SAS Urban Survival Handbook (54 page)

FLASHOVER

As fire takes hold two things happen. Firstly, the air temperature in a room increases dramatically, discolouring furniture and causing scorching which can produce smoke and poisonous gases. Secondly, fresh supplies of air are sucked into the room as hot air rises and escapes. The air temperature increases until it becomes superheated and flashover occurs. Parts of the room not in contact with the flames are set alight by the heat of the air itself – engulfing a room in flames in a matter of seconds! Once flashover has occurred the air remaining in the room will be hot enough to cook the lungs of anyone breathing it!

HOW FIRE KILLS

Fire does not just ‘burn people to death’. Understanding how fire kills could save lives. In most cases death occurs BEFORE flames have reached the victim—caused by SMOKE and TOXIC GASES. These lead to:
ASPHYXIATION
Carbon monoxide and the large volume of ash and carbon particles present in smoke prevent oxygen from reaching the lungs and the bloodstream. A person will lose consciousness and suffocate very quickly (see SAFETY FIRST:
Carbon monoxide
).

POISONING
When some materials burn, particularly man-made ones, not only do they produce carbon monoxide but also toxic gases. These are often highly poisonous and will kill much faster than the effects of smoke.

The stark truth is that most of the contents of our homes contain or are made from products that produce toxic fumes when burnt. Old foam-filled furniture can be a killer! The most common and potentially-lethal types of man-made or synthetic materials and the toxic fumes that they give off are:

Polyurethane foam
(often used in furniture and mattresses)

▶ Cyanides including hydrogen cyanide

PVC
(used to cover electrical wires and in plastic goods)

▶ Hydrogen chloride

EXPLOSION

Like fire, to which they are linked, we should have a fuller understanding of explosions in order to prevent them. Fire dramatically increases the risk of explosions – gas, cylinder gas,

petrol, paraffin (kerosene) and solvents all have the potential to explode.

Flammable substances may combust rapidly, with a blast-like force. There is a risk of ‘explosion’ with any such substances stored in sealed containers – for example, a petrol canister, aerosol can or gas cylinder. If the contents are ignited through a rupture or defective valve or if the container is subjected to heat, the pressure built up in the container will cause an explosion. The initial force of the explosion releases the contents at high speed – in a shower or cloud. This burns as it mixes with oxygen in the air. All this happens in a fraction of a second.

Explosions can also happen if an explosive atmosphere is created. Gas, heavy fumes from solvents and liquid fuels and certain types of dust are all flammable and can build up in a confined atmosphere until a critical level is reached. A strong smell of gas, for example, is a warning of this. There are very few circumstances where this will by itself result in explosion unless the substance is highly volatile. But if the mixture of air and flammable gas or particles is ignited – even by a tiny spark – an explosion will occur.

Domestic gas causes many explosions. The source of the ignition is usually electrical. Even turning on or off a light switch, ringing a doorbell or using the telephone may provide the spark! Other causes include lighted cigarettes and matches – even static electricity, which you can produce by combing dry hair! In addition to the threat from gas leaks, many industrial and DIY processes involve substances that can create an explosive atmosphere.

FLASHPOINT

The flashpoint is the lowest temperature at which a substance can give off a mixture of vapour and air, which may be ignited by a spark or static electricity. Flammable substances MUST be kept and used at a lower temperature than their flashpoint to reduce the likelihood of ignition. The main categories are:

• ■
  HIGHLY FLAMMABLE Substances with a flashpoint of 32° C (90° F) or below
  
• ■
  FLAMMABLE Substances with a flashpoint above 32 °C (90 °F) Some petroleum mixtures have a flashpoint below 23 °C (73° F), making them extremely flammable.
  

EQUIPMENT & DRILLS

With the threat of fire all around you must know how it behaves in order to be able to prepare the right sort of defence. This can be done in two ways: firstly by reducing the causes of fire, and secondly by planning what to do if a fire breaks out. The fight against fire has led to the development of a wide range of equipment that either detects the presence of fire or acts as protection against it. It ranges from the latest in high-tech sophistication to a simple bucket of water. But in order for any equipment to be truly effective, at home or anywhere else, you MUST understand how it works.

Be prepared

Your own level of preparation for fire is just as important as equipment—how will you react? What will you do? Asking the right questions is essential and, when put into the form of a fire drill, will help to eliminate panic. In a fire situation, if you know what to do, you can protect yourself and others.

SMOKE DETECTORS

The most effective early warning device for fire is a smoke detector/alarm. Smoke detectors are NOT a substitute for taking every possible precaution against fire, but they do alert the occupants in the early stages of fire while conditions may still allow for a safe escape.

There are two basic types of smoke detector, both of which are reliable. Most are the ionization type: these contain a tiny radioactive source which ionizes air inside the detector, producing electrically-charged particles (ions) and allowing a small current to flow from a battery. When smoke enters the detector, it impedes the current flow and triggers the alarm.
Ionization detectors are better at detecting hot blazing fires.

The other type of detector uses a photoelectric device, which triggers an alarm when a light beam is interrupted by smoke.
Photoelectric detectors tend to be more sensitive to smoke from smouldering fires.

WARNING

Even the minute amount of radioactive material in an ionization detector may be hazardous. Do NOT break open the sealed parts of the detector and always follow manufacturers’ recommendations for disposal.

SMOKE ALARM FEATURES

• ■
  All smoke detectors are electrical, usually battery powered, in most cases using a small nine-volt battery which should last about a year
  
• ■
  They should have a bleep warning indicating that the battery is running down and a button to test the detector
  
• ■
  Many models have a small red light, which flashes from time to time to show that all is well
  
• ■
  Some models have a built-in emergency light (powered by another battery), which may help you to see where you’re going if the electricity supply fails
  

REMEMBER

False alarms can sometimes be caused by DIY jobs or cooking. Some models give you the chance to avoid this happening with an override button, which disables or desensitizes the detector for a short time.

WARNING

More and more smoke detectors are coming on to the market. ALWAYS check for the features listed above and look for a label that shows the detector meets national safety standards. Don’t be hurried into buying a smoke detector by sales people – a useless detector will give you a false sense of security – take your time and shop around.

REMEMBER

Choose a smoke alarm that is small and light to take with you when you travel. Try to sleep with the air conditioning off – it helps to prevent the rapid spread of smoke in the event of a hotel fire.