For a fire to occur you must have all three sides of the fire triangle present, namely
Eliminating any of these will make it impossible to start a fire or extinguish one that is already going.
The hazards of fire include:
- Heat – causing burns;
- Smoke and fumes that can be toxic;
- Oxygen depletion;
- Structural damage to buildings etc.
Fuels and fire classes
There are many different types of substance that can act as a fuel. They are arranged into different classes:
Class A – solids (e.g. paper, wood, plastic);
Class B – flammable liquids (e.g. paraffin, petrol, oil);
Class C – flammable gases (e.g. propane, butane, methane);
Class D – metals (e.g. aluminium, magnesium, titanium);
Class E – Fires involving electrical apparatus;
Class F – Cooking oil and fat.
Also, oxidising agents, whilst not necessarily fuels in their own right can cause other substances to catch fire, possibly without oxygen being present.
Sources of ignition
The following can act as sources of ignition, causing a fire to start if there is fuel and oxygen present:
- Hot surfaces (may be caused by friction);
- Electricity (including static);
- Smoking material (e.g. cigarettes).
Spread of fire
Fire can spread, causing more fire and subsequently more harm and damage. There are three main mechanisms that allow fire to spread. They are:
- Conduction – heat moving through solid material;
- Convection – heat moving through a fluid or gas (i.e. hot air rising);
- Radiation – emission of infra-red energy that can then be absorbed and cause items to get hot.
The main ways of preventing fire are by controlling fuels and ignition sources. In particular using suitable equipment for storing and transporting highly flammable materials. Also, selecting equipment for use in flammable hazardous areas that will not act as an ignition source.
Oxidising agents need to be handled carefully and kept away from flammable materials.
The possibility of arson must be considered, and keeping sites secure and free from rubbish and other flammable items is important.
Fires can be extinguished by eliminating any side of the fire triangle. This usually involves cooling, creating a barrier between fuel and oxygen, using a chemical that interferes with the fire process, or replacing oxygen with another non-flammable gas. Types of extinguishing device include:
- Water from extinguisher, hose, sprinkler, deluge (cools);
- Foam (cools and seals over fuel) – good for liquids;
- Powder (chemical interference);
- Carbon dioxide (displaces air/oxygen) – good for electrical fires;
- Fire blanket (smothers) – chip pans.
A British Standard (BS 5306-3:2009) sets out good practice for the commissioning and maintenance of portable fire extinguishers. It requires that new extinguishers are properly and comprehensively commissioned at the place they are to be installed by a Competent Person (which is defined in the standard). All extinguishers should be subject to weekly checks, monthly visual inspections, an annual basic service and an extended service and overhaul at specified frequencies.
People need to know there is a fire so that they can escape. Options for detection include:
- Flame (UV);
- Manual (e.g. break glass).
Escape from fire
Factors that affect ease of escape from fire (and other emergency situations) include:
- The number of accessible fire escapes (ideally always more than two independent safe routes from any location);
- The distance to an exit;
- Presence of any clutter on route;
- Fire integrity of the escape route – fire doors that close automatically;
- Ability to open fire doors – they must not be locked and should open outwards;
- Emergency lighting;
- (Safe) assembly points;
- Knowledge of procedures – of staff and visitors;
As a general rule lifts (elevators) should not be used for evacuation. Also, it is necessary to make special arrangements for disabled people including those with physical disabilities that affect their mobility, visual disabilities and the deaf who cannot hear alarms and instructions.
From 1 October 2006 the Regulatory Reform (Fire Safety) Order 2005 is law. The cornerstone of the regulations is fire risk assessment. Through this the following need to be considered:
- Preventing fire occurring;
- Preventing fire spreading (design of premises as well as fire fighting);
- Ensuring people are adequately protected if a fire occurs – this includes employees, visitors, neighbours and fire service personnel.
Emphasis is on the employer being responsible for managing risks from fire. To achieve this they need to have competence to assess and control the risks. A series of guides has been published covering different types of establishment including offices and shops, factories and workshops, residential care and educational premises.
Reference – Department for Communities and Local Government website at
For places of work that manufacture, store, process or use dangerous substances (as defined), the Dangerous Substances and Explosive Atmosphere Regulations 2002 (DSEAR) apply. The definition includes:
- Substances classified as explosive, oxidising, extremely flammable, highly flammable or flammable;
- A substance or preparation which because of its physico-chemical or chemical properties and the way it is used or is present at the workplace creates a risk of fire or explosion;
- Any dust that can form an explosive mixture with air or an explosive atmosphere.
The regulations require employers to make a suitable and sufficient assessment of risks to his employees which arise from the substance. This shall include the potential for a flammable or explosion atmosphere to occur and the likelihood and control of potential ignition sources.
Reference – Dangerous substances and explosive atmospheres ACOP available free at http://www.hse.gov.uk/pubns/priced/l138.pdf