configuration that is not comparable to the rod-to-rod gap used for
phase-to-ground exposures on which OSHA based the minimum approach
distances in existing Sec.  1910.269. Second, the choices for some of
the parameters used in the equations for the electrical component of
the minimum approach distance appear to be arbitrary. Third, the IEEE
method is based on papers that explore the dielectric strength of
electric power lines rather than the dielectric strength of circuit
parts configured as they would be when employees are performing live-
line barehand work.
    (1) Conductor-to-conductor-based method does not accurately model
employee exposure. OSHA considered the evidence in the record and
concludes that the IEEE method, which is based on testing on conductor-
to-conductor electrodes, does not accurately model employee exposure.
As noted by Dr. Horton, the approach taken by existing Sec.  1910.269
and earlier editions of IEEE Std 516 based the calculation of minimum
air-insulation distances for both phase-to-ground and phase-to-phase
exposures on phase-to-ground testing of rod-to-rod electrodes (Tr2.
85).\230\ By adopting the approach taken in IEEE Std 516-1987 in
promulgating existing Sec.  1910.269, OSHA deemed it reasonable to rely
on rod-to-rod gap data (59 FR 4383-4384). The record in this rulemaking
contains reports of tests on a variety of electrode configurations,
showing clearly that the dielectric strength of air varies with the
configuration (269-Ex. 60; Exs. 0553, 0554). In reviewing the record,
OSHA has again concluded that phase-to-ground rod-to-rod gap test data
forms a reasonable basis for the determination of minimum approach
distances because it falls in the middle range of various electrode
configurations (that is, it is neither the best case nor the worst). In
addition, OSHA believes that employees performing work on energized
lines are rarely exposed to the worst-case configuration, rod-to-plane
electrodes, or to the best-case configuration, sphere-to-sphere
electrodes. Thus, an exposure representing the middle range of various
electrode configurations is reasonable for a model based on phase-to-
ground testing.
---------------------------------------------------------------------------

    \230\ Typical configurations include rod-rod, rod-plane, and
conductor-plane. The terminology refers to the configuration of the
two electrodes. For example, in a rod-plane configuration, one of
the electrodes is a rod perpendicular to an electrode in the shape
of a plane.
---------------------------------------------------------------------------

    A paper by Gallet \231\ reports on a variety of phase-to-phase gap
factors, including supported busbars and asymmetrical geometries, as
shown in the following table (Ex. 0553):
---------------------------------------------------------------------------

    \231\ Gallet, G, Hutzler, B., and Riu, J-P., op cit.

------------------------------------------------------------------------
       Electrode geometry             alpha = 0.5        alpha = 0.33
------------------------------------------------------------------------
Rings or large, smooth                          1.80                1.70
 electrodes.....................
Crossed conductors..............                1.65                1.53
Rod-rod or conductor-conductor..                1.62                1.52
Supported busbars...............                1.50                1.40
Asymmetrical geometries.........                1.45                1.36
------------------------------------------------------------------------
Table reprinted with permission from the Institute for Electrical and
  Electronics Engineers (IEEE). OSHA revised the table from IEEE's
  original.

    Although the performance during phase-to-phase tests are the same
for rod-to-rod and conductor-to-conductor electrodes, OSHA concludes
that phase-to-phase exposures are more likely to correspond to
asymmetrical geometries, which, as can be seen from the table in the
Gallet paper, have a lower dielectric strength than rod-to-rod or
conductor-

