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        Hazards Associated with Aerosol Containers and Compressed Gas Cylinders
                                                       - Draft Final Report -

                                                                  Prepared for:

                                Occupational Safety & Health Administration
                                                     200 Constitution Avenue NW
                                                         Washington, D.C. 20210

                                                                   Prepared by:

                                                   Eastern Research Group, Inc.
                                                            110 Hartwell Avenue
                                                            Lexington, MA 02421

                                                                      July 2015

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                                   CONTENTS
                                                                           Page
1.	Executive Summary	1
2.	Container Characteristics	2
2.1	Gases under Pressure	2
2.1.1	Definition and Function	2
2.1.2	DOT Regulations	3
2.1.3	Cylinder Sizes	3
2.1.4	Cylinder Pressures	5
2.1.5	Amounts of Contents	6
2.2	Aerosols	7
2.2.1	Definition and Function	7
2.2.2	DOT Regulations	9
2.2.3	Container Sizes	11
2.2.4	Container Pressures	12
2.2.5	Amounts of Contents	13
3.	Failure Mechanisms	14
4.	Previous Incidents	15
4.1	Compressed Gas Incidents	16
4.2	Aerosol Incidents	19
5.	Summary and Recommendations	23
5.1	Principal Differences between Compressed Gases and Aerosols	23
5.2	Additional Observations	24
6.	References	25
Attachment 1. Specific Insights on "Bulk Aerosol" Products	38

                                LIST OF TABLES

Table 1. Selected DOT Specifications for Cylinders	28
Table 2. Ranges of Compressed Gas Cylinder Properties, by Manufacturer	29
Table 3. Mandatory Specifications for Selected Metal Aerosol Containers	30
Table 4. Ranges of Aerosol Container Properties, by Container Manufacturer	31
Table 5. Compressed Gas and Aerosol Incidents Documented by CPSC, 1999-2013	32
Table 6. Body Parts Injured in Incidents Involving Container Explosions from 2011-2013	33
Table 7. Type of Injury Sustained in Incidents Involving Container Explosions from 2011-2013	34
Table 8. Aerosol Definitions in Selected Government Regulations, Consensus Standards, and Trade Association Publications	35

Executive Summary
In May 2012, OSHA promulgated a new Hazard Communication standard (HazCom 2012). The new standard set forth hazard classification criteria based on categories of health and physical hazards, established new labeling requirements specific to the different hazard categories, and implemented various other requirements.
The new standard was developed to align with requirements in the international Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. That classification system has undergone multiple revisions in the past decade: Revisions 1 through 5 were published in 2005, 2007, 2009, 2011, and 2013. HazCom 2012 is consistent with GHS Revision 3, and specifications in more current GHS Revisions are not necessarily reflected in HazCom 2012.
All GHS Revisions present schemes for classifying physical hazards for 16 different categories of substances. These categories include flammable gases, flammable aerosols, gases under pressure, flammable liquids, and flammable solids. Treatment of aerosols across these categories has differed between GHS Revision 3 -- the version upon which HazCom 2012 is based -- and GHS Revision 4. Some examples of the differences between the Revisions follow:

                                GHS Revision 3
                                GHS Revision 4
Chapter 2.3 applies to "Flammable Aerosols" and has two categories of physical hazards: "extremely flammable aerosols" (Category 1) and "flammable aerosols" (Category 2).
Chapter 2.3 applies to "Aerosols" and has three categories of physical hazards: "extremely flammable aerosols" (Category 1), "flammable aerosols" (Category 2), and "non-flammable aerosols (Category 3).
The mandatory hazard statement for both aerosol categories does not address hazards of high temperatures, as this issue is covered under gases under pressure.
A new mandatory hazard statement -- "Pressurized container: May burst if heated" -- was added in this Revision. (Note: Revision 4 uses "burst" in the hazard statement while Revision 3 uses "explode.")
Aerosols are specifically excluded from the definitions of flammable gases, flammable liquids, and flammable solids. They are not specifically excluded from the definition of gases under pressure.
Aerosols are specifically excluded from the definitions of flammable gases, flammable liquids, and flammable solids. They are also excluded from the definition of gases under pressure.

The subtle differences between the two Revisions have important implications for manufacturers of aerosol products. Under GHS Revision 3 and therefore HazCom 2012, some aerosol products are classified as both "Flammable Aerosols" and "Gases Under Pressure." As a result, these products require two sets of mandatory labels (e.g., symbols, signal words, hazard statements). On the other hand, under GHS Revision 4, all aerosol products fall into one of the three categories under "Aerosols" and therefore need only meet the labeling requirements of one physical hazard category.
This report was developed to document how aerosol products and gases under pressure differ in terms of container characteristics (see Section 2), failure mechanisms (see Section 3), and previous incidents (see Section 4). These differences are important considerations for deciding how best to implement hazard communication requirements for aerosols. Section 6 of this report provides citations for all references used to compile this report.
Container Characteristics
This section reviews the various observations that ERG gathered regarding characteristics of containers used to store and transport gases under pressure and aerosols. Issues considered include applicable U.S. Department of Transportation (DOT) regulations, container design, size ranges, pressure ranges, and quantities of contents.
Gases under Pressure
A broad array of products fall under the category of gases under pressure, but GHS classifies these gases into four categories:
 Compressed gases -- chemicals that are gases under ambient conditions and are also gases when compressed in their containers
 Liquefied gases -- chemicals that are gases under ambient conditions but are at least partially liquid when compressed in their containers
 Refrigerated liquefied gas -- chemicals that are gases under ambient conditions but are at least partially liquid due to low temperatures used in compressed containers
 Dissolved gas -- chemicals that are gases under ambient conditions but are dissolved in liquid solvents when found in compressed containers
This section reviews all information that ERG compiled on containers for gases under pressure, regardless of the categories of gases considered. Section 2.1.1 reviews GHS definitions of gases under pressure, Section 2.1.2 summarizes transportation requirements, and the remaining sections present ERG's observations based on research of product literature from five manufacturers -- Airgas, Air Liquide, Air Products, Matheson, and Praxair.
Definition and Function
GHS Revisions 3 and 4 have similar definitions of gases under pressure. The GHS Revision 3 definition states that gases under pressure are: "...gases which are contained in a receptacle at a pressure of 200 kPa (gauge) or more, or which are liquefied or liquefied and refrigerated." GHS Revision 4 adds to the definition that the 200 kPa pressure cutoff applies at ambient temperature (20 [o]C). Note that 200 kPa corresponds to a pressure of approximately 30 pounds per square inch (psi).
The GHS definitions for gases under pressure and aerosols differ in two ways of relevance to this evaluation: gases under pressure are distributed in containers that can be fillable (and refilled) and gases under pressure are not equipped with hand-activated release devices that allow contents to be dispersed. Rather, gases under pressure are distributed in containers equipped with valves that must be opened for contents to be released. Industrial uses of compressed gas cylinders appear to always involve connections by some means (e.g., hoses, pipes) to other equipment such that gases can be delivered directly to the processes or operations for use. ERG found no industrial applications in which cylinders are intentionally vacated without such connections, but perhaps some exist.
Compressed gas cylinders are used in a broad range of applications. The manufacturers classify their products differently, but examples of niche markets include process gases, medical gases, welding gases, research grade gases, specialty gases, gases for semiconductor applications, lighting gases, and fuels.
DOT Regulations
DOT regulations were reviewed because they limit the size, pressure ranges, and other aspects of compressed gas cylinders transported in the United States. The most relevant DOT regulations are found at 49 CFR 178, Subpart C -- "Specifications for Cylinders." That Subpart outlines compressed gas cylinder requirements for materials of construction, inspections, markings, leakage tests, and limits on sizes, pressures, and wall thicknesses. Table 1 gives an overview of the different cylinder specifications outlined in the DOT regulations.

The many different types of compressed gas cylinders have several commonalities. All cylinders, for instance, are constructed from metal alloys; and some subset of manufactured cylinders must undergo various quality control tests prior to use. Depending on the cylinder type, those tests may include some combination of hydrostatic tests to characterize the elastic expansion of cylinder walls following pressurization, cycling tests to assess performance from repeated pressurization and de-pressurization, burst tests to determine the pressures at which destruction occurs, and leak tests.

Cylinder Sizes
This section summarizes observations on the range of sizes for commercially available compressed gas cylinders. This section focuses on cylinders because most product literature that ERG reviewed referred to compressed gases being available in cylinders; other vessel shapes (e.g., spheres) are used less frequently. Below are ranges of cylinder sizes identified during the project. Refer to Table 2 for a summary of the observations.

 Airgas. The second appendix in the Airgas 2014 specialty gas product catalog presents information on 29 different cylinders used to ship compressed gases (Airgas, 2014). The outside diameters of these 29 cylinders range from 2 inches to 30 inches; the cylinder lengths (or heights) range from 12 inches to 82 inches; the internal volumes across these cylinders range from 0.43 liters to 731 liters; and the tare weights are between 2 pounds and 2,254 pounds.

 Air Liquide. The 2006 specialty gas catalog for Air Liquide -- the most recent complete version accessible online -- presents information on 27 different cylinders used to ship compressed gases (Air Liquide, 2006). The cylinders are presented in three categories: lower pressure cylinders, high pressure mild steel cylinders, and high pressure aluminum cylinders. Overall, the outside diameters of these 27 cylinders range from 3 to 15 inches; the cylinder lengths (or heights) range from 9.5 inches to 55 inches; the internal volumes range from 0.44 to 125 liters; and the tare weights fall between 2 pounds and 303 pounds.

 Air Products. ERG could not locate a comprehensive product guide on the Air Products website, but identified an Air Products "Specialty Gas Cylinder Information" document from a client website (Air Products, not dated). That document identifies 27 distinct cylinders that Air Products uses to ship compressed gases: 10 are categorized as high pressure cylinders, 10 are categorized as low pressure cylinders, and the remaining 7 cylinders are not assigned a category name. According to product specifications, the outside diameters of these 27 cylinders range from 2 to 30 inches; the cylinder lengths (or heights) range from 10 inches to 90 inches; the internal volumes range from 0.43 to 731 liters; and the tare weights fall between 2 pounds and 2,254 pounds. Note that the three largest Air Products "cylinder" products listed in the reference are bulk items that are essentially shipped as small pressurized tanks (see schematics in lower right-hand corner of the first page of the "Air Products, not dated" reference).

 Matheson. Details on Matheson's compressed gas cylinder dimensions are provided in a document titled "Common Industrial Cylinder Dimensions" (Matheson, not dated). That report presents data on 8 cylinders used for acetylene, 4 cylinders used for propane, 4 cylinders used for propylene, and 8 cylinders used for other compressed gas products. Across these 24 cylinders, outside diameters range from 4 inches to 15 inches; cylinder lengths (or heights) range from 13 inches to 55 inches; internal volumes range from 2 liters to 108.4 liters; and tare weights fall between 8 pounds and 178 pounds.

