Safe Use of Oxygen and Acetylene Cylinders

Gas cylinder safety: three gases, three different hazards

In a metal workshop, an oxy-acetylene cutting set and a MIG/MAG welding machine often stand against the same wall. The cylinders look alike, but the hazards of the gases inside them are very different. Gas cylinder safety means knowing this difference and using each cylinder by its own rules.

The colour code is a helpful indication; the real way to identify the gas is the cylinder label. Do not use a cylinder whose label cannot be read. For the other risks a welder is exposed to, see our article on welders' safety risks.

Securing upright: why must a cylinder not fall over?

The most dangerous consequence of a cylinder falling over is a broken valve. When the valve of a high-pressure cylinder breaks off, the cylinder can be propelled uncontrollably by the thrust of the gas inside it. An acetylene cylinder has an additional problem: the gas is dissolved in acetone absorbed into the porous filling inside the cylinder. If the cylinder is used lying down, acetone can come out with the gas, disturb the flame and damage the regulator.

The rules in practice are as follows:

1. Cylinders stand upright in use and in storage; they are secured against falling with a chain, a clamp or the securing device of a cylinder trolley.
2. The chain is attached at a height where it actually prevents the cylinder from falling; a chain fastened near the foot of the cylinder will not hold it.
3. An acetylene cylinder is not used lying down. A cylinder that has been transported lying down is left standing upright for the time specified by the manufacturer or supplier before use.
4. The cylinder is kept at a distance that welding spatter and cutting slag cannot reach, and away from heat sources.
5. The cylinder must not become part of an electrical circuit; the electrode holder or earth cable must not rest against the cylinder.

Acetylene cylinder storage and separation from oxygen

The acetylene cylinder storage area is one of the places where the risk of fire and explosion is greatest. Apply the following principles in storage:

• Oxygen and flammable gases are kept apart. Because oxygen intensifies combustion, its presence next to flammable gas cylinders in a fire makes the incident worse. As an example of international practice, the welding and cutting standard of OSHA, the US occupational safety administration, requires oxygen cylinders in storage to be kept at least 6.1 metres from flammable gas cylinders, or separated from them by a non-combustible barrier at least 1.5 metres high with a fire resistance of at least half an hour.
• Ventilation. The store is well ventilated; preferably outside the building, in an area protected from sun and rain.
• Distance from ignition sources. No smoking, open flames, welding or spark-producing work near the store; electrical panels and heaters are not located inside the store.
• Full and empty separation. Full and empty cylinders are kept in separately marked places; the valve of an empty cylinder is also closed and its cap fitted.
• Away from oily materials. Oxygen cylinders are not placed on the same shelf or in the same area as oil, grease and flammable materials.
• Signage. Signs showing the gases inside and a "no naked flames" warning are posted at the store entrance.

Stored gases should also be entered into the explosion protection document, which assesses areas where a flammable atmosphere may form. For storing substances of different hazard classes together, see our article on chemical storage compatibility.

Flashback arrestor and hose arrangement

In an oxy-acetylene set, the flame can travel back from the torch tip into the hoses and towards the regulator. This is called flashback, and in the worst case it can reach the cylinder. A flashback arrestor (flame arrestor) is the safety device that stops this travel.

• A flame arrestor is fitted at the outlet of both the oxygen and the acetylene regulators; non-return valves are also used at the torch inlets.
• If a flashback has occurred, the set is checked before use; whether the flame arrestor needs replacing is determined according to the manufacturer's instructions.
• A regulator is used only for the gas it is made for; an oxygen regulator is not fitted to a flammable gas cylinder.
• Because acetylene is unstable at high pressure, the regulator outlet must not exceed the maximum working pressure specified by the manufacturer.
• The cylinder valve is opened slowly and only as far as necessary; the valve key is left on the acetylene cylinder so that it can be closed quickly in an emergency.
• Hoses are of the correct colour code, connected with suitable clamps and undamaged. Hoses "repaired" with tape are not used.
• Leak checks are carried out with a suitable leak detection fluid; never look for leaks with a flame.

If welding and cutting work is to be carried out in areas with a fire risk, a hot work permit should be issued.

Oxygen cylinders, oil and grease: why must they never meet?

The risk that arises when an oxygen cylinder comes into contact with oil runs counter to most workers' intuition: oil ignites very easily in a pure oxygen environment and can catch fire spontaneously under high pressure. The same OSHA standard also requires cylinders, valves, fittings, regulators and hoses to be kept free of oily substances, and oxygen equipment not to be handled with oily hands or gloves.

• The oxygen cylinder valve, regulator threads and fittings are never lubricated.
• Oxygen equipment is not handled with oily gloves, oily rags or oil-contaminated work clothing.
• Oxygen cylinders are not kept next to oil drums and grease buckets.

Cylinder trolley and rules for moving cylinders

Accidents during the moving of cylinders usually result from haste: the cylinder is rolled along the floor, lifted by its valve protection cap, or placed on a forklift's forks without being secured.

1. Cylinders are moved on a cylinder trolley with a securing chain; on site, the oxy-acetylene set also operates on this trolley.
2. During moving, the regulator is removed and the valve protection cap is fitted.
3. A cylinder is not lifted by its cap. OSHA also requires slings and electromagnets not to be used when lifting by crane, and a suitable cradle or platform to be used instead.
4. Cylinders are not thrown, knocked against each other or rolled along the floor.
5. When transported by vehicle, cylinders are carried upright and secured in a ventilated load compartment; they are not carried in the driver's cab.

Daily checklist and acceptance on delivery

When accepting delivery from the supplier, check the cylinder's label, valve protection cap and inspection markings; do not accept a cylinder that is dented, shows burn marks, has a damaged valve or has an illegible label. Pressure equipment in the workshop such as air receivers and compressors undergoes periodic inspection at least once a year under Annex III of the Regulation on Work Equipment; for details see our article on pressure vessels and compressor receivers. The general legal basis is Art. 10 of Law No. 6331 on Occupational Health and Safety, which obliges the employer to carry out a risk assessment and have the necessary inspections carried out, and the Regulation on Work Equipment.

In metal and machinery workshops in Bursa and neighbouring provinces, we check cylinder arrangements, the layout of welding areas and hot work permits together on site as part of our OHS specialist service; you can plan the annual inspections of pressure equipment through our periodic inspection service. For a list covering the workshop as a whole, you can also use our article on the machining workshop checklist.

Frequently Asked Questions

Can an acetylene cylinder be used lying down?

No. Acetylene is dissolved in acetone in the cylinder; when used lying down, acetone can come out with the gas. A cylinder transported lying down should be left standing upright for the time specified by the manufacturer before use.

Can oxygen and acetylene cylinders be stored in the same place?

They should be kept apart in storage. As an example of international practice, OSHA requires oxygen cylinders to be kept at least 6.1 metres from flammable gas cylinders or separated from them by a non-combustible barrier at least 1.5 metres high with a fire resistance of at least half an hour. During use, however, the set can stand together on a secured trolley.

Where is a flashback arrestor fitted?

At the outlet of both the oxygen and the acetylene regulators; non-return valves are also used at the torch inlets. After a flashback, the set is not used until it has been checked.

Can the valve of an oxygen cylinder be lubricated?

No. Oil and grease ignite very easily in a pure oxygen environment. The oxygen cylinder valve, regulator and fittings are not lubricated, nor are they handled with oily gloves.