Flammable substances are among the most common hazardous materials found in laboratories. The main objective in working safely with flammable liquids is to avoid accumulation of vapors and to control sources of ignition. However, the ability of a material to vaporize, ignite or explode varies with the type or class of substance. Prevention of fires and explosions requires knowledge of the flammability characteristics (e.g. upper and lower flammability limits, ignition requirements, and burning rates) of materials encountered in the laboratory.