to-conductor electrodes.\232\ Employees performing live-line barehand
work face a wide variety of exposure conditions reflecting a number of
different electrode configurations. Several of these electrode
configurations are not equivalent to conductor-to-conductor electrodes.
Employees working on energized supported busbars could experience
phase-to-phase exposures. Additionally, during live-line barehand work
on energized conductors, employees are working on the conductors, and
the installation may be configured differently when maintained or
installed. For example, a damaged portion of a bundled conductor may
protrude from the bundle, or an employee may be holding an armor rod
perpendicular to the conductor. The equipment used to position the
employee also can affect the shape of one of the electrodes. The Agency
believes that these examples may more closely resemble asymmetrical
geometries. Consequently, the gap factor for those electrode
configurations, as shown in the table, would be lower than the gap
factor used in IEEE Std 516-2009. The IEEE standard reduced the gap
factor by accounting for a conductive object in the gap. However, the
Agency believes that such a reduction also would be necessary when
another conductive object is in the air gap while an employee is
working on an energized conductor, which could occur as equipment is
transferred to the employee or if a second worker is in the air gap.
Thus, OSHA concludes that a model based on phase-to-phase testing
should be based on asymmetrical electrode geometries and that the IEEE
committee's choice of a conductor-to-conductor gap is not appropriate.
---------------------------------------------------------------------------

    \232\ Dielectric strength is proportional to the gap factor.
Thus, a smaller gap factor yields a lower dielectric strength.
---------------------------------------------------------------------------

    (2) The values of some of the parameters used in the IEEE method
appear to be arbitrary. The ratio of the negative switching impulse
voltage to the total phase-to-phase impulse voltage is designated as
alpha. Dr. Horton described this parameter, and its importance, as
follows:

    A phase-to-phase surge between two phases is the voltage
difference between the phase-to-ground surges which may be of
opposite polarity and displaced in time, (and many times are)
whereas a maximum phase-to-ground surge is considered uni-polar.
    [Figure 5] shows how two separate phase-to-ground surges combine
to form a line-to-line surge. . . .
    [W]e have one [transient] for phase 1 and we have . . . one for
phase 2, and . . . they are displaced by some amount of time. The
resulting transient overvoltage or surge that would be across the
air gap, which would be the line-to-line air gap, would be . . . a
combination of the [two] curve[s]. [Tr2. 83-84]

[GRAPHIC] [TIFF OMITTED] TR11AP14.009

    The IEEE committee used an alpha of 0.33 for system voltages up to
242 kilovolts. However, the committee used a value of 0.41 for higher
system voltages. It described the rationale for this latter decision
with a quote from the Vaisman paper:

    \233\ Figure 5, which is a copy of Figure 4 from Ex. 0545.1, was
included in the presentation by Dr. Horton at the October 28, 2009,
public hearing. (See, also, Ex. 0567.) EEI identified the source of
this figure as EPRI Transmission Line Reference Book: 115-345-kV
Compact Line Design, 2007 (Blue Book).
---------------------------------------------------------------------------

    In [extra-high voltage] systems, where there is efficient
overvoltage control and hence the overvoltage factor a tends to lie
in the range of 0.41 to 0.50, the ratio between the line-to-line
(D1) and the line-to-ground (D) clearance equal to 2.0 is the one
which provides a more balanced distribution of flashovers between
the two gaps. [Ex. 0532]

    OSHA has two concerns about this choice. First, the paper does not
indicate that an alpha of 0.41 is the smallest expected for these
systems. A smaller value of alpha will produce a smaller value for the
gap factor, k, and, consequently, a larger electrical component of the
minimum approach distance.\234\ Second, it is not clear why efficient
overvoltage control has any effect on alpha. Overvoltage control limits
the maximum transient overvoltage on each individual phase, but it does
not necessarily limit the delay between the peak transient overvoltage
on each phase, which appears as [Delta]Tcr in Figure 5. The
Vaisman paper also explored the effect of [Delta]Tcr, which
is not accounted for in the IEEE method:
---------------------------------------------------------------------------

    \234\ In the IEEE method, the critical sparkover voltage,
V50, is directly proportional to k, and the minimum air-
insulation distance (the electrical component of the minimum
approach distance) is inversely proportional to V50.
Thus, the electrical component of the minimum approach distance is
inversely proportional to k.

