Smokeless powder is the name given to a number of propellants used in firearms and artillery which produce negligible smoke when fired, unlike the older gunpowder (black powder) which they replaced. The basis of the term smokeless is that the combustion products are mainly gaseous, compared to around 55% solid products (mostly potassium carbonate, potassium sulfate, and potassium sulfide) for black powder. Despite its name smokeless powder is actually not completely smoke-free and does not take the form of a true powder (see granular material). Smokeless powder allowed the development of modern semi- and fully automatic firearms. Burnt black powder leaves a thick, heavy fouling which is hygroscopic and which causes the rusting of the barrel. Smokeless powder fouling exhibits none of these properties. This makes an autoloading firearm with many moving parts feasible (which would otherwise jam or seize under heavy black powder fouling). Smokeless powders are classified as, typically, division 1.3 explosives under the UN Recommendations on the transportation of Dangerous goods - Model Regulations, regional regulations such as ADR and national regulations, such the United States' ATF. However they are used as solid propellants, so in normal use they undergo deflagration, rather than detonation.