These recommendations are intended to apply to the preparation for welding or cutting (or both) of metal containers that have held combustible solids, liquids or gases, or substances that may produce flammable vapors or gases. Cleaning the container is necessary in all cases before welding or cutting.

Flammable and explosive substances may be present in a container because it previously contained one of the following substances:

(a) Gasoline, light oil or other volatile liquid that releases potentially hazardous vapors at atmospheric pressure.

(b) An acid that reacts with metals to produce hydrogen.

(c) A nonvolatile oil or a solid that, at ordinary temperature, will not release potentially hazardous vapors, but will release such vapors if the container is exposed to heat. (For example, combustible vapors may be generated by the heat of welding or cutting from sludge or scale deposits in such containers or in their riveted seams.)

(d) A combustible solid, finely divided particles of which may still be present in the form of an explosive dust cloud.

The safe practices enumerated here are not intended to apply to the following classes of containers:

(a) Containers that can be entered by workmen for cleaning from the inside.

(b) Tanks, bunkers or compartments on ships. (For information on cleaning such tanks, etc., see A Manual for the Safe Handling of Inflammable and combustible Liquids, issued March 1964 by the U.S. Coast Guard, Washington, D.C. 20226 and Standard for the Control of Gas Hazards on Vessels to be Repaired, NFPA 306, issued by the National Fire Protection Association, 60 Batterymarch St., Boston, Mass. 02110.)

(c) Outside, above-ground vertical petroleum storage tanks. (For information on cleaning such tanks, see API Bulletin 2016, Cleaning Tanks Used for Gasoline or Similar Low-Flash Products published by the American Petroleum Institute, 1271 Avenue of the Americas, New York, N.Y. 10020.)

(d) Gasometers or gas holders for natural and manufactured gas. (For information on cleaning gasometers, etc., see Purging Principles and Practices, published by the American Gas Association Inc., 605 Third Avenue, New York, N.Y. 10016.)

(e) Compressed gas cylinders. (Any hot work on compressed gas cylinders should be done only by a regular manufacturer of the type of cylinder involved.)

(f) Containers that have held nitrocellulose or pyroxylin solutions. (For information on cleaning such containers, consult the manufacturer or supplier of the solution. Remember that inert gas will not prevent or put out fires in such solutions, as the solutions themselves contain enough oxygen for supporting combustion.)

The safe practices enumerated here are not intended to apply to industries (e.g., petroleum, air transport) which have expert knowledge of handling flammables and have developed methods of container preparation (ventilation and purging with air, or inerting) for specific applications to their own equipment.