    In other tests, where only the negative wave was displaced, the
observed reductions were:

                          Table 2--Reduction in [V50] When Displacing the Negative Wave
----------------------------------------------------------------------------------------------------------------
                  [alpha]  Desired                     [alpha]  Obtained   [Delta]Tcr  (ms)     Reduction  (%)
----------------------------------------------------------------------------------------------------------------
0.33................................................                0.28                   1                 1.5
0.50................................................                0.43                   1                 3.1
0.33................................................                0.22                   2                 4.0
0.50................................................                0.36                   2                 8.7
----------------------------------------------------------------------------------------------------------------

    Nevertheless, under these conditions, besides the shift between
impulses, there was also a decrease of [alpha].
    From all the results a maximum reduction of 8.7% in the value of
U50 can be observed when the positive and negative components of
phase-to-phase overvoltage are not synchronized [Ex. 0555].

    From Figure 5, it is clear that the maximum overvoltage occurs when
the positive and negative transient waves are synchronized, that is,
when [Delta]Tcr = 0. In addition, it is clear from the BPA
report that the poles of a circuit breaker do not trip simultaneously
(Ex. 0575.1). In addition, circuit characteristics also may contribute
to the size of [Delta]Tcr. The [Delta]Tcr range
shown in the Vaisman paper does not seem unreasonable. Thus, from this
paper, on which the IEEE committee relied, it appears that the maximum
phase-to-phase transient overvoltage should be calculated, as shown by
Table 2 in the Vaisman paper, by using an alpha of 0.50 and reducing
the critical sparkover voltage by 8.7 percent. In this case, the peak
overvoltage on each phase has the same value, which seems reasonable if
the phases are identical in most respects, but displaced by 2
milliseconds, which, based on the BPA report, also seems reasonable.
    (3) The IEEE method is based on papers on the design of lines
rather than employee safety during maintenance. Finally, OSHA has a
concern that the IEEE method is based almost exclusively on papers that
explore the dielectric strength of lines. Employees perform work on
energized lines and equipment. In addition, the lines on which
employees work during maintenance and repair may not be in the same
condition as the lines were when they were first installed. The Agency
believes that it is appropriate to base minimum approach distances for
workers on papers and scientific data derived from actual working
conditions.
    The Agency agrees with Dr. Horton and EEI that phase-to-phase
overvoltages are more complicated than phase-to-ground overvoltages.
However, the Gallet formula on which the IEEE method is based models
phase-to-ground, as well as phase-to-phase, critical sparkover
voltages. In addition, the IEEE committee chose not to use it for
phase-to-ground exposures, presumably because the papers supporting the
method for phase-to-ground exposures examined the safety of employees
performing live-line maintenance.\235\ OSHA believes that these papers
support the method used in the final rule to calculate minimum approach
distances for phase-to-phase exposures, as well as phase-to-ground
exposures. Therefore, for all the foregoing reasons, OSHA concludes
that the IEEE approach does not reasonably represent the range of
overvoltages or the dielectric strength of air gaps that a worker will
encounter during phase-to-phase exposures.
---------------------------------------------------------------------------

    \235\ IEEE Std 516-2009 listed three papers that supported the
method used for phase-to-ground exposures:
    Elek, A., and Simpson, J. W., ``Safe clearance and protection
against shocks during live-line work,'' AIEE Transaction on Power
Apparatus and Systems, vol. 80, pt. III, pp. 897-902, Feb. 1962.
    IEEE Committee Report, ``Live-line maintenance methods,'' IEEE
Transactions on Power Apparatus and Systems, vol. PAS-92, pp. 1642-
1648, Sept./Oct. 1973.
    IEEE Committee Report, ``Recommendations for safety in live-line
maintenance,'' IEEE Transactions on Power Apparatus and Systems,
vol. PAS-87, no. 2, pp. 346-352, Feb. 1968.
    All three of these papers examined minimum approach distances
for live-line work (Ex. 0532).
---------------------------------------------------------------------------

