Production-weighted average calculated from data in Table D-3 in Appendix D
Minimum emission rate for data in Table D-3 in Appendix D
Maximum emission rate for data in Table D-3 in Appendix D

Analytical Option 1: CARB Phase 1
Production-weighted average calculated from data in Table D-4 in Appendix D
Minimum emission rate for data in Table D-4 in Appendix D
Maximum emission rate for data in Table D-4 in Appendix D

Analytical Option 2: FSCWPA/ CARB Phase 2
Production-weighted average calculated from data in Table D-5 in Appendix D
Minimum emission rate for data in Table D-5 in Appendix D
Maximum emission rate for data in Table D-5 in Appendix D

Analytical Option 3: NAF
Production-weighted average calculated from data in Table D-6 in Appendix D
Minimum emission rate for data in Table D-6 in Appendix D
Maximum emission rate for data in Table D-6 in Appendix D
Ambient (outdoor) Air Concentration of Formaldehyde
Average value for the industrial land use category from Table 3-1 in USEPA 2009b.

Method for Estimation of Indoor Air Concentration for Office Buildings
At steady-state, a mass balance equates the formaldehyde generation rate due to off-gassing from HWPW, PB, and MDF that are components of an office workstation to the rate at which airborne formaldehyde is exhausted from the volume of the office building containing the workstation through ventilation with outdoor air.  Based on the work by Carter and Zhang (Carter 2007a), formaldehyde indoor air concentration is estimated for two types of workstations: open plan workstations and private office workstations.  Furthermore, both workstation types contain the following components that may emit formaldehyde: panels, work surfaces, and storage external areas, but storage external areas are assumed to not have any formaldehyde emissions.
The office building mathematical model is described in greater detail in Appendix E and is displayed in Equation 2.
C=ECWPx1-BExFinpanels+ECWPx1-FinpanelsxApanels+ECWPx1-BExFinwork surfaces+ECWPx1-Finwork surfacesxAwork surfacesQ+Cocom          Eqn (2)

where:
      C	= 	Average airborne formaldehyde concentration in the volume of the office building containing the workstation (ug/m[3]);
      Apanels	= 	Emitting surface area of panels in the office workstation (m[2]);
      Awork surfaces	= 	Emitting surface area of work surfaces in the office workstation (m[2]);
      Q	= 	The rate of ventilation with outdoor air that affects the volume of the office building containing the workstation (m[3]/h);
      ECWP	=	Emissive flux (emission rate) of the composite wood product used to construct the workstation component type (ug/m[2]-h) (CWP = HWPW, PB, or MDF);
      BE	=	Barrier effectiveness of the finishing, or overlay, of the workstation component type, expressed as a unitless fraction;
      Finpanels	=	Fraction of the panels' surface area that is finished, or overlayed, with a barrier effectiveness of BE, expressed as a unitless fraction;
      Finwork surfaces	=	Fraction of the work surfaces' surface area that is finished, or overlayed, with a barrier effectiveness of BE, expressed as a unitless fraction; and
      Co[com]	=	Concentration of formaldehyde in the outdoor air for commercial land use areas (ug/m[3]).

Representative values for some of the model parameters of this mathematical model, including workstation component emitting surface area, ventilation rate, formaldehyde emission rates for each of HWPW, PB, and MDF, and outdoor air formaldehyde concentration, were obtained through a literature search.  On the other hand, information was lacking on the relative amounts of the three CWPs used in the fabrication of office workstations, representative values for the extent to which the workstation components are finished or overlayed, and the barrier effectiveness of the finish or overlay.  Due to these data gaps on representative values for these model parameters, what-if values for indoor air concentration were estimated.  What-if values for indoor air concentration were estimated by first estimating the range of possible values for the following parameters: formaldehyde emission rates for all three CWP types; extent of finishing or overlay of each workstation component; and the barrier effectiveness of the finishing or overlay.  Then, these ranges of parameter values and the representative values for the remaining model parameters were used in Equation 2 to estimate what-if values for indoor air concentration.
What-If Method for Calculating Indoor Air Concentration
The ranges of possible values for three model parameters (CWP emission rate, extent of finishing or overlay, and barrier effectiveness) were estimated as further discussed below.  These ranges consist of low- and high-end values and average or intermediate values, which are presented in Table 3-8, which also contains the representative values for the remaining model parameters.  For the purpose of this assessment, "intermediate" is defined as a value in-between the low-end and the high-end estimates.  Low and high ends of the range of what-if average formaldehyde indoor air concentrations in the workstation volumes were estimated using Equation 2 from the bounding values of the range of values for the above mentioned three model parameters and from the representative values of the remaining model parameters so as to obtain a wide range of indoor air concentration.  Due to data gaps with respect to the relative amounts of the three CWP types used in the construction of office furniture, this approach for estimating what-if indoor air concentration was applied to three limiting cases for the type of CWP of which the office furniture is constructed: only HWPW, only PB, or only MDF.  The results of the three limiting cases are combined into ranges to account for mixtures of different CWP types as discussed in Section 4.5.4.  What-if values for low-end and high-end indoor air concentration were estimated as summarized in Table 3-6.  An intermediate indoor air concentration was also calculated for each of the three limiting cases for the CWP type from the intermediate values of the model parameters.  The representativeness of the range of values for intermediate indoor air concentration (calculated from the three limiting cases for CWP type) is limited by the representativeness of the intermediate values for the extent of finishing and barrier effectiveness, which are unknown.  The intermediate values for the remaining model parameters are expected to be representative of real world values.
Table 3-6. Summary of What-if Method for the Estimation of the What-if Range of Average Indoor Air Concentrations of Formaldehyde in Workstation Volumes
                          Limiting Cases for CWP Type
   Method for Calculating What-if Low- and High-End Indoor Air Concentration

What-if Values for Emission Rate, Extent of Finish or Overlay, and Barrier Effectiveness that are used to Calculate a What-if Low-End Indoor Air Concentration [1]
What-if Values for Emission Rate, Extent of Finish or Overlay, and Barrier Effectiveness that are used to Calculate a What-if High-End Indoor Air Concentration [1]
Workstation panels and work surfaces are constructed of:
* Only HWPW;
* Only PB; or
* Only MDF
* The emission rate of the (unfinished) CWP is equal to the low-end value in a range of values for the emission rates for the unfinished CWP.
* Both sides of workstation panels and workstation work surface are finished or overlayed, and the barrier effectiveness of the finishing or overlay is equal to a highest value in a range of values for barrier effectiveness.
* The emission rate of the (unfinished) CWP is equal to the high-end value in a range of emission rates for the unfinished CWP.
* Both sides of workstation panels and the lower side of the workstation work surface are unfinished (their barrier effectiveness is 0%), and the upper side of the workstation work surface is finished or overlayed and has a barrier effectiveness equal to the lowest value in a range of values for the barrier effectiveness.
[1] The representative values for the remaining model parameters (ventilation rate, workstation component emitting surface area, and outdoor air formaldehyde concentration) were used in the calculation.

The values of all of the model parameters and their bases are given in Table 3-8 below.
Values for Emitting Surface Area and Ventilation Rate
The emitting surface area of each workstation component and the ventilation rate of the work space volume containing the workstation with outdoor air were obtained from the BIFMA / ANSI M7.1-2007 standard test method (BIFMA 2007a), which is based on the work by Carter and Zhang (Carter 2007a) and their analysis of actual office building floor plans and actual office workstations.  The BIFMA / ANSI M7.1-2007 standard test method uses representative values of workstation component emitting surface areas and ventilation rates for the purpose of modeling the impact on office indoor air volatile organic compound (VOC) concentrations due to office furniture emissions.  Therefore, the values for these parameters obtained from BIFMA M7.1-2007 are treated as representative values for the purpose of this assessment.  These values are kept constant and are not varied.
Range of Values for Workstation Component Emission Rate
The BIFMA standard M7.1-2007 and the work by Carter and Zhang do not contain any information on observed formaldehyde emission rates of actual office workstations.  Carter and Zhang provide example workstation emission rates of formaldehyde but do not discuss the statistical significance of these values such as being representative, worst case, etc.  Therefore, workstation component emission rates (emission rates for finished CWPs used to construct the workstation) were estimated using information on CWP emission rates, extent of finishing, and barrier effectiveness.  These three model parameters are discussed in this subsection.
The CWP emission rate is the only parameter of the mass balance equation that will be affected by the FSCWPA; therefore, values for this parameter were obtained for the baseline and for each of the analytical options.  Emission levels for the baseline and for the analytical options were obtained from the EPA market profile (USEPA 2010a) and the EPA draft exposure assessment (USEPA 2009b), respectively, and are presented in Appendix D.  The low-end and high-end emission rates for each CWP type are chosen from the low-end and high-end values from Appendix D.  An average emission rate for each CWP type is calculated as a volume-weighted average of the domestic and imported CWPs that are consumed domestically as was done in the CWP fabrication calculation method.  Table 3-8 summarizes the emission rates used for each calculation step of the what-if method.
As summarized in Table 3-8, the what-if values of the extent of finishing or overlaying of panels used for calculating what-if low-end and high-end indoor air concentrations are zero percent and 100 percent of their emitting surface area.  These values are logical bounding values, as panels may have both surfaces finished for aesthetic reasons or no finishing at all as a conservative estimate.  Similarly, the what-if values of the extent of finishing or overlaying of work surfaces are 50 percent and 100 percent of their emitting surface area.  These values are again logical bounding values, as work surfaces are expected to at least be finished on their upper surface for functional purposes.  In both cases, the surface area of edges was not accounted for because its effect is negligible.
The what-if values for barrier effectiveness used for calculating what-if low- and high-end indoor air concentrations are given in Table 3-8.  The low-end and high-end values for barrier effectiveness were the low-end and high-end values identified in the source CPA 2003a.  Although this source listed example barrier effectiveness values, it did not describe the extent to which any given value represented actual office workstations.  The intermediate barrier effectiveness was calculated using BIFMA standard M7.1-2007 and BIFMA standard X7.1-2007 (BIFMA 2007b).  BIFMA standard X7.1-2007, which was also adopted as an ANSI standard, is a voluntary standard for meeting VOC emission limits from office furniture.  This standard specifies a formaldehyde limit of 50 ppb as measured using the BIFMA M7.1-2007 chamber test for all workstation configuration types.  Fabricators of office furniture who choose to fabricate workstations that meet the requirement of this standard must construct workstations such that they result in a measured chamber concentration using BIFMA M7.1-2007 that does not exceed 50 ppb.  The intermediate value for barrier effectiveness was calculated using Equation 2 subject to the following conditions:
The workstation is tested according to M7.1-2007 and results in a test chamber formaldehyde concentration of 50 ppb according to X7.1-2007;
The panels have 100 percent of their surfaces finished and the work surfaces have 50 percent of their surfaces finished; and
The workstation panel and work surface components are constructed of CWPs such that the CWP emission rate is equal to an average pre-baseline emission rate.

