Storing Compressed Gas Cylinders at the Shop

Why this matters

A cylinder corner is where a shop's most stored energy sits, usually behind the parts racks where nobody looks. A full nitrogen or oxygen cylinder holds gas above 2,000 psi, and a valve sheared off a cylinder that tipped over turns it into a projectile that can go through a block wall. Oxygen parked beside acetylene with a pile of oily rags between them is how a small shop fire becomes one the fire department will not enter. The rules that prevent both are short, specific, and checked by inspectors on sight.

Two hazards in every cylinder

Every cylinder carries two separate hazards, and storage has to handle both.

• The pressure. Oxygen, nitrogen, argon and similar gases are stored as compressed gas at high pressure. The valve is the weak point. Knock a cylinder over without its cap and the valve can break off, and the escaping gas drives the cylinder. This is why securing and capping are not optional, even for an inert gas.
• The contents. Fuel gases (acetylene, propylene blends, propane) burn. Oxygen does not burn, but it makes everything else burn faster and hotter, and oil or grease in contact with high-pressure oxygen can ignite on its own. Nitrogen and argon are inert, and their hazard is displacement: a leak in a closed room lowers the oxygen in the air with no smell and no warning.

Acetylene adds one more quirk. It is dissolved in acetone inside a porous filler, at around 250 psi rather than thousands. Stored on its side, the acetone can reach the valve and come out with the gas at the torch. Acetylene is stored and used valve end up, and a cylinder found lying down is stood upright and left for the time the supplier specifies before anyone opens it.

The separation rule, and what counts as a barrier

For a shop doing oxy-fuel brazing or cutting, OSHA's general-industry welding standard sets the core distance. Under 29 CFR 1910.253(b)(4)(iii), oxygen cylinders in storage are separated from fuel-gas cylinders and from combustible materials, especially oil or grease, by at least 20 feet, or by a noncombustible barrier at least 5 feet high with a fire-resistance rating of at least one-half hour.

Two words in that sentence do most of the work.

"Noncombustible" and "fire-resistance rating" are both required. A sheet of steel is noncombustible but it is not a rated assembly; it heats through and fails as a barrier. Plywood is neither. A concrete block wall qualifies easily. A gypsum-on-steel-stud partition qualifies if it is built to a listed assembly with at least a half-hour rating, which your building department or the gypsum maker's assembly listing can confirm. Build it at least 5 feet high and taller than the tallest cylinder beside it, and at least as wide as the cylinder groups on either side.

"In storage" is the scope. A torch cart with regulators attached, being used that day, is in use and may carry oxygen and fuel gas side by side. A cart that sits idle in the corner between jobs for days is storage in the way OSHA interpretations have read it, and the 20 feet or the barrier applies to it. If the cart lives in the shop, plan for the regulators to come off and the cylinders to go back in their racks.

 EXTERIOR WALL: louver high and louver low
 +------------------------------------------------+
 | OXYGEN RACK         B | FUEL GAS RACK           |
 | [O2] [O2]           A | [AC-B] [AC-B] [AC-MC]   |
 | chained, caps on    R | valve end up, chained   |
 | FULL  /  EMPTY tags R | FULL  /  EMPTY tags     |
 |                     R |                         |
 | NITROGEN (inert)    I | no rags, oil, grease    |
 | [N2] [N2] [N2]      E | within 20 ft of O2 side |
 |                     R |                         |
 +------------------------------------------------+
  BARRIER: noncombustible, 5 ft min, 1/2 hr rated,
           taller and wider than the cylinders
  OR: no barrier, 20 ft clear between O2 and fuel
  Exit door, stair, electrical panel: elsewhere

Securing and capping

Chain every cylinder upright. Use a chain or strap to a wall rack, a stand, or a cylinder cart, placed above the cylinder's midpoint, commonly about two-thirds of the way up, so it cannot rock out from under the restraint. A single chain around a row of six cylinders lets the end cylinders slide out; each one is captured, or the row is short enough that the chain holds every cylinder against the wall. Tall cylinders on a wall that gets bumped by a pallet jack get two restraints.

Caps on whenever the regulator is off. 29 CFR 1910.253(b)(2) requires valve protection caps in place on cylinders designed to take them, except while the cylinder is in use or connected for use. The cap is what keeps a tipped cylinder from losing its valve. Do not lift a cylinder by its cap or by the valve; use a cylinder cart.

Keep the area clean of oil and grease. Oxygen fittings and the hands that handle them stay oil-free. A greasy rag left on top of an oxygen cylinder is the specific combination the standard names.

Where the storage area goes

The general welding paragraph, 29 CFR 1910.253(b)(2), wants cylinders inside buildings kept in a well-protected, well-ventilated, dry location, at least 20 feet from highly combustible materials, and in assigned places away from elevators, stairs and gangways. Translated to a small shop:

• Ventilated. An outside wall with high and low louvers is better than a closet. A nitrogen leak in a closed storeroom is an oxygen-deficient atmosphere; a fuel-gas leak needs somewhere to go other than toward the water heater.
• Dry and off bare dirt. Standing water rusts cylinder bottoms, and a supplier can refuse a corroded cylinder.
• Away from exits. A cylinder fire beside the only door traps people. Put the cage away from the egress path and the main electrical panel.
• Away from heat. CGA P-1, which OSHA's 29 CFR 1910.101(b) incorporates for compressed gas handling, keeps cylinders from temperatures above 125 F. That rules out the space beside a unit heater flue, the wall behind a parts washer heater, and the van left in the sun with cylinders inside overnight.
• Protected from traffic. A pallet jack or forklift aisle beside the rack needs a bollard or guard between the aisle and the cylinders.

