In the latest of our back-to-basics series exploring core OSH topics, we focus on understanding the IOSH Fire Risk Management Group’s five current principles of fire safety.
The historic principles of fire safety have always been determined by three concepts:
- Life safety
- Property protection
- Business continuity.
Protecting and saving life is paramount, as it is in every other area of OSH.
1 Understanding the science of fire
Exemplary fire safety relies on a strong understanding of the combustion process, which is defined through the interrelationships between fuel, heat and oxygen – the fire triangle – and the products of combustion.
Fuel
Fuel may be characterised by its moisture content, particle size and shape. This determines how easily the fuel will burn and at what temperature. All combustible fuels give off flammable vapours that can ignite when heat is present.
Heat
Heat must be present for ignition to take place. Heat also removes moisture from nearby fuel, warms the surrounding area and pre-heats fuel in its path, enabling flames to travel.
Means of ignition
Means of ignition include direct ignition, with an open or naked flame, hot works, cooking, heating and process equipment, auto-ignition (spontaneous microbiological ignition, overpressure or unstable chemicals), electrical and electrostatic ignition, friction, and mechanical heat.
Oxygen
Fires need at least 16% oxygen to burn. The atmosphere comprises approximately 21% oxygen, so air acts as an oxidising agent in the chemical reaction.
Products of combustion
The outputs from combustion are:
- Smoke damage, soot, carbon particulates, carbon dioxide (CO₂), carbon monoxide and steam
- Heat, which feeds back into combustion
- Physically weakened structures, scorching of nearby property, buildings, etc.
Extinguishing the fire
To stop a fire, one of the three sides of the fire triangle must be removed. So, if a fire runs out of fuel, flames will smoulder out; if cooled, it will lose heat and extinguish; and if oxygen is removed, the fire will suffocate. Fire extinguishers are designed to eliminate one of these three elements.
2 Fire prevention
Fire prevention is the theory behind practical fire precautions and fire protection measures aimed at preventing outbreaks of fire and mitigating the spread of fire. Care must be taken to safely store flammable materials, which should not be located in potentially dangerous locations. OSH professionals need to consider whether storage of flammable and combustible materials in general has been considered at the building and process design stage.
3 Fire precautions
Fire precautions are protection measures aimed at preventing, or at least minimising, the risks to persons and property in the event of a fire. Fire prevention stops fires starting in the first place, fire precautions manage the risks.
General fire precautions are primarily concerned with provision of:
- Means of detecting the ignition and development of a fire, typically with automated fire detection equipment
- Means of raising the alarm
- Fire safety signs and Action Notices
- Provision of fire fighting equipment, where appropriate
- A safe means of escape with escape lighting where necessary and a safe assembly point.
Fire extinguisher types
Selection for provision and use of fire extinguishers has to be customised for the ignition source and the fuel loading that could be expected in the area where a fire may break out. The categories are:
- A: Carbon-based fires
- B: Liquid fires
- C: Gases
- D: Metal fires
- F: Cooking fats, deep fat fryers
- E: Electrical fires.
Specialised applications
Halons (BCF) are not now commonly used but are still available in aviation and military applications. Specialist extinguishants such as condensed aerosols can now be used for sensitive applications and Lith-Extinguishers with aqueous vermiculite dispersion (AVD) are designed to fight lithium battery fires.
Inert gas fire suppression systems such as Inergen, FM200 and Green Agents are used in IT suites, data banks and document stores.
Naturally occurring ‘green’ atmospheric gases are often used as blends, typically 50% argon (Ar) with 42% nitrogen (N2) and 8% CO₂, or a 50% Ar/N₂ mix. These blends are engineered to reduce oxygen to below 15% but to maintain a level above 12%. Oxygen levels below 10% are extremely dangerous to life.
Passive fire protection
Key roles of passive fire protection in the event of a fire comprise:
- Providing routes of escape from buildings that are protected from fire and smoke
- Creating compartments within buildings that prevent smoke spreading throughout a building during evacuation
- Protecting the building from a fire to protect people as they evacuate the building and to protect property.
4 Fire investigation
So, why do we investigate fires exactly? We do it to:
- Establish the origin and the cause of the fire
- Determine what went wrong
- Prevent them happening again.
5 Designing for fire safety
Designing for fire safety (D4FS) looks at a whole-life, integrated approach to fire risk management. D4FS embodies the theories and practice behind intrinsic fire safety in the construction, fit-out, commissioning, use, facilities management, maintenance and disposal of buildings and structures.
A fire risk assessment is essential in identifying fire risks and managing them appropriately. The five key principles of fire risk assessment are:
- Identify the fire hazards
- Identify people at risk
- Evaluate, remove or reduce the risks
- Record findings, prepare an emergency plan and provide training
- Review and update the fire risk assessment regularly.
Ian MB Scott is a chartered scientist, physicist and engineer specialising in science, technology, fire safety and safety engineering with designed infrastructure solutions for the built environment. He is a volunteer member of IOSH’s Fire Risk Management Group.
