(1) Used containers. You must not perform any welding, cutting, or other hot work on used drums, barrels, tanks or other containers until they have been cleaned so thoroughly as to make absolutely certain that there are no flammable materials present or any substances such as greases, tars, acids, or other materials which when subjected to heat, might produce flammable or toxic vapors. You must disconnect or blank any pipe lines or connections to the drum or vessel.

(2) Venting and purging. All hollow spaces, cavities or containers must be vented to permit the escape of air or gases before preheating, cutting or welding. Purging with inert gas is recommended.