Step 3. Evaluating risk

The management of the premises and the way people use it will have an effect on your evaluation of risk. Management may be your responsibility alone or there may be others, such as the building owners or managing agents, who also have responsibilities. In multi-occupied buildings all those with some control must co-operate and you need to consider the risk generated by others in the building.

The chances of a fire starting will be low if your premises has few ignition sources and combustible materials are kept away from them.

In general, fires start in one of three ways:

• Accidentally, such as when smoking materials are not properly extinguished or when lighting displays are knocked over
• By act or omission, such as when electrical office equipment is not properly maintained, or when waste packaging is allowed to accumulate near to a heat source
• Deliberately, such as an arson attack involving setting fire to external rubbish bins placed too close to the building

Look critically at your premises and try to identify any accidents waiting to happen and any acts or omissions which might allow a fire to start. You should also look for any situation that may present an opportunity for an arsonist.

Having identified the people likely to be at risk, should a fire start anywhere in the premises and having identified the chances of a fire occurring, it is unlikely that you will have concluded that there is no chance of a fire starting anywhere in your premises, so you now need to evaluate the actual risk to those people should a fire start and spread from the various locations that you have identified.

While determining the possible incidents, you should also consider the likelihood of any particular incident; but be aware that some very unlikely incidents can put many people at risk.

To evaluate the risk to people in your premises, you will need to understand the way fire can spread. Fire is spread by three methods:

• Convection
• Conduction
• Radiation

Fire spread by convection is the most dangerous and causes the largest number of injuries and deaths. When fires start in enclosed spaces such as buildings, the smoke rising from the fire gets trapped by the ceiling and then spreads in all directions to form an ever-deepening layer over the entire room space. The smoke will pass through any holes or gaps in the walls, ceiling and floor into other parts of the building. The heat from the fire gets trapped in the building and the temperature rises.

Some materials, such as metal shutters and ducting, can absorb heat and transmit it to the next room, where it can set fire to combustible items that are in contact with the heated material.

Radiation heats the air in the same way as an electric bar heater heats a room. Any material close to a fire will absorb the heat until the item starts to smoulder and then burn. Smoke produced by a fire also contains toxic gases which are harmful to people. A fire in a building with modern fittings and materials generates smoke that is thick and black, obscures vision, causes great difficulty in breathing and can block the escape routes.

It is essential that the means of escape and other fire precautions are adequate to ensure that everyone can make their escape to a place of total safety before the fire and its effects can trap them in the building. In evaluating this risk to people you will need to consider situations such as:

• Fire starting on a lower floor affecting the only escape route for people on upper floors or the only escape route for people with disabilities
• Fire developing in an unoccupied space that people have to pass by to escape from the building
• Fire or smoke spreading through a building via routes such as vertical shafts, service ducts, ventilation systems, poorly installed, poorly maintained or damaged walls, partitions and ceilings affecting people in remote areas
• Rapid vertical fire spread in racked displays
• Fire and smoke spreading through a building due to poor installation of fire precautions, e.g. incorrectly installed fire doors or incorrectly installed services penetrating fire walls
• Fire and smoke spreading through the building due to poorly maintained and damaged fire doors or fire doors being wedged open.
• Fire starting in a service room and affecting hazardous materials
• Fire spreading rapidly through the building because of combustible structural elements and/or large quantities of combustible goods.