Pre-baseline emission rates were used because these would be the prevalent emission rates at the time the standard was established.  Therefore, the calculated intermediate barrier effectiveness is for the pre-baseline period and is assumed to be relevant to the baseline.  Appendix E describes the method for calculating an intermediate barrier effectiveness in greater detail.
The emission rates used in this analysis are for new composite wood products; therefore, the estimated indoor air concentrations are for new office furniture.  The applicability of the utilized emission level values to the estimation of emissions from new office furniture is uncertain because decay in formaldehyde emissions from newly-manufactured CWPs, which is discussed in Section <IP_ADDRESS>, can occur in the intervening time between manufacture of the CWPs and their use as components of office furniture in an office building.  Hence, the actual emission levels from the unfinished CWPs would be lower than the values used here resulting in an overestimate of the initial steady-state indoor air concentration associated with new office furniture.  Emission level decay can continue after the initial introduction of office furniture into an office.  Such continued decay of emissions with time and consequent decline of indoor air concentration from the initial steady-state level associated with new furniture was not accounted for because the literature search did not yield the necessary information for the estimation of this effect.
In addition to the uncertainty of the temporal decay of emission rates, the uncertainties of emission rates discussed for the CWP fabrication method also apply for the office buildings method.  Some survey responders only stated the compliance standard they would achieve and not the specific emission levels of their products; therefore, all survey data are assumed to represent actual emission levels of products.  CARB ATCM emission standards are based on the ASTM E1333 chamber test method (ASTM 2002a).  Therefore, the emission levels reported in the EPA survey and provided from PSI described in Section <IP_ADDRESS> are assumed to be based on the ASTM E1333 chamber test method (see Appendix E for a description of ASTM E1333).  The emission levels from the survey and the PSI presentation are converted to emission rates in units of flux for use in the indoor air concentration mathematical model according to the equations described in ASTM E1333 (see Appendix E).  ASTM E1333 discusses the precision and bias of the large chamber test method in general.  However, ASTM E1333 does not discuss the accuracy and precision of the analytical test method recommended in ASTM E1333 for measuring formaldehyde levels in the chamber air samples: NIOSH 3500 chromotropic acid test procedure.  The accuracy and precision of this procedure is discussed in NIOSH 3500 (NIOSH 1994a).  ASTM E1333 does not discuss the overall accuracy of the test chamber method for determining accurate formaldehyde off-gassing emission rates.
To determine if chamber test results from ASTM E1333 accurately represent actual off-gassing rates in office buildings, the ASTM E1333 test parameters should be compared with typical office building environment properties.  Using the typical values for ventilation rate and component emitting surface area from Table 3-8 and the typical open plan and private office volumes determined by Carter and Zhang (Carter 2007a) and BIFMA M7.1-2007, the CWP loading ratio and air change rate can be calculated and compared to those values specified in ASTM E1333.  See Appendix E for the associated equations, a description of the ASTM E1333 test parameters, and the typical office environment dimensions.  For this comparison, only the workstation panels and work surfaces were used in the calculation of loading ratio, since this assessment assumes storage surfaces are not constructed of CWPs.  Table 3-7 provides a comparison of the ASTM E1333 parameter values for CWP loading ratio and air change rate with those in typical office environments.  The ASTM E1333 parameter values for the private office environment result in an air change rate consistent with that in a typical private office.  The ASTM E1333 loading ratio for MDF is similar to the total CWP loading ratio in typical private offices, but the loading ratios for HWPW and PB are approximately twice the value for typical private offices.  The ASTM E1333 parameter values for air change rate and all three loading ratios are significantly different from those specified in typical open plan environments.  This assessment did not consider how ASTM E1333 uncertainties would impact the overall uncertainty of the assessment results.  However, it is likely that ASTM E1333 uncertainties are of small impact to the assessment results compared to the uncertainties of other mathematical model parameters.  It is also uncertain as to what extent manufacturers will actually obtain their predicted emission levels in 2013.
Table 3-7. Comparison of ASTM E1333 Parameter Values with Typical Office Environment Properties
                                   Parameter
                               ASTM E1333 Values
                  Typical Office Environment Property Values

                             Open Plan Environment
                          Private Office Environment
Air Change Rate (h[-1])
                                  0.5 +-0.05
                                     0.92
                                     0.53
CWP Loading Ratio (m[2]/m[3]):
HWPW
                                     0.43
                                      1.1
                                     0.22
PB
                                     0.43

MDF
                                     0.26

         Sources: ASTM 2002a; BIFMA 2007a, and Carter 2007a

This office environment model treats a workstation (either private office or open plan) as a single exposure zone.  It also only models the mitigation of airborne concentrations due to the ventilation rate of outdoor air.  The ventilation rate of recirculated indoor air, which can vary from building to building, is not included in the model.  The premise behind this assumption is that recirculated indoor air would contain the same concentration of formaldehyde as is in the exposure zone.  This model assumes that each exposure zone is of the same type (open plan or private office), results in the same formaldehyde concentration, and, therefore, the exposure zones do not affect one another.  Additionally, this model does not account for materials present in office buildings that may act as sinks of formaldehyde, such as carpets and wallboards (Koontz 1996a).
Ambient (Outdoor) Air Formaldehyde Concentration
An average value for the ambient air concentration of formaldehyde is available from the EPA draft report Formaldehyde from Pressed Wood Products: Exposure Assessment (USEPA 2009b).  Table 3-1 of the EPA draft exposure assessment provides ambient air formaldehyde concentrations for various land use categories.  The average value for the commercial land use category, 3.26 ug/m[3], is used as an estimate of the formaldehyde concentration in the outdoor air used in office building ventilation.  This value is kept constant throughout the what-if analysis.

Table 3-8. Estimated Values for Parameters in the Mathematical Model for Average Indoor Air Concentration Resulting from Emissions from Private Office and Open Plan Workstations for the Baseline and Analytical Options
                                Parameter Name
                               Workstation Type
                                   Scenario
                     Value of Parameter Used to Determine:
                                Source of Data

                                     Units
                          Intermediate Concentration
                             Low-End Concentration
                            High-End Concentration

Component Emitting Surface Area
Private office workstation
All scenarios
m[2]
Panels: 7.63
Work surfaces: 6.73
External storage surfaces: 10.55
Indoor air concentration was not assessed for a range of values of emitting surface area because representative values for this parameter were obtained from the BIFMA / ANSI M7.1-2007 test method and used for all calculations. Storage surfaces are assumed not to be constructed from CWPs and do not factor into the final equation.
BIFMA /ANSI M7.1-2007 test method

Open Plan workstation
All scenarios

Panels: 11.08
Work surfaces: 6.10
External storage surfaces: 4.57

Ventilation Rate
Private office work station
All Scenarios
m[3]/h
34.7
Indoor air concentration was not assessed for a range of values of ventilation rate because representative values for this parameter were obtained from the BIFMA / ANSI M7.1-2007 test method and used for all calculations.
BIFMA /ANSI M7.1-2007 test method

Open Plan workstation

15.0

HWPW Emission Rate
Applicable to both private office and open plan workstations.
Baseline
ppm (ug/m[2]-h)

0.043 (60.9)
0.013 (18.6)
0.163 (232.9)
USEPA 2010a

Analytical Option 1: CARB Phase 1

0.025 (36.0)
0.013 (18.6)
0.058 (82.9)
Appendix D: Table D-4 through Table D-6

Analytical Option 2: CARB Phase 2

0.021 (29.8)
0.013 (18.6)
0.032 (45.7)

Analytical Option 3: NAF

0.013 (18.6)
0.013 (18.6)
0.013 (18.6)

PB  Emission Rate
Applicable to both private office and open plan workstations
Baseline
ppm (ug/m[2]-h)
0.057 (81.7)
0.013 (18.6)
0.384 (548.8)
USEPA 2010a

Analytical Option 1: CARB Phase 1

0.054 (77.1)
0.013 (18.6)
0.09 (128.6)
Appendix D: Table D-4 through Table D-6

Analytical Option 2: CARB Phase 2

0.053 (75.8)
0.013 (18.6)
0.057 (81.5)

Analytical Option 3: NAF

0.013 (18.6)
0.013 (18.6)
0.013 (18.6)

MDF Emission Rate
Applicable to both private office and open plan workstations
Baseline
ppm (ug/m[2]-h)
0.076 (180.5)
0.024 (56.7)
0.502 (1,186.5)
USEPA 2010a

Analytical Option 1: CARB Phase 1

0.073 (173.6)
0.024 (56.7)
0.140 (330.9)
Appendix D: Table D-4 through Table D-6

Analytical Option 2: CARB Phase 2

0.073 (172.5)
0.024 (56.7)
0.082 (193.8)

Analytical Option 3: NAF

0.035 (81.6)
0.024 (56.7)
0.035 (82.7)

Extent to Which CWP is Finished
Applicable to both private office and open plan workstations
All Scenarios
Percent of surface area that is finished
100% of panel; 50% of work surface
100% of panel; 100% of work surface
0% of panel; 50% of work surface
Assumed by EPA
Barrier Effectiveness of CWP Finish

Private office workstation
All Scenarios
Percent reduction in emission factor of unfinished CWP
65 [a]
95 [b]
50 [c]
CPA 2007a

Open Plan workstation

71 [a]

Ambient (outdoor) Air Concentration of Formaldehyde
Applicable to both private office and open plan workstations
All Scenarios
ug/m[3]
                                     3.26
Indoor air concentration was not assessed for a range of values of ambient air concentration of formaldehyde because an average value for this parameter was obtained from the EPA draft exposure assessment and used for all calculations.
USEPA 2009b
    a - The barrier effectiveness used to estimate the intermediate concentration was estimated by using the average pre-baseline emission rate of all CWPs (306.7 ug/m[2]-h) and calculating the barrier effectiveness needed to match the BIFMA/ANSI X7.1-2007 emission standard of 50 ppb assuming that 100% of panels and 50% of work surfaces are finished. The calculated barrier effectiveness for private office and open plan workstations were 65% and 71%, respectively.
    b - The highest barrier effectiveness for various barrier types provided in CPA 2003a was 95%.  The highest barrier effectiveness yields the lowest concentration for all else being equal.
    c - The lowest barrier effectiveness for various barrier types provided in CPA 2003a was 50%.  The lowest barrier effectiveness yields the highest concentration for all else being equal.

