Forensics

Hot Work Accidents

Cutting steel

The cutting of these high-carbon steel strands at dusk at a site in Taiwan produced a spectacular display of sparks, illustrating the potential for initiation of fire.

The term hot work is used in industry to denote work involving equipment which causes a significant rise in temperature, sufficient to cause ignition. The ignition might be of materials, resulting in smoldering or flaming combustion, or of flammable gases, resulting in explosion.

Various types of hot work are as follows:

  • Electric welding
  • Cutting with an oxygen/acetylene gas torch.
  • Soldering, brazing or welding with a gas torch.
  • The use of a hot air or flame blower to strip paint or lay bitumen.
  • Sometimes included are grinding or other mechanical processes that create sparks. Although not conventionally classed as hot work, the sparks are for a brief moment in excess of 1000°C and are capable of starting smoldering fires or igniting flammable gases.

Fires and Hot Work

Grinding

A number of severe fires have been started by grinding or abrasive cutting in inappropriate environments.

Many destructive fires are started by hot work. In our experience a significant proportion involve contractors. More than half of the marine fires and explosions that we have investigated were initiated by hot work.

Ignition of Solids

Common materials such as paper, wood and textiles will ignite if heated to 300-400°C and are also capable of smoldering. By comparison, a flame involves temperatures of 600°C or more, while welding and oxy-acetylene cutting involve temperatures of at least 2000°C.

RattanFactory1 RattanFactory2 Smoke
This rattan furniture factory was destroyed by a contractor working unsupervised on a weekend. He was welding on one side of a wall and ignited foam on the other side. The equipment left behind can be seen on the right. Smoke from burning paint along a line of weld being laid down on the other side of this steel plate.

Ignition of Liquids, Vapours & Gases

With liquids, vapours and gases, hot work can ignite a mixture of the flammable gases or vapour in correct proportion with air. By comparison with solid ignition, very low ignition energies are required and all of the hot work processes, including grinding, are capable of ignition.

Danger1 Danger2 Danger3
A worker cutting through a steel vessel with an oxy-acetylene torch. The man was obviously aware of the danger, squinting through lidded eyes, but chose not to wear any eye protection. A worker cutting through piping with an oxy-acetylene torch. The balancing act on a plank high off the ground, with no safety shoes, gloves or eye protection typifies a casual approach to hot work that is so prevalent in many countries The use of an oxyacetylene torch on a busy street in Makati, Manila. Molten metal and slag rained down on the footpath, with no barricades or other attempts to stop passers-by from being injured.

Oxy-acetylene Cutting

From our experience it is justifiable to highlight the particular hazards of oxy-acetylene cutting. Large globules of molten metal and slag in excess of 1600°C can be projected considerable distances vertically and horizontally. It is also apparent from watching building sites at night that red hot globules of metal can remain hot enough to ignite fires while falling 10 storeys or more.

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