What 29 CFR 1910.253 requires (plain English)
29 CFR 1910.253 governs oxygen-fuel gas welding and cutting: the storage, handling, and use of the compressed oxygen and fuel-gas (such as acetylene) cylinders used in torch welding, cutting, and brazing. These cylinders hold gases under high pressure, and the combination of pure oxygen with a fuel gas, grease, or a spark can produce violent fire or explosion. The standard focuses on keeping oxygen and fuel gases properly stored, separated, secured, and handled so that a cylinder does not become a bomb or an ignition source.
The signature requirement is separation. Oxygen cylinders in storage must be separated from fuel-gas cylinders or combustible materials, especially oil and grease, by a minimum distance of 20 feet, or by a noncombustible barrier at least 5 feet high with a fire-resistance rating of at least one-half hour. This is because pure oxygen dramatically accelerates combustion: oil or grease that would merely smolder in air can ignite explosively in the presence of oxygen, and a fuel-gas leak next to an oxygen cylinder creates an ideal fire mixture. Keeping the two apart in storage is a fundamental control.
Handling and use rules protect the cylinders themselves. Cylinders must be secured in an upright position (acetylene cylinders stored valve end up), kept away from heat and ignition sources, and have their valve protection caps in place when not in use. Cylinders must not be used as rollers or supports, dropped, or struck, and must be moved with the regulators removed and caps on. In use, regulators, hoses, and torches must be maintained and leak-checked, and flashback arrestors help prevent flame from traveling back into the hoses. Together these rules make oxy-fuel work, a common but high-energy operation, reasonably safe.