Estimation of Dermal Exposures to Formaldehyde in Liquid Resin
EPA has developed a series of standard models for quantitatively estimating worker dermal exposures to liquid and solid chemicals during various types of activities.  To estimate dermal exposure, all of these dermal exposure models assume a specific surface area of the skin that is contacted by a material containing the chemical of interest, as well as a specific surface density of the material on the skin.  These exposures can be further normalized by accounting for the body weight of the worker.  The specific methods used to estimate dermal exposures are discussed in detail in Appendix E.
Dermal exposures to formaldehyde contained in liquid urea-formaldehyde (UF) resins are assessed quantitatively during manufacturing according to EPA's standard default model for estimating dermal exposures due to two-hand dermal contact with liquids.  Dermal exposures to formaldehyde due to pressed CWPs are not quantifiable using the EPA dermal exposure models for liquids and solids.  Due to data gaps, quantitative dermal exposure estimates for manufacturing were only made for pre-baseline conditions; baseline and analytical option dermal exposures could not be estimated.  The qualitative dermal exposure assessments for CWP fabrication, wholesale, retail, and commercial use were made for baseline and analytical options.
Exposure Assessment By Life Cycle Stage
Occupational exposures resulting from the manufacture and use of baseline CWPs and effects of the analytical options on the baseline exposures were estimated for CWP fabrication and office building occupancy using the methods described in Section 3.  Exposures were not assessed quantitatively for CWP manufacture, wholesale, and retail due to data gaps.  Instead, qualitative assessments were made for these life cycle stages.  Exposures were not assessed for on-site construction using CWPs and for recycling and disposal of CWPs due to data gaps as discussed in Section 2.
Exposure Assessment for Manufacturing
The assessment of formaldehyde exposures resulting from manufacturing of composite wood products is presented in this section.
Description of Life Cycle Stage
The HWPW, PB, and MDF manufacturing processes include the following general steps: the wood components are prepared, assembled, and bonded together using resin, heat, and pressure.  Urea-formaldehyde (UF) has historically been used in the manufacture of these CWP (USEPA 2010a), and has recently been used in the production of most of the volumes of these CWPs (OAQPS 1999a; OAQPS 2000a).  Hot pressing cures this thermosetting resin which bonds the wood components into panel products (OAQPS 2000b).  UF resin is synthesized from the reaction of urea with formaldehyde; it contains un-reacted formaldehyde and formaldehyde that is generated during its synthesis reaction.  Also, formaldehyde may be formed as the resin cures during hot pressing in the CWP manufacturing process.  Emissions from the CWP result from hydrolytic degradation of the cured resin (which is the reverse of the synthesis reaction), or from the un-reacted (free) formaldehyde (Tohmura 2000a); these emissions are a function of humidity and temperature (USEPA 1996a).  Currently other resins in addition to UF resin are used in the manufacture of the three CWPs.  Poly(vinyl acetate) (PVA) and phenol-formaldehyde (PF) resins are used in the manufacture of HWPW (USEPA 2010a).  Melamine-urea-formaldehyde (MUF) and poly(methylene diphenyl diisocyanate) (pMDI) resins are used in the manufacture of PB and MDF and PF is used in the manufacture of PB as well (OAQPS 2000a).
The HWPW, PB, and MDF manufacturing processes are further described below with emphasis on aspects related to resin processing and potential sources of formaldehyde exposure.  The market profile (USEPA 2010a) provides broad descriptions of the manufacturing processes that complement the descriptions given here.  Most of the references used to obtain the process descriptions below are dated prior to 2006.  In 2006, EPA implemented the National Emission Standards for Hazardous Air Pollutants (NESHAP) for plywood and composite wood products manufacturing industries.  It is unknown whether any process changes were implemented in response to this NESHAP.
Description of HWPW Manufacturing Process
HWPW is generally made by assembling a hardwood veneer to the face and back of a core of veneer, lumber, particleboard, MDF, a combination of these materials, or other special cores (USEPA 2010a).
The overall HWPW manufacturing process consists of the following steps that are presented here as two groups of processing steps (OAQPS 2002b):
Log selection, debarking, bucking (cutting), heating and then further cutting into veneers and drying of veneers; and
Adhesive mixing, veneer assembly and adhesive application, hot pressing, cutting, and finishing.
The two groups combined constitute the manufacturing process in log-based mills; in these mills, the process starts with the conversion of logs into veneer and ends with the production of hardwood plywood.  The processing steps in the first group constitute the manufacturing process in a hardwood veneer plant, which are outside the scope of work because they will not be impacted by the FSCWPA.  The processing steps in the second group constitute the manufacturing process in purchased veneer-based mills and 3-ply mills for which the raw materials are wood veneers or other platforms (USEPA 2010a).
Resin constitutes between 4.5 and eight percent of HWPW by weight (HPVA 2009a).  It is mixed with fillers and extenders prior to application.  The resin is used during the veneer assembly step of HWPW manufacture.  In general, veneer assembly involves coating resin onto various plies of hardwood veneer or other materials and stacking the plies into a glue-bonded assembly.  Most hardwood plywood mills manually lay-up their assemblies.  In the majority of hardwood plywood mills (regardless of size), roll coaters are used to spread resin (USEPA 2010a), and the panels are fed manually into these coaters.  Generally, resin is applied to one side of a back or face ply and then a core ply is laid onto the resin-coated surface of the back or face ply.  This process continues with a subsequent resin application to the core ply followed by the lay-up of another ply.  This process is repeated until the last ply (a back or face ply) is in place (OAQPS 2000b).  An alternative to roll coaters is curtain coaters (pressure head or gravity feed), spray coaters (the glue is either mixed with atomized air or directly atomized using high pressure), and extrusion (glue is turned into foam at 5 times its original volume and the foam is laid on the veneer surface in beads that are spread during pressing) (USEPA 2010a).  Spray coating occurs in spray booths.  The alternative glue application systems may be used in automated lay-up and may allow for reduction in waste glue resulting from the operation of roll coaters.  Other means of reduced adhesive consumption include improved process control (for example, avoidance of over-dried or unevenly dried veneer) and production line cleanliness (to allow quick identification of resin spill sources).  Panel design is also a factor in reduced adhesive consumption (Baldwin 1995a).  After application of the resin, the bundle then moves to a prepress or hot press pre-loader.  Once pressed, the hardwood plywood then is taken to a finishing process where edges are trimmed and the face and back may or may not be sanded smooth.
The primary source of formaldehyde emissions in the HWPW manufacturing process is the veneer dryer (OAQPS 2002b).  Emissions from dryer exhausts are may be controlled with an air pollution control device (OAQPS 2002b).  Even when that is not so, it is likely that a dryer exhaust is vented through a stack.  Hence, it is unknown whether this emission source results in worker exposure.  The press is another source of formaldehyde emissions; emissions from press vents are typically not controlled (OAQPS 2002b).  In addition to vent emissions, formaldehyde may be emitted from the hot press as it opens during the pressing operation (Tohmura 2000a).  Exposure to formaldehyde may also occur while handling the HWPW or performing activities in proximity to the press (OAQPS 1997a; OAQPS 1998a, and OAQPS 1999b).
Description of PB Manufacturing Process
The raw materials for PB manufacturing, or furnish, are wood particles (wood chips, sawdust, planer shavings and other recycled materials).  The manufacturing process consists of wood particle generation or procurement, milling, drying, and blending of the furnish with resin and other additives, forming the resinated material into a mat, hot pressing, and finishing (USEPA 2010a).
In order to ensure that the resin bonds correctly with the particles, which affects both the board's structural characteristics and final HCHO emissions, it is important that the furnish attain a specific moisture content (USEPA 2010a).  The moisture content of the particles entering the dryer may be as high as 50 percent on a wet basis (OAQPS 2000b).  The furnish is dried to a very low moisture content to allow for moisture gained by adding resins and other additives (USEPA 1996a).  Dryer temperature is routinely adjusted based on furnish moisture measurements (OAQPS 2000b).  After drying, face material, or the furnish that will be present on the face of a panel, may be screened for a second time to remove fines, which often absorb too much resin (OAQPS 2002b).  The dried furnish is sent to holding bins, which provide surge capacity (USEPA 2010a).
From the holding bins the furnish is conveyed to blenders and mixed with resin and other additives.  Resin is usually received on-site as a solution of 65% solids in water, stored in tanks, and pumped to the blenders.  Additives may include wax (to impart water resistance to the manufactured product and reduce the tendency for equipment plugging), catalyst (to accelerate resin cure and reduce press time), and scavengers for reduction of emissions from the process and the manufactured product (USEPA 1996a; OAQPS 2000b; USEPA 2010a, and Maloney 1993a).  Furnishes are generally no warmer than 100 F when blended to avoid pre-curing and drying out of the resin (USEPA 1996a).  The furnish may be sampled before and after blending to ensure proper moisture control (OAQPS 1998c).
The dominant type of blender consists of a small horizontal drum with high-speed, high shear impellers (USEPA 1996a; Maloney 1993a).  Resin and its additives are sprayed through air or airless atomizing nozzles or applied by centrifugal atomization.  In the air spray system, the supplied air must be exhausted from the blender but in the airless systems the elimination of atomizing air eliminates the associated air pollution problem.  Additionally, because of the high speed and number of its impellers, the blender, especially when not fully loaded with furnish, can act as an axial-type fan and discharge air causing dusting problems; this may be limited by restricting its air intake (Maloney 1993a).  Most blenders vent through baghouses (OAQPS 2000b).  Blenders generally are designed to discharge the resinated particles into a plenum over a belt conveyor that feeds the blended material to a forming machine (OAQPS 2000b).  In some installations, this plenum is vented back to the blender for recirculation of fines while in other installations it is vented to the suction side of the forming machine (Maloney 1993a).  Some evaporation of moisture (and hence formaldehyde as well) from the furnish may occur from air exposure when conveyed from the blenders to the forming station (USEPA 1996a).
After the blending process, the resinated material is fed to the forming machine that deposits the blended material into a continuous mat. To produce multilayer particleboard, several forming heads can be used in series, or air currents can produce a gradation of particle sizes from face to core (OAQPS 2002b).  Most formers vent to a baghouse (OAQPS 2000b).  The formed mat is pre-pressed (optional), cut into desired lengths, and conveyed to the hot press.  Few presses are vented to an air pollution control device and some of these presses are fully enclosed (OAQPS 2000b).  After pressing, the particleboard panels are cooled, sanded, trimmed to desired final dimensions, and may undergo other finishing operations.  Emissions from most coolers are not controlled and some coolers whose emissions are controlled are fully enclosed.
The primary sources of formaldehyde emissions are the dryers, hot presses, board coolers and blenders (OAQPS 2002b).
Description of MDF Manufacturing Process
The raw materials for MDF manufacturing consist of wood chips, sawdust, planer shavings and other recycled materials which are typically delivered from off-site locations.  The manufacturing process consists of pulping the raw material to fibers in a refiner, drying, blending the fibers with resin and additives, forming the resinated material in a mat, pressing, and finishing (OAQPS 2002b; USEPA 2010a).
Raw material is processed through a steam pressurized refiner which discharges through a blow valve into a blowpipe that is connected to a tube dryer (USEPA 1996a; OAQPS 2000b, and USEPA 2010a).  The pressurized refiner may also vent into the tube dryer.  The tube dryers are directly fired or indirectly heated.  Dryer inlet temperature are on average as high as 270°F.  The wood fiber is pneumatically drawn through the tube dryers and is separated from the dryer exhaust gas in a cyclonic collector.  The dried wood fibers are discharged from the cyclonic collectors through air locks into dry storage bins which provide surge capacity.  The dryer gas exhaust may be vented to an air pollution control device, including incineration based controls or scrubbers (OAQPS 2000b; USEPA 2010a).  Most mills blend resin, wax and other additives by injection into the blowline where they readily mix with the fibers under the turbulent flow conditions present in the bowline.  This occurs prior to the drying of the fiber in the tube dryer but some mills use mechanical blending that applies the additives to the dried fiber (USEPA 2010a).  The blowline system is more frequently used because it is fully enclosed, thereby reducing worker exposure and has superior blending performance.  However, the resin may lose some reactivity as a result of the hot, wet environment in the blowline tube and therefore a higher resin-to-fiber ratio is required as compared to the conventional blender system.  Based on a 1998 site visit report to the Medite Division of Sierra Pine MDF plant, the plant personnel stated that methylene diphenyl diisocyanate (MDI) resins are always added using the blowline system due to potential worker exposure concerns (OAQPS 1998b).
The resinated fibers are conveyed from the dry storage bin, where they are deposited as a mat on a continuously moving screen system (OAQPS 2002b).  Most formers vent to a baghouse (USEPA 1996a).  The deposited mat is pre-pressed and sometimes pre-trimmed prior to transferring to the hot press.  Hot pressing activates the thermosetting resin and bonds the resinated material into a solid panel.  The press may be vented to an air pollution control device, including incineration based controls, scrubbers or a baghouse (OAQPS 2000b).  Additionally, the press area may be partially or fully enclosed and may be vented with fans (OAQPS 2002a).  Based on non-CBI responses from the 1998 information collection request, seven of the 21 presses were fully enclosed at MDF manufacturing facilities (OAQPS 2000a).  After hot pressing, the panels are cooled and finished. The board cooler may be vented to incineration based controls and additionally the cooler may be fully enclosed in a vented enclosure (OAQPS 2000b).  Finishing operations include sanding, trimming, and sawing.
The primary sources of hazardous air pollutant (HAP) emissions (including formaldehyde emissions) at MDF plants include emissions from pressurized refiners, wood dryers, blenders, formers, presses, and board coolers; the finishing operations may also be a source of HAP emissions (OAQPS 2000b).  The largest emission sources are wood dryers and press vents. Formaldehyde emissions are significantly higher after resin application.  For example, dryer emissions from a blowline system are much higher than the dryer emissions from a conventional blender system due to the presence of formaldehyde-based resin in the wood material in the former dryer system.  While fugitive emissions from the blender, former, and cooler may occur, these emissions are much lower and are typically not controlled (OAQPS 2002b).
 Production Volumes and Number of Establishments, Workers, Production Hours, and Work Days
The domestic production volumes and number of sites, or mills, for the manufacture of the three composite wood products are given in Table 4-1 and Table 4-2.  These data are provided for reference purposes only and are not used in the assessment.  These tables present data on the number of mills from the Composite Panel Association (CPA) (AWFS 2009a) and the U.S. International Trade Commission (USITC) (USITC 2008a).  The number of mills reported by the 2007 Economic Census (Census 2007a) is presented in Table 4-3.  The U.S. Census reported a greater number of mills for both NAICS codes than the CPA and USITC sources.  Note that the U.S. Census classifies PB and MDF manufacture under a single NAICS code: 321219  -  Reconstituted Wood Product Manufacturing.  This NAICS code also includes fiberboard, hardboard (HB), oriented-strand board (OSB), waferboard, flakeboard, and chipboard, which are outside of the scope of the assessment.  Similarly, NAICS code 321211 - Hardwood Veneer and Plywood Manufacturing includes the manufacture of hardwood veneers, which are outside the scope of the assessment (see Section 2).  Therefore, the number of mills data for both manufacturing NAICS codes represent mills that manufacture products outside the scope of this assessment.
Estimates for the total number of workers and aggregate production hours worked for the manufacturing of the three composite wood products were obtained from the EPA market profile (EPA 2010a) and the 2007 Economic Census (Census 2007a) and are presented in Table 4-3.  The 2007 Economic Census data are likely an overestimate of the number of workers for the following reasons:
Trade associations reported that mills have closed down; and
NAICS codes 321219  -  Reconstituted Wood Product Manufacturing and 321211 - Hardwood Veneer and Plywood Manufacturing both include products outside the scope of this assessment.
However, it is assumed that the census data on number of workers and aggregate production hours worked are proportionally overestimated such that their ratio, used to calculate production hours per day and days per year, is representative of mills within the scope of the assessment.
Using these data, the average production days per year per worker (assuming eight hours per day), and average production hours per day per worker (assuming 250 days per year) were calculated, and the results are given in Table 4-3.  These calculated values are compared to the OPPT default values.  As default, OPPT assumes people work five days per week and 50 weeks per year (with two weeks of vacation), which results in 250 work days per year.  OPPT also assumes a typical work day is eight hours per day.  As seen in Table 4-3, the calculated production days per year (assuming 8 hours per day) do not deviate from the OPPT default value for frequency of exposure of 250 days per year by more than 10 percent.  Based on this comparison, the frequency of exposure for manufacturing is assessed as 250 days per year.  Similarly, all of the calculated values for production hours per day (assuming 250 days per year) do not deviate from the OPPT default value for duration of exposure of 8 hours per day by more than 10 percent.  Based on this comparison, the duration of exposure for manufacturing is assessed as 8 hours per day.
Table 4-1.  U.S. Hardwood Plywood Production Data and Number of Mills
Hardwood Veneer and Plywood Mill
                          Composite Wood Product Type
             2008 U.S. Production Volume of Composite Wood Product
                            (thousands of ft[2])[1]
                            Number of U.S. Mills[2]
Hardwood Plywood Mills
Hardwood Plywood
                                    748,400
                                      24
  [1] U.S. production volume data obtained from personal communication with HPVA (HPVA 2009a). The plywood thickness basis was not provided.
  [2] Number of U.S. mills obtained from the U.S. International Trade Commission report on wood flooring and hardwood plywood (USITC 2008a).

