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Aerosol Flammability Explanation

One issue that we are often asked to explain is aerosol flammability. The following was taken from a white paper we published a number of years ago.

Aerosol flammability is something of a difficult and quirky subject to discuss. The easiest and most accurate statement that can be made is that the more flammable an aerosol formulation is, the greater the propensity for an issue to occur relating to a fire event. Aerosol products have their flammability rated on a zero to four scale with zero being the least flammable and four being the highest flammable rating. Products with a zero rating generally contain no flammable ingredients, while those with a four rating are required to utilize an “Extremely Flammable” warning and designation.

The flammability rating for an aerosol product is determined by a simple test named the Aerosol Flame Projection Test. This test has the spray from an aerosol directed at the base of a lit paraffin candle from a distance of 6 inches. The length of any subsequent flame extension is then measured. That extension length then determines the flammability level for that particular product. The generally accepted scale is:

• 0 – will not burn (contains no flammable ingredients)
• 1 – possible to burn (contains flammable ingredients but no flame extension)
• 2 – burns if heated (contains flammable ingredients but less than 18 inch flame extension)
• 3 – easily burns (contains flammable ingredients with a flame extension greater than 18 inches)
• 4 – very easily burns (contains flammable ingredients and flame draws back toward the aerosol can)

Only aerosol products with a flame extension greater than 18 inches long are required to be labeled as “Flammable”. And only those aerosol products that have a flame extension that moves backwards up the spray toward the aerosol can are required to be labeled as “Extremely Flammable”.

An “Extremely Flammable” aerosol product is inherently more dangerous since that flame extension has the ability to move back up toward the can and the operator spraying the product. It is conceivable that the flame could potentially move up the spray pattern and even back into the aerosol can, causing a catastrophic can failure and dangerous situation. This is true only for cans labeled as “Extremely Flammable” and having the 4 designation for flammability on the HMIS warning section of the MSDS.

One more word about flammability; any aerosol product, no matter how flammable, can safely be used as long as there is no ignition source present. But any ignition source (open flame, welding spark, static discharge, etc.) needs be to considered and properly managed when using any aerosol formulation, especially those rated as “Extremely Flammable” and having the propensity for a flame to travel backup toward the can and operator.

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