30 CFR § 57.6802
Bulk delivery vehicles.
No welding or cutting shall be performed on a bulk delivery vehicle until the
vehicle has been washed down and all explosive material has been removed.
Before welding or cutting on a hollow shaft, the shaft shall be thoroughly
cleaned inside and out and vented with a minimum 1/2-inch diameter opening
to allow for sufficient ventilation.
[58 FR 69596, Dec. 30, 1993]