Table 4-2.  U.S. Reconstituted Wood Product Production Data and Number of Mills
                     Reconstituted Wood Product Mill Type
                          Composite Wood Product Type
2007 U.S. Production Volume of Composite Wood Product (thousands of ft[2] at 3/4" thickness basis)[1]
                            Number of U.S. Mills[2]
Particleboard Mills
Particleboard
                                   3,542,666
                                      34
Medium-Density Fiberboard Mills
Medium-Density Fiberboard
                                   1,884,264
                                      27
  [1] U.S. production volume data obtained from the 2007 North American Downstream Market Report (CPA 2008a).
  [2] Number of U.S. mills obtained from "Update on California's Composite Wood Products Regulation" presented at AWFS Show in Las Vegas, NV on July 18, 2009 provided by CARB to EPA (AWFS 2009a). The presentation was co-presented by CARB and CPA. The number of MDF mills is a high-end estimate that may include some hardboard mills: the presentation did not differentiate between non-CPA-member MDF and HB mills.

Table 4-3.  Summary of 2007 Economic Census Data and Exposure Frequency and
Duration Calculated from These Data for U.S. Manufacturing Mills
                           2007 Economic Census Data
    Parameters Calculated from the Corresponding 2007 Economic Census Data
                                  NAICS Code
                          NAICS Industry Description
                           Number of Establishments
                     Maximum Number of Production Workers
                   Aggregate Production Hours Worked (hours)
            Average Production Days per Year (assuming 8 hours/day)
            Average Production Hours per Day (assuming 250 days/yr)
321219
Reconstituted wood product manufacturing
                                      262
                                    16,076
                                  34,615,000
                                      269
                                     8.61
321211
Hardwood veneer & plywood manufacturing
                                      304
                                    15,504
                                  32,256,000
                                      260
                                     8.32
Source: EPA market profile (USEPA 2010a) and 2007 Economic Census (Census 2007a).

Pre-Baseline Exposure Monitoring Data
This section presents a summary of the inhalation exposure monitoring data collected from OSHA IMIS for the period 2002 to 2009 on the manufacture of HWPW, MDF, and PB as well as a summary of the other compiled inhalation exposure monitoring data on CWP manufacturing.
Table 4-4 provides the maximum, median, and minimum 8-hour TWA personal inhalation monitoring formaldehyde concentrations by worker activity category for the manufacture of HWPW from OSHA IMIS.  Table 4-5 provides the maximum, median, and minimum 8-hour TWA personal inhalation monitoring formaldehyde concentrations by worker activity category for the manufacture of reconstituted wood products, including PB and MDF from OSHA IMIS.

Table 4-4.  Summary of Formaldehyde Inhalation Monitoring Data for Hardwood Plywood Manufacturing Mills from the OSHA IMIS Database
                          Worker Activity Description
                Total Number of Sites where Monitoring Occurred
                          Total Number of Data Points
                    Monitored Formaldehyde Concentration[1]
             Year Monitoring Occurred for the Summary Data Points

                                    Maximum
                                    Median
                                    Minimum
                             Maximum Concentration
                            Median Concentration[2]
                             Minimum Concentration

                                     (ppm)
                                  (ug/m[3])
                                     (ppm)
                                  (ug/m[3])
                                     (ppm)
                                  (ug/m[3])

Press Operation
                                       2
                                       4
                                     1.56
                                    1,917.2
                                     0.695
                                     854.2
                                     0.213
                                     261.8
                                     2003
                                  2003 / 2003
                                     2006
Glue Spreading
                                       2
                                       2
                                     0.32
                                     393.3
                                     0.28
                                     344.1
                                     0.24
                                     295.0
                                     2003
                                  2003 / 2006
                                     2006
Mixing Adhesive
                                       1
                                       1
                                     0.119
                                     146.3
                                     0.119
                                     146.3
                                     0.119
                                     146.3
                                     2006
                                     2006
                                     2006
Lathe Operation
                                       1
                                       1
                                     0.022
                                     27.0
                                     0.022
                                     27.0
                                     0.022
                                     27.0
                                     2004
                                     2004
                                     2004
Production Laborer or Other Operator
                                       2
                                       4
                                     0.142
                                     174.5
                                    0.0695
                                     85.4
                                     0.021
                                     25.8
                                     2007
                                  2004 / 2007
                                     2004
Overall Statistics for All Data Points
                                       4
                                      12
                                     1.56
                                    1,917.2
                                    0.1775
                                     218.1
                                     0.021
                                     25.8
                                     2003
                                  2006 / 2007
                                     2004
    [1] The formaldehyde concentration in ug/m[3] was calculated from the provided concentration in ppm by multiplying the concentration in ppm by 1,229 ug/m[3]/ppm (see Appendix E).
    [2] For worker activities with an even number of data points, the median was calculated as the average of the two middle values.  The years are provided for the two middle values.

Table 4-5.  Summary of Formaldehyde Inhalation Monitoring Data for Reconstituted Wood Product Manufacturing Mills from the OSHA IMIS Database
                                    Worker
                                   Activity
                                  Description
                Total Number of Sites where Monitoring Occurred
                          Total Number of Data Points
                    Monitored Formaldehyde Concentration[1]
             Year Monitoring Occurred for the Summary Data Points

                                    Maximum
                                    Median
                                    Minimum
                             Maximum Concentration
                                    Median
                               Concentration[2]
                                   Minimum
                                 Concentration

                                     (ppm)
                                  (ug/m[3])
                                     (ppm)
                                  (ug/m[3])
                                     (ppm)
                                  (ug/m[3])

Press Operation
                                       1
                                       3
                                     0.12
                                      147
                                     0.089
                                      109
                                     0.009
                                      11
                                     2005
                                     2005
                                     2005
Production Laborer or Other Operator and CSHO
                                       4
                                       6
                                     0.243
                                      299
                                     0.043
                                      53
                                     0.02
                                      25
                                     2005
                                  2006 / 2005
                                     2006
Overall Statistics for All Data Points
                                       4
                                       9
                                     0.243
                                      299
                                     0.051
                                     62.7
                                     0.009
                                      11
                                     2005
                                     2005
                                     2005
   [1] The formaldehyde concentration in ug/m[3] was calculated from the provided concentration in ppm by multiplying the concentration in ppm by 1,229 ug/m[3]/ppm (see Appendix E).
   [2] For worker activities with an even number of data points, the median was calculated as the average of the two middle values.  The years are provided for the two middle values.