Full, empty and in use

Mark the rack with FULL and EMPTY sections, or tag each cylinder, and never mix them. An empty cylinder still holds residual pressure and residual gas, so it gets the same chaining, capping and separation as a full one. Close the valve on an empty before it goes back in the rack, so moisture and air cannot get in. The supplier's exchange cylinders go back to the supplier; a shop-owned cylinder that has reached the end of its life goes through the disposal route in Disposing of Empty Gas and Refrigerant Cylinders, not into the scrap bin.

A cylinder whose test date has lapsed is also not refilled. Reading that stamp is its own skill: see How to Read a Cylinder Requalification Stamp.

How much fuel gas may sit indoors

OSHA caps fuel gas stored inside a building, other than cylinders in use or connected for use, at a total of 2,000 cubic feet of gas or 300 pounds of liquefied petroleum gas; larger amounts need a separate room or building built to the standard (the fuel-gas storage paragraphs of 29 CFR 1910.253(b); check the current text). Most small shops are far under it. The cylinder's size tells you how much gas it holds: an acetylene "B" cylinder holds about 40 cubic feet, and an "MC" about 10.

Propane is the trap. OSHA's indoor figure is not the only gate. NFPA 58, through the fire code as your jurisdiction adopted it, restricts storing LP-gas cylinders inside buildings, and many fire marshals want spare propane cylinders in a ventilated outdoor cage, away from building openings. Ask before counting a propane cylinder as indoor storage.

A worked example: a 16-foot corner

A six-person HVAC and plumbing shop has one cylinder corner on an exterior wall. The usable wall is 16 feet long. Inventory:

• 2 oxygen cylinders
• 2 acetylene "B" cylinders and 1 "MC"
• 3 nitrogen cylinders for brazing purge and pressure testing
• 2 spare 20-pound propane cylinders for torches

Fuel gas total, indoors. Acetylene: 2 x 40 plus 10 is 90 cubic feet, against a 2,000 cubic foot ceiling. Propane: 2 x 20 is 40 pounds, against 300. Both are far under OSHA's indoor figure. The propane still moves to an outdoor cage because the fire marshal's reading of NFPA 58 is what governs propane in this building, and that answer came from a phone call, not from the OSHA number.

Separation. The wall is 16 feet, so 20 feet between oxygen and acetylene cannot be had along it. The answer is the barrier. The owner builds a short concrete block wing wall, 6 feet high (taller than the 5-foot oxygen cylinders beside it) and 3 feet deep, perpendicular to the exterior wall, with oxygen and nitrogen on one side and acetylene on the other. Block is noncombustible and rated well beyond a half hour. A steel sheet partition was the cheaper idea and it would not have qualified.

Securing. Each cylinder gets its own chain at about two-thirds height on a wall rack, five positions on the oxygen side and three on the fuel side. The three acetylene cylinders stand valve end up. The acetylene MC is small enough to rattle in a full-size slot, so it gets a small dedicated bracket.

Heat and traffic. The unit heater 9 feet away blows toward the corner. Its discharge is redirected away from the cylinders, and two bollards go in where the pallet jack turns at the end of the parts aisle.

What changed the answer. If the shop had no oxy-acetylene at all, only nitrogen and propane torches, the oxygen separation rule would have nothing to separate; the remaining duties would be securing, capping, ventilation, heat, and the fire marshal's propane answer. If the torch cart had been treated as in use permanently, the whole exercise would have been skipped, and the cart's oxygen and acetylene would have spent every weekend beside each other.

Who each rule binds

OSHA's 29 CFR 1910 rules bind the employer and protect employees; they reach any shop with employees, and a sole owner with no employees is outside OSHA but not outside the fire code. The fire code (IFC Chapter 53 for compressed gases in the 2021 edition, plus its LP-gas chapter) binds the building and its occupant through the fire marshal, as your jurisdiction adopted it. CGA P-1 is a consensus standard that binds through OSHA's incorporation and through the supplier's terms. Where the fire code and OSHA differ, meet the stricter of the two. See related: What Occupancy Classification Decides.

References

• 29 CFR 1910.253, oxygen-fuel gas welding and cutting, including (b)(2) storage and (b)(4)(iii) oxygen separation, OSHA general industry
• 29 CFR 1910.101(b) and CGA P-1, Safe Handling of Compressed Gases in Containers
• International Fire Code, Chapter 53 (compressed gases), 2021 edition, and NFPA 58 for LP-gas, as adopted by your jurisdiction
• See related: Disposing of Empty Gas and Refrigerant Cylinders; How to Read a Cylinder Requalification Stamp