30 CFR § 19.7
Protection against explosion hazard.
Unless properly designed, electric cap lamps may present two sources of
probable explosion hazards: Ignition of an explosive atmosphere by the heated
filament of the bulb in case the bulb glass is accidentally broken, and
ignition by sparks or flashes from the battery. MSHA therefore requires the
(a) Safety device or design. The headpiece shall have a
safety device to prevent the ignition of explosive mixtures of methane and
air if the bulb glass surrounding the filament is broken. Alternatively, if
the lamp is designed and constructed to prevent the ignition of explosive
mixtures of methane and air by protecting the bulb from breakage and
preventing exposure of the hot filament, no safety device is required.
(b) Headpiece lock or seal. The headpiece shall be provided
with a lock or seal to prevent unauthorized removal of the lens and
tampering with the safety device, the bulb, or the electrical contacts.
(c) Locks on charging terminals. Lamps shall be equipped with
a magnetic or other equally effective lock at the battery, the headpiece, or
the cord assembly to prevent unauthorized access to live charging
(d) Protection of battery terminals. The battery covers of
lamps that are recharged through the cord shall be so constructed and
assembled as to prevent unauthorized access to the battery terminals.
(e) Battery current restricted. The amount of current flow
between the conductors of the cord, if short-circuited just outside of the
battery casing or cord armor, shall be limited by the design of the battery
or by a fuse to such a value4 as will not produce sparks that will
ignite an explosive mixture of methane and air.
4 The following maximum short-circuit current values may be used as
a guide in the design of cap lamp batteries: 100 amperes for a 4-volt
battery; 75 amperes for a 6-volt battery; 50 amperes for an 8-volt
(f) It shall not be possible to obtain a difference of potential
between any two accessible points of the cap lamp when assembled for use.
NOTE: Paragraph (a) of this section is issued under the authority of §
101 of the Federal Mine Safety and Health
Act of 1977, Pub. L. 91-173 as amended by Pub. L. 95-164, 91 Stat. 1291 (30
U.S.C. 811). All other paragraphs in this section continue under the original
( § 101, Federal Mine Safety and Health
Act of 1977, 91 Stat. 1291 (30 U.S.C. 811))
[Sched. 6D, 4 FR 4003, Sept. 21, 1939, as amended at 47 FR 11369, Mar. 16,