    The third method, described in Drafts 9 and 10 of IEEE Std 516 and
incorporated in this final rule, uses Equation (3) \236\ to determine
the maximum per-unit transient overvoltage, calculates the saturation
factor, a, based on the maximum phase-to-phase transient overvoltage,
and uses Equation (1) \237\ to determine the minimum approach distance
(Exs. 0524, 0525). The calculation of the saturation factor uses a
curve-fitted equation, which extrapolated the value for that factor
beyond the 1,600-kilovolt limitation on the test data noted earlier.
OSHA refers to this method as the ``extrapolation method'' in the
following discussion. In comments responding to the 2008 reopening
notice, Mr. Brian Erga with ESCI supported the adoption of this method
because it corrects the calculation error present in the 2003 edition
of IEEE Std 516 (Ex. 0521).
---------------------------------------------------------------------------

    \236\ TL-L = 1.35TL-G + 0.45. OSHA is
adopting this equation in Table V-2. Drafts 9 and 10 of IEEE Std 516
and final IEEE Std 516 adopt this equation for calculating the
phase-to-phase maximum per-unit transient overvoltage (Exs. 0524,
0525, and 0532), and there is no evidence in the record to indicate
that it does not accurately represent the phase-to-phase maximum
per-unit transient overvoltage.
    \237\ D = (C + a) x pu x Vmax.
---------------------------------------------------------------------------

    Other rulemaking participants objected to the extrapolation of the
saturation factor. (See, for example, Exs. 0545.1, 0548.1; Tr2. 77-79.)
These rulemaking participants maintained that there was no test data to
support extrapolating this factor and argued that other methods of
estimating the dielectric strength of air demonstrated that
extrapolating the saturation factor would result in minimum approach
distances that are ``dangerously inaccurate'' (Ex. 0548.1). The
Southern Company explained its objections as follows:

    [T]here are at least two methods of estimating the dielectric
strength of air gaps that show that extrapolating the saturation
factor, ``a'', beyond the test data [reference omitted] for which it
was based is not valid. A comparison of the MAID values computed
using the [extrapolation] formula and those of Gallet and CRIEPI
[238]  [references omitted] show that extrapolating test
points beyond the 1650 kV range is dangerously inaccurate. [Id.]
---------------------------------------------------------------------------

    \238\ Central Research Institute of Electric Power Industry.

The Southern Company described how it ``manipulated'' the formulas and
plotted the results, comparing the extrapolation method with the other
two methods (the Gallet and CRIEPI formulas), as shown in Figure 6.

[GRAPHIC] [TIFF OMITTED] TR11AP14.010

Southern Company included a second figure (not shown here) consisting
of the area beyond 1,600 kilovolts, where test data is unavailable to
support either Equation (1) or the determination of the saturation
factor, a. The commenter concluded:

    [These figures] show that three methods agree rather closely for
transient overvoltages less than 1600 kV (the limitation of the
[Drafts 9 and 10] IEEE method). However, at approximately 1800 kV,
the results found using the Gallet and CRIEPI formulas diverge
significantly from the [extrapolation] method. The reason for this
is primarily due to the fact that the Gallet and CRIEPI formulae are
based on test data in this voltage range, whereas, the
[extrapolation] formula is not. [Id.]

    OSHA notes that there is a similar divergence between these
formulas at voltages from 600 to 750 kilovolts. The following table
shows minimum air-insulation distances for two voltages \239\ using the
Equation (1) extrapolation method and Southern Company's modified
Gallet formula:
---------------------------------------------------------------------------

    \239\ OSHA chose 592.8 and 2,149 kilovolts (which correspond to
systems of 161 kilovolts at 3.0 per-unit maximum transient
overvoltage and 800 kilovolts at 2.1 per-unit maximum transient
overvoltage) because these values generally represent the low and
high end of the voltage range covered by Figure 6. In addition,
there is rod-gap test data supporting the current method at 592.8
kilovolts, but not at 2,149 kilovolts.

----------------------------------------------------------------------------------------------------------------
                                       Equation (1) based on
              Voltage                 extrapolation method \1\     Modified gallet formula    Percent difference
----------------------------------------------------------------------------------------------------------------
592.8 kV..........................  1.28 meters................  1.50 meters................                  17
2149.0 kV.........................  9.23 meters................  10.68 meters...............                  16
----------------------------------------------------------------------------------------------------------------
\1\ Based on IEEE Standard 516 Draft 9 (Ex. 0524).

