Welding, Cutting and Brazing

6.1 Why Hot Work Is Dangerous

Burns to the skin, flash burns to the eyes and fire are the most immediate and serious hazards of welding, cutting and brazing. The OSHA standard requires employers to use good work practices to prevent injuries, fires and explosions. It sets basic measures for fire hazards and special measures for especially dangerous work, such as welding or cutting containers and welding inside confined spaces.

Key terms

6.2 Preventing Fires

• Keep suitable fire extinguishing equipment ready for instant use and in good condition. It may be buckets of sand, pails of water, fire extinguishers or hoses, depending on the work and the amount of combustible material nearby.
• Station a fire watch when welding or cutting is done and a considerable amount of combustible material is closer than 35 feet to the work.
• Station a fire watch also when large amounts of material that sparks could ignite are present at more than 35 feet.
• Keep the fire watch for at least half an hour after the work is finished.
• Do not weld or cut on barrels, drums, tanks or other containers until they have been cleaned so that no flammable or toxic substance remains.

6.3 Confined Spaces

• Ventilate the space thoroughly to get rid of flammable or toxic gases before the work starts.
• Leave gas cylinders and welding machines outside the space.
• If the welder enters through a small opening such as a manhole, station an attendant outside who watches the welder at all times and can start a rescue.

6.4 Protection, Health and Ventilation

Welders also need protection against other hazards than fire: falls, eye injury and burns, so they need fall protection, eye protection and protective clothing. Some materials used in welding can be extremely hazardous even with precautions, and ventilation must remove them. They include fluorine compounds, zinc, lead, beryllium, cadmium, mercury, some cleaning compounds and stainless steel.

6.5 Oxygen Fuel Gas Welding and Cutting

• Never allow a fuel gas to mix with air or oxygen before burning, unless the device is approved.
• Acetylene must never be generated or stored except in approved cylinders. It is kept dissolved in liquid in specially designed cylinders so that it does not decompose.
• Portable cylinders for compressed gas must be built and maintained to the transport regulations. Everyone must know the marking, storage and operation of cylinders.

Operating rules

• Remove all traces of oil and grease from cylinders, valves, regulators, couplings, hoses and other equipment. Never handle cylinders with oily hands or gloves, and never expose oily surfaces or greasy clothes to a jet of oxygen.
• Valve protection caps protect the valve outlet, but never lift a cylinder by its cap, which may come loose and let the cylinder fall or release pressure suddenly.
• Remove regulators and put the valve protection caps on before moving a cylinder.
• Always fit a regulator before using a cylinder, unless it is connected to a manifold. The regulator must suit the gas and its pressure, and must be clean with a clean filter.

6.6 Arc Welding and Cutting

In arc welding, an electric current is forced to jump across a gap, producing heat intense enough to weld and cut. Most of the precautions are the same as for gas welding, with some features of its own:

• Shielding. Keeping air away from the weld puddle gives better welds, because oxygen, hydrogen and nitrogen with moisture can spoil the weld. Shielding gas protects the joint.
• Machines must be built to a standard, carry their rated load without too great a rise in temperature, and be enclosed except for operating wheels, levers or handles. Input terminals, tap changing devices and live metal parts must be enclosed so that they can only be reached with tools.

6.7 Resistance Welding

Resistance welding uses pressure and heat produced by resistance to an electric current in the pieces that are joined.

• A qualified electrician installs the equipment.
• Each machine has a disconnecting switch or circuit breaker at or near it, and ignitron tubes have thermal protection switches.
• Workers must be trained before they carry out the work.
• Where practical, fit a guard of safety glass or fire resistant plastic at the point of operation against flying sparks, with shields to protect people who pass.
• Portable welding guns and transformers that are hung from overhead structures need safety chains or cables that can take the shock load if the support fails.
• The outer case of a portable welding transformer must be earthed, and a flash welding machine must have a hood to control flying flash.

A study aid, not published or endorsed by IOSH or OSHA. Laws and limits differ between countries.