 Praxair. An online specialty gas catalog documents dimensions for Praxair's various compressed gas products (Praxair, not dated). Praxair uses 30 different compressed gas cylinders for its products -- and this does not include the containers used to distribute liquid helium, cryogenic containers, and Praxair's "microbulk" containers. The 30 compressed gas cylinders are classified into different categories: ultra high-pressure steel cylinders, high-pressure steel cylinders (large capacity and small capacity), high-pressure aluminum cylinders, low-pressure steel cylinders, and low-pressure stainless steel drums and cylinders. Across these 30 container types, outside diameters range from 2 inches to 29.75 inches; cylinder lengths (or heights) range from 14 inches to 55 inches; internal volumes range from 0.42 liters to 454.49 liters; and tare weights fall between 4 pounds and 315 pounds.

Overall, cylinder sizes varied considerably across different compressed gas products and vendors. This variability is not surprising given the broad range of end-use applications, which includes small quantity applications for research laboratory settings through large quantity applications in industrial manufacturing processes. As Table 2 shows, the range of cylinder factors across all five vendors was: 2-30 inches in diameter; 9.5-82 inches in length (or height); 0.43-454.49 liters in internal volume; and 2-2,254 in tare weight.

Cylinder Pressures
Compressed gas cylinder pressures also vary considerably from one gaseous product to the next. Below are ranges of pressures that ERG identified during its research. Refer to Table 2 for a summary of the observations.

 Airgas. The Airgas 2014 specialty gas product catalog includes cylinder pressure information on 46 pure gases (Airgas, 2014). For many of these gases, Airgas offers products of varying purity, moisture content, and other characteristics. Therefore, these 46 pure gases actually reflect hundreds of individual products. ERG viewed pressure specifications for every entry in the 2014 specialty gas product catalog and found that container pressures ranged from 4.4 psig to 6,000 psig. The gases sold at highest pressures (greater than 1,000 psig) were primarily atmospheric gases or inert gases (e.g., air, argon, helium, hydrogen, krypton, neon, nitrogen, oxygen). Airgas also sells hundreds of gas mixture products. While product specifications for these mixtures do not include the container pressures, ERG does not expect any of the mixtures to have pressures considerably outside the range for the pure gas products (i.e., 4.4 psig to 6,000 psig).

 Air Liquide. The Air Liquide catalog is organized into different categories of gases. Data on cylinder pressure were obtained for the 26 "pure gases" identified in the 2006 catalog (Air Liquide, 2006). Across these products, container pressures ranged from 10 psig to 2,640 psig. Consistent with the previous bulleted item, the gases sold at highest pressures tended to be atmospheric gases or inert gases. Although a detailed accounting of cylinder pressures for Air Liquide's gas mixture products was not located, ERG does not expect them to be considerably different from the pressures identified for the pure gas products.

 Air Products. Unlike the online product literature for Airgas and Air Liquide, the product specifications for Air Products are not readily searchable for compressed gas cylinder pressure ranges. ERG therefore did not compile cylinder pressure statistics for this manufacturer.

 Matheson. The Matheson online catalog presents cylinder pressure information for 47 different specialty pure gases (Matheson, not dated). These products had container pressures ranging from 4.4 psig to 6,000 psig. Consistent with previous bulleted items, the gases sold at highest pressures tended to be atmospheric gases or inert gases (e.g., argon, helium, nitrogen). The Matheson online catalog also includes cylinder specifications for hundreds of compressed gas mixtures. ERG did not review and document cylinder pressures for these mixtures, but does not expect them to be considerably different from the pressures identified for the pure gas products.

 Praxair. The Praxair online catalog presents cylinder pressure information for 52 different specialty pure gases (Praxair, not dated). These pure gas products, which do not include gas mixtures or cryogenic liquids, had container pressures ranging from 2 psig to 6,000 psig. Consistent with the previous bulleted item, the gases sold at highest pressures tended to be atmospheric gases (e.g., air, hydrogen, nitrogen, oxygen) or inert gases (e.g., argon, helium, neon). The online catalog also includes cylinder specifications for hundreds of compressed gas mixtures. ERG did not review and document cylinder pressures for these mixtures, but does not expect them to be considerably different from the pressures identified for the pure gas products.

Table 2 summarizes the broad range of pressures -- 2 to 6,000 psig -- that ERG identified when reviewing pure gas products offered by five manufacturers. Generally, the highest pressure cylinders were used for atmospheric gases and inert gases. The lower pressure cylinders (i.e., with varying pressures between 2 and 1,000 psig) were for more toxic substances, such as gases used in semiconductor manufacturing (e.g., arsine, phosphine), refrigerants, organic compounds, and various others.

Amounts of Contents
The amount of product gas within a compressed gas cylinder ultimately depends on the cylinder volume and pressure. Below are ranges of gas contents identified during the project. Refer to Table 2 for a summary of the observations.

 Airgas. The Airgas 2014 specialty gas product catalog includes information on "contents" for 46 pure gases (Airgas, 2014). For 33 of these pure gas products, contents are expressed in units of pounds, and the values range from 4 pounds to 1,300 pounds; for 10 of these products, contents are expressed in units of cubic feet, with values ranging from 8 to 575 cubic feet; and for the remaining 3 products, contents are expressed in units of liters, and the values range from 25 to 9,000 liters. As noted previously, Airgas also sells hundreds of gas mixture products. However, ERG does not anticipate the contents for these mixtures to fall considerably outside the range for the pure gas products.

 Air Liquide. Of the 26 pure gases listed in the Air Liquide catalog (Air Liquide, 2006), 12 gases -- mostly organic compounds -- had contents expressed in units of pounds. For these gases, the contents weighed anywhere from 0.25 pounds (for a research grade product) to 420 pounds (for a high-volume product). For the remaining 14 gases -- mostly atmospheric gases and noble gases -- contents were expressed as volumes and ranged from 0.4 cubic feet to 13,540 cubic feet.

 Air Products. Unlike the online product literature for Airgas and Air Liquide, the product specifications for Air Products are not readily searchable for the amount of contents across all product gases. ERG therefore did not compile these data for this manufacturer.

 Matheson. The 47 pure gases listed in the Matheson online catalog (Matheson, not dated) present information on gas contents in different units. For 33 of the pure gases, contents are expressed in units of pounds, and these values ranged from 0.25 pounds to 1,055 pounds. For the remaining 14 gases -- which again are mostly atmospheric gases and noble gases -- contents were expressed as volumes and ranged from 0.25 cubic feet to 3,360 cubic feet.

 Praxair. The 52 pure gas products listed in the Praxair catalog (Praxair, not dated) presented similar gas content information to that of other manufacturers. For the pure gases with contents expressed in units of pounds, the values ranged from less than 1 pound to 600 pounds. For the pure gases with contents expressed in units of cubic feet (which primarily occurred for atmospheric gases and noble gases), quantities ranged from 19 cubic feet to 575 cubic feet.

Table 2 summarizes the observations listed above. In general, manufacturer specifications for atmospheric gases and noble gases (with some exceptions) expressed contents in units of cubic feet. The range of values across all five manufacturers considered was 0.4 cubic feet to 13,540 cubic feet, with the largest value being a helium product offered by Air Liquide. For the remaining gases, contents were expressed in units of pounds and ranged from 0.25 to 1,300 pounds.

Aerosols
Aerosols are an extremely broad range of products used for consumer applications (e.g., personal grooming products, cooking sprays, air fresheners), medical and pharmaceutical applications (e.g., inhalers, first aid sprays), industrial applications (e.g., janitorial products, insecticides, automotive products, polishes), and various other uses. Aerosols can be used to apply liquids, solids, and foams to surfaces. GHS Revision 3 classifies "flammable aerosols" in two categories: "extremely flammable aerosols" and "flammable aerosols." Further, according to GHS Revision 3, some aerosol products may also be "not classified" depending on their properties. These properties include heat of combustion, ignition distance test results, and deflagration density for spray aerosols; and they include flame height and flame duration during foam tests for foam aerosols. On the other hand, under GHS Revision 4, all aerosol products are classified into one of three categories: "extremely flammable aerosols," "flammable aerosols," and "non-flammable aerosols."

This section reviews all information that ERG compiled on aerosol containers and products, regardless of their GHS classifications. Section 2.2.1 reviews GHS definitions of aerosols and discusses implications of those definitions, Section 2.2.2 summarizes transportation requirements, and the remaining sections present ERG's observations based on information obtained from manufacturers of aerosol containers and manufacturers of aerosol products.

Definition and Function
Although GHS Revision 3 has a physical hazard chapter on "Flammable Aerosols" and GHS Revision 4 has a chapter on "Aerosols," the two Revisions' definitions for aerosols are identical. Those definitions state: "Aerosols, this means aerosol dispensers, are any non-refillable receptacles made of metal, glass or plastics and containing a gas compressed, liquefied or dissolved under pressure, with or without a liquid, paste or powder, and fitted with a release device allowing for the contents to be ejected as solid or liquid particles in suspension in a gas, as a foam, paste or powder or in a liquid state or in a gaseous state." In short, this definition covers virtually any pressurized product in non-refillable containers that is equipped with a device that allows the contents to be sprayed.
The basic premise behind virtually all aerosol products is the use of pressurized propellants to disperse an active ingredient, which may be a gas, liquid, or solid. The chemicals used as propellants have changed considerably in recent decades. Chlorofluorocarbon propellants were previously used in many products, but their use has been largely eliminated -- except for some pharmaceutical products (e.g., inhalers) and other specialty applications -- due to concerns over their role in stratospheric ozone depletion. To identify propellants commonly used in aerosol products today, ERG reviewed multiple online catalogs, product specifications, and trade association publications, and consulted with an aerosol manufacturing company (e.g., O'Brien, 2015; Diversified Products, 2015; Consumer Aerosol Products Council, 2015). Propellants are categorized in different ways, with one categorization scheme being:
 Inert gases (e.g., air, carbon dioxide, nitrogen)
 Hydrocarbon gases (e.g., formulations containing varying amounts of low molecular weight hydrocarbons, such as ethane, propane, butane isomers, and pentane isomers)
 Ether gases (e.g., dimethyl ether)
 Fluorocarbons (e.g., 1,1-difluoroethane [or HFC-152a], 1,1,1,2-tetrafluoroethane [or HFC-134a])
According to multiple accounts (e.g., Consumer Products Aerosols Council, 2015), the most commonly used propellants in aerosol products are mixtures of hydrocarbon gases. In addition to the above examples, aerosol manufacturers also prepare binary and tertiary mixtures of propellants and custom blends for specific applications (Diversified Products, 2015). The propellant selected for a given product ultimately depends on desired properties and multiple factors, which typically include cost, chemical compatibility, flammability, toxicity (especially for pharmaceutical and medical applications), and regulatory considerations.
The amount of propellant within an aerosol product varies. One review of aerosol formulations indicates that hydrocarbon propellants -- the most common propellants for aerosol products -- are typically found at 4 to 10 percent of the products' net content (Geer, 2011). This composition is consistent with insights ERG gained during discussions with an employee from an aerosol product manufacturer (O'Brien, 2015). As the exception, that individual noted that their company has one aerosol product in which propellants account for nearly 50 percent of the net content; however, he emphasized that such a high propellant composition is rarely encountered.
Another important consideration in performance of an aerosol product is container design, particularly that of the spray valve. The release mechanism is carefully designed to control the flow rate at which products are dispersed, the extent of atomization, and the velocity with which contents are ejected -- all of which are tailored to individual product demands (e.g., desired droplet size, spray area). Sections 2.2.3 through 2.2.5 present further information on characteristics of aerosol containers.
Finally, in researching aerosol products, ERG identified different means by which containers release products, and these differences have direct bearing on the likelihood of worker exposure to aerosol-related hazards. For purposes of this report, we define the following use categories:
 Manual "on-demand" activation: This appears to be the most common form of aerosol use, in which products are dispersed when -- and only when -- the user opens the release valve by depressing an actuator. According to one manufacturer, more than 95 percent of their products fall into this use category (O'Brien, 2015). In terms of potential exposures to products and propellants, it is important to note that a user operates and dispenses these products typically within an arm's reach of his or her breathing zone.
 Manual release of all contents: These products -- sometimes referred to as "total-release foggers" -- are similar to those from the previous category, except that the entire contents of fogger products are gradually released after the user depresses the actuator. Most fogger products identified by ERG are used as pesticides (e.g., "bug bombs"), though other applications may also exist.
 Remote activation products: These aerosol products release contents without a user depressing the actuator. ERG's research identified two general categories of such products: some products are activated by motion sensors and some are activated by timers, usually at fixed intervals. Air freshener aerosol products are available in both motion-activated and time-release containers. Other examples include motion-activated pet deterrents (i.e., products that release sprays when pets approach locations where they are not supposed to be) and time-release bird repellants used to deter birds from nesting in unwanted locations.
DOT Regulations
DOT regulations were reviewed because they limit the size, pressure ranges, markings, and other aspects of aerosol containers. At 49 CFR 171.8, DOT defines aerosols as "any non-refillable receptacle containing a gas compressed, liquefied or dissolved under pressure, the sole purpose of which is to expel a nonpoisonous (other than a Division 6.1 Packing Group III material) liquid, paste, or powder and fitted with a self-closing release device allowing the contents to be ejected by the gas." Under this definition, DOT would not classify products in non-refillable containers fitted with release device that only contain gases as aerosols, but GHS would classify such products as aerosols.

