Vaporisers are devices that convert liquids to gases. They function like boilers, but instead of boiling water, they boil hazardous substances.
Vaporisers are directly or indirectly fired. When directly fired, an open flame is directly applied to the heat exchange surface, which in turn contacts the liquid to be vaporised. Indirectly fired means the heat is furnished by an outside source such as steam, electricity or hot water.