Aerosol Flammability Classification & Testing
Federal regulations require that the aerosols be classified for flammability. These regulations are found in 49 CFR Part 173. Furthermore, the regulations define what an aerosol is. Per the Federal Regulations, an aerosol is “an article consisting of 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.” Although aerosols can be produced in a variety of ways, the federal regulations for aerosol flammability only apply to non-refillable containers with self-closing valves. The regulations also only apply to those containers containing a compressed, liquified or dissolved gas.
Aerosols, as defined in the preceding paragraph, are considered as compressed gases. The Global Harmonized Standard (GHS) rules classify gases into one of 3 divisions:
- Division 2.1: Flammable gases
- Division 2.2: Non-flammable gases
- or Division 2.3: Toxic gases
Classification is necessary for transportation purposes. Toxic gases are not permitted to be transported in an aerosol container. Division 2.1 aerosols are further divided into two categories, extremely flammable or flammable, depending on the composition, heat of combustion and flammability properties of the aerosol contents. An aerosol is assigned to Division 2.1 if the contents include 85% by mass or more flammable components and the chemical heat of combustion is 30 kJ/g or more. An aerosol is assigned to Division 2.2, non-flammable, if the contents contain 1% by mass or less flammable components and the heat of combustion is less than 20 kJ/g. For aerosols that do not meet definitions listed above, testing is required to classify the aerosol into the appropriate group: Division 2.1 extremely flammable, Division 2.1 Flammable or Division 2.2 Non-flammable. The required tests are defined in the UN Manual of Tests and Criteria, Section 31. For aerosol foams, the required tests are the heat of combustion measurement and the foam flammability test. For spray aerosols, the required tests are the heat of combustion measurement, an ignition distance test and possibly the enclosed space ignition test.
The UN Manual, Section 31, provides the flow chart shown in Figure 1 to determine the flammability classification of an aerosol foam. The flow chart in Figure 2 is used to determine the flammability classification of a spray aerosol. The first test required is the heat of combustion. The heat of combustion can be measured using a bomb calorimeter using an ASTM method such as ASTM D-240. In this test, the aerosol can is first chilled using dry ice and then punctured. The can is warmed to ambient temperature and any compressed, liquified or dissolved gas is vented. A measured amount of the liquid from the can is then placed in a high-pressure metal reactor (the “bomb”), the reactor is pressurized with oxygen to 3 MPa (30 atm) and the reactor is placed in a calorimeter. The sample is then ignited. The calorimeter measures the heat generated by the oxidation of the liquid. The measured heat is used to calculate the heat of combustion.
For aerosol foams, the foam flammability test is required if the classification cannot be done after measuring the heat of combustion, as shown in Figure 1. In the foam flammability test, 5 g of foam is dispensed onto a watch glass. The foam is ignited, and the flame height and duration measured. An aerosol foam is classified as extremely flammable if the flame height is greater than or equal to 20 cm and the flame duration is greater than or equal to 2 seconds or if the flame height is greater than or equal to 4 cm and the flame duration is greater than or equal to 7 seconds. The foam is flammable if the flame height is greater than or equal to 4 cm and the flame duration is greater than or equal to 2 seconds. Otherwise, the aerosol foam is classified as not flammable.
For spray aerosols, an ignition distance test is required if the classification cannot be done after measuring the heat of combustion, as shown in Figure 2. The ignition distance test consists of spraying an aerosol towards a gas burner ignition source, where the distance between the aerosol and the ignition source is increased in 15 cm increments from 15 cm to >75 cm. Depending on the heat of combustion and the distance where the spray ignites, the aerosol is classified as extremely flammable, flammable or non-flammable. If the aerosol has a heat of combustion of < 20 kJ/g and it does not ignite at 15 cm, an enclosed space ignition test is required. In the enclosed space test, a candle is placed inside a 55-gallon drum. One end of the drum is covered with a plastic sheet while the second end of the drum has a 50 mm diameter hole. The aerosol is sprayed into the drum through the hole until an ignition occurs. The amount of material sprayed and the time for ignition are measured. Depending on how much material sprays before an ignition occurs, and the time required for ignition, an aerosol is classified as either flammable, or not classified as a flammable aerosol.
Classification of the flammability of an aerosol is needed to properly label the aerosol and to safely transport the material. The testing laboratories at DEKRA Process Safety and our experienced lab personnel are ready to help you classify the flammability of your aerosols. Reach out to us with your testing requirements.
Figure 1. Flow chart from the UN Manual, Chapter 31, to determine the flammability of an aerosol foam
Figure 2. Flow chart from the UN Manual, Chapter 31, to determine the flammability of a spray aerosol