The most relevant DOT regulations addressing container properties are found at 49 CFR 173.306 ("Limited Quantities of Compressed Gases") and 49 CFR 178, Subpart B ("Specifications for Packagings"). These regulations specify maximum capacities, filling limits, performance test requirements, maximum sustainable pressures for aerosol containers, and various other parameters that must be met for products shipped within the United States. The regulations and their exceptions effectively result in the overwhelming majority of aerosol products being distributed in the following DOT containers:

 Non-specification Containers: These containers are made of metal with pressures below 140 psig at 130 [o]F, and they cannot have volumes greater than 1 liter. 49 CFR 173.306 lists performance requirements for all aerosol containers, including the non-specification ones. For instance, these containers must be able to withstand pressures of 1.5-times the "equilibrium pressure of the contents" at 130 [o]F. These containers do not have minimum wall thickness or marking requirements.

 Metal "2P" Containers: This specification is required for metal containers when aerosol pressures fall between 140 psig and 160 psig at 130 [o]F. As with the non-specification containers, the 2P containers must be no larger than 1 liter. Refer to Table 3 for further details on mandatory requirements for 2P containers.

 Metal "2Q" Containers: This specification is required for metal containers when aerosol pressures fall between 160 psig and 180 psig at 130 [o]F. As with the non-specification containers, the 2Q containers must be no larger than 1 liter. Refer to Table 3 for further details on mandatory requirements for 2Q containers.

 Plastic "2S" Containers: A relatively new development in this industry is use of plastic aerosol containers. Unlike the DOT metal container requirements, some of which date back to the 1960s, the requirements for 2S plastic containers at 49 CFR 178.33b were only promulgated in 2008. Those requirements limit 2S plastic containers to 1 liter in volume and inside diameters to no more than 3 inches. Manufacturers are also required to conduct "drop tests" to assure the integrity of the containers and burst testing to demonstrate that containers can withstand pressures up to 240 psig.

 DOT-39 Containers: Although DOT's requirements for "39" containers are listed under the "Cylinder" specifications at 49 CFR Part 178, Subpart C, some of the 39 containers appear to be technically classified as aerosol products. These containers must be made from steel or aluminum and their maximum capacity depends on the container pressure: containers with pressures greater than 500 psig must have "maximum water capacities" less than 277 cubic inches (10 pounds water), and containers with pressures less than 500 psig are allowed to have capacities up to 1,526 cubic inches (55 pounds water equivalent). An absolute maximum pressure is not specified, but the regulation states that service pressures must be less than 80 percent of test pressures.

Of the previous five categories of containers, the non-specification, 2P, and 2Q containers appear to account for the overwhelming market share of aerosol products used in consumer and industrial applications. This statement is based on ERG's observations when searching aerosol products and aerosol literature over the last several months, and is supported by the input provided by a manufacturing representative who stated that all of their aerosol products are shipped in these three types of containers (O'Brien, 2015).

Despite efforts to place all aerosol products in the aforementioned categories, some exceptions clearly exist. Most notably, manufacturers may petition DOT for special permits to use containers with contents, dimensions, pressures, or other features outside the mandatory ranges. In these cases, manufacturers must first demonstrate that their proposed containers achieve an equivalent level of safety as an authorized container. DOT will then review the justification before issuing a special permit or rejecting the application. As an example of a special permit, DOT currently allows a manufacturer to ship certain 2P aerosol products in containers with inside diameters up to 4.18 inches (as opposed to the regulatory limit of 3 inches), but the special permit requires thicker container walls for the wider containers, as well as other additional requirements (DOT, 2014). Through direct consultation with DOT, ERG learned that most recent special permits for aerosol containers have been issued for certain refrigerant and liquefied petroleum gas (LPG) products. Special permits were needed for these products for various reasons, but largely because they are entirely gaseous, and therefore would not be classified as "aerosols" by DOT. Earlier this year (2015), DOT issued a Notice of Proposed Rulemaking -- "Hazardous Materials: Incorporation of Special Permits into the Hazardous Materials Regulations (MAP-21)" -- that will essentially allow these gaseous products to be shipped in aerosol containers without the need for special permits. The proposed rulemaking introduces a "2Q1" container type that has virtually identical specifications to those for 2Q containers, except they allow for higher pressures and have other minor differences. For other types of products (i.e., outside of refrigerants and LPG products), DOT receives considerably less special permit requests, and the nature of these requests varies from one product to the next.

The previous discussion provides an overview of DOT regulations and their implications for aerosol products affected by the Hazard Communication standard requirements (e.g., products used in industrial settings). ERG notes that additional aerosol containers are allowed for various applications that tend to be found primarily in consumer products. For instance, DOT regulations allow for perfumes and certain other consumer aerosol scent products to be transported in glass containers. These examples are not reviewed here because their labeling, packaging, and other specifications would fall under Consumer Product Safety Commission (CPSC) requirements.

Container Sizes
Although DOT regulations (see Section 2.2.2) limit container sizes for most commercially available aerosol products, ERG still reviewed product literature and manufacturers' specifications to determine the range of container sizes in use today. The following list (and Table 4) summarizes ERG's observations, organized by aerosol container manufacturer, with insights on "bulk aerosol" containers included at the end of this section. (Note: By convention, manufacturers in this field round their container sizes to sixteenths of inches; ERG converted those numbers to tenths of inches for this summary.)

 Ball Corporation products. Ball Corporation -- a Colorado-based manufacturing company -- has a product website that lists 24 different aerosol containers that the company distributes to customers (Ball, 2015). The container diameters range from 1.8 inches to 2.9 inches; the container heights range from 2.9 inches to 10.0 inches; and the container volumes range from 4.7 fluid ounces to 33.8 fluid ounces.

 Illing Company products. Illing Company is based in Wisconsin and manufactures a wide range of packaging products. Illing's website (Illing, 2015) lists 12 aerosol container products with dimensions ranging as follows: the container diameters range from 2.1 inches to 2.9 inches; the container heights range from 3.9 inches to 9.5 inches; and container volumes range from 6.0 fluid ounces to 25.0 fluid ounces.

 ITW Sexton products. ITW Sexton, headquartered in Illinois, manufactures aerosol containers at an Alabama facility for eventual use in surface coating, adhesives, and sealants. The company makes more than 50 distinct parts which are shipped in 10 different container sizes. According to the ITW Sexton online catalog for aerosol containers (ITX Sexton, 2015), these 10 containers have diameters between 2.1 inches and 3.0 inches; heights between 3.9 inches and 10.4 inches; and container volumes between 7.7 fluid ounces and 33.8 fluid ounces.

 McKernan products. McKernan Packaging Clearing House is a Nevada-based distributor of "discount packaging" products, and the company's online catalog lists 57 different aerosol containers (McKernan, 2015). The container diameters range from less than 1 inch to 2.7 inches; the container heights range from less than 1 inch to 9.5 inches; and the container volumes range from 1.1 fluid ounces to 28 fluid ounces.

The previous list confirms that the four container manufacturers produce aerosol containers with dimensions that fall within the ranges specified for DOT 2P and 2Q categories. However, as noted in the previous section, ERG also found evidence of larger aerosol products (i.e., those that fall within DOT 39 cylinder specifications). For instance, ERG identified a manufacturer that produces an "aerosol bulk product" container (Sprits, 2015), but the website does not specify the container dimensions. We also identified specific products shipped in DOT 39 containers that appear to meet the definition of GHS aerosols (under Revision 3 and 4), depending on how one interprets "fitted with a release device" (see Attachment 1). This issue may be open for interpretation because the manufacturer ships the containers along with the release device fittings (i.e., hoses, spray guns), but the customer connects the fittings to the containers.

As one example of these larger aerosol containers, 3M manufacturers an entire product line of "cylinder spray adhesives" (e.g., 3M, 2013) that are shipped in DOT 39 containers, with some of these products being non-refillable containers. The largest of these products is shipped as a cylinder that is 24 inches in diameter and 45 inches tall -- this product is equipped with pallet legs to better enable workers to operate the equipment. Container volumes range from 5 gallons to 50 gallons (3M, 2013); and the smaller containers offered by this manufacturer are generally not refilled. Further, Amtrol offers a line of refrigerant products that are sold in non-refillable DOT 39 containers; these containers have maximum dimensions of 12 inches in diameter and 17.6 inches in height (Amtrol, 2011). Images of these larger DOT 39 containers can be viewed at the websites listed in the corresponding references and in Attachment 1 to this report. However, without information on the full range of test parameters for the product chemicals and the release mechanisms, it is not clear if these non-refillable containers would fit the GHS Revision 3 definition for "Flammable Aerosols" (i.e., they could be "not classified" if the contents do not meet GHS Revision 3 flammability criteria). See Attachment 1 for further information.

Container Pressures
This section reviews information that ERG accessed on container pressures for aerosol products. ERG summarizes container pressure information first for the typical, hand-held aerosol containers and then for the "bulk aerosol" containers:

 Pressures for 2P and 2Q containers. The companies listed in the previous section generally manufacture -- but do not fill -- aerosol containers. Therefore, the resources cited in Section 2.2.3 provided no insights on container pressures for aerosol products. However, the overwhelming majority of aerosol containers that ERG identified are classified under DOT regulations either as non-specification, 2P, or 2Q. As Table 3 shows, the highest allowable pressures allowed for these containers is 180 psig at 130 [o]F. The limited insights ERG received on actual products confirms that pressures for small aerosol containers indeed fell within this range. Specifically, one manufacturer representative emailed OSHA a list of sample aerosol products and their corresponding container pressures at 70 [o]F, all of which ranged from 43 psig to 161 psig (O'Brien, 2014); and this individual subsequently confirmed that these products are only distributed in non-specification, 2P, or 2Q containers (O'Brien, 2015). Higher pressures for these containers would only be allowed if manufacturers obtained special permits from DOT.

