The MSDS HyperGlossary: Aerosol

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Definition

Under Section B.3.1.1 of Appendix B of 29 CFR 1910.1200, the OSHA Hazard Communication Standard (HCS 2024), an aerosol means any non-refillable receptacle containing a gas compressed, liquefied or dissolved under pressure, and fitted with a release device allowing the contents to be ejected as particles in suspension in a gas, or as a foam, paste, powder, liquid or gas.

The definition of aerosol used in HCS 2024 addresses aerosol products such as spray paint, insulating foam, or cans of bug spray. A broader, more general, definition of aerosol is a suspension of fine solid particles or liquid droplets in a gas, especially air. Fogs and mists are examples of aerosols. This broader definition does not require a container.

Additional Info

Section B.3.1.2 of Appendix B of 29 CFR 1910.1200 formally classifies aerosols into one of three categories depending on their flammability properties and their heats of combustion. Aerosols meeting the applicable flammability criteria are classified as Category 1 or Category 2. Aerosols that do not meet those criteria or those containing <1% flammable components by mass and having heats of combustion less than 20 kJ/g are assigned to Category 3. Some additional nuances are described in the Table B.3.1 Notes.

Flammable Aerosols

Table B.3.1—Criteria for Aerosols
Category	Criteria
1	Contains ≥85% flammable components and the chemical heat of combustion is ≥30 kJ/g; or For spray aerosols, in the ignition distance test, ignition occurs at a distance ≥75 cm (29.5 in), or For foam aerosols, in the aerosol foam flammability test. The flame height is ≥20 cm (7.87 in) and the flame duration ≥2 s; or The flame height is ≥4 cm (1.57 in) and the flame duration ≥7 s.
2	Contains >1% flammable components, or the heat of combustion is ≥20 kJ/g; and For spray aerosols, in the ignition distance test, ignition occurs at a distance ≥15 cm (5.9 in), or in the enclosed space ignition test, the Time equivalent is ≤300 s/m³; or Deflagration density is ≤300 g/m³ For foam aerosols, in the aerosol foam flammability test, the flame height is ≥4 cm and the flame duration is ≥2 s and it does not meet the criteria for Category 1.
3	(1) The chemical does not meet the criteria for Categories 1 and 2; or (2) The chemical contains ≤1% flammable components (by mass) and has a heat of combustion <20 kJ/g.

The term flammable aerosol was formally defined in HCS 1994 as an aerosol that, when tested by the method described in 16 CFR 1500.45, yields a flame projection exceeding 18 inches at full valve opening, or a flashback (a flame extending back to the valve) at any degree of valve opening;

At the same time, OSHA's Flammable Liquids standard, 29 CFR 1910.106, used a different definition for purposes of that standard. It defined a flammable aerosol as an aerosol which is required to be labeled flammable under the Federal Hazardous Substances Act and specified that, for purposes of §1910.106(d), such aerosols were considered Class IA liquids. Thus, prior to HCS 2012, two different OSHA standards used the term flammable aerosol for somewhat different regulatory purposes.

HCS 2012 was adopted to bring US Safety Data Sheets into alignment with the Globally Harmonized System. The labeling provisions of HCS 2012 required that Category 1 or 2 flammable aerosol containers carry the flame pictogram (shown on the right) to provide a quick visual warning of the flammability hazard. The GHS does not require pictograms to appear on the SDS itself, however most responsible manufacturers will do so to preserve the correspondence between a substance's SDS and label.

With the adoption of HCS 2024 which is based primarily on GHS Revision 7, Flammable Aerosols is no longer the name of the hazard class. Instead, aerosols are now classified into Categories 1, 2, or 3 as discussed above. The phrase, however, remains in the hazard statements for Category 1 ("extremely flammable aerosol") and Class 2 ("flammable aerosol") in Appendix C of the Standard. Thus, "flammable aerosol" remains a useful regulatory description even though it is no longer the formal hazard-class name.

Currently, one inconsistency of the term flammable aerosol remains in OSHA's regulations. Section 1910.106(a)(13) states that a flammable aerosol means a flammable aerosol as defined by Appendix B to § 1910.1200. Strictly speaking, however, HCS 2024 Appendix B does not define flammable aerosol it defines aerosol and classifies aerosols into Categories 1, 2, and 3, with Categories 1 and 2 assigned flammability hazard statements. Section 1910.106 further specifies that, for purposes of 1910.106(d), such aerosols are considered Category 1 flammable liquids. Complicating matters slightly, §1910.106(a)(1) retains its own definition of aerosol as a material dispensed from its container as a mist, spray, or foam by a propellant under pressure, a definition that differs from the one used in HCS 2024 Appendix B. Because the definitions in §1910.106(a) expressly apply "as used in this section", the reader should be aware that the terminology is not completely harmonized between the two OSHA standards.

SDS Relevance

If an aerosol has a Safety Data Sheet, that means the manufacturer has identified specific hazards that may pose risks when using the product. For example, the contents of an aerosol spray can could be flammable, toxic when inhaled, or pose a carcinogenic risk. In addition, the contents are under pressure, so the SDS may list storage recommendations, conditions to avoid, disposal considerations, or more.

Section 9 of the SDS lists the material's physical and chemical properties including flammability. The flammability of aerosols is often due to flammable solvents (such as butane) as a propellant or carrier. Use caution when using materials such as spray paints or aerosol solvents to avoid accidental ignition by a heat source or open flame. Some equipment may not be adequate to keep a flammable aerosol from flashing back into the container and result in an explosion or deflagration.

Most SDS's and fire safety experts recommend storing flammable aerosols in a flammable liquid storage cabinet. These are sold commercially by many vendors.

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Definition

Additional Info

Flammable Aerosols

SDS Relevance

Further Reading