Permissible explosives are a specialty type of explosives used in environments which may contain ignition hazards, such as methane gas in underground coal mines. Permissible explosives have lower flash points and are meant to be used without igniting external gas (and thus causing coal dust explosions.) Permissible explosives are usually fuel-deficient and have chemically limited flame temperature and duration. In the US, only permissibles may be used in underground coal mines and they must be approved by the Mine Safety and Health Administration (MSHA).