 Pressures for "bulk aerosol" containers. In terms of larger containers, the most detailed pressure data ERG located was for a product line of "cylinder spray adhesives." As noted previously, it is not clear how these containers should be classified under GHS, because the classification will ultimately depend on the chemical properties of the contents. The products appear to meet the definition for "Aerosol" (GHS Revisions 3 and 4) because the containers are not fillable and they eject liquid particles in a propellant gas stream, but the release device is a spray gun at the end of connective hosing (see image on page 1 of 3M, 2013; and see Attachment 1 of this report). This particular product line offers the adhesive in three container volumes: 5 gallons, 25 gallons, and 50 gallons; and all three containers have working pressures of 200 psig (NFPA, 2013). The smallest containers in this series are generally not refilled.

Amounts of Contents
For a given container volume, the amount (weight) of contents depends on the relative quantities of propellant and product, the densities of the propellant and product, and the container pressures. Consistent with Section 2.2.4, this section presents data ERG obtained on aerosol contents separately for the typical hand-held containers and for the bulk aerosols:

 Contents for 2P and 2Q containers. Net weight of aerosol containers, which includes the weight of the product and the propellant, appears on the labels of most products. ERG found no regulation or standard (e.g., DOT, NFPA, etc.) that limits the net weight of aerosol containers. However, limits on container sizes and container pressures (see Table 3) effectively limits the net contents. To assess the range of aerosol net weights across products, ERG reviewed information published for aerosol cleaners on the "IHS Engineering 360" website (IHS, 2015). This website includes data sheets for aerosol products from more than 25 different manufacturers and distributors. However, only a subset of the products included net weights in their data sheets. Of the more than 100 data sheets that ERG reviewed on this website, the highest net weight listed was 24 ounces (1.5 pounds) (IHS, 2015). Consistent with these observations, a manufacturer's representative informed ERG that the heaviest aerosol product that his company ever offered was 24 ounces -- for a rug cleaning product that is no longer on the market (O'Brien, 2015). Taken together, these observations suggest that individual aerosol containers with DOT designations of 2P or 2Q (or non-specification) have net weights of 1.5 pounds or less.

 Contents for "bulk aerosol" containers. The most detailed aerosol content data ERG located for larger aerosol containers are for the same "cylinder spray adhesives" product line reviewed in Section 2.2.4. In terms of contents, ERG identified four different container sizes for these adhesives. For these four products, the net weights are 19.8 pounds, 26.2 pounds, 128 pounds, and 266 pounds (3M, 2015); and the reported "empty weights" for these same containers are 3.7 pounds, 10.8 pounds, 75 pounds, and 225 pounds, respectively (3M, 2013). (Note: The considerably higher rate for the largest product results in part because it is equipped with pallet legs.) Therefore, the net weights of these containers are 23.5 pounds, 37.0 pounds, 203 pounds, and 491 pounds. Attachment 1 presents more information on so-called "bulk aerosol" containers.

Failure Mechanisms
When researching hazards associated with compressed gas cylinders and aerosols, ERG identified and summarized previous incidents associated with various gas and aerosol products. Section 4 of this report presents that summary. Although a broad array of incidents was identified, the underlying mechanisms that contributed to the incidents generally fell into three common categories, reviewed below:
 Rupture due to thermal expansion of contents under high temperature. Because the volume of compressed gas cylinders and aerosol containers is fixed and the amount of material within the containers is fixed (when not in use), any increases in temperature will cause proportional increases in internal pressures. Should ambient temperatures in gas or aerosol storage areas reach dangerously high levels, whether due to prolonged exposure to direct sunlight, an adjacent fire, or other factors, internal pressures may increase beyond levels that the containers can tolerate.
      The consequences of these high pressures vary between gases and aerosols. In the case of compressed gas cylinders, DOT requirements mandate use of pressure relief devices on most cylinders; and these devices must meet specifications of the Compressed Gas Association, Inc. Therefore, for compressed gases, increased temperature can result in activation of the pressure relief device and a subsequent release of contents, which can have serious consequences depending on the gas' properties (e.g., toxicity, flammability, corrosivity). On the other hand, aerosol containers are not equipped with such pressure relief systems; therefore, when temperatures cause internal pressures to increase, the aerosol containers can eventually fail catastrophically. This scenario is not expected to occur under ambient temperatures, and even extremes in ambient temperatures, due to DOT container requirements (see Table 3). However, media stories (e.g., CBS, 2013; NBC, 2014) and many anecdotal accounts demonstrate that aerosol containers can fail catastrophically when placed in or near fires or other heating sources. Section 4 summarizes further insights ERG located on such failures.
 Rupture due to mechanical deformation. Both compressed gas cylinders and aerosol containers can release contents after being dropped, crushed, punctured, hit by vehicles, or by experiencing some other form of physical damage. A known hazard for compressed gas cylinders is their potential to fall, which may break the cylinder valve and instantly release the contents -- a scenario that can also cause the cylinder to become a projectile or pinwheel, depending on the pressure of its contents and its net weight. Additionally, due to their sheer size and weight, falling compressed gas cylinders present a crushing hazard to employees in the area. Similarly, aerosol containers can be compromised due to various types of mechanical deformations, which include anything from simply dropping an aerosol container (Fox, 2011) to individuals inadvertently puncturing containers when using a screwdriver to pry open caps (Chemaxx, 2015).
 Leaking due to corrosion. Both compressed gas cylinders and aerosol containers are prone to corrosion. External corrosion of compressed gas cylinders and their fittings may occur when they are stored in locations with moisture, salt, or other corrosive chemicals; and ERG identified at least one fatal incident involve corrosion of compressed gas cylinder fittings (see Section 4.1). However, mandatory visual inspection of cylinders and periodic testing requirements should minimize the extent to which corroded cylinders lead to compressed gas leaks.
      Unlike compressed gas cylinders, which can be in service for more than 10 years, aerosol containers are used only once and disposed of (or recycled) after the contents are spent -- thus limiting the time frame over which corrosion may occur. ERG identified no mandatory requirements limiting the "shelf life" of aerosol products, though some publications suggest an important factor is the gradual loss of propellant over time. For instance, one manufacturer states that all aerosol products should "perform consistent to its intended purpose" within 3 years of the date of fill, after which propellant quantities might fall to levels that may make products no longer usable (Callington, not dated). Even though aerosol containers are expected to be used over relatively short time frames, corrosion can compromise container integrity. Internal corrosion of aerosol containers has been raised as a concern, especially as more manufacturers develop water-based products in order to comply with environmental regulations that limit solvent (volatile organic compound) content (DuPont, 2011). This issue is apparently being addressed in various ways, such as formulating products with corrosion inhibitors and conducting tests and simulations to predict corrosion behavior for different combinations of products and containers (DuPont, 2011). Despite finding a fair amount of online resources describing potential corrosion issues for aerosol containers, ERG found no reported incidents (e.g., leaks) that were attributed to container corrosion.
Previous Incidents
For further insights into hazards and failures associated with compressed gas cylinders and aerosol containers, ERG reviewed four data sources for relevant incidents. The data sources were OSHA's online archive of "Reports of Fatalities and Catastrophes," the CPSC's "National Electronic Injury Surveillance System," incident investigations published by the Chemical Safety Board (CSB), and other observations from online searches. While CPSC data pertain to use of consumer products, they are included here to the extent that they provide insights on failure mechanisms for gases under pressure and aerosols. This section first reviews incidents associated with compressed gas cylinders (Section 4.1) and then incidents associated with aerosol containers (Section 4.2).
Compressed Gas Incidents
ERG identified the following accounts of incidents involving compressed gases, both for products used in industrial settings and consumer environments:
 OSHA's Reports of Fatalities and Catastrophes. ERG reviewed entries in the archive covering a 20-year time period from January 1, 1995 to December 31, 2014. In that time period, 903 incidents had abstracts containing the words "compressed gas," "cylinder," or "CNG." Of these incidents, 129 unique incidents appeared to be related to portable compressed gas tanks and cylinders, though it was difficult to tell exactly which incidents involved compressed gas cylinders of the type examined in this study. 196 people were injured in these incidents. Of those injuries, 38 were fatal, 118 resulted in hospitalizations, 37 were injuries that did not result in hospitalization, and details were not available on the severity of injuries for the remaining three incidents. The following types of injuries were reported, and some incidents involved multiple injury types:
 Burning and scalding from heat (51)
 Systemic poisoning (22)
 Bone fractures (14)
 Asphyxia (14)
 Chemical burns (12)
 Amputations (11)
 Cuts or lacerations (5)
 Punctures (4)
 Bruises (4)
 Eye injuries (2)
 Hearing loss (2)
 Sprains (2)
 Concussions (2)
 Dislocations (1)

      The causes leading up to each incident varied, though some patterns were apparent. Many incidents concerning gas cylinders were the result of the cylinder exploding and occurred while a worker was soldering, welding, torch-cutting, or performing some other operation that involved high-temperature flames. The events leading up to the explosion were not always provided, as some incident reports stated only that the explosion occurred while the worker was using high-temperature flames. More specific reports linked some explosions to escaped vapors that ignited, while other cases linked explosions to cylinders that fell during use and ruptured, frequently at the cylinder's neck. The majority of these incidents resulted in a burn injury to the affected employee. Other incidents leading to burn injuries included failures in the valves, lines, and hoses used to transfer gas into or out of the cylinders. These failures would release flammable vapors that ignited, causing fires -- and sometimes an explosion of the attached cylinder. Chemical burns and exposures also occurred when workers made erroneous assumptions regarding the contents of cylinders or mistakenly assumed that cylinder valves were closed.
      Outside of incidents involving fires and explosions, a frequent cause of injury was the over-pressurization of a cylinder or the system to which it was attached. Common causes of failure in these cases were cylinders filled beyond their design limits, cylinders with interior corrosion that could not be observed externally, and cylinders filled with high-pressure gas that were wrongly attached to low-pressure equipment. Many of these incidents resulted in fatalities when highly pressurized pieces of equipment came loose and struck the workers. Another common source of injuries was cylinders that fell during transport. In most cases, either the cylinders were not properly secured or improper equipment was being used to transport cylinders. The incidents of this type resulted in physical injuries to the affected workers, the majority of which were either fractures or amputations. A final frequent cause of injury involved the processing or recycling of used cylinders at scrap yards. Workers would load cylinders they believed were empty into shearing machines for transport or processing. Activation of the machine would pressurize the cylinder and cause it to explode, injuring workers and exposing them to the cylinders' contents.
 CPSC's National Electronic Injury Surveillance System. Table 5 summarizes CPSC incident data for gases under pressure, specifically for any incident pertaining to "propane, liquefied propane (LP), and butane gas tanks or fittings." Between 1999 and 2013, CPSC recorded an average of 59 incidents per year associated with these tanks and fittings. To investigate the nature of these incidents, ERG reviewed the detailed text descriptions for every event in the most recent 3-year period (i.e., 2011 to 2013). Of the 199 incidents during this time frame, the most common underlying cause was people getting injured when moving tanks, generally as a result of dropping tanks onto themselves -- this accounted for 50 of the incidents. ERG classified the incidents as follows:
 Injuries associated with moving tanks (50)
 Tank explosions (39)
 Tripping on, running into, or other physical contact with tanks (37)
 Tank fires and subsequent burns (23)
 Inhalation exposure to carbon monoxide and fumes (13)
 "Chemical burns" associated with exposure to tank contents (11)
 Burns from touching hot surfaces (6)
 Cuts or bruises from handling tanks (5)
 Tanks falling on people (5)

