30 CFR § 18.62 Tests to determine explosion-proof characteristics.
(a) In testing for explosion-proof characteristics of an enclosure,
it shall be filled and surrounded with various explosive mixtures of natural
gas and air. The explosive mixture within the enclosure will be ignited
electrically and the explosion pressure developed therefrom recorded. The
point of ignition within the enclosure will be varied. Motor armatures
and/or rotors will be stationary in some tests and revolving in others. Coal
dust having a minimum of 22 percent dry volatile matter and a minimum heat
constant of 11,000 moist BTU (coal containing natural bed moisture but not
visible surface water) ground to a fineness of minus 200 mesh U.S. Standard
sieve series. At MSHA's discretion dummies may be substituted for internal
electrical components during some of the tests. Not less than 16 explosion
tests shall be conducted; however, the nature of the enclosure and the
results obtained during the tests will determine whether additional tests
shall be made.
(b) Explosion tests of an enclosure shall not result in:
(1) Discharge of flame.
(2) Ignition of an explosive mixture surrounding the
(3) Development of afterburning.
(4) Rupture of any part of the enclosure or any panel or
divider within the enclosure.
(5) Permanent distortion of the enclosure exceeding 0.040
inch per linear foot.
(c) When a pressure exceeding 125 pounds per square inch (gage) is
developed during explosion tests, MSHA reserves the right to reject an
enclosure(s) unless (1) constructional changes are made that result in a
reduction of pressure to 125 pounds per square inch (gage) or less, or (2)
the enclosure withstands a dynamic pressure of twice the highest value
recorded in the initial test.