Appendix H presents additional historical exposure monitoring data from a variety of studies and reports.  These data are briefly summarized here for reference purposes.  Note that these data include studies from countries other than the United States and their relevance to U.S. mills has not been established.
Plywood Manufacturing Mills Monitoring Data
Sampling data collected in British Columbia from 1992 to 2003 indicate that formaldehyde levels in the plywood manufacturing industry are predominantly below 0.3 ppm (WorksafeBC 2009a).  Other data indicate an exposure range of 0.08 ppm to 0.60 ppm (Fransman 2003a) in the plywood manufacturing sector.
Short-term exposure levels and instantaneous ceiling limit values for plywood manufacturing available from one discussion paper (WorksafeBC 2009a) ranged from 0.14 to 0.29 ppm and 0.33 to 0.44 ppm, respectively, in a 2002 survey.
MDF Manufacturing Mills Monitoring Data
For MDF manufacturing, the highest estimated geometric mean for ambient formaldehyde levels was reported as 0.43 ppm in the main production area of manufacturing facilities in Quebec (Lavoue 2005a).  In one study (Chung et al. 2000a), free formaldehyde levels were determined to be less than 0.14 ppm during machining of the Class B (higher formaldehyde potential) MDF.  According to one Swedish report, formaldehyde levels were at 0.2 ppm (arithmetic mean) between 1980 and 1989 in facilities manufacturing MDF (IARC 1995a).
Particleboard and Fiberboard Manufacturing Mills Monitoring Data
Time-weighted average (8-hour) levels of formaldehyde have been noted to be generally higher than 0.3 ppm in sampling data collected over a period of 15 years (1990 to 2005) for particleboard and fiberboard manufacturing in British Columbia, Ontario, Quebec, and the Netherlands (WorksafeBC 2009a).  Exposures in fiberboard manufacturing ranged from 0.07 to 5.0 ppm for samples taken between 1996 and 2000 (WorksafeBC 2009a). Exposure levels from between 0.1 and 0.4 ppm (Quebec) (Lavoue 2005a) to 1.15 ppm (Scandinavia) (Niemelä and Vainio 1981a) have been noted in other studies of the particleboard and MDF manufacturing industry.
Eight-hour TWA levels of formaldehyde ranging from 0.07 to 0.20 ppm and instantaneous ceiling values that were as high as 7.47 ppm were reported in particleboard manufacturing plants in 2002 (WorksafeBC 2009a).  A median of 0.62 ppm was observed for particleboard workers in measurements taken in 1987/1988 (Horvath et al. 1988a) and a value of 0.3 ppm was reported for particleboard manufacture between 1980 and 1989 (IARC 1995a).
For particleboard manufacturing, formaldehyde exposure levels in the range of 0.08 to 0.9 ppm, with peaks reaching 4.1 ppm, were observed from measurements taken between 1975 to 1983 (Edling 1988a).  Mean levels between 0.4 and 2.3 ppm have been reported for particleboard manufacture by other researchers between 1975 and 1984 (Kauppinen and Niemelä 1985a).  A mean level less than 1 ppm and a maximum level of 1.4 ppm during particleboard manufacture were also reported in 1982 (Preuss et al. 1985a).
Occupational hygienists from WorkSafeBC sampled different locations in a fiberboard plant in British Columbia from January to June 2006 and found formaldehyde levels ranging from 0.03 to 1.19 ppm.  The highest exposure was in the press outfeed area, ranging from 0.32 to 1.19 ppm.
Respiratory Protection Usage During Manufacturing
Since OSHA IMIS data do not provide information on personal protective equipment use, OSHA inspection reports associated with the IMIS data were examined to get an idea of the use of respiratory protection by workers when engaged in manufacturing activities.  Appendix G presents a summary of each reviewed inspection report.
The nine TWA, personal monitoring IMIS data points for PB and MDF manufacturing in Table 4-5 discussed in Section 4.1.3 are associated with four inspections.  Of these four inspections, a total of two inspection reports for PB and MDF manufacturing facilities were requested from OSHA.  One of the two inspection reports (inspection number 307061689; see Appendix G), which accounts for four of the nine TWA, personal monitoring IMIS data points, has been received and reviewed, but the other inspection report was no longer available due to its age.  Additionally, two other inspection reports were requested from inspections prior to 2002 and hence are not associated with the nine data points discussed above.  One of these two inspection reports (inspection number 303864029; see Appendix G) has been received and reviewed, but the other inspection report was no longer available due to its age.  Finally, an additional inspection report (inspection number 312479835; see Appendix G) associated with the CWP fabrication IMIS data (see Section 4.2.3) was requested, received, and reviewed.  Although the facility was identified in IMIS by a fabricator NAICS code, the inspection report states that the facility manufactures MDF and then fabricates flooring from the MDF.  As the monitored workers were associated with the manufacture of MDF, this inspection report is discussed in this section and Appendix G with the manufacturer inspection reports.
Of the three reviewed inspection reports, only one report for a facility that manufactures MDF primarily for flooring indicated the use of respirators by production workers (press assistants) (inspection number 312479835; see Section 4.2.4 and Appendix G).  The workers were observed wearing 3M 6300 half masks with formaldehyde cartridges and had the option to use full-facepiece respirators.  The two TWA measurements taken for press assistants were both below the PEL of 0.75 ppm, although one exceeded OSHA's TWA action level (AL) of 0.5 ppm for formaldehyde.  The two facilities associated with the remaining two inspection reports had TWA measurements below the action level.
The 12 TWA, personal monitoring IMIS data points for HWPW manufacturing in Table 4-4 discussed in Section 4.1.3 are associated with four inspections.  None of these four inspection reports for HWPW manufacturing facilities were requested from OSHA.  However, two inspection reports for HWPW manufacturing facilities were requested from inspections prior to 2002 and hence are not associated with the 12 data points discussed above.  Both of these inspection reports have been received and reviewed.  Neither report indicated the use of respiratory protection.  The first facility had four TWA measurements and three STEL measurements (inspection number 303713325; see Appendix G).  All four TWA measurements were below the action level and all three STEL measurements were below the OSHA STEL of 2 ppm.  The second facility had ten TWA measurements and six STEL measurements (inspection number 123445595); see Appendix G).  All STEL measurements were below the OSHA STEL of 2 ppm.  Two of the TWA measurements were above the OSHA AL but below the PEL; the remainder were below the action level.  This facility was cited by OSHA for formaldehyde overexposure.  The inspection report noted that workers were not observed wearing respiratory protection during the inspection.
Although one inspection report (inspection number 123445595; see Appendix G) for HWPW manufacturing noted that workers were not wearing respirators in spite of exposure levels that exceeded the AL (but were below the PEL), respirator use has been noted in another case in MDF manufacturing (inspection number 312479835; see Appendix G) when exposure levels exceeded the AL (but were below the PEL).  The need to protect against chemicals and particulates other than formaldehyde might also dictate respirator use.  Therefore, the reported use of respirators in the inspection report for the MDF manufacturing facility could have been for protection against chemicals other than formaldehyde or it could be a precautionary practice.  Overall, the limited number of inspection reports that were available and examined does not provide conclusive evidence that respirators are necessarily worn by workers when their exposure meets or exceeds the formaldehyde AL or PEL.
Baseline Exposure and the Effect of Analytical Options on Baseline Exposure for Manufacturing
Baseline exposures and exposures for the analytical options were not assessed quantitatively due to data gaps.  The emission rate data for CWPs presented in Appendix D apply to the CWPs after their manufacture.  Hence, these emission rates are only relevant to the manufacturing process after the pressing operation and are not applicable to the remainder of the process, which includes unit operations in which uncured resins are present and the press.  These sources of formaldehyde cannot be assumed negligible in manufacturing mills.  As indicated in the pre-baseline OSHA IMIS monitoring data presented in Section 4.1.3, formaldehyde exposures have been observed associated with mixing and applying adhesives and pressing operations.  The literature search did not yield information on modeling indoor air concentrations from these sources.  Therefore, exposures during baseline and analytical options are assessed qualitatively.
At baseline, approximately all domestic production of HWPW, MDF, and PB will be in compliance with the CARB ATCM Phase 2 standard, as shown in Table D-3 in Appendix D.  Only small fractions of HWPW and PB domestic production will not be in compliance with the CARB ATCM Phase 2 standard at baseline.
Approximately 0.28% of domestic HWPW production will not be in compliance with any CARB ATCM standard.  However, the emission level of this fraction of HWPW production is estimated to be 0.058 ppm, which is close to the CARB ATCM Phase 2 standard of 0.05 ppm and less than the CARB ATCM Phase 1 standard of 0.08 ppm for HWPW.
Approximately 2% of domestic PB production will not be in compliance with the CARB ATCM Phase 2 standard.[7]  Of this 2% of domestic PB production, approximately 0.2% of domestic PB production will not meet any CARB ATCM emission standard.  However, the emission level of this 0.2% of domestic PB production is estimated to be 0.058 ppm, which is less than the CARB ATCM Phase 2 standard of 0.09 ppm for PB.  Additionally, approximately 1.8% of domestic PB production will be in compliance with the CARB ATCM Phase 1 standard with an estimated emission level of 0.09 ppm.  Hence, the CARB Phase 1 and FSCWPA/CARB Phase 2 analytical options will result in a negligible effect on baseline exposure levels for manufacturing.  Since approximately all domestic production of CWPs are expected to meet the CARB ATCM Phase 2 standard at baseline, only the NAF analytical option will affect baseline exposures.
NAF resins do not contain any formaldehyde.  Therefore, mills that use NAF resins in compliance with NAF standards should achieve a reduction in formaldehyde exposures due to the elimination of the formaldehyde content of resins.  However, wood naturally emits formaldehyde, and it is possible that workers in mills that use only NAF resins may still experience some formaldehyde exposures due to the natural emission of formaldehyde from wood.  Other sources of formaldehyde can exist for mills that apply value-added surfaces.  However, it is uncertain how many mills apply value-added surfaces.
Dermal Exposures during Manufacturing
Dermal exposures to workers during manufacturing can occur during unloading of liquid UF resin.  The free formaldehyde content immediately after manufacture is approximately 0.59% but reduces to 0.15% after 24 hours (Fink 2005a).  For the purpose of this assessment, EPA assumes a formaldehyde concentration of 0.59% in the UF resin.
The EPA/OPPT 2-Hand Dermal Contact with Liquid Model estimates a dermal exposure of 590 to 1,800 mg/day for exposure to a chemical at 100% concentration.  For the assumed formaldehyde concentration of 0.59%, the model estimates worker exposure of 3.5 to 10.6 mg/day.  This results in an estimated dose of 0.05 to 0.15 mg/kg/day for an average 70 kg worker.
The source (Fink 2005) does not specify whether the provided free formaldehyde contents in UF resins are specific to UF resins for CWPs or other applications.  Additionally, Fink (2005) does not specify the statistical significance of the formaldehyde contents, such as being typical, maximum, minimum, etc.  This assessment assumes these formaldehyde contents are typical for UF resins specific for CWPs and representative of pre-baseline conditions.  Additionally, it is uncertain how the free formaldehyde content of CWP resins will change as manufacturers adopt the CARB ATCM limits.  The source (Fink 2005) is from 2005 and may not represent resins at baseline or analytical options.  Therefore, both baseline dermal exposures and the effect of analytical options on baseline dermal exposures are uncertain and cannot be estimated.
Exposure Assessment for Composite Wood Product Fabrication
The assessment of formaldehyde exposures resulting from the use of the three composite wood products (CWPs) in composite wood product fabrication is presented in this section.
Description of Life Cycle Stage
A general description of the manufacturing process is presented below.  The literature search did not yield detailed information on the manufacture of specific composite wood fabrication products (downstream products).  The Office of Enforcement and Compliance Assurance (OECA) sector notebook Profile of the Wood Furniture and Fixtures Industry (OECA 1995a) provides a general process description for wood furniture and fixtures constructed from raw lumber, which does not include composite wood products.  Activities involved in fabrication of wood furniture from raw lumber include drying raw wood; sawing into appropriate sizes, planing and bending (i.e., machining); assembling the wood material into parts; sanding; prefinishing (e.g., watering, sanding, derosination, bleaching); coating by spraying, brushing, or dipping; and finishing (OECA 1995a).  As described below, similar activities are used to produce furniture and fixtures from the composite wood products that are the focus of this assessment.
The following activities (unit operations) are typically used to manufacture wood products, based on a survey of Georgia wood products manufacturers (GDNR 1996a).  Although the reference does not describe if the surveyed manufacturers used composite wood products or raw lumber, it explains that wood product manufacturers may use similar processes to produce different products using different raw materials.  Therefore, the cited activities are likely used to manufacture downstream products using composite wood products as raw materials.  The cited activities include the following:
Application of overlays or decorative surfaces (other than wood or woody-grass veneers);
Assembling;
Gluing;
Spray application;
Painting and coating;
Water-based coating;
Solvent-based coating;
Staining;
Sealing;
Water-based cleaning; and
Solvent-based coating.
These process activities apply to the following CWP fabrication sectors: millwork, cabinet makers, veneer plywood, trusses, prefabricated construction, particleboard and reconstituted wood, wood furniture, miscellaneous furniture, exhibits and showrooms (GDNR 1996a).  Workers are potentially exposed to formaldehyde during the above-listed activities from unfinished and finished (e.g., overlayed, coated, or painted) composite wood products.  However, emission rates from the finished products are generally lower than those from the unfinished products (Battelle 1996a).
Additionally, the following materials, which are used in CWP fabrication, may also be a potential source of formaldehyde exposure during CWP fabrication:
Adhesives used in gluing and overlaying barrier surfaces;
Overlay materials; and
Coatings and varnishes used in finishing operations.
Formaldehyde-based adhesives may be used in upholstered furniture manufacturing based on the contents of an OSHA inspection report associated with the compiled IMIS data (OSHA 2003a).  At the inspected site, formaldehyde-based adhesive is mixed and applied by hand to glue wood sections together.  The inspection report noted that proper PPE was not used during this activity and formaldehyde sampling results were below the action level (OSHA 2003a; see Appendix G).  Workers also use a formaldehyde-based adhesive with a pneumatic gun to assemble wooden chairs.  Workers wear a half-face respirator while assembling the wooden chairs, although the inspection report stated past air sampling indicated formaldehyde levels were below the PEL (OSHA 2003a; see Appendix G).
During the application of overlay materials, adhesive is applied to the decorative overlay, and the overlay and the substrate (composite wood product) are subsequently bonded through a pressing operation.  Based on information associated with similar activities that occur during manufacturing of composite wood products, it is inferred that formaldehyde vapor would be emitted during glue application and hot pressing, resulting in potential for inhalation exposure.  Some overlay materials do not require additional adhesive to be bonded with the wood substrate as they are saturated with reactive resins and partially cured as supplied (CPA 2007a).  The overlays may be saturated with formaldehyde-based resins and thereby serve as another source of formaldehyde.  A CPA technical bulletin indicates that several types of adhesives may be used for the application of overlays to PB and MDF, such as hot melt adhesives, PVA, acrylic-based formulations, UF, PF, and MF resins (CPA 2007a).
The finishing operation for wood furniture and cabinets includes the application of several clear and/or color coatings.  The coating process may be manual or automatic.  The most common manual techniques are wiping, dipping and spraying via spray guns.  Automatic application techniques include robotic spraying, roll coating and curtain coating.  While spraying and coating processes typically occur in ventilated booths equipped with dry filters to control particulates (USEPA 2000a), workers inside the booth can be significantly exposed if they are located in the direction of flow of the coating mist (IRSST undated).  An OSHA inspection report indicates the use of formaldehyde-based coating in the finishing of wood cabinets.  The employer provided respirators to reduce worker exposure to formaldehyde from the coating (OSHA 2008a; see Appendix G).  OSHA offers guidance on safe practices in the woodworking industry through its Woodworking eTool (OSHA 2002a).  OSHA recommends using ventilated, automated systems for applying coatings and adhesives when feasible.  OSHA also recommends that manual spray operations be performed in a spray booth or separate, ventilated area.  Dip coating should be ventilated with an enclosure or capture hood.  The prevalence of the engineering controls described in the OSHA Woodworking eTool is unknown.  In addition to the Woodworking eTool, OSHA has a standard for spray finishing operations (29 CFR 1910.107), which provides detailed requirements for the design and construction of spray booths and rooms (OSHA 2002a).
Some information is available on the amount of natural wood products and composite wood products outside the scope of this assessment in fabricator sites.  According to the EPA market profile (USEPA 2010a), natural wood products and composite wood products outside the scope of this assessment (e.g., hardboard) may be used in the composite wood fabrication sectors.  While the three composite wood products within the scope of work have the highest formaldehyde emission rates, the relative contribution to overall exposure of these other wood products may be considerable if they are present at a site in large quantities relative to the three composite wood products.  Tables 6-4 through 6-20 in the EPA market profile (USEPA 2010a) provide the value of raw materials in each of the sectors.  For the following sectors, the other composite wood products (such as softwood plywood and hardboard) comprise 10% or greater of the total composite wood product material costs, and therefore, could be present in significant quantities relative to HWPW, PB and MDF:
Wood window and door manufacturing (NAICS code 321911);
Other millwork (including flooring) (NAICS code 321918);
Manufactured home (mobile home) manufacturing (NAICS code 321991);
Upholstered household furniture manufacturing (NAICS code 337121);
Wood television, radio, and sewing machine cabinet manufacturing (NAICS code 337129); and
Showcase, partition, shelving, and locker manufacturing (NAICS code 337215).
Therefore, for these sectors, other composite wood products may contribute to overall exposure.  However, this analysis is based only on the costs of the materials and not on the actual volumes of the materials.  Data on actual volumes consumed per sector and data to convert material costs to material volumes were not available.
The information above indicates the possibility of the existence of potential formaldehyde exposure sources other than the composite wood products of interest.  The relative significance of these other sources is not known.  For example, the extent to which formaldehyde-containing coatings are used in CWP fabrication is not known and where such materials are used, the extent to which engineering controls such as ventilated spray booths are used to control exposure is also not known.
Number of Establishments, Workers, Production Hours, and Work Days
Estimates for the number of establishments, total number of workers, and aggregate production hours worked for each of the industry sectors that comprise the composite wood product fabrication life cycle stage were obtained from the 2007 U.S. Economic Census (Census 2007a), and are presented in Table 4-6.  It is uncertain whether all sites within each identified NAICS sector use the composite wood products of interest.  Therefore, the number of sites and workers identified in Table 4-6 may represent facilities that do not use composite wood products and are considered maximum values.  Using these data, the average number of workers per site, average production days per year per worker (assuming eight hours per day), and average production hours per day per worker (assuming 250 days per year) were calculated, and the results are given in Table 4-6.  As seen in Table 4-6, all of the calculated values for production days per year (assuming 8 hours per day) do not deviate from the OPPT default value for frequency of exposure of 250 days per year by more than 10 percent.  Based on this observation, the frequency of exposure for composite wood fabrication in general is assessed to be 250 days per year.  Similarly, all of the calculated values for production hours per day (assuming 250 days per year) do not deviate from the OPPT default value for duration of exposure of 8 hours days by more than 10 percent.  Based on this observation, the average duration of exposure for composite wood fabrication in general is assessed to be 8 hours per day.
The result for duration of exposure of 8 hours per day derived from aggregate census data is supported by duration data given in IMIS.  For all composite wood product fabrication industries identified in Table 4-6 and all exposure types (e.g., TWA, STEL), 182 exposure data points (sampled in the year 2002 through 2009) were collected.  These 182 data points have the following exposure duration data:
Exposure durations of blank, "daily", or other frequency estimate without a duration estimate: 88 data points (48%);
Exposure durations of eight hours per day: 80 data points (44%);
Exposure durations of less than eight hours per day: 10 data points (5%); and
Exposure durations of greater than eight hours per day: four data points (2%).

