11 Fire Safety Flashcards
Explain the triangle of fire
For fire to exist, three things must be present:
• Fuel – a combustible material or substance that is consumed during the combustion process. In a typical workplace, fuels can include paper and cardboard, wood and soft furnishings, structural materials, petrol
and diesel fuels, butane, acetylene and other gases, solvents and other chemicals.
• Oxygen – consumed during combustion when it is chemically combined with the fuel. Oxygen is present
in air at a concentration of 21%. During a fire oxygen can also come from other sources, including certain
oxygen-rich chemicals (usually called oxidising agents) such as ammonium nitrate.
• Sources of ignition (heat) – a heat or ignition source is essential to start the combustion process. Once
combustion has started it generates its own heat which is usually sufficient to keep the fire burning (in
other words once the fire starts the heat source can be removed and the fire stays alight). Some examples will be described later in this element.
The fire triangle is useful for two reasons:
• Fire prevention – keep the three elements apart and fire cannot start.
• Fire-fighting – remove one of the elements and the fire will go out.
Classification of fires:
- Class A – solid materials, usually organic, such as paper, wood, coal and textiles.
- Class B - flammable liquids, such as petrol, oil and solvents.
- Class C – gases, such as methane, propane and acetylene.
- Class D – metals, such as aluminium or magnesium.
- Class F – high temperature fats and oils, such as cooking fat fire.
Principles of heat Transmission and fire spread
• Direct Burning
The simplest method of fire spread, where a flame front moves along or through the burning
material. For example, if the corner of a piece of paper catches fire, the flame front will spread
across the paper.
• Convection
The principle that hot air rises and cold air sinks. Hot gases generated by the fire rise straight up
from the fire:
–– Inside a building these hot gases will hit the ceiling and then spread out to form a layer
underneath the ceiling. When these hot gases touch any combustible material (such
as a wooden curtain pole) they may heat that material up sufficiently so that it bursts into
flame.
–– Outdoors these convection currents will contain burning embers that are carried
on the currents until the air cools and the embers are dropped to the ground. This is
a common way for forest fires to travel and jump over obstacles (such as roads).
• Conduction
The principle that heat can be transmitted through solid materials. Some metals, in
particular, conduct heat very efficiently (e.g. copper). Any pipes, wires, ducts or services
running from room to room can act as conduits for heat and spread the fire.
• Radiation
Heat energy can be radiated through air in the form of infrared heat waves which travel in
straight lines (just like light) and can pass through transparent surfaces (such as glass). Radiant
heat generated by a fire shines onto nearby surfaces and is absorbed. If the material heats up
sufficiently it can burst into flames.
Common causes and consequences of fires in workplaces
Causes
• Electrical equipment – faulty wiring, overloaded conductors, misused equipment and the incorrect use
of electrical equipment in inappropriate environments (see Element 5).
• Deliberate ignition – many workplace fires are started deliberately. In some cases the workplace has been targeted, e.g. by a disgruntled employee or an unhappy customer. In other cases it has not, e.g. youths playing with matches on an industrial estate.
• Hot work – any work involving the use of naked flames (e.g. a propane torch or oxy-acetylene cutting
equipment) or that creates a significant ignition source (e.g. arc-welding and grinding).
• Smoking – in particular carelessly discarded smoking materials such as cigarette butts and matches.
• Cooking appliances, e.g. fat pans left unattended.
• Heating appliances, e.g. electric fan heaters and space heaters, especially when left unattended.
• Unsafe use and storage of flammable liquids and gases, e.g. petrol, acetone and liquefied petroleum
gas (LPG). Static sparks can be generated which could ignite a flammable vapour.
• Mechanical heat – generated by friction between moving parts such as a motor and its bearings, or cold
work generating sparks.
• Chemical reactions - can also generate heat, e.g. oxidisers (rags soaked in oil and solvents are a
fire hazard, because as the oil or solvents oxidise, heat is replaced and there is a risk of spontaneous
combustion).
Consequences
Damage to buildings and building contents
Damage to the people
Fire fighting, can also do significant damage to the environment
Factors to be considered in fire risk assessment
• Identify the fire hazards:
–– Sources of fuel.
–– Sources of ignition.
–– Sources of oxygen.
• Identify the people who might be at risk:
–– People in the premises.
–– Give special consideration to vulnerable people.
• Evaluate, identify and implement the fire precautions that are required:
The risk of a fire occurring must be evaluated thinking about:
• Potential fuels, ignition sources and oxygen sources.
• Methods by which fire might spread.
• How smoke and flames might travel in the workplace.
• The locations of the people in the premises.
• The structural fire resistance of the building (e.g. presence of timber structures).
