OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 10 Fire and Explosion Hazards

Requirements

For a fire to occur, three elements must come together at the same time and in the right proportions … fuel, heat and oxygen. This is commonly known as the “fire triangle” (see Figure 10.1). Fuels are flammable or combustible materials and can be gases, liquids or solids. Heat is the ignition source and can include open flames and sparks as well as chemical reactions that create heat. The most common source of oxygen is air, but oxygen can also come from chemicals called oxidizers e.g. chlorine, potassium permanganate, potassium chlorate, etc. and from membrane-generated nitrogen.

Fire prevention consists of making sure that the three legs of the fire triangle do not occur at the same time. It is important to note that even when all three sides co-exist, there is not always a 100 percent certainty that a fire will start. The three elements need to be present in the right amount and near one another. Important factors include:

  • upper/lower explosive limits — the concentration range of a flammable gas or vapour in air that will form an ignitable mixture;
     
  • ignition source energy — a source of energy that will produce enough heat to ignite a flammable concentration of gas or vapour in air;
     
  • mixture — mixing compounds with different chemical properties can result in unique substances with significantly different explosive limits and/or ignition temperatures; and
     
  • flash point — the minimum temperature of a liquid at which sufficient vapour is given off to form an ignitable mixture with air, near the surface of the liquid. Materials such as diesel fuel, lubricating oils and solvents that are used below their flash points will not form an ignitable mixture in air. However, when liquids are released in the form of a mist the mist may be ignitable below the liquid’s flash point.

Figure 10.1 Fire or Explosion Triangle

Source: Industry Recommended Practice #18, Enform