      The remaining incidents could not be easily classified or were incidents that did not involve tanks in the first place (i.e., they showed up as being related to tanks during keyword searches, but the incident details suggested otherwise). While incidents associated with consumer products do not necessarily parallel the nature of incidents expected to occur in occupational settings, they do suggest some underlying causes that are likely relevant (e.g., physical injuries associated with moving cylinders, fires and explosions when handling flammable gases, incidents associated with exposure to toxic substances).
      For the 39 incidents related to the explosion of compressed gas tanks, Table 6 provides summary statistics concerning the type of injury suffered and Table 7 provides summary statistics relating to where on the body injuries were sustained. Most of the injuries occurred to the face (24), hands (12), or arms (12), and the vast majority of injuries suffered were thermal burns (32). In most cases, the database did not report the degree of the burn. Where the degree was reported, first and second degree burns occurred with approximately the same frequency. The database also mentioned one instance of a third degree burn involving compressed gas tanks, which occurred to a man using a gas tank while cooking in a tent. Of the injuries that were not burns, five involved people hit by either the exploding tank itself or by debris from the tank after it exploded, and one involved a person knocked to the ground by the force of the explosion. One final case involved a gas tank which exploded while a man was refilling it with butane, resulting in a burn to the man's hand.
      In most cases, the CPSC database did not identify the cause of the gas tank explosion or provide enough information to infer what may have started it. Five of the incidents appeared related to the use of a compressed gas tank while cooking, while four others were related to a tank placed in or near a pre-existing fire, such as a campfire. An additional five incidents appeared related to the installation or maintenance of tanks, while two incidents involved people lighting cigarettes near propane tanks. Other incidents mentioned in the database included one in which a tank was burned in a pile of trash, another in which a tank was shot with a handgun, and another related to an explosion that occurred during an underwater welding procedure.
      CSB's Incident Investigations. In addition to querying the OSHA/CPSC databases, ERG searched a database of 83 completed CSB incident investigations, and the following three pertained to compressed gas cylinders:
 Praxair Propylene Gas Fire (CSB, 2006). On June 24, 2005, during a summer heat wave at the Praxair gas filling and distribution facility in St. Louis, Missouri, a small fire began near a propylene cylinder. The fire was believed to be caused by propylene gas expanding due to the high temperatures and eventually reaching a pressure that triggered the cylinder's relief device. The propylene that was released eventually ignited, causing the initial fire. The heat from this initial fire caused gases from other nearby propylene, propane, and acetylene cylinders to release. As the released gases ignited, exploding cylinders became projectiles -- some flying more than 800 feet in the air, damaging property and starting fires in the neighboring community. The CSB determined that the industry standard threshold pressure for activating relief valves in propylene cylinders was set too low, and could have been set higher without damage to the cylinders. Similar incidents involving overheated exploding propylene cylinders on hot summer days occurred at an Airgas facility in Tulsa, Oklahoma in 2003, an Air Liquide facility in Phoenix, Arizona in 1997, and another Praxair facility in Fresno, California in 2005.
 DuPont Corporation Toxic Chemical Releases (CSB, 2011). On January 23, 2010, an incident involving the release of phosgene gas occurred at the DuPont facility in Belle, West Virginia. The gas release led to the fatal exposure of a worker, and two other employees were exposed to the toxic gas. The incident was caused when a flexible hose attached to a phosgene cylinder ruptured, causing an employee to be sprayed with phosgene liquid and gas. The failure was associated with corrosion of the stainless steel hoses used to transfer phosgene out of the cylinders. The maintenance plan for the change-out of the hoses prescribed a regular change-out schedule of 30 days, but at the time of the incident, the hoses had been in service for more than 6 months. While this incident did not involve failure of the compressed gas cylinder or its regulator, it underscores the nature and extent of hazards associated with operating compressed gas cylinders containing highly toxic substances.
 Honeywell Chemical Incident (CSB, 2005). On July 29, 2003, a one-ton cylinder at the Honeywell International, Inc. chemical plant in Baton Rouge, Louisiana, released its contents to the atmosphere, fatally injuring a plant worker by exposing him to lethal amounts of contaminated antimony pentachloride. The operator was preparing empty one-ton refrigerant cylinders for offsite testing. During this procedure, he removed plugs from empty cylinders. However, the cylinder in question was actually full and its contents were released, engulfing the operator in a cloud of the toxic chemical. The mistake was largely due to the fact that the cylinder had been mislabeled, and insufficient checks were in place to catch such errors. As a result, the full cylinder was wrongly placed in an area of the plant reserved for empty refrigerant cylinders. This incident further underscores the hazards of working with compressed gas cylinders containing highly toxic substances.
 Other accounts. The previous bulleted items summarize the overwhelming majority of incidents ERG identified pertaining to compressed gases. Some additional anecdotal accounts and news articles suggest that major household explosions have also occurred due to leaking propane tanks (e.g., Taunton Daily Gazette, 2015), but the frequency of these incidents is not readily available and it is unclear if they would be covered in the CPSC data summary.
Aerosol Incidents
ERG identified the following accounts of incidents involving aerosol containers, both for products used in industrial settings and consumer environments:
 OSHA's Reports of Fatalities and Catastrophes. ERG reviewed entries in the archive covering a 20-year time period between January 1, 1995 and December 31, 2014. In that time period, 701 incidents had abstracts containing the words "aerosol," "spray," or "foam." Of these incidents, 38 appeared to be related to aerosol containers and spray cans, though it was difficult to tell exactly which incidents involved containers of the type examined in this study. 63 people were injured in these incidents. Of those injuries, 3 were fatal, 48 resulted in hospitalizations, and 12 were injuries that did not require hospitalization. The following types of injuries were reported:
 Burning or scalding from heat (34)
 Chemical burns (3)
 Cuts or lacerations (2)
 Systemic poisoning (1)
 Bruises (1)
 Fractures (1)

      The causes leading up to each incident varied, though some consistent patterns were apparent. Most incidents concerning aerosol containers involved the containers' explosion due to an obvious cause. Of these incidents, a few occurred when workers intentionally heated or punctured an aerosol container, causing the container to explode. Two cases involved workers intentionally puncturing containers to dispose of them, while another instance involved a worker intentionally heating a container to improve its performance. Other explosions occurred when an aerosol container accidentally came in contact with an external heat source. Eight explosions occurred during torch cutting or welding operations, reportedly when workers were unaware that aerosol containers were nearby. In two other instances, one of which led to a fatality, explosions occurred as workers were disposing of trash containing aerosol containers. In the instant that led to a fatality, the machine crushing the containers also exploded, causing fire to spread rapidly through the facility. Three additional instances involved aerosol containers placed near cooking equipment. In one case, the container was placed on a hot griddle, while in two other instances the container fell into a hot fryer. All but one of these incidents resulted in burn injuries to the affected employees.
      Of the incidents that did not involve the direct application of heat, four explosions occurred when workers lifted, moved, or shook an aerosol container. In each case, the cause of the container's failure was not immediately apparent from the description of the incident. A further five incidents occurred when vapors released by the containers ignited. Two of these incidents occurred after workers had sprayed the aerosols in an enclosed space and turned on equipment to either filter or ventilate the air. In both cases, the equipment was not certified for use where flammable vapors were present and led to the ignition of the vapors. Four final incidents occurred as the result of workers' inhalation of the contents of aerosol containers during routine use. Two of these incidents resulted in fatalities.
 CPSC's National Electronic Injury Surveillance System. Table 5 summarizes CPSC data for consumer incidents with "aerosol" as a keyword. Between 1999 and 2013, 1,550 incidents met this criterion, for an average of 103 incidents per year. For further insights into the nature of these incidents and their contributing factors, ERG examined full text descriptions for the 367 incidents that occurred during the most recent 3-year period (2011-2013). ERG classified these incidents as follows:
 Inadvertent exposure to contents to user or someone in their vicinity (122)
 Ignition of aerosol container or contents, often by tossing containers into fires or burning containers with garbage, many times intentionally (75)
 Users intentionally exposing themselves to contents ("huffing") (68)
 Individuals being struck by containers, often after containers fall from shelves or other ledges (42)
 Allergic reaction or over exposures when using container as intended (34)
 Children ingesting parts of the can or people intentionally inserting cans into their own bodies (8)

