Oxy-fuel welding and cutting, and many arc processes, rely on compressed gases. These include oxygen, acetylene, propane, and shielding gases such as argon and carbon dioxide. Misused, these gases can cause fires, explosions and suffocation.

This module covers the safe storage and handling of gas cylinders, flashback protection, the dangers of too much or too little oxygen, and the special precautions needed for welding in confined spaces.

By the end of this module, you will be able to:

• Store, move and use gas cylinders safely.
• Explain the purpose of flashback arrestors, and how to leak test equipment.
• Describe the dangers of oxygen enrichment and oxygen depletion.
• Outline the safe system of work needed for welding in a confined space.

• Store cylinders upright and secured, with a chain or strap, so they cannot fall.
• Keep them in a well-ventilated area, preferably outdoors, away from heat, ignition sources and drains.
• Store oxygen apart from fuel gases, such as acetylene and propane. As a guide, keep them at least 3 metres apart, or separated by a fire-resisting wall.
• Keep valves closed when cylinders are not in use, and protect the valves from damage.
• Keep full and empty cylinders apart, and clearly identified.

Part 8 of the General Application Regulations 2007, on explosive atmospheres, and the Chemical Agents Regulations require the fire and explosion risks of flammable gases to be assessed and controlled.

In practice, this means keeping the amount of gas on site to a minimum, preventing leaks, controlling ignition sources, ventilating storage and work areas, and having plans for an emergency.

• Never roll, drag or drop a cylinder. Use a purpose-made trolley, with the cylinders secured.
• Never lift a cylinder by its valve or regulator.
• In use, keep cylinders upright and secured.
• Use the correct regulator for the gas.
• Use hoses of the right colour for the gas they carry: blue for oxygen, red for acetylene and orange for propane.
• Close the cylinder valves at the end of the job, and whenever equipment is left unattended.

A flashback is a flame travelling back through the torch and hose towards the cylinder. It can make a hose or regulator burst, or set the cylinder on fire.

To prevent it, fit flashback arrestors to the regulator outlets on both the oxygen and the fuel gas lines. Fit non-return valves at the torch.

Have flashback arrestors checked regularly, and replace them after a flashback, or as the manufacturer recommends.

• Purge the hoses before lighting up, and follow the correct lighting up and shutting down sequence for your equipment.
• Check connections for leaks before use, and whenever a fitting has been disturbed.
• Use an approved leak detection fluid, and look for bubbles. Never use a flame to look for a leak.
• Replace damaged hoses. Never repair them with tape.
• Use a proper spark lighter, never a cigarette lighter.

A cylinder that is heated, for example in a fire, can burst violently. Acetylene cylinders are a particular danger, because acetylene can break down inside the cylinder and keep heating it, even after the fire is out.

If an acetylene cylinder becomes hot or is involved in a fire, do not try to move it. Evacuate the area, raise the alarm and call the fire service. Tell them where the cylinders are.

Extra oxygen in the air makes materials catch fire easily and burn far more fiercely. Oily rags, clothing and even hair can ignite and burn intensely.

• Never use oxygen to cool yourself down, freshen the air, or blow dust off clothing.
• Never use oil or grease on oxygen fittings.
• Check oxygen hoses and connections for leaks.
• Close the oxygen valve when you stop work.

Shielding gases such as argon, carbon dioxide and nitrogen do the opposite. They push out the oxygen in the air.

Argon and carbon dioxide are heavier than air, and collect in pits, tanks, trenches and other low areas. Breathing air that is short of oxygen can cause collapse and death within minutes. These gases give no warning: you cannot see them or smell them.

Never enter a space where gas may have collected without proper testing and controls.

Welding in a confined space is dangerous mainly because welding fume and gases build up quickly, and oxygen can be displaced by shielding gas. Oxygen enrichment, heat and the risk of electric shock add to the danger.

Confined spaces include tanks, vessels, pits, ducts, sewers and enclosed rooms.

Under the Safety, Health and Welfare at Work (Confined Spaces) Regulations 2001, entry must be avoided if the work can be done another way.

Where entry cannot be avoided, a safe system of work is required, including:

• A permit to work.
• Testing the atmosphere before entry and during the work.
• Forced ventilation and fume extraction.
• Gas cylinders kept outside the space.
• A trained attendant outside, in constant contact with the welder.
• Emergency rescue arrangements and equipment in place before anyone enters.

Only trained and competent people may enter.