30 CFR § 7.507
(a) Each refuge alternative shall have an air-monitoring component
that provides persons inside with the ability to determine the
concentrations of carbon dioxide, carbon monoxide, oxygen, and methane,
inside and outside the structure, including the airlock.
(b) Refuge alternatives designed for use in mines with a history of
harmful gases, other than carbon monoxide, carbon dioxide, and methane,
shall be equipped to measure the harmful gases' concentrations.
(c) The air-monitoring component shall be inspected or tested and
the test results shall be included in the application.
(d) The air-monitoring component shall meet the following:
(1) The total measurement error, including the cross-sensitivity to
other gases, shall not exceed ± 10 percent of the reading,
except as specified in the approval.
(2) The measurement error limits shall not be exceeded after start-
up, after 8 hours of continuous operation, after 96 hours of storage,
and after exposure to atmospheres with a carbon monoxide concentration
of 999 ppm (full-scale), a carbon dioxide concentration of 3 percent,
and full-scale concentrations of other gases.
(3) Calibration gas values shall be traceable to the National
Institute for Standards and Technology (NIST) ``Standard Reference
(4) The analytical accuracy of the calibration gas and span gas
values shall be within 2.0 percent of NIST gas standards.
(5) The detectors shall be capable of being kept fully charged and
ready for immediate use.