      The remaining incidents could not be easily classified or were incidents that did not involve aerosols in the first place (i.e., they showed up as being related to aerosols during keyword searches, but the incident details suggested otherwise). While incidents associated with consumer products do not necessarily parallel the nature of incidents expected to occur in occupational settings, ERG learned during this project that some aerosol manufacturers make consumer products and industrial products that have identical or highly similar formulations (e.g., for kitchen and cafeteria products, housekeeping and janitorial products), but they are simply labeled and distributed differently (O'Brien, 2015).
      Of the 75 incidents related to the ignition of an aerosol container or its contents, 65 of these mentioned the explosion of the container itself. For these 65 incidents, Table 6 provides summary statistics concerning the type of injury suffered and Table 7 provides summary statistics relating to where on the body injuries were sustained. Most of the incidents involved injuries to the face (27), hands (27), or arms (19). The majority of the injuries sustained were thermal burns (45), though exposure to the chemicals in the containers was also common (13). Nearly all of the documented eye injuries were the result of a chemical exposure, as were the two internal injuries. The CPSC database generally did not record the degree of the thermal burns. Where the degree was recorded, first and second degree burns occurred with approximately the same frequency. The database did not mention any instances of third degree burns related to aerosols in the years examined.
      Nearly every incident involving the explosion of an aerosol container was the result of the container's proximity to an external heat source. 19 of the explosions occurred when an aerosol container was burned along with other trash, and 23 occurred to aerosol containers either in or near an open fire. Many of these incidents involved someone throwing an aerosol container into a campfire or bonfire, causing the container to explode and injure people nearby. In addition to these, six incidents involved containers exploding due to contact with a stove, water heater, or kerosene heater; two involved proximity to hot water; and two involved proximity to a candle. For those explosions that did not involve proximity to external heat, four involved a person hammering, cutting, or driving a nail into an aerosol container, and one occurred when a woman used the container itself as a hammer. Four of these five incidents resulted in a chemical exposure, while only one resulted in a thermal burn. The cause of the remaining incidents was not clear from the descriptions provided in the database.
 CSB's Incident Investigations. ERG did not find any CSB incident investigations directly attributed to use of aerosol containers.
 Other accounts. ERG identified additional accounts of catastrophic incidents involving aerosol use (and storage) through online searches and other references. These incidents include:
 NFPA Loss Incidents. Appendix G of NFPA-30B -- the association's "Code for the Manufacture and Storage of Aerosol Products" -- presents a review of loss incidents involving storage of aerosols, primarily in warehouses (NFPA, 2015). These loss incidents focus on property damages, and it is unclear if any of the incidents also included worker injuries or fatalities. The appendix presents the breakdown of incidents by total cost of damages, but does not specify the total number of incidents reviewed. Appendix G.3 presents more detailed information on the two largest incidents, in terms of property loss, and those are reviewed here.
            The first incident occurred in 1979 at a supermarket warehouse. A fire began in a part of the warehouse where aerosols were stored, and the cause of the fire was suspected to be arson. Before employees could control the fire with portable fire extinguishers, the fire spread to pallets containing highly flammable aerosol products and then quickly spread. The building was equipped with sprinkler systems in the ceiling, but not with "in-rack sprinklers." The entire warehouse and its contents were destroyed in the fire, with property damage estimated to cost $30,000,000.
            The second incident occurred in 1982 at a distribution center that stored a wide range of aerosol products and other products. Similar to the previous incident, this building was equipped with ceiling sprinkler systems, but not "in-rack sprinklers." The fire began after a carton containing a flammable aerosol product fell from a pallet. A nearby employee heard a "hissing" sound, and the fire began immediately thereafter. Employees attempted to extinguish the fire using portable units, but the fire quickly spread. The entire warehouse and its contents were destroyed. Those contents included more than 1,000,000 containers of flammable aerosol products -- many of which became projectiles during the fire. The estimated property damage for this incident was more than $100,000,000.
            While the CPSC incidents highlight dangers associated with use of individual aerosol containers, the incidents reviewed by NFPA demonstrate the significant hazards associated with storage of numerous aerosol containers. The two incidents reviewed here likely would have been prevented had the facilities been compliant with today's fire protection standards, which include "in-rack sprinklers" for certain storage scenarios (NFPA, 2015).
 Excessive use of foggers. When researching hazards of aerosol products, ERG heard anecdotal accounts of dangers associated with use of "total-release foggers." The principal concern for these products is misuse by consumers -- instead of using an individual product, some consumers reportedly have used multiple "total-release foggers" at the same time. If the flammable contents within these foggers are sufficiently concentrated and contact an ignition source (e.g., a pilot light), fires and explosions may result. ERG did not locate original documentation for such incidents, but a publication from the Centers for Disease Control and Prevention states: "...numerous media reports in recent years have described injuries and property destruction resulting from explosions caused by activation of TRFs [total-release foggers] in the presence of ignition sources" (CDC, 2008). The CDC publication also documents poisoning incidents associated with improper use of foggers, generally caused by consumers using excessive amounts of fogger products for the intended space, re-entering buildings too soon after foggers have been dispersed, and failing to notify others of fogger use.
 Other accounts. ERG viewed additional websites that provide accounts of incidents involving aerosol containers, but details of these incidents are difficult to verify. One website hosted by an expert witness in chemical-related consumer products (http://www.chemaxx.com/aerosol.htm) describes numerous incidents that harmed consumers when using aerosol products. Another website that ERG located (http://www.snopes.com/photos/accident/aerosol.asp) presents photographs of incidents involving exploding aerosol containers, but the website itself acknowledges that the authenticity of the photographs cannot be confirmed.
Summary and Recommendations
Principal Differences between Compressed Gases and Aerosols
The research documented throughout this report identifies important differences between compressed gas cylinders and aerosol containers. As documented throughout Section 2 of this report, compressed gas cylinders can hold numerous products and are shipped in a broad range of cylinder sizes and pressures. The sizes and pressures far exceed those routinely used for hand-held aerosol products. This difference makes sense because hand-held operation of extremely large or heavy aerosol containers is not practical. (Note: An important exception about chemical quantities is for warehouses that store thousands of aerosol containers. In these cases, the cumulative quantities of hazardous chemicals can be significant, even if they are stored in individual containers with limited quantities.)

Further, compressed gas cylinders contain chemicals with a broad range of toxicities, including some that can generate clouds of lethal exposure levels if the contents are released. On the other hand, aerosol containers generally do not contain extremely toxic chemicals at levels that would kill bystanders, most likely due to the fact that users spray these products within arms' reach of their breathing zones. However, exceptions exist, as some aerosol products -- particularly pesticides in foggers -- have caused numerous poisonings among consumers (CDC, 2008).

Another difference between compressed gas cylinders and aerosol containers is their construction. Compressed gas cylinders are generally designed to withstand relatively high pressures, to last for at least 10 years, and to be refilled and transported numerous times within their service life. In contrast, aerosol containers are designed to be used once and subsequently disposed of or recycled.

The previous differences would suggest more serious work-related incidents associated with handling compressed gas cylinders versus aerosol containers -- a hypothesis supported by the OSHA injury and illness data reviewed in Section 4. While the CPSC data indicate a higher number of consumer incidents involving aerosols, this trend most likely results from the fact that aerosol containers are more prevalent in households than compressed gas cylinders. (Note: The "bulk aerosol" products that ERG identified during this research are developed for industrial and professional markets, and are not available in consumer markets.)

Additional Observations
When conducting this research, ERG encountered several different definitions for aerosols, including those in GHS, those published by NFPA, and container requirements for DOT. Some state and local authorities have also published their own definitions, and even though the state/local regulations apply only within their jurisdictions, it is not uncommon for these regulations to affect how manufacturers develop and label products that are distributed nationwide. These definitions vary in key factors, particularly in container size limits and the actuation mechanism; and it is conceivable that certain products would be considered aerosols under certain definitions, but not under others. As specific examples, DOT definitions currently do not include purely gaseous products as aerosols (while other definitions do); NFPA definitions do not include any containers larger than 1 liter as aerosols (while other definitions do); and so on. Table 8 presents a brief summary of selected definitions found in various agency regulations, standards, and other publications.

References
3M, 2013. Cylinder Spray Adhesive  -  User's Guide. February, 2013. Available at: http://multimedia.3m.com/mws/media/856301O/cylinder-spray-adhesive-user-guide.pdff.

3M, 2015. 3M[TM] Hi-Strength 94 ET Adhesive: Product Specifications. Available at: http://solutions.3m.com/wps/portal/3M/en_US/Adhesives/Tapes/Products/~/3M-Hi-Strength-94-ET-Adhesive?N=5396314+3294310558&rt=rud#variantView.

Airgas, 2014. Specialty Gases and Equipment Product Reference Guide -- Catalog Web Version. Available at: http://www.airgassgcatalog.com/catalog.

Air Liquide, 2006. Specialty Gas Catalog. Available at: http://www.us.airliquide.com/file/otherelement/pj/spec%20gas%20cat_06_search31136.pdf.

Air Products, not dated. Specialty Gas Cylinder Information. Available at: http://rmehs.fullerton.edu/_documents/policiesandguidelines/gas%20cyclinder%20reference%20information.pdf.

Amtrol, 2011. Refrigerant cylinders: Refillable, Non-refillable, and Recovery. Available at: http://www.amtrol.com/media/documents/refrigerant_recovery/Refrigerant_Cylinders_Brochure_MC10229.pdf.

Ball, 2015. Ball Corporation, Product Catalog, Aerosols. Available at: http://www.ball.com/product-catalog/view/aerosols/necked-in-aerosol-cans/.

Callington, not dated. NDT Shelf Life and Storage Recommendations. Available at: http://www.callingtonhaven.com/_assets/NDT-Shelf-Life-Storage-Recommendations.pdf.

CBS, 2013. Beware Homeowners -- Aerosol Cans Explode Like "Missiles." August 13, 2013. Available at: http://minnesota.cbslocal.com/2013/08/13/beware-homeowners-aerosol-cans-explode-like-missiles/.

CDC, 2008. Illnesses and Injuries Related to Total Release Foggers -- Eight States, 2001-2006. Morbidity and Mortality Weekly Report, 57(41):1125-1129. Available at: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5741a3.htm.

Chemaxx, 2015. Chemical Accident Reconstruction Services, Inc. website. Available at: http://www.chemaxx.com/aerosol7a.htm.

Consumer Aerosol Products Council, 2015. What Is a Propellant? Available at: http://www.aerosolproducts.org/propellant/.

CPSC, 2015. Data accessed from CPSC's National Electronic Injury Surveillance System. Available at: https://www.cpsc.gov/cgibin/NEISSQuery/home.aspx.

CSB, 2005. Investigation Report: Contaminated Antimony Pentachloride Exposure. Report No. 2003-13-I-LA. U.S. Chemical Safety and Hazard Investigation Board. August, 2005. Available at: http://www.csb.gov/assets/1/19/Honeywell_Report.pdf.

CSB, 2006. Dangers of Propylene Cylinders in High Temperatures. U.S. Chemical Safety and Hazard Investigation Board. Safety Bulletin No. 2005-05-B. June, 2006. Available at: http://www.csb.gov/assets/1/19/Praxair_Report.pdf.

CSB, 2011. Investigation Report: E.I. DuPont de Nemours and Co., Inc.: Phosgene Release. U.S. Chemical Safety and Hazard Investigation Board. Report No. 2010-6-I-WV. September, 2011. Available at: http://www.csb.gov/assets/1/19/CSB%20Final%20Report.pdf.

Diversified Products, 2015. An Introduction to Aerosol Propellants. Available at: http://www.diversifiedcpc.com/PDF/intro.pdf.

DOT, 2014. DOT-SP 10590; eighth revision. Available at: http://www.phmsa.dot.gov/pv_obj_cache/pv_obj_id_88AA591A6A56A8577EAF4965DF6F1E1DED000100/filename/SP10590_2011020626.pdf.

DuPont, 2011. Corrosion Inhibitors for Water-Based Dymel[(R)] 152a Aerosol Formulations. Available at: http://www2.dupont.com/Dymel_Propellants/en_US/assets/downloads/h71046_Dymel_152a_corrosion_inhibitors.pdf.

Fox, 2011. Circumferential Catastrophic Burst Failures of Pressurized Cylinders. Journal of Failure Analysis and Prevention 11(4):320-331. Abstract available at: http://link.springer.com/article/10.1007%2Fs11668-011-9431-6.

Geer, 2011. Aerosol Formulation Considerations. Presentation by Robert D. Geer. Available at: http://www.southernaerosol.com/Power%20Point/Spring%202011/Formulation%20Considerations.pdf.

IATA, 2012. Dangerous Goods Regulations, 54[th] Edition: Effective 1 January -- 31 December 2013. International Air Transport Association. Printed in September, 2012.

IHS, 2015. IHS Engineering 360: Aerosol Cleaners and Contact Cleaners Data Sheets. Available at: http://datasheets.globalspec.com/ds/5598.

Illing Company, Inc., 2015. Online Product Directory: Metal Containers, Aerosol Cans. Available at: http://illingcompany.com/product/aerosol-cans/.

ITX Sexton, 2015. Online Product Specifications: Aerosol Can Data. Available at: http://www.sextoncan.com/pdf/ITW-Sexton_AerosolCanDatasheets-INCH-1309.pdf.

