Oxidising materials: Involved in fire
Oxidising substances present an additional hazard primarily because they can initiate or support combustion of other substances. This is evident from the definition of oxidising materials given in the Classification, Labelling and Packaging (CLP) regulation:
Oxidising gas – ‘Any gas or gas mixture which may, generally by providing oxygen, cause or contribute to the combustion of other material more than air does.’
Oxidising liquid or solid – ‘A substance or mixture which, while in itself not necessarily combustible, may, generally by yielding oxygen, cause, or contribute to, the combustion of other material.’
In addition to the main oxidising hazard, they may have other hazardous properties such as corrosivity and toxicity and therefore, guidance should be sought regarding those hazards.
The most common way that oxidising substances support combustion is through the release of oxygen, although other chemical reactants will have the same effect, primarily chlorine, fluorine and bromine.
In terms of operational response, there are two main concerns around the loss of stability of oxidising materials, aligned to the two main classes of oxidisers:
- 5.1 Oxidising substances
- 5.2 Organic peroxides
This type of oxidising material presents a high level of hazard as it contains both a supply of chemically available oxygen to support combustion, along with organic material that can combust. Therefore, two sides of the fire triangle are present within the substance. This results in a situation where a small amount of energy, for example, from heat or friction, can complete the triangle, resulting in fire. This has the potential to be an intense fire with the risk that, under containment, an explosion can occur.
For this reason, organic peroxides are typically stored and transported under temperature-controlled conditions.
Oxidising substances other than organic peroxides
This group of oxidisers will provide oxygen, or in some cases other substances (e.g. fluorine, chlorine and bromine), that will support combustion. They are not flammable themselves and therefore need to be combined with a fuel source before combustion can be initiated. The main concern around these substances relates to losing containment or them becoming contaminated with organic materials.
Combustion due to oxidising agents and fuel mixing together may occur instantly, as the oxidising agent oxidises the fuel in an exothermic reaction and adds heat to the mixture. This increases the rate of the reaction, which will in turn add more heat to the mixture until the ignition temperature is reached and fire starts.
For detailed information on classification and labelling see Foundation for Hazardous Materials.
Knowledge and understanding
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