The numeric half of an ASHRAE 34 safety designation: 1 for no flame propagation, 2L for mild flammability with low burning velocity, 2 for flammable, 3 for higher flammability such as hydrocarbons.
The numeric half of an ASHRAE 34 safety designation: 1 for no flame propagation, 2L for mild flammability with low burning velocity, 2 for flammable, 3 for higher flammability such as hydrocarbons.