Table 4-6.  Summary of 2007 Economic Census Data and Exposure Frequency and Duration Calculated from These Data for Composite Wood Product Fabricating Sites
                           2007 Economic Census Data
    Parameters Calculated from the Corresponding 2007 Economic Census Data
                                  NAICS Code
                          NAICS Industry Description
                       Maximum Number of Establishments
                     Maximum Number of Production Workers
                  Maximum Aggregate Production Hours Worked
                             (thousands of hours)
                     Average Production Workers per Site
      Average Production Days per Year Per Worker (assuming 8 hours/day)
      Average Production Hours per Day Per Worker (assuming 250 days/yr)
321911
Wood Window and Door Manufacturing
                                     1,494
                                    62,089
                                    116,209
                                      42
                                      234
                                     7.49
321918
Other Millwork (including flooring) Manufacturing
                                     2,101
                                    34,394
                                    68,475
                                      16
                                      249
                                     7.96
321991
Manufactured Home (mobile home) Manufacturing
                                      376
                                    32,010
                                    60,725
                                      85
                                      237
                                     7.59
321999
All Other Miscellaneous Wood Product Manufacturing
                                     1,964
                                    27,952
                                    54,290
                                      14
                                      243
                                     7.77
337110
Wood Kitchen Cabinets and Countertop Manufacturing
                                     9,683
                                    107,206
                                    213,487
                                      11
                                      249
                                     7.97
337121
Upholstered Household Furniture Manufacturing
                                     1,633
                                    60,721
                                    118,966
                                      37
                                      245
                                     7.84
337122
Nonupholstered Household Furniture Manufacturing
                                     3,428
                                    49,764
                                    95,685
                                      15
                                      240
                                     7.69
337124
Metal Household Furniture Manufacturing
                                      330
                                     8,827
                                    18,527
                                      27
                                      262
                                     8.40
337127
Institutional Furniture Manufacturing
                                      782
                                    25,848
                                    52,006
                                      33
                                      251
                                     8.05
337129
Wood Television, Radio, Phonograph, and Sewing Machine Cabinet Manufacturing
                                      270
                                     1,541
                                     3,094
                                       6
                                      251
                                     8.03
337211
Wood Office Furniture Manufacturing
                                      457
                                    15,167
                                    31,614
                                      33
                                      261
                                     8.34
337212
Custom Architectural Woodwork and Millwork Manufacturing
                                     2,228
                                    32,184
                                    64,362
                                      14
                                      250
                                     8.00
337214
Office Furniture (except wood) Manufacturing
                                      289
                                    19,307
                                    40,614
                                      67
                                      263
                                     8.41
337215
Showcase, Partition, Shelving, and Locker Manufacturing
                                     1,377
                                    34,481
                                    67,716
                                      25
                                      245
                                     7.86
339950
Sign Manufacturing
                                     6,383
                                    52,755
                                    103,305
                                       8
                                      245
                                     7.83
336213
Motor Home Manufacturing
                                      80
                                    14,152
                                    27,550
                                      177
                                      243
                                     7.79
336214
Travel Trailer & Camper Manufacturing
                                      862
                                    39,282
                                    75,327
                                      46
                                      240
                                     7.67
Totals
                                    33,737
                                    617,680
                                   1,211,952
                                      18
                                      245
                                     7.85
     Sources: 2007 U.S. Economic Census (Census 2007a) and EPA market profile (USEPA 2010a)
Pre-Baseline Exposure Monitoring Data
The exposure monitoring data collected from IMIS for the period 2002 to 2009 on composite wood product fabrication are presented in this section.
Table 4-7 provides a summary of all IMIS 8-hour TWA, personal inhalation monitoring data for industry sectors within the composite wood product fabrication life cycle stage.  Summary data for the individual sectors is provided in Appendix F.  Appendix F also provides the maximum, median, and minimum values of the compiled formaldehyde monitoring data for worker activity categories in each sector.  As discussed in Section 4.2.1, sources of potential exposure in CWP fabrication sites include off-gassing of composite wood products and possibly other sources such as paints, adhesives and coatings, etc.  However, the specific sources of exposure associated with the compiled IMIS data are unknown.
Table 4-7.  Summary of All IMIS TWA Personal Monitoring Data for Industries Within the CWP Fabricator Life Cycle Stage
                                   Statistic
                               Concentration [1]

                                      ppm
                                    mg/m[3]
Maximum
                                       1
                                     1.229
Median
                                     0.091
                                     0.112
Minimum
                                    0.00001
                                   0.000012
Average
                                     0.170
                                     0.209
Number of Data Points
                                      120
          Source: OSHA 2009a
          [1] The formaldehyde concentration in mg/m[3] was calculated from the provided concentration in ppm by multiplying the concentration in ppm by 1.229 mg/m[3]/ppm (see Appendix E).

