30 CFR 22.2 - Definitions.
(a) Methane detector. A methane detector is a device that may be used to detect the presence of methane in a gassy mine.
(b) Methane-indicating detector. A methane-indicating detector is a device that will show, within certain limits of error, on an adequate scale, the percentage of methane in a gassy atmosphere.
(c) Permissible. Completely assembled and conforming in every respect with the design formally approved by MSHA under this part. (Approvals under this part are given only to equipment for use in gassy and dusty mines.)