Class 3 materials are liquids that are flammable or combustible. Flammable liquids cause more fires than flammable gases because they are more abundant. Vapors of many flammable liquids are heavier than air. Most flammable liquids have a specific gravity of less than 1, so they float in water. They may also be incompatible with ammonium nitrate, chromic acid, hydrogen peroxide, sodium peroxide, nitric acid, and the halogens. According to the DOT, flammable liquids “have a flash point of not more than 141°F, or [are] any material in a liquid phase with a flash point at or above 100°F, that is intentionally heated and offered for transportation or transported at or above its flash point in bulk packaging.” There is an exception to this definition that involves flammable liquids with a flash point between 100° and 140°F. Those liquids may be reclassified as combustible liquids, and at the option of the shipper, may be placarded flammable, combustible, or fuel oil. Even though the DOT wanted all liquids up to 140°F to be placarded flammable, this exception was made because of public comments, particularly from the fuel oil industry. Combustible liquids are defined as “materials that do not meet the definition of any other hazard class specified in the DOT flammable liquid regulations and have flash points above 141°F and below 200°F.”