Respiratory Protection Usage During Composite Wood Product Fabrication
Since OSHA IMIS data do not provide information on personal protective equipment use, OSHA guidance on safe practices in the woodworking industry was reviewed to get an idea of OSHA's recommendations for respiratory protection use during composite wood product fabrication.  Inspection reports associated with the IMIS data were also examined to get an idea of the observed use of respiratory protection by workers when engaged in composite wood product fabrication activities.  Appendix G contains a summary of each reviewed inspection report.
The OSHA Woodworking eTool (OSHA 2002a) offers guidance on safe practices in the woodworking industry.  The eTool requires provision of respirators and gloves to workers performing manual spray activities.  Workers downstream of the spraying operation within the spray booth must be provided with an air-supplying respirator (OSHA 2002a).  The prevalence of the practices required or recommended in the OSHA Woodworking eTool is unknown for the composite wood product fabrication industry.
The 120 TWA, personal monitoring data points discussed in Section 4.2.3 are associated with 61 inspections.  Of these 61 inspections, a total of 13 inspection reports for composite wood product fabrication facilities were obtained from OSHA and reviewed.  These 13 inspection reports account for 39 of the 120 TWA, personal monitoring data points.  Six other inspection reports were requested but not reviewed either because they are no longer available due to their age or because they were not obtained in time to be considered for this assessment.  As previously discussed in Section 4.1.4, one of the 13 reviewed inspection reports (inspection number 312479835; see Appendix G) was for a facility identified by NAICS code as a fabricator.  However, the inspection report stated that the facility manufactures MDF and then fabricates flooring from the MDF.  As the monitored workers were associated with the manufacture of MDF, this inspection report is discussed in Section 4.1.4 and Appendix G with the manufacturer inspection reports.  Although this inspection report is associated with the 120 data points discussed in Section 4.2.3, it is not included in the discussion of this section below.
In addition to the 13 reviewed inspection reports, two inspection reports (inspection numbers 303424014 and 304064835) were obtained and reviewed for inspections that occurred prior to 2002 and hence are not associated with the 120 data points discussed above.  Four other inspection reports for inspections dating prior to 2002 were requested but not reviewed either because they are no longer available due to their age or because they were not obtained in time to be considered for this assessment.  Additionally, a single wholesale facility inspection report was requested, received, and reviewed (inspection number 306629171; see Appendix G).  This inspection report is associated with the single wholesale facility IMIS data discussed in Section 4.3.3.  Although IMIS identifies the facility with a wholesaler NAICS code, worker activities described in the IMIS data and inspection report indicate the presence of fabrication activities.  Therefore, this inspection report is discussed in this section and Appendix G with the CWP fabrication inspection reports.  In conclusion, a total of 16 inspection reports were reviewed, and 15 of the reviewed inspection reports are discussed in this section.
In the 15 reviewed reports discussed in this section, all measured formaldehyde concentrations were below the OSHA PEL of 0.75 ppm for formaldehyde, with levels exceeding the action level (AL) of 0.5 ppm in only one facility (inspection number 306021239; see Appendix G).  This single facility is a manufacturer of bath and kitchen wood cabinets and had three TWA measurements exceed the action level.  Workers were not observed to be wearing respirators during the inspection at this site.
Five of the fifteen reports (33%) reviewed indicated the use of a respirator by workers as follows:
One of the five reports identified the use of a half-face air purifying respirator in the mixing area where a formaldehyde-based glue is mixed and applied to wooden frame chairs via pneumatic guns.
Two other reports identified the use of cartridge respirators during spray application of formaldehyde-based coatings.
Another report identified a facility that did not require respirator use in the spray booths, although some workers were observed to be wearing organic vapor cartridge respirators during spraying activities.
The fifth report was for the inspection of a facility in which the only identified inhalation PPE in use was the N95 disposal particulate respirator.
An additional report indicated voluntary use of respirators but respirators were not worn during the inspection.  The remaining nine inspection reports did not note the use or availability of respirators.
As in MDF manufacturing, respirator use by workers in composite wood product fabrication facilities has been noted when formaldehyde levels are below its AL.  This may be a precautionary practice because spraying activities can increase the potential for exposure to formaldehyde or it might result from the need to protect against chemicals and particulates other than formaldehyde.  Only a single instance of the lack of respirator use has been noted (inspection number 306021239; see Appendix G) when exposure levels exceeded the AL (but were below the PEL).
The limited number of inspection reports that were available and examined show worker exposures to be below the formaldehyde PEL but do not provide enough information to conclude that respirators would necessarily be worn by workers when their exposure meets or exceeds the formaldehyde action level or PEL.
Baseline Exposure and the Effect of Analytical Options on Baseline Exposure for Composite Wood Product Fabrication
Monitoring data are a preferred approach for assessing exposure.  However, as previously discussed in Section 3.2, the monitoring data are not adequate for assessing exposure at the baseline and for the analytical options.  Therefore, this exposure assessment uses mathematical modeling to estimate indoor air concentration for the baseline and the analytical options.  The mathematical modeling for indoor air concentration is presented in Section <IP_ADDRESS> and described in detail in Appendix E.
The model parameters include total emitting surface areas for the three CWPs in a CWP fabrication site, CWP formaldehyde off-gassing emission rates, total effective ventilation rate for a CWP fabrication site, and concentration of formaldehyde in the outside air.  As discussed in Section <IP_ADDRESS>, due to data gaps in information on the values of these four parameters at representative CWP fabrication sites, a range of what-if values for indoor air concentration was calculated from bounding values for the ranges of three of the above four parameters.  The what-if method for estimating indoor air concentration was applied to three limiting cases for the CWP type present in the CWP fabrication sites: only HWPW, or only PB, or only MDF.  The calculation of concentration followed the algorithm outlined in Table 3-2.  For each iteration of the algorithm, one parameter is varied between its minimum and maximum values while the other two varying parameters remain at their intermediate values.  The fourth parameter, ambient air concentration of formaldehyde, is kept at a constant value.  These steps were repeated for each CWP type.  The what-if method used values for each parameter according to Table 3-4.
Results for Indoor Air Concentration Calculation Trials and Sensitivity Analysis
Results for the calculation trials for indoor air concentration that summarized in Table 3-2 are presented below.  A sensitivity analysis based on these results was conducted and is discussed below.  Results are presented in Table 4-8 for each of the three calculation trials for the baseline low-end air concentration for each of the three limiting cases for CWP type and similarly for the high-end indoor air concentration.  This table also contains the results of the calculation of a baseline intermediate indoor air concentration for each of the three CWP types.  Similar results are presented in Table 4-9 through Table 4-11 for the CARB ATCM Phase 1, the FSCWPA / CARB ATCM Phase 2, and the NAF analytical options.
The results in Table 4-8 through Table 4-11 demonstrate the sensitivity of the calculated indoor air concentration to variation in the value of each model parameter.  The purpose of observing the sensitivity of the mass balance equation is to understand the impact of the estimated range of values for each parameter of the equation on the calculated concentration.  As the value of one parameter is varied while the other parameters are kept constant, the changes in the calculated concentration resulting from the variation of a single parameter can be compared to the changes in concentration resulting from the variation of other parameters.  For example, the row labeled "Vary Emitting Surface Area" shows the changes in indoor air concentration from varying the emitting surface area from its minimum to its maximum values while keeping effective ventilation rate and emission rate constant at their intermediate values.  This trend is shown for each CWP type.  The results indicate that, for each CWP type, the indoor air concentration is least sensitive to emission rate.  The row "Vary Emission Rate" shows the smallest relative changes in indoor air concentration from low-end to high-end value (relative change is defined as the difference between the high-end and low-end values divided by the low-end value).  Note that for each "vary scenario" the MDF scenario estimates higher exposures than the HWPW and PB scenarios due to the higher emission rates of MDF.
The rows "Vary Emitting Surface Area" and "Vary Effective Ventilation Rate" show relative changes in indoor air concentration of a similar order of magnitude.  At baseline, the relative changes in indoor air concentration due to varying emitting surface area and effective ventilation rate are approximately two to nine times higher than the relative changes due to varying emission rate.  The relative changes in indoor air concentration due to varying emitting surface area are higher than the relative changes due to varying effective ventilation rate.  This effect is due to the wide range of values of emitting surface area chosen (10% and 1,000% of the intermediate value).  This is especially notable given that mathematically the mass balance equation would show greater sensitivity to the effective ventilation rate in general since indoor air concentration is inversely proportional to the effective ventilation rate.  Therefore, particularly at lower values of effective ventilation rate, the indoor air concentration will change more rapidly as effective ventilation rate is changed.  On the other hand, indoor air concentration is directly proportional to emitting surface area and emission rate.  Therefore, indoor air concentration changes linearly with both emitting surface area and emission rate.
Estimation of a Range of Values for the What-If Low-End and the What-If High-End Indoor Air Concentrations that Account for All CWP Types
As summarized in Table 3-2, the what-if low-end and high-end indoor air concentrations for each CWP type were estimated by choosing the minimum and maximum, respectively, of the results of the three calculation trials made for each of these two concentration values.  As discussed in Section <IP_ADDRESS>, the concentration values that were chosen as the estimate of the what-if low-end indoor air concentration for each CWP type were combined into a single range of what-if low-end indoor air concentrations that encompasses all three estimates to account for the possibility that a mixture of the three CWP types is used in a CWP fabrication site.  This was also done for the chosen high-end indoor air concentration for each CWP type.  These ranges for the values of the what-if low-end indoor air concentration and what-if high-end indoor air concentration are given Table 4-12 in for the baseline and the analytical options.
Final Results for the Estimation of What-If Indoor Air Concentrations
The estimated ranges for low- and high-end what-if indoor air concentration given in Table 4-12 were combined into an overall range for the baseline and each of the analytical options.  The overall range is defined as the range bound by the low-end concentration from the low-end range and the high-end concentration from the high-end range.  These overall ranges are presented in Table 4-13.  The best estimate concentration values summarized in Table 4-13 are calculated as the midpoint of the overall range of estimated concentration values for the baseline and each analytical option.  The midpoint of the overall range of estimated concentrations is chosen to represent the best estimate due to the varying uncertainties of the model parameter values, which are discussed in Section <IP_ADDRESS>.  Table 4-13 also provides the percentage reductions in indoor air concentration from the baseline value for the analytical options.
The rationale for this best estimate comes from considering pre-baseline IMIS data for fabrication and uncertainties in model parameters.  Modeling results obtained using pre-baseline emission levels were compared to the pre-baseline IMIS data for fabrication.  This comparison is presented in Figure 4-1 and shows that the midpoint of the lowest and highest model results (the midpoint of the overall range of model results) compares well to the median value of the IMIS data.  The pre-baseline emission levels used in the calculations are given in Appendix D and the corresponding modeling results are given in Appendix I.  However, comparing IMIS data, which are aggregate exposures that may have one or more sources of formaldehyde of which CWPs may or may not be included, to model results for off-gassing alone, is highly uncertain.  Likewise, the representativeness of the model parameter values are of varying uncertainty, as discussed in Section <IP_ADDRESS>.  Therefore, it is most logical to select the midpoint of the lowest and highest model results as the best estimate of formaldehyde concentration.

Figure 4-1. Comparison of Model Results for Ranges of What-If Indoor Air Concentrations using Pre-Baseline Emission Rates with OSHA IMIS Data
The range of what-if indoor air concentrations given in Table 4-13 is the estimate of the range of values for the average concentration of airborne formaldehyde in a CWP fabrication site that is due to off-gassing from HWPW, PB, and MDF.  As presented in Section <IP_ADDRESS> and described in detail in Appendix E, these concentration values were estimated based on a steady-state mass balance that equates the formaldehyde generation rate due to off-gassing from HWPW, PB, and MDF present at a CWP fabrication site to the rate at which airborne formaldehyde is exhausted from the CWP fabrication site through ventilation with outdoor air.  In this model, which is discussed in detail in Section <IP_ADDRESS>, the off-gassing emissions from all of the exposed CWP surfaces are diluted with outside air, which contains the ambient concentration of formaldehyde, and the fabrication site is assumed to be a well-mixed box resulting in a uniform indoor air concentration throughout the site.  The assumption of a well-mixed box model is based on the assumption that the CWP as well as the ventilation sources are for the most part uniformly distributed in a CWP fabrication site.
As discussed in Section <IP_ADDRESS>, due to data gaps in information on the values of the four model parameters at representative CWP fabrication sites, a range of what-if values for indoor air concentration was calculated from bounding values for the ranges of three of the four parameters.  The estimated range for average indoor air concentration at a CWP fabrication site is characterized as a range of what-if results because each concentration value in this range corresponds to combinations of choices, or what-if values, for the model parameters.  Although the prevalence of the model parameter what-if values at actual CWP fabrication sites is unknown, the ranges of the model parameter values should be realistic such that any given choice, or what-if value, for any model parameter represents a possible value at actual CWP fabrication sites.  However, as discussed in Section <IP_ADDRESS>, the ranges of the model parameters were estimated with varying levels of accuracy.  It was not possible to validate the modeling results for indoor air concentration as further discussed in Section 5.1.1.
The Assessment of Exposure Level for the Baseline and the Analytical Options
The duration of exposure was assessed to be eight hours per day as presented in Section 4.2.2; therefore, the estimated what-if steady-state average indoor air concentrations in a CWP fabrication site presented in Table 4-13 are assessed as the 8-hour TWA exposure concentration.  As discussed in Section 4.2.4, there is insufficient information to determine whether respiratory PPE is utilized by workers and therefore the estimated what-if indoor air concentration was assessed as the exposure concentration.
This exposure concentration is due only to off-gassing from the CWP products.  As discussed in Section 4.2.1, there is some indication of potential sources of formaldehyde inhalation exposure in a CWP fabrication site other than off-gassing of formaldehyde from the three CWPs (such as adhesives and the application of overlays).  The relative significance of the contribution of these other potential sources to aggregate exposure is unknown.  Different approaches were considered for their assessment but they were not assessed due to data gaps.
Average daily concentration (ADC) and lifetime average daily concentration (LADC) were calculated for each indoor air concentration value reported in Table 4-13.  As described in Appendix E, ADC and LADC were calculated assuming exposure duration of 8 hours per day and exposure frequency of 250 days per year over 40 working years per lifetime for ADC and over a lifetime of 70 years for LADC.   The ADC and LADC results are presented in Table 4-14 and Table 4-15.
Results in Table 4-13 show that the maximum formaldehyde exposure concentration decreases as lower (more stringent) emission standards are implemented.  However, the CARB ATCM Phase 1 limits result in little or no reduction in exposure from the baseline year.  This effect is because many composite wood products are expected to be already meeting more stringent standards by 2013.  Note the minimum exposure concentrations remain constant throughout the different analytical option periods.  This effect is because a small portion of the market is expected to be already meeting the NAF standards by the baseline period.  The emission levels of NAF-compliant composite wood products are assumed to remain unchanged and no effect of analytical options is expected for these products.

