Welding and cutting are among the most common causes of fires in industry. Sparks and drops of molten metal can travel many metres, smoulder unseen for hours, and set fire to materials well away from the work.
Hot work means any work that produces heat, sparks or flame, such as welding, cutting, brazing and grinding. This module explains the fire and explosion hazards of hot work, and the controls that prevent them.
By the end of this module, you will be able to:
Welding and cutting produce sparks and molten spatter at temperatures of over a thousand degrees Celsius. Sparks can travel a considerable distance, many metres from the work, roll into gaps and cracks, and fall through openings to lower floors.
They can smoulder in dust, insulation, packaging or timber for a long time before bursting into flame. That is why many fires start after the welding has finished, and after everyone has gone home.
Welding near flammable liquids, gases, vapours or dusts can cause a fire or an explosion. Flammable vapour can travel some distance from its source, and fine dust can explode when it is stirred up into a cloud.
Before hot work starts, the area must be checked for flammable vapours and gases, using a suitable gas detector where needed. If there is any doubt, the work must not go ahead.
Drums, tanks and pipes that have held flammable substances are especially dangerous, even when they look empty. Vapour or residue can remain inside, and a spark or heat can cause a violent explosion.
Never weld or cut on or near a container that has held flammable material until it has been properly cleaned, tested and certified safe by a competent person. This work needs a specific safe system of work.
A fire needs three things: fuel, oxygen and a source of ignition. Take one away, and the fire cannot start or continue.
Welding supplies the heat in abundance, so controlling fire means removing or separating the fuel, and, where relevant, controlling the oxygen.
Oxygen enrichment, for example from a leaking oxygen hose, makes materials catch fire easily and burn far more fiercely. It must always be avoided.
In England and Wales, the Regulatory Reform (Fire Safety) Order 2005 requires the responsible person for the premises to assess fire risks, including hot work, and to put precautions in place.
Where flammable gases, vapours or dusts could form an explosive atmosphere, the Dangerous Substances and Explosive Atmospheres Regulations 2002, known as DSEAR, require the risk to be assessed and controlled.
A hot work permit is a formal, written authorisation to carry out welding, cutting or other hot work in an area where there is a fire risk.
It is issued by a responsible person after checking the area. It is valid only for a set time and a set place.
The permit confirms that the area has been made safe, the right precautions are in place, and a fire watch has been arranged. If conditions change, work must stop, and the permit must be reviewed.
Before starting, make sure that:
A fire watch is a trained person who watches for fire while the hot work is going on. They stay on watch for at least 30 minutes after the work finishes, and up to 60 minutes where a fire could be slow to develop, because smouldering material can take time to burst into flame.
The fire watch must have fire-fighting equipment to hand, and know how to raise the alarm. Before leaving, they check hidden areas and neighbouring areas, including the floors above and below, and behind walls.
Suitable fire extinguishers must be immediately available wherever hot work takes place. The right type depends on what could burn: water or foam for wood, paper and textiles, and dry powder or carbon dioxide where flammable liquids or electrical equipment are present.
Staff must know how to use them. Only tackle a fire in its very early stages, and only if it is safe. Otherwise, raise the alarm, get out, and let the fire service deal with it.
In this module, you have learned that:
Sparks and hot metal can travel many metres and smoulder for hours, so fires often start after welding stops.
A hot work permit formally authorises hot work in a fire-risk area, and confirms the precautions are in place.
A fire watch stays for at least 30 minutes afterwards, longer where needed, with extinguishers to hand and a way to raise the alarm.
In the next module, we will look at physical hazards, including radiation, burns, electricity and noise.