The Flammable Limits refer to the conditions under which a mixture of a flammable material and air may catch fire or explode. If the percentage of flammable material in the air is between the minimum and maximum limits, the presence of a flame or a source of ignition is likely to lead to rapid combustion or explosion. Flammable limits for many materials are in the range 2 - 10%, but for some materials the limits are much wider. Ether (diethyl ether) for example, has flammable limits of 1.7 - 48%, which is an unusually wide range. This, coupled with the low boiling point of ether (34.6 C) and high vapour pressure at room temperature (400 mm Hg at 18C) means that it is easy to create a potentially explosive mixture of ether in air, and renders this compound an extreme fire hazard. The material for which flammable limits are quoted may be a flammable liquid, such as ether or methanol, or a powder or dust such as flour or grain dust. Flammable limits are also sometimes refered to as explosion limits.