Table 4-8. Results for the Calculation Trials for the What-If Low- and High-End Baseline Indoor Air Concentrations
                               Varied Parameter
                  Calculated Concentration for Baseline, ppm

                               Intermediate [4]
                                  Low End [5]
                                 High End [6]

                                     HWPW
                                      PB
                                      MDF
                                     HWPW
                                      PB
                                      MDF
                                     HWPW
                                      PB
                                      MDF
Vary Emitting Surface Area [1]
                                    0.0095

                                    0.0110

                                    0.0181

                                    0.0055
                                    0.0057
                                    0.0064
                                    0.0488
                                    0.0637
                                    0.1345
Vary Effective Ventilation Rate [2]

                                    0.0058
                                    0.0060
                                    0.0071
                                    0.1362
                                    0.1809
                                    0.3934
Vary Emission Rate [3]

                                    0.0064
                                    0.0064
                                    0.0092
                                    0.0218
                                    0.0445
                                    0.0902
  [1] For area, the intermediate value is based on the aggregate average per-site throughput calculated using domestic composite wood product consumption data from the EPA market profile. The high-end and low-end values are calculated assuming 1,000% and 10% of the aggregate average throughput, respectively.
  [2] Effective ventilation is varied based on values shown in Table 3-3. The low-end, typical, and high-end values are 50, 1,500 and 10,000 cfm, respectively.
  3 Emission rate is varied based on values shown in Table 3-4.
  [4] Intermediate concentration is calculated using intermediate value for surface area, typical value for effective ventilation rate, and weighted-average baseline emission rate for each CWP type.
  [5] Low-end values calculated according to Table 3-2.
  [6] High-end values calculated according to Table 3-2.

Table 4-9. Results for the Calculation Trials for the What-If Low- and High-End CARB Phase 1 Indoor Air Concentrations
                               Varied Parameter
Calculated Concentration for Phase 1, ppm, and % Change from Corresponding Baseline Value

                               Intermediate [4]
                                  Low End [5]
                                 High End [6]

                                     HWPW
                                      PB
                                      MDF
                                     HWPW
                                      PB
                                      MDF
                                     HWPW
                                      PB
                                      MDF
Vary Emitting Surface Area [1]
                                    0.0077
                                   (-18.8%)

                                     0.011
                                    (-3.0%)

                                    0.0176
                                    (-2.7%)

                                    0.0054
                                    (-3.2%)
                                    0.0057
                                    (-0.6%)
                                    0.0064
                                    (-0.8%)
                                    0.0309
                                   (-36.6%)
                                    0.0604
                                    (-5.2%)
                                    0.1296
                                    (-3.6%)
Vary Effective Ventilation Rate [2]

                                    0.0055
                                    (-4.6%)
                                    0.0059
                                    (-0.8%)
                                    0.0070
                                    (-1.0%)
                                    0.0826
                                   (-39.3%)
                                    0.1710
                                    (-5.5%)
                                    0.3787
                                    (-3.7%)
Vary Emission Rate [3]

                                    0.0064
                                     (0%)
                                    0.0064
                                     (0%)
                                    0.0092
                                     (0%)
                                    0.0111
                                   (-49.3%)
                                    0.0143
                                   (-67.8%)
                                    0.0288
                                   (-68.0%)
  [1] For area, the intermediate value is based on the aggregate average per-site throughput calculated using domestic composite wood product consumption data from the EPA market profile. The high-end and low-end values are calculated assuming 1,000% and 10% of the aggregate average throughput, respectively.
  [2] Effective ventilation is varied based on values shown in Table 3-3. The low-end, typical, and high-end values are 50, 1,500 and 10,000 cfm, respectively.
  3 Emission rate is varied based on values shown in Table 3-4.
  [4] Intermediate concentration is calculated using intermediate value for surface area, typical value for effective ventilation rate, and weighted-average Phase 1 emission rate for each CWP type.
  [5] Low-end values calculated according to Table 3-2.
  [6] High-end values calculated according to Table 3-2.

Table 4-10. Results for the Calculation Trials for the What-If Low- and High-End FSCWPA / CARB Phase 2 Indoor Air Concentrations
                               Varied Parameter
Calculated Concentration for FSCWPA / Phase 2, ppm, and % Change from Corresponding Baseline Value

                               Intermediate [4]
                                  Low End [5]
                                 High End [6]

                                     HWPW
                                      PB
                                      MDF
                                     HWPW
                                      PB
                                      MDF
                                     HWPW
                                      PB
                                      MDF
Vary Emitting Surface Area [1]
                                    0.0072
                                   (-23.5%)

                                     0.011
                                    (-3.9%)

                                    0.0175
                                    (-3.2%)

                                    0.0053
                                    (-4.0%)
                                    0.0057
                                    (-0.7%)
                                    0.0063
                                    (-0.9%)
                                    0.0265
                                   (-45.7%)
                                    0.0595
                                    (-6.7%)
                                    0.1288
                                    (-4.2%)
Vary Effective Ventilation Rate [2]

                                    0.0054
                                    (-5.8%)
                                    0.0059
                                    (-1.1%)
                                    0.0070
                                    (-1.2%)
                                    0.0693
                                   (-49.1%)
                                    0.1681
                                    (-7.1%)
                                    0.3763
                                    (-4.3%)
Vary Emission Rate [3]

                                    0.0064
                                     (0%)
                                    0.0064
                                     (0%)
                                    0.0092
                                     (0%)
                                    0.0084
                                   (-61.5%)
                                    0.0110
                                   (-75.4%)
                                    0.0190
                                   (-78.9%)
  [1] For area, the intermediate value is based on the aggregate average per-site throughput calculated using domestic composite wood product consumption data from the EPA market profile. The high-end and low-end values are calculated assuming 1,000% and 10% of the aggregate average throughput, respectively.
  [2] Effective ventilation is varied based on values shown in Table 3-3. The low-end, typical, and high-end values are 50, 1,500 and 10,000 cfm, respectively.
  3 Emission rate is varied based on values shown in Table 3-4.
  [4] Intermediate concentration is calculated using intermediate value for surface area, typical value for effective ventilation rate, and weighted-average Phase 2 emission rate for each CWP type.
  [5] Low-end values calculated according to Table 3-2.
  [6] High-end values calculated according to Table 3-2.

Table 4-11. Results for the Calculation Trials for the What-If Low- and High-End NAF Indoor Air Concentrations
                               Varied Parameter
Calculated Concentration for Phase NAF, ppm, and % Change from Corresponding Baseline Value

                               Intermediate [4]
                                  Low End [5]
                                 High End [6]

                                     HWPW
                                      PB
                                      MDF
                                     HWPW
                                      PB
                                      MDF
                                     HWPW
                                      PB
                                      MDF
Vary Emitting Surface Area [1]
                                    0.0064
                                   (-32.0%)

                                    0.0064
                                   (-41.3%)

                                    0.0110
                                   (-39.3%)

                                    0.0052
                                    (-5.5%)
                                    0.0052
                                    (-8.0%)
                                    0.0057
                                   (-11.1%)
                                    0.0184
                                   (-62.2%)
                                    0.0184
                                   (-71.1%)
                                    0.0637
                                   (-52.7%)
Vary Effective Ventilation Rate [2]

                                    0.0053
                                    (-7.9%)
                                    0.0053
                                   (-11.3%)
                                    0.0060
                                   (-15.1%)
                                    0.0451
                                   (-66.9%)
                                    0.0451
                                   (-75.1%)
                                    0.1807
                                   (-54.1%)
Vary Emission Rate [3]

                                    0.0064
                                     (0%)
                                    0.0064
                                     (0%)
                                    0.0092
                                     (0%)
                                    0.0064
                                   (-70.5%)
                                    0.0064
                                   (-85.5%)
                                    0.0110
                                   (-87.8%)
    [1] For area, the intermediate value is based on the aggregate average per-site throughput calculated using domestic composite wood product consumption data from the EPA market profile. The high-end and low-end values are calculated assuming 1,000% and 10% of the aggregate average throughput, respectively.
    [2] Effective ventilation is varied based on values shown in Table 3-3. The low-end, typical, and high-end values are 50, 1,500 and 10,000 cfm, respectively.
    3 Emission rate is varied based on values shown in Table 3-4.
    [4] Intermediate concentration is calculated using intermediate value for surface area, typical value for effective ventilation rate, and weighted-average NAF emission rate for each CWP type.
    [5] Low-end values calculated according to Table 3-2.
    [6] High-end values calculated according to Table 3-2.

Table 4-12.  Estimated Low-End, Intermediate, and High-End Ranges of Values for the Site-Average Indoor Air Concentration at the Baseline and for the Analytical Options
                                     Case
                              Intermediate (ppm)
                                 Low End (ppm)
                                High End (ppm)
Baseline
                               0.0095  -  0.0181
                               0.0055  -  0.0092
                               0.0218  -  0.3934
Phase 1
                      0.0077 (-18.8%)  -  0.0176 (-2.7%)
                        0.0054 (-3.2%)  -  0.0092 (0%)
                      0.0111 (-49.3%)  -  0.3787 (-3.7%)
FSCWPA / Phase 2
                      0.0072 (-23.5%)  -  0.0175 (-3.2%)
                        0.0053 (-4.0%)  -  0.0092 (0%)
                      0.0084 (-61.5%)  -  0.3763 (-4.3%)
NAF
                      0.0064 (-32.0%)  -  0.0110 (-39.3%)
                        0.0052 (-5.5%)  -  0.0092 (0%)
                      0.0064 (-70.5%)  -  0.1807 (-54.1%)

Table 4-13. Estimated Overall Range and Best Estimate Site-Average Indoor Air Concentration at the Baseline and for the Analytical Options
                                     Case
                              Overall Range (ppm)
                      Best Estimate Concentration1 (ppm)
                          Reduction from Baseline (%)
Baseline
                               0.0055  -  0.3934
                                    0.1995
                                      --
Phase 1
                               0.0054  -  0.3787
                                    0.1920
                                     -3.7
FSCWPA / Phase 2
                               0.0053  -  0.3763
                                    0.1908
                                     -4.3
NAF
                               0.0052  -  0.1807
                                    0.0930
                                     -53.4
                               [1] The best estimate concentration is the midpoint of the overall range. The overall range is defined as the low-end value from the low-end range and the high-end value from the high-end range. The reduction from baseline, ADC, and LADC values are calculated from the best estimate concentration value.

Table 4-14. Overall Range and Best Estimate ADC at the Baseline and for the Analytical Options
                                     Case
                           Overall Range (ug/m[3])
                         Best Estimate ADC (ug/m[3])
Baseline
                                1.556  -  110.4
                                     56.0
Phase 1
                                1.506  -  106.3
                                     53.9
FSCWPA / Phase 2
                                1.494  -  105.6
                                     53.5
NAF
                                1.471  -  50.71
                                     26.1

Table 4-15. Overall Range and Best Estimate LADC at the Baseline and for the Analytical Options
                                     Case
                            Intermediate (ug/m[3])
                         Best Estimate LADC (ug/m[3])
Baseline
                               0.8894  -  63.08
                                     32.0
Phase 1
                               0.8607  -  60.72
                                     30.8
FSCWPA / Phase 2
                               0.8536  -  60.34
                                     30.6
NAF
                               0.8407  -  28.98
                                     14.9

Dermal Exposures during Composite Wood Product Fabrication