    This table shows a substantial difference between the Southern
Company's modified Gallet formula and the extrapolation method at
voltages where test data exist. Southern Company's modified Gallet
formula produces minimum approach distances that are much higher at
voltage levels where test data exist than they are where test data do
not exist. Because the modified Gallet formula does not accurately
produce minimum approach distances where test data exists, there is no
reason to believe that it will accurately calculate minimum approach
distances where there is no test data. Therefore, OSHA concludes that
it cannot rely on the Southern Company's analysis to show that the
extrapolation method does not provide adequate employee
protection.\240\ The results of this comparison are not surprising. The
curves representing these formulas have slightly different shapes. In
comparison to Equation (1), in which the saturation factor increases
nearly linearly before and after extrapolation, the Gallet formula
results in a small increase in the saturation factor at lower voltages,
but a large increase at higher voltages. Thus, despite the similarity
in appearance between the two equations, OSHA concludes that, compared
to the extrapolation method, the modified Gallet formula does not
equally represent the strength of the air gap.
---------------------------------------------------------------------------

    \240\ The Agency did not compare the modified CRIEPI formula as
there is no evidence in the record to suggest that OSHA base the
final rule on that formula.
---------------------------------------------------------------------------

    Further exploration of the modified Gallet and CRIEPI formulas
sheds additional light on this issue. The Gallet formula uses a gap
factor as one parameter. Southern Company used a gap factor of 1.3 in
its comparison. Although the comment stated that Southern Company based
the gap factor on rod-to-rod electrode configurations,

there is no record support for this value. The lowest value for the gap
factor provided in the Gallet paper was 1.36 (Ex. 0553). Had Southern
Company used a gap factor of 1.33 instead,\241\ the differences between
the equations would be generally smaller, and the high-voltage
``difference'' noted by Southern Company would not be apparent until
approximately 2,100 kilovolts. At system voltages higher than 242
kilovolts, IEEE Std 516-2009 uses a gap factor equivalent to 1.377,
which results in smaller rather than larger minimum air-insulation
distances at voltages between approximately 800 and 2,200 kilovolts
(Ex. 0532). Therefore, the Agency is rejecting Southern Company's
argument that the modified Gallet and CREIPI formulas show that the
extrapolation method is not sufficiently protective.
---------------------------------------------------------------------------

    \241\ With no record support for a gap factor of 1.3, it appears
that Southern Company chose the gap factor arbitrarily. In this
example, OSHA has chosen an equally arbitrary gap factor simply to
show how the curves can be manipulated.
---------------------------------------------------------------------------

    The concern about the lack of test data appears to be unfounded, at
least for the range of overvoltages addressed by the final rule. The
largest overvoltage addressed by the final rule is approximately 2,500
kilovolts, which corresponds to an 800-kilovolt system with a phase-to-
ground maximum per-unit transient overvoltage of 2.5 pu. The test data
for rod-to-rod gaps extends to 1,600 kilovolts. Thus, the data cover
about two thirds of the voltage range covered by the final rule, and
the test data provide substantial support for maximum transient
overvoltages of 1,600 kilovolts (which corresponds to an 800-kilovolt
system with a 1.5 per-unit maximum transient overvoltage) regardless of
whether the exposure is phase-to-phase or phase-to-ground. In addition,
the saturation factor varies almost linearly with voltage, as can be
seen from the table and graphs of voltage vs. saturation factor in the
IEEE reports on which Equation (1) is based (Exs. 0556, 0558). Figure 7
reproduces the relevant graphs in those papers.\242\ Thus, an
extrapolation of the saturation factor likely will produce reasonable
results.
---------------------------------------------------------------------------

    \242\ This graph is Figure 1 in Ex. 0556 and Figure 2 in Ex.
0558.
---------------------------------------------------------------------------

