30 CFR § 57.6904
Smoking and open flames.
Smoking and use of open flames shall not be permitted within 50 feet of
explosive material except when separated by permanent noncombustible barriers.
This standard does not apply to devices designed to ignite safety fuse or to
heating devices which do not create a fire or explosion hazard.
[58 FR 69596, Dec. 30, 1993]