139. To reduce the risk to persons if there is a fire, it is necessary to consider how to control or restrict the spread of fire and smoke. The majority of people who die in fires are overcome by the smoke and gases. To evaluate the risk to people in premises requires a basic appreciation of the way fires grow and how smoke and poisonous gases can spread through a building. A fire in a building can generate smoke that is thick and black, obscures vision, causes great difficulty in breathing, and can block the escape routes. Smoke is a serious threat to life which should not be underestimated.
140. Fire is spread by three methods:
141. Fire and smoke spread by convection is the most dangerous and causes the major proportion of injuries and deaths. When fire starts in an enclosed space such as a building, the smoke rising from the fire becomes 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.
142. Some materials, such as metal can absorb heat readily and transmit it to other rooms by conduction, where it can set fire to combustible items that are in contact with the heated material. Radiation transfers heat in the air in the same way that 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.
143. In this chapter, restricting the spread of fire is considered under the headings of:
144. These areas should be considered to the extent that they are appropriate to life safety objectives in individual premises. The protection of fire spread into escape routes is covered in Chapter 8.
145. To limit the severity of fire, a building may be divided into different fire-resisting compartments by fire-resisting doors, walls and floors which will provide a physical barrier to a fire. The intention is to confine the fire to the compartment of origin, avoiding the spread of fire, products of combustion, smoke, heat and toxic gases.
146. The life safety objectives of fire compartmentation may be to:
147. Technical Annexe 13.1 contains benchmarks against which existing provision can be compared.
148. A closed door may restrict fire spread by holding back fire and smoke. A 'fire door' is a fire-resisting door which is rated by performance to fire when tested to an appropriate standard. Fire doors are an essential part of a fire compartment and for the protection of means of escape. A self-closing device is a normal feature of a fire door other than for some doors such as cupboards which are kept locked when not in use.
149. In determining the fire-resistance of a door, it is necessary to consider all the doorset components including the frame, glazing, side-panels, transoms and ironmongery.
150. Technical Annexe 13.9 contains guidance and benchmarks against which existing provision can be compared.
151. In shopping complexes, fire safety measures may include an automatic smoke and heat exhaust ventilation system (SHEVS) in the mall area and in some large units. These systems are designed to collect heat and smoke in a smoke reservoir at roof level where the heat and smoke will vent to the outside. This maintains the smoke layer above head height to allow persons to use the mall as an escape route. SHEVS are used in conjunction with automatic fire suppression systems which are used to limit the size of any fire which may occur.
152. In atrium buildings and buildings with large open areas, SHEVS and an automatic fire suppression system may be installed to control smoke and limit the size of a potential fire.
153. Smoke control in this context is a subject that requires specialist advice. Technical Annexe 13.15 contains further information in respect of Enclosed Shopping Centres.
154. Where buildings or parts of buildings are in different occupation this poses particular problems in terms of fire safety, as one occupier does not usually have any control over the working practices of their co-occupiers. The purpose of fire separation is to restrict fire spread between different occupancies.
155. Where the premises adjoin or are part of a larger building, such as where it is a unit, is semi-detached or in a terrace, the potential for an outbreak of fire in the neighbouring building or occupancy ultimately spreading to the premises should be considered. The provision of fire separation will ensure that in the event of an outbreak of fire within the building, fire and smoke is inhibited from spreading beyond the area of occupation where the fire originated.
156. Technical Annexe 13.2 contains benchmarks against which existing provision can be compared.
157. A cavity is a concealed space enclosed by elements of a building or contained within a building element. The unseen spread of fire and smoke within concealed spaces in the structure and fabric could pose a risk to occupants.
158. The premises should be examined to see if there are any easy paths through which smoke and fire may spread. Many buildings will have void areas, possibly hidden from view, which will allow smoke and fire to spread away from its source. It will be necessary to consider the provision of cavity barriers to restrict the spread of fire in the following:
159. In particular, certain types of buildings which are of a modular construction have hidden voids through which fire may spread. In this type of building it is important that appropriate assessment is carried out and cavity barriers that restrict the spread of fire are installed if appropriate, especially to walls and floors that need to be fire-resisting.
160. Insulated core panels (sandwich panels) may be used in buildings as exterior cladding or for internal structures and partitions. The retail sector in particular, uses insulated core panels because they are easily constructed and suitable for internal alterations. These panels normally consist of a central insulated core, sandwiched between an inner and outer metal skin. The central core can be made of various insulating materials, ranging from non-combustible through to combustible.
161. Fire may spread through sandwich panels which have a combustible core. The existence of panels with a combustible core needs to be carefully considered, particularly in areas of buildings where large numbers of people are present. Some of the practices which should be followed are:
162. Technical Annexe 13.4 contains benchmarks against which existing provision can be compared.
163. The potential for ventilation systems to allow the spread of fire and smoke should be considered. A powered circulation system may assist the spread of smoke unless it is designed to shut down automatically if fire is detected. The ducting of any ventilation system may also provide a pathway for the spread of heat and smoke and this needs to be considered to prevent potential spread between compartments. The integrity of compartments can be achieved by means of fire dampers which close automatically and hold back fire and smoke in the event of a fire.
164. Technical Annexe 13.1 contains benchmarks against which existing provision can be compared.
165. Materials used on the surfaces of walls and ceilings can significantly affect the spread of fire and its rate of growth. The potential for fire spread on internal linings in escape routes is particularly important as rapid fire spread could prevent occupants from escaping. The internal linings of premises should be such that in the event of an outbreak of fire within the building, the development of fire and smoke from the surfaces of walls and ceilings within the area of origin is inhibited.
166. Multiple layers of wallpaper or certain paints applied to the face of a wall or ceiling surface can increase flame spread and hence the fire growth rate. For this reason, multiple layers of paper or paints are not recommended when carrying out refurbishment work involving the re-decoration of wall and ceiling surfaces.
167. Technical Annexe 13.5 contains benchmarks against which existing provision can be compared.
168. If there is combustible external wall cladding, such as timber, it will be necessary to consider the potential for an outbreak of fire within the building, or from an external source, to spread on the external walls of the building and pose a risk to occupants. Fire can spread horizontally along the face of the building and vertically up the face of the building and this can result in extensive fire spread both externally and internally.
169. Technical Annexe 13.6 contains benchmarks against which existing provision can be compared.
170. An assessment should be made to what extent a fire may spread to the premises from a neighbouring building or structure and whether this could pose a risk to occupants. In some building configurations, such as a courtyard, the fire spread potential may be from one compartment in the building across an open space to another compartment of the same building. This is of particular relevance if any external wall cladding is of a combustible material. The results of the assessment should then be considered and appropriate fire safety measures put in place.
171. Technical Annexe 13.7 contains benchmarks against which existing provision can be compared.