A range of preventive and precautionary measures will be necessary, these will include:
–– Fire prevention. –– Prevention of the spread of smoke and flames. –– Fire detection and alarm. –– Fire-fighting equipment. –– Means of escape. –– Signs and notices. –– Lighting. • Record findings, plan and train: –– Emergency plans. –– Information and instruction. –– Training. • Review and revise the assessment as necessary
Control of Combustible and Flammable Material
Eliminate-for instance old stocks of materials
Substitute - Changing petrol-powered equipment by diesel-powered equipment, since petrol is highly flammable and diesel not
Minimised, requires good stock control, housekeeping and waste management
Safe use and storage of combustible and flammable materials.
How to storage LPG? (9)
- Bottles (cylinders) should be stored outside.
- The storage area should be fenced with a secure, lockable gate.
- Warning signs should be displayed.
- Ignition sources should be eliminated from the area.
- Bottles should be kept upright and chained together.
- The storage area should be separate from other buildings.
- Empty and full bottles should be kept separate.
- Oxygen bottles should not be stored with LPG.
- Only those bottles actually required should be removed from the storage area and should be returned after use.
Control of ignition Sources (6)
• Electrical equipment should be routinely inspected and tested to ensure that it is safe. This will prevent
faults developing that might cause sparks or overheating. Both portable appliances and fixed
installations should be checked.
• Hot work should be controlled with a permit-to-work system unless it is being carried out in a purpose-built area such as a welding bay in a workshop.
• Smoking should be controlled in the workplace. It is illegal to smoke in indoor workplaces in some
countries. Even when it is not illegal, smoking can be controlled by company policies that ban or restrict it. In all events, attention must be given to the safe disposal of smoking materials.
• Cooking and heating appliances should be used carefully and their use closely supervised. In particular,
they should not be left unattended.
• Mechanical heat (such as friction from machinery and bearings) can be controlled by routine maintenance.
• Deliberate ignition can be controlled by making good security arrangements for the workplace. A perimeter fence, security staff at entrances, CCTV, security lighting, etc. can help.
Typical Controls for Hot Works(7)
- Combustible and flammable materials are removed from the work area.
- Items that cannot be removed are covered with fire-retardant blankets.
- The floor is swept clean.
- Any wooden floor is damped down.
- A suitable fire extinguisher is at hand.
- A “fire-watcher” is present in the area while the work is carried out.
- The work area is visited routinely after the work has finished to check the area for smoldering.
Classification of flammable liquids
Flammable liquids have a relatively low flash-point (between 21°C and 55°C) and can be quite easily ignited with a heat source (such as a match) at room temperature.
Highly flammable liquids have a lower flash-point (from around 0°C to 21°C) and are therefore easier to ignite.
Extremely flammable liquids have an even lower flashpoint (well below 0°C) and are very easy to ignite at room temperature. Petrol (gasoline) is a common example of an extremely flammable liquid.
The lower the flash-point, the more dangerous the substance. It is therefore essential that flammable liquids are used and stored safely.
Safe use of flammable liquids:
- Use the minimum volume of liquid required.
- Liquid should be in a properly labelled container.
- Ideally the container will be metal with a self closing lid.
- Use a metal tray to catch spills and have absorbent material available.
- Use the liquid away from heat and ignition sources.
- Ensure that the workspace is well ventilated.
- Return containers to safe storage after use.
Safe storage of flammable liquids in workrooms:
• Store minimal volumes only.
• Store in a purpose-built flammables cabinet, which should:
–– Be fire-resistant (usually metal).
–– Have lockable doors and fire-resistant hinges and fastenings.
–– Be clearly signed.
–– Have a built-in catch tray to contain spillages.
–– Store away from ignition sources.
Safe storage of flammable liquids in other locations:
• Store liquids in a purpose-built, single-storey flammables store, which should:
–– Be built of non-combustible materials.
–– Have a lightweight roof for explosion relief.
–– Ideally be built outdoors, away from other buildings or with firewall protection.
–– Suitably fenced in a secure area.
–– Be well ventilated at high and low levels.
–– Have lockable access doors with sills to contain spillages.
–– Have clear and safe access for the fire service.
• All electrical systems should be intrinsically safe.
• All other ignition sources should be eliminated.
• Adequate fire-fighting equipment and suitable fire-safety signs provided.
• Regular checks for security, secure and safe storage, leaks of liquids, etc should be carried out.
Typical characteristics of a fire door are:
• Rated to withstand fire for a minimum period of time
(e.g. 30 minutes).
• Fitted with a self-closing device.
• Fitted with an intumescent strip.
• Fitted with a cold smoke seal.
• Vision panel of fire-resistant glass.
• Clearly labelled (e.g. Fire Door – Keep Shut).
Heavier fire doors may be needed to:
• contain fire within compartments that contain greater fire risk (e.g. a plant room); or
• keep fire out of compartments that contain fire sensitive contents (e.g. a computer room), in which
case a higher rating will be required (one hour, two hours, etc.).
Structural Measures for preventing the spread of fire and smoke
Compartmentation Properties of Common Building Materials • Concret • Stell • Brickk • Timber • Others considerations Insulation, Wall Covering. Protection of opening Voids • Lift shafts. • Service conduits. • Air handling ducts. • Voids between floors. • Roof voids, etc.
