The Factory Mutual Engineering Corporation’s (FM) Loss Prevention Data Sheet (1977) shows that nearly 10% of losses in industrial properties are due to incidents involving cutting and welding of materials, generally metals. It is clear that the high temperatures required to melt the metals during these operations can start fires, as can the sparks generated in many of these processes. The FM Data Sheet (1977) indicates that the materials most frequently involved in fires due to welding and cutting are flammable liquids, oily deposits, combustible dusts and wood. The types of industrial areas where accidents are most likely are storage areas, building construction sites, facilities undergoing repair or alteration and waste disposal systems. Sparks from cutting and welding can often travel up to 10 m and lodge in combustible materials where smouldering and later flaming fires can occur.
Electrical processes
Arc welding and ar kers from electrocution, spark flashes and intense arc radiation is required.
Oxy-fuel gas processes
This process uses c cutting are examples of processes involving electricity to provide the arc that is the heat source for melting and joining metals. Flashes of sparks are common, and protection of wor the heat of combustion of the fuel gas and oxygen to generate flames of high temperature that melt the metals being joined or cut. Manz (1991) indicated that acetylene is the most widely used fuel gas because of its high flame temperature of about 3,000 °C. The presence of a fuel and oxygen at high pressure makes for an increased hazard, as is leakage of these gases from their storage cylinders. It is important to remember that many materials that do not burn, or only burn slowly in air, burn violently in pure oxygen.
Safeguards and precautions
Good safety practices are identified by Manz (1991) in the NFPA Fire Protection Handbook.
These safeguards and precautions include:
· proper design, installation and maintenance of welding and cutting equipment, particularly storage and leak testing of fuel and oxygen cylinders
· proper preparation of work areas to remove all chance of accidental ignition of surrounding combustibles
· strict management control over all welding and cutting processes
· training of all operators in safe practices
· proper fire-resistant clothing and eye protection for operators and nearby workers
· adequate ventilation to prevent exposure of operators or nearby workers to noxious gases and fumes.
Special precautions are required when welding or cutting tanks or other vessels that have held flammable materials. A useful guide is the American Welding Society’s Recommended Safe Practices for the Preparation for Welding and Cutting of Containers that have held Hazardous Substances (1988). For building works and alterations, a UK publication, the Loss Prevention Council’s Fire Prevention on Construction Sites (1992) is useful. It contains a sample hot-work permit to control cutting and welding operations. This would be useful for management in any plant or industrial site. A similar sample permit is provided in the FM Data Sheet on cutting and welding (1977).