30 CFR § 27.34
Test for intrinsic safety.
Assemblies, subassemblies, or components that are designed for intrinsic
safety shall be tested by introducing into the circuit(s) thereof a
circuit-interrupting device which produces an electric spark from the current
in the circuit. The circuit-interrupting device shall be placed in a gallery
containing various flammable natural gas-air mixtures. To meet the
requirements of this test, the spark shall not ignite the flammable mixture.
For this test the circuit-interrupting device shall be operated not less than
100 times at 125 percent of the normal operating voltage of the particular