BILLING CODE 4510-26-P

[GRAPHIC] [TIFF OMITTED] TR11AP14.011

BILLING CODE 4510-26-C
    In addition, as noted earlier, the Gallet and CRIEPI formulas, the
other two formulas described by Southern Company for determining
sparkover voltages, have a similar shape. (See Figure 6.) The
extrapolation method might not be as conservative at the highest
voltages as the Gallet and CRIEPI formulas. However, because the
modified Gallet and CREIPI formulas rely on a gap factor that is
unsupported on the record, and because the gap factor adopted in IEEE
Std 516-2009 yields minimum approach distances that are less
conservative than the extrapolation method, the Agency believes that
the extrapolation method will provide adequate protection for workers.
For these reasons, OSHA concludes that it is reasonable to extrapolate
the test data to determine minimum approach distances. Consequently,
the final rule adopts the extrapolation method of determining minimum
approach distances by providing equations for calculating the
saturation factor, a, as described in the following paragraphs.
    Drafts 9 and 10 of the 2009 revision of IEEE Std 516, as well as
the approved edition of that standard, provided linear equations for
the saturation factor. These equations varied depending on the voltage
range (Exs. 0524, 0525, 0532). IEEE Std 516-2009 limits the

equation for the highest range to transient overvoltages of 1,600
kilovolts (Ex. 0532).\243\ Drafts 9 and 10 of the 2009 revision of that
IEEE standard extrapolated the saturation factor by applying the
equation for the highest voltage range without limit (Exs. 0524, 0525).
OSHA notes that Drafts 9 and 10 of IEEE Std 516 used slightly different
equations for the calculation of the saturation factor than does IEEE
Std 516-2009 (Exs. 0524, 0525, 0532). The Agency compared the results
of the two sets of equations with the data from the original IEEE
reports on which Equation (1) is based and determined that the
equations from IEEE Std 516-2009 fit the data precisely. However, IEEE
Std 516-2009 notes:
---------------------------------------------------------------------------

    \243\ It should be noted that, despite the 1,600-kilovolt
limitation, IEEE Std 516-2009 apparently applies this equation to
1,633 kilovolts (the maximum transient overvoltage on an 800-
kilovolt system with a 2.5 per-unit maximum transient overvoltage)
in the minimum approach distance tables in Appendix D of that
standard.

    [T]here is a different value of the ``a'' [saturation] factor
for same voltage used to calculate MAID and MTID. To avoid having
values of the ``a'' factors for MAID and MTID, the working group
decided to use only the MTID ``a'' factor since it matches the
---------------------------------------------------------------------------
values of the ``a'' factor shown on the figure. [Ex. 0532]

Thus, the IEEE standard bases the saturation factor on the withstand
voltages with tools in the gap. OSHA believes that this approach is
appropriate for phase-to-ground exposures. However, for phase-to-phase
exposures, which almost never involve tools across the gap, the Agency
believes that this approach is unnecessarily conservative. Draft 9 of
the IEEE standard uses equations for the saturation factor based on
test data for air gaps without tools. Therefore, the final rule bases
the saturation factor on: (1) The equations from IEEE Std 516-2009 for
phase-to-ground exposures and (2) the equations in Draft 9 of that
standard for phase-to-phase exposures. Therefore, Table V-2 applies the
equations for the saturation factor, a, from IEEE Std 516-2009 to
phase-to-ground exposures, while using the equations for this factor
from Draft 9 of that standard for phase-to-phase exposures. To
extrapolate the saturation factor to the highest voltage addressed by
the final rule, OSHA is extending the application limit of Equation 59
from IEEE Std 516-2009. The Agency based these equations on the
assumption that no insulated tool or large conductive object are in the
gap. Note 3 to Table V-2 indicates that, if an insulated tool spans the
gap or if a large conductive object is in the gap, employers are to use
the equations for phase-to-ground exposures (with VPeak for phase-to-
phase exposures).
    Circuits operating at 362.1 to 420 kilovolts. In the 2009 reopening
notice, OSHA noted that IEEE Std 516-2009 included an additional
voltage range, 362.1 to 420 kilovolts, in its minimum approach distance
tables; this range did not appear in OSHA's proposed rule (74 FR
46962). The Agency requested comments on whether it should add this
voltage range to the minimum approach tables in the final rule.
Rulemaking participants recommended adding this voltage range to the
OSHA standard, though no electric utilities responding to the issue
operated any system in this voltage range. (See, for example, Exs.
0545.1, 0548.1, 0551.1; Tr2. 93, 159.) Dr. Randy Horton, testifying on
behalf of EEI, stated:

    OSHA should include these voltage ranges in the final [r]ule in
order to provide complete guidance to the industry. However, there
are not many lines that operate at these voltages within the
American electric utility industry. [Tr2. 93]

    Although it appears that there are few, if any, electric power
transmission systems in the United States operating at 362.1 to 420
kilovolts, OSHA is including this voltage range in the final standard.
Otherwise, an employer with a system operating in this voltage range
would have to set minimum approach distances based on a maximum system
voltage of 550 kilovolts, the highest voltage in the next higher
voltage range listed in Table V-6. Even if systems operating in the
362.1- to 420-kilovolt range are extremely rare, OSHA is not requiring
employers to adhere to minimum approach distances that are
substantially higher than necessary to protect employees doing work at
those voltages. Therefore, OSHA decided to include the 362.1- to 420-
kilovolt range in Table V-6 in the final rule, which specifies
alternative minimum approach distances for worksites at an elevation of
900 meters or less. Employers not using that table can establish
minimum approach distances for any particular voltage, including
voltages in the 362.1- to 420-kilovolt range, using the equations in
Table V-2 for the maximum voltage on the particular circuit involved.
    The electrical component of MAD--DC exposures. OSHA proposed
minimum approach distances for dc circuits in Table V-5. OSHA received
no comments on these minimum approach distances and, therefore, is
adopting them in Table V-7 of the final rule as proposed.
    OSHA's requirements on minimum approach distances better effectuate
the purpose of the OSH Act than the national consensus standard.
Whenever a final rule differs substantially from an existing national
consensus standard, Section 6(b)(8) of the OSH Act requires OSHA to
publish a statement of reasons in the Federal Register explaining why
the final rule will better effectuate the purposes of the Act than the
national consensus standard. This final rule contains requirements for
minimum approach distances that differ substantially from those in the
2012 NESC, which the Agency determined is the current, relevant
national consensus standard.
    Paragraph (g) of Sec.  1910.2 defines ``national consensus
standard''. There are currently two existing consensus standards
addressing minimum approach distances for electric power generation,
transmission, and distribution work: ANSI/IEEE C2-2012 and IEEE Std
516-2009. The 2012 NESC, which also is an IEEE standard, was approved
as an ANSI standard on June 3, 2011.\244\ IEEE Std 516-2009 is not
currently an ANSI standard, although the 2003 edition was an ANSI
standard.\245\ Many States adopt the NESC (Tr2. 151).\246\ Mr. Charles
Kelly of EEI called the NESC ``the preeminent National Consensus
Standard on clearance distances for electric utility work on high
voltage lines and equipment'' (Tr2. 73). Mr. James Tomaseski,
testifying on behalf of the NESC, called that document ``the authority
on safety requirements for power . . . systems'' (Tr2. 35). In
contrast, rulemaking participants characterized IEEE Std 516 as ``an
engineering document'' containing engineering principles and guidelines

(Tr2. 56; see also, for example, Tr2. 59, 74, 129-130, 174). However,
the NESC takes those engineering principles and produces work rules,
taking into account the practical effects of the requirements. (See,
for example, Tr2. 57, 73, 175-176.) OSHA, therefore, concludes that the
2012 NESC is the existing national consensus standard for the purposes
of Section 6(b)(8).
---------------------------------------------------------------------------

    \244\ IEEE is the secretariat of the National Electrical Safety
Code, which IEEE adopted and which ANSI approved subsequently as a