What are oxidising materials?

Oxidising materials can significantly increase the intensity of fires, turning substances that generally do not burn readily into almost instant tinderboxes for chaos and destruction. The true danger of oxidising materials lies in their ability to create spontaneous combustion reactions that can occur without a clear ignition source.

For those unfamiliar with chemistry, oxidising materials can have ambiguous origins and are often misidentified. It’s important to note that not all oxidisers can cause spontaneous ignition, and the severity of the resulting burn rate varies depending on their classification. Oxidising materials can exist in the form of liquids, solids, or gases.

The principal oxidising agents commonly found in commerce and industry are typically chemical compounds that contain significant amounts of oxygen. These include peroxides, superoxides, nitrates, chlorates, dichromates, permanganates, and persulfates. Inorganic oxidising agents are more frequently encountered in industrial applications compared to organic ones. This category includes various salts such as barium, lithium, magnesium, potassium, sodium, strontium, calcium, lead, and zinc.

Oxidising materials can react adversely with one another and should be stored separately in well-ventilated areas. Oxidising materials can supply combustible substances with oxygen and support a fire even when air is not present. They can cause combustible materials to burn spontaneously without the presence of an ignition source such as a spark or flame. Combustion – Some oxidising materials are themselves combustible

When dealing with oxidising gases, liquids, and solids, temperature control is crucial. An inappropriate temperature or sudden changes in conditions can create the perfect ignition source for these volatile compounds.

The chemical equation clearly illustrates that the reaction involves the addition of an oxygen molecule to a carbon atom, resulting in the formation of carbon dioxide. This process also releases energy in the form of heat.

The equation can be represented as:??

C + O2 → CO2 + heat.

A straightforward example is the use of rags to apply linseed oil. The heat generated by the oxidation reaction may not dissipate quickly enough. In the case of linseed oil, the insulating properties of the crumpled cloth can allow the heat to build up until it reaches a temperature high enough to ignite the materials.

Legal requirements

There are several pieces of legislation concerning oxidising substances, including the following:

1. Regulatory Reform (Fire Safety) Order 2005: This applies in England and Wales and mandates that a suitable and sufficient fire risk assessment of the workplace must be conducted.

2. Equivalent Legislation in Scotland and Northern Ireland: These also require similar fire risk assessments.

3. Dangerous Substances and Explosive Atmospheres Regulations 2002: This regulation requires a risk assessment for any work activities involving dangerous substances.

These laws ensure that proper safety measures are implemented to protect against the risks associated with oxidising substances. This includes safe storage in a secure, cool, dry, and dark place, away from heat, direct sunlight. It is important to store these substances in a dedicated chemical storage shed that is separate from machinery and people.

Extinguishing Agents for Oxidiser Fires

Extinguishing fires involving an oxidiser can be challenging. A carbon dioxide extinguisher is not effective for these types of fires because it works by removing atmospheric oxygen, which is not needed for a fire that is fueled by an oxidiser. Additionally, dry chemical extinguishing agents are generally ineffective as well. While they can interrupt the chemical chain reaction of a fire, they are often overwhelmed by the oxidiser, especially in larger fires. Water is often the only effective extinguishing agent for certain fires. When a fire burns, the heat generated must first convert the water into steam before it can cool the burning material enough to prevent re-ignition. Some combustible materials, such as wood, can retain significant heat even after being cooled down. Therefore, simply adding water until the flames go out may not eliminate the risk of re-ignition since these materials can drive off the water and still have enough heat to catch fire again. An example of this is campfires that can reignite after being extinguished with water.

It is important to use drenching quantities of water. However, if a fire involves a non-miscible flammable liquid, using water may cause the fire to spread. In such cases, evacuation and isolation of the fire may be necessary. Additionally, if the fire involves an oxidising gas, the gas supply should be turned off safely. This is why hospitals are equipped with remote oxygen shut-off valves located in hallways outside patient rooms using oxygen.