Matheson, not dated. Common Industrial Cylinder Dimensions. Available at: http://www.mathesongas.com/industrialgas/pdfs/Industrial-Cylinder-Dimensions.pdf.

McKernan, 2015. McKernan Packaging Clearing House: Aerosol Cans. Available at: http://mckernan.com/store/Aerosol-Cans/.

NBC, 2014. 4 Injured in Aerosol Blast at Macy's in Chicago's Loop. November 21, 2014. Available at: http://www.nbcchicago.com/news/local/Propane-Chicago-Loop-Injuries-283488831.html.

NFPA, 2013. NFPA 30 Technical Committee on Storage and Warehousing of Containers and Portable Tanks. National Fire Protection Association Memorandum. June 11, 2013. Available at: http://www.nfpa.org/Assets/files/AboutTheCodes/30/30_FLC-SWC_SDsupagenda_06-13.pdf.

NFPA, 2015. NFPA-30B. Code for the Manufacture and Storage of Aerosol Products. 2015 Edition.

O'Brien, 2014. Email correspondence between Robert O'Brien, S.C. Johnson & Son, Inc., and Maureen Ruskin, OSHA. April, 2014.

O'Brien, 2015. Personal communication between Robert O'Brien, S.C. Johnson & Son, Inc., and John Wilhelmi, Eastern Research Group, Inc. March 2015.

Praxair, not dated. Specialty Gases Reference Guide. Available at: http://catalogs.praxairdirect.com/issue/25778.

Sprits, 2015. Packaging website. Available at: http://www.spritsrelease.com/packaging.html.

Taunton Daily Gazette, 2015. Explosion, fire destroy Taunton home; signs point to propane gas leak. Available at: http://www.tauntongazette.com/article/20150311/News/150319302.

Table 1. Selected DOT Specifications for Cylinders
                                     Type
                                   Reference
                           Material of Construction
                            Size/Volume Limitations
                                Pressure Range
                            Minimum Wall Thickness
3A
§178.36
Seamless steel
<1,000 pounds nominal water capacity
>150 psig
0.1 inch
3AX
§178.36
Seamless steel
<1,000 pounds nominal water capacity
>500 psig
0.1 inch
3AA
§178.37
Seamless steel
<1,000 pounds nominal water capacity
>150 psig
0.1 inch
3AAX
§178.37
Seamless steel
<1,000 pounds nominal water capacity
>500 psig
0.1 inch
3B
§178.38
Seamless steel
<1,000 pounds nominal water capacity
150-500 psig
0.09 inch
3BN
§178.39
Seamless nickel
<125 pounds nominal water capacity
150-500 psig
0.1 inch
3E
§178.42
Seamless steel
Length less than 2 feet
1,800 psig
Not specified
3HT
§178.44
Seamless steel
<150 pounds nominal water capacity
>900 psig
0.05 inch
3T
§178.45
Seamless steel
>1,000 pounds nominal water capacity
>1,800 psig
0.225 inch
3AL
§178.46
Seamless aluminum
<1,000 pounds nominal water capacity
>150 psig
0.125 inch
4DS
§178.47
Welded stainless steel
<100 pounds nominal water capacity
500-900 psig
0.04 inch
4B
§178.50
Welded or brazed steel
<1,000 pounds nominal water capacity
150-500 psig
0.09 inch
4BA
§178.51
Welded or brazed steel
<1,000 pounds nominal water capacity
225-500 psig
0.078 inch
4D
§178.53
Welded steel
<100 pounds nominal water capacity
300-500 psig
0.04 inch
4B240ET
§178.55
Electric resistance welded tubing
<12 pounds nominal water capacity
240 psig
0.44 inch
4AA480
§178.56
Welded steel
<1,000 pounds nominal water capacity
480 psig
0.078 inch
4L
§178.57
Fusion welded insulated cylinder
<1,000 pounds nominal water capacity
40-500 psig
Not specified
4DA
§178.58
Welded steel
<100 pounds nominal water capacity
500-900 psig
0.04 inch
4BW
§178.61
Welded steel with seam
<1,000 pounds nominal water capacity
225-500 psig
0.078 inch
39
§178.65
Non-refillable cylinders
< 55 pounds nominal water capacity for pressure <500 psig
< 10 pounds nominal water capacity for pressure >500 psig
Not specified
4E
§178.68
Welded aluminum
<1,000 pounds nominal water capacity
225-500 psig
0.14 inch

Notes:
 All regulatory references pertain to 49 CFR Part 178, Subpart C.
 Minimal wall thickness requirements are more complex than shown in the table, which only shows the lowest allowable thickness for a given cylinder type, but the actual minimum wall thickness may depend on various other factors (e.g., cylinder dimensions, wall stresses, pressures). Entries of "not specified" refer to instances where DOT specifies criteria for determining the minimum wall thickness but does not list a discrete value.
 Table does not include entries for cylinders with porous fillings for acetylene.
 Type 39 is classified by DOT as a cylinder, but some manufacturers sell "bulk aerosol" products in these containers. See Section 2.2.2 for further detail.

Table 2. Ranges of Compressed Gas Cylinder Properties, by Manufacturer
                                   Parameter
                                    Airgas
                                  Air Liquide
                                 Air Products
                                   Matheson
                                    Praxair
Outside diameters
                                  2-30 inches
                                  3-15 inches
                                  2-30 inches
                                  4-15 inches
                                2-29.75 inches
Cylinder lengths (heights)
                                 12-82 inches
                                 9.5-55 inches
                                 10-90 inches
                                 13-55 inches
                                 14-55 inches
Cylinder internal volumes
                                0.43-731 liters
                                0.44-125 liters
                                0.43-731 liters
                                2-108.4 liters
                              0.42-454.49 liters
Tare weights
                                2-2,254 pounds
                                 2-303 pounds
                                2-2,254 pounds
                                 8-178 pounds
                                 4-315 pounds
Cylinder pressures
                                4.4-6,000 psig
                                 10-2,640 psig
                                See "Notes"
                                4.4-6,000 psig
                                 2-6,000 psig
Amount of contents
                                4-1,300 pounds
                                0.25-420 pounds
                                See "Notes"
                               0.25-1,055 pounds
                               <1-600 pounds

                               8-575 cubic feet
                             0.4-13,540 cubic feet
                                See "Notes"
                             0.25-3,360 cubic feet
                               19-575 cubic feet

Notes:
 Ranges are presented for pure gas products identified through searches of manufacturers' online catalogs. Cylinder properties for compressed gas mixtures are expected to fall within the ranges shown above.
 The online product literature for Air Products was not readily searchable for the ranges of compressed gas cylinder pressures and content quantities.
Table 3. Mandatory Specifications for Selected Metal Aerosol Containers
                                   Parameter
                                      2P
                                      2Q
Applicable DOT regulation
                                 49 CFR 178.33
                                49 CFR 178.33a
Pressure range
                           140-160 psig at 130 [o]F
                           160-180 psig at 130 [o]F
Maximum volume
                           1 liter (61 cubic inches)
                           1 liter (61 cubic inches)
Maximum inside diameter
                                   3 inches
                                   3 inches
Material
                          Steel or non-ferrous metal
                          Steel or non-ferrous metal
Wall thickness
                                  0.007 inch
                                  0.008 inch
Destruction testing freq.
                  1 container per lot (25,000 units or less)
Destruction testing result
                         Must not burst below 240 psig
                         Must not burst below 270 psig

Table 4. Ranges of Aerosol Container Properties, by Container Manufacturer
                                   Parameter
                               Ball Corporation
                            Illing Company Products
                              ITW Sexton Products
                              McKernan Packaging
Number of containers reviewed
                                      24
                                      12
                                      10
                                      57
Outside diameters
                                1.8-2.9 inches
                                2.1-2.9 inches
                                2.1-3.0 inches
                                1.0-2.7 inches
Container heights
                                2.9-10.0 inches
                                3.9-9.5 inches
                                3.9-10.4 inches
                                1.0-9.5 inches
Container contents
                            4.74-33.8 fluid ounces
                             6.0-25.0 fluid ounces
                             7.7-33.8 fluid ounces
                             1.1-28.0 fluid ounces

Notes:
 Ranges are presented for aerosol containers identified through searches of manufacturers' online catalogs.
 The table presents dimensions of containers that manufacturers produce in DOT non-specification, 2P, and 2Q categories (see Section 2.2.2 and Table 3). Refer to the end of Section 2.2.3 for information ERG obtained on larger aerosol containers.
 This section does not include data on container pressures and contents because those parameters are determined when the aerosol containers are filled, not when the containers themselves are manufactured. Refer to Sections 2.2.4 and 2.2.5 for information ERG obtained on typical aerosol pressures and contents.

Table 5. Compressed Gas and Aerosol Incidents Documented by CPSC, 1999-2013
                                     Year
                           Compressed Gas Incidents
                               Aerosol Incidents
                                     1999
                                      42
                                      110
                                     2000
                                      66
                                      93
                                     2001
                                      55
                                      104
                                     2002
                                      55
                                      94
                                     2003
                                      54
                                      98
                                     2004
                                      58
                                      112
                                     2005
                                      50
                                      95
                                     2006
                                      42
                                      85
                                     2007
                                      50
                                      94
                                     2008
                                      68
                                      109
                                     2009
                                      61
                                      80
                                     2010
                                      81
                                      109
                                     2011
                                      62
                                      132
                                     2012
                                      68
                                      110
                                     2013
                                      69
                                      125

Notes:
 Data accessed from CPSC's National Electronic Injury Surveillance System (CPSC, 2015).
 Compressed gas incidents refer to any incident classified as being associated with "propane, liquefied propane, and butane gas tanks or fittings." Aerosol incidents refer to any incident classified as being associated with the keyword "aerosol."

Table 6. Body Parts Injured in Incidents Involving Container Explosions from 2011-2013
                                   Body Part
                           Compressed Gas Incidents
                               (out of 39 total)
                              Aerosol Incidents
                               (out of 65 total)

                                    Number
                               Percent of Total
                                    Number
                               Percent of Total
                                     Face
                                      24
                                      62%
                                      27
                                      42%
                                     Eyes
                                       1
                                      3%
                                       8
                                      12%
                                     Neck
                                       2
                                      5%
                                       1
                                      2%
                                     Head
                                       2
                                      5%
                                       4
                                      6%
                                     Hand
                                      12
                                      31%
                                      27
                                      42%
                                      Arm
                                      12
                                      31%
                                      19
                                      29%
                                      Leg
                                       8
                                      21%
                                      10
                                      15%
                                  Foot/Ankle
                                       1
                                      3%
                                       2
                                      3%
                                     Torso
                                       2
                                      5%
                                       0
                                      0%
                                     Chest
                                       4
                                      10%
                                       5
                                      8%
                                     Back
                                       5
                                      13%
                                       0
                                      0%
                                    Abdomen
                                       1
                                      3%
                                       1
                                      2%
                                   Internal
                                       0
                                      0%
                                       2
                                      3%

Notes:
 Data accessed from CPSC's National Electronic Injury Surveillance System (CPSC, 2015).
 Compressed gas incidents refer to any incident classified as being associated with "propane, liquefied propane, and butane gas tanks or fittings." Aerosol incidents refer to any incident classified as being associated with the keyword "aerosol." Only incidents that referred to exploding containers were included in this table.

