30 CFR §27.22

1. (a)A methane detector component shall be suitably constructed for incorporation in or with permissible and approved equipment that is operated in gassy mines and tunnels.
2. (b)A methane detector shall include:
   1. (1)A method of continuous sampling of the atmosphere in which it functions.
   2. (2)A method for actuating a warning device which shall function automatically at a methane content of the mine atmosphere between 1.0 to 1.5 volume percent. The warning device shall also function automatically at all higher concentrations of methane in the mine atmosphere.
   3. (3)A method for actuating a power-shutoff component, which shall function automatically when the methane content of the mine atmosphere is 2.0 volume percent and at all higher concentrations of methane.
   4. (4)A suitable filter on the sampling intake to prevent dust and moisture from entering and interfering with normal operation.
3. (c)A methane detector may provide means for sampling at more than one point; provided, the methane detector shall separately detect the methane in the atmosphere at each sampling point with, in MSHA's opinion, sufficient frequency.