(a) An automatic warning device shall be suitably constructed for
incorporation in or with permissible and approved equipment that is operated
in gassy mines and tunnels.
(b) An automatic warning device shall include an alarm signal
(audible or colored light), which shall be made to function automatically at
a methane content of the mine atmosphere between 1.0 to 1.5 volume percent
and at all higher concentrations of methane.
(c) It is recommended that the automatic warning device be
supplemented by a meter calibrated in volume percent of methane.