Table 7. Type of Injury Sustained in Incidents Involving Container Explosions from 2011-2013
                                Type of Injury
                           Compressed Gas Incidents
                               (out of 39 total)
                               Aerosol Incidents
                               (out of 65 total)

                                    Number
                               Percent of Total
                                    Number
                               Percent of Total
                                 Thermal burn
                                      32
                                      82%
                                      45
                                      69%
                                 Chemical burn
                                       0
                                      0%
                                       2
                                      3%
                                   Cold burn
                                       1
                                      3%
                                       0
                                      0%
                             Bruise or cut by can
                                       5
                                      13%
                                       8
                                      12%
                               Knocked to ground
                                       1
                                      3%
                                       1
                                      2%
                               Chemical exposure
                                       0
                                      0%
                                      13
                                      20%
                               Smoke Inhalation
                                       0
                                      0%
                                       1
                                      2%

Notes:
 Data accessed from CPSC's National Electronic Injury Surveillance System (CPSC, 2015).
 Compressed gas incidents refer to any incident classified as being associated with "propane, liquefied propane, and butane gas tanks or fittings." Aerosol incidents refer to any incident classified as being associated with the keyword "aerosol." Only incidents that referred to exploding containers were included in this table.

Table 8. Aerosol Definitions in Selected Government Regulations, Consensus Standards, and Trade Association Publications
                                    Source
                                  Definition
                                   Comments
GHS Revision 3
"Aerosol, this means aerosol dispensers, are any non-refillable receptacles made of metal, glass or plastics and containing a gas compressed, liquefied or dissolved under pressure, with or without a liquid, paste or powder, and fitted with a release device allowing the contents to be ejected as solid or liquid particles in suspension in a gas, as a foam, paste or powder or in a liquid state or in a gaseous state."
  Products that do not meet certain flammability criteria are considered "not classified," and some of these products would also not be classified as "gases under pressure."
  Products that meet certain flammability criteria are classified either as "extremely flammable aerosols" (category 1) or "flammable aerosols" (category 2).
  This definition has no restrictions on the aerosol container size.
  "Fitted with a release device" could be open to interpretation -- see the SCAQMD and CARB definitions for more precise language.
  Some products that do not meet the flammability criteria completely fall out of the overall characterization scheme (including for gases under pressure), even though GHS Revision 4 has hazard statements that apply to these products.
GHS Revision 4
With one exception, definitions are identical to GHS Revision 3. The main notable difference is that products that do not meet the flammability criteria are classified under GHS Revision 4 as "non-flammable aerosols" (category 3). These products will have the hazard statement: "Pressurized container: May burst if heated."
  The first two comments from GHS Revision 3 apply here.
  In this revision, all aerosol products will be classified in one of three categories, with attendant hazard statements. Therefore, GHS Revision 4 is more comprehensive.
IATA 2013
"For the purpose of these Regulations an aerosol or aerosol dispenser means any non-refillable receptacle made of metal, glass or plastic and containing a gas compressed, liquefied or dissolved under pressure, with or without a liquid, paste or powder, and fitted with a self-closing release device allowing contents to be ejected as solid or liquid particles in suspension in a gas, as a foam, paste or powder, or in a liquid or gaseous state."
  Definition is nearly identical to the GHS Revision 3 and 4 definitions.
  This definition refers to a "self-closing release device" and the GHS definitions refer to only a "release device."
U.S. DOT (see 49 CFR 171.8)
"Aerosol means any non-refillable receptacle containing a gas compressed, liquefied or dissolved under pressure, the sole purpose of which is to expel a nonpoisonous (other than a Division 6.1 Packing Group III material) liquid, paste, or powder and fitted with a self-closing release device allowing the contents to be ejected by the gas."
  Consistent with all definitions in terms of non-refillable receptacle.
  The definition has no limits on container size, but such limits are established in other DOT regulations.
  "Self-closing release device" is not further defined.
OSHA (other than HazCom)
"Aerosol shall mean a material which is dispensed from its container as a mist, spray, or foam by a propellant under pressure."
  Definition appears in the Flammable Liquids standard (29 CFR 1910.106).
  Definition does not appear to conflict with the GHS definitions.
EPA
Regulation on volatile organic content in consumer products
"Aerosol product means a product characterized by a pressurized spray system that dispenses product ingredients in aerosol form by means of a propellant (i.e., a liquefied or compressed gas that is used in whole or in part, such as a co‐solvent, to expel a liquid or any other material from the same self‐pressurized container or from a separate container) or mechanically induced force. `Aerosol product' does not include pump sprays."
  Definition does not set limits for container sizes.
  The type and placement of the actuation device is not addressed in the EPA definition.
NFPA-30B
(2015 Edition)
"3.3.1. Aerosol product. A combination of container, a propellant, and a material that is dispensed. 3.3.2. Aerosol container. A metal can or plastic container, up to a maximum size of 1000 ml (33.8 fluid ounces), or a glass, stone, or metal bottle, up to a maximum size of 118 ml (4 fluid ounces), that is designed and intended to dispense an aerosol."
  Definition places an upper limit on aerosol container sizes -- a notable difference from the GHS definitions.
  The type and placement of the actuation device is not addressed in the NFPA definitions.
CPSC
ERG did not locate CPSC definitions for aerosol. The agency generally refers to aerosols as "self-pressurized products" that are distributed in "self-pressurized containers."
  Consistency with CPSC terminology may not be a priority, given that manufacturers typically differentiate products for industrial and consumer applications.
CARB
Consumer Products Regulation
"`Aerosol Product' means a pressurized spray system that dispenses product ingredients by means of a propellant contained in a product or a product's container, or by means of a mechanically induced force. `Aerosol Product' does not include `Pump Spray.'"
However, sub-categories of aerosol products had more restrictive definitions, such as: "`Aerosol Adhesive' means any adhesive packaged as an aerosol product in which the spray mechanism is permanently housed in a non-refillable can designed for hand-held application without the need for ancillary hoses or spray equipment. Aerosol adhesives include special purpose spray adhesives, mist spray adhesives, and web spray adhesives."
  Definition does not place any upper limit on aerosol container sizes.
  Sub-categories are defined in a manner that clearly describe actuation devices that are considered for aerosols. These descriptions exclude "bulk" products identified in this report that are shipped in pressurized containers with ancillary hoses and guns that are connected to the containers at the user location.
SCAQMD (South Coast Air Quality Management District, in the Los Angeles Basin of California)
"AEROSOL SPRAY CAN is a hand held, pressurized, non-refillable container which expels adhesives from the container in a finely divided spray when a valve on the container is depressed." And: "AEROSOL ADHESIVE means any adhesive packaged as an aerosol product in which the spray mechanism is permanently housed in a non-refillable can designed for hand-held application without the need for ancillary hoses or spray equipment."
  Definition does not place any upper limit on aerosol container sizes.
  Definitions state that the actuation device is on the container itself, suggesting that pressurized containers with hose/gun attachments would not be considered aerosols.
Consumer Specialty Products Association
"Aerosol product: A self‐dispensing pressurized packaging form, consisting of a metal, glass or plastic container with a permanently attached continuous or metering valve, and designed to dispense products as sprays, streams, gels, foams, lotions or gases. Sizes range from about 0.1 fluid ounce (2.8 mL) to 33.8 fluid ounces (1 liter). (Note: The scientific term `aerosol' refers to small particles of a liquid or solid suspended in a gas.)"
  Definition for industry trade association uses size limits.
  Definition clarifies that a typical scientific understanding of "aerosols" differs from conventions used in industry to describe these products.
  The actuation device must be "permanently attached" to the container in aerosol products.

Note: 	Contents in table derived in part from a National Institute of Standards and Technology (NIST) publication on aerosol definitions. See: http://www.nist.gov/pml/wmd/upload/Definitions-of-Aerosol-Product.pdf.

Attachment 1. Specific Insights on "Bulk Aerosol" Products
The following photographs are examples of "bulk aerosol" products that ERG identified during the course of this project. We use the term "bulk aerosol" to describe aerosol products available in containers larger than the 2P/2Q aerosol containers described in Table 3 and Section 2.2 of this report. However, some parties might question use of the word "aerosol" to describe these products, in light of certain definitions listed in Table 9.

Figure 1-1. Image of Cylinder Spray Adhesives Available from 3M
(Reference: http://multimedia.3m.com/mws/media/856301O/cylinder-spray-adhesive-user-guide.pdf) Note -- only some of these cylinders are non-refillable.

Figure 1-2. Image of "Aerosol Bulk" Container Available from Sprits Mold Releases Company
(Reference: http://www.spritsrelease.com/packaging.html)

Figure 1-3. Image of "Bulk Aerosol Cylinders" Available from Price Driscoll Corporation
(Reference: http://moldrelease.price-driscoll.com/viewitems/investment-casting-releases/investment-casting-release)

Figure 1-4. Image of "Ester 4A Tank -- Product Type: Aerosol" Available from Industrial Molding Supplies
(Reference: https://www.imscompany.com/ProductNavigation/ItemDetail?ItemNumber=131408)

To evaluate Hazard Communication requirements for the previous product lines, ERG first considered the GHS definition for aerosol, which is identical in Revisions 3 and 4. These definitions state: "Aerosol, this means aerosol dispensers, are any non-refillable receptacles made of metal, glass or plastics and containing a gas compressed, liquefied or dissolved under pressure, with or without a liquid, paste or powder, and fitted with a release device allowing the contents to be ejected as solid or liquid particles in suspension in a gas, as a foam, paste or powder or in a liquid state or in a gaseous state."

The product literature that ERG reviewed generally confirmed that most of the aforementioned products met the following aspects of the GHS aerosol definition:

 Products distributed in receptacles that are filled just once
 Products distributed in metal receptacles
 Products contained at least some compressed gases (propellants)
 Products are shipped under pressure
 Products are designed to be sprayed as aerosols
 Once assembled at customer locations, hand-actuated devices are used to spray aerosols

The one aspect of the aerosol definition that may not be met is that the products must be "...fitted with a release device allowing the contents to be ejected as solid or liquid particles." When shipped to customers, these products are typically sent as the bulk aerosol container along with hoses and spray guns. Once at the customer location, the ancillary equipment is connected to the containers for use. It is unclear if OSHA will interpret this scenario as a product "...fitted with a release device."

In consultation with one manufacturer, ERG learned that their products were assigned a GHS physical hazard category of "flammable liquid." They apparently did not assign the "flammable aerosol" category due to their interpretation of "fitted with a release device" (and because these containers are clearly not considered aerosols by other definitions in Table 9). Additionally, the products were not considered "gases under pressure" due to their liquid contents.

ERG also asked one manufacturer about the UN numbers and shipping names used on the bulk aerosol products. Based on the 2013 version of the IATA Dangerous Goods Regulations, this manufacturer classified their "bulk aerosol" products as UN-3500, "chemical under pressure, n.o.s." According to the IATA document, these containers are limited to liquid capacity of no more than 50 liters, and "...cylinders must not be offered for transport when connected with spray application equipment such as a hose and wand assembly" (IATA, 2012). Therefore, the products are essentially shipped as cylinders, but are subsequently connected at the user locations to hoses and other peripheral equipment.