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124. 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.
125. Fire is spread by three methods:
126. 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.
127. 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.
128. In this chapter, restricting the spread of fire is considered under the headings of:
129. The protection of fire spread into escape routes is covered in Chapter 8.
Fire Separation
130. To limit the severity of fire, a building may be divided into different fire-resisting areas 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 area of origin, avoiding the spread of fire, products of combustion, smoke, heat and toxic gases. Information on the fire protection of common stairs, corridors and escape routes can be found in Chapter 8.
131. 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. Where the premises adjoin or are part of a larger building, such as where it is semi-detached, in a terrace or within a flatted property, the potential for an outbreak of fire in the neighbouring building or occupancy ultimately spreading to the premises should be considered. The following are benchmarks against which existing provision can be compared.
132. To maintain integrity in buildings in different occupation, there should be no openings or doors in separating walls and, ideally, every part of a separating wall or separating floor should be of materials that are non-combustible and which achieve a medium duration (60 minutes) fire-resistance or higher. However, if combustible materials have been used in existing premises, they should achieve the same fire-resistance as indicated above.
133. In buildings with a basement (including those in single occupation), any basement storey should be separated from the storey above by at least short duration (30 minutes) fire-resisting construction.
134. A separating wall or separating floor with at least short duration (30 minutes) fire-resistance should be provided between an integral or attached garage and a unit of residential accommodation in the same occupation.
135. Every lift well should be enclosed by separating walls with a medium duration (60 minutes) fire-resistance. Where the lift well does not extend the full height of the building, the lift well should form a junction with a separating floor with a medium duration (60 minutes) fire-resistance. A separating wall is not needed between a lift well and a protected zone. Where a lift is installed, the landing controls and lift car controls should be of a type that do not operate on heat or pressure resulting from a fire.
136. Where services (pipes and cables) pass through a separating floor, wall or cavity barrier they should, where appropriate, be fitted with proprietary fire-stopping materials capable of maintaining the required fire-resistance of the floor, wall or cavity barrier.
Doors
137. A closed door may restrict fire spread by holding back fire and smoke. A fire door is rated by its fire-resistance performance under test conditions: normally 30 minutes (short duration) or 60 minutes (medium duration). This test rating is an indication of test performance and not necessarily how a door will perform in a real fire. The following are benchmarks against which existing provision can be compared.
138. 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. The gap between the door leaf and the frame is normally fitted with intumescent strips, in either the door or preferably the frame. The strips expand in the early stages of a fire in response to heat and enhance the protection given by the door. In nearly all cases, smoke seals will be required to prevent the spread of smoke at ambient temperatures. A self-closing device complying with BS EN 1154 is a normal feature of a fire door other than for some doors such as cupboards which are kept locked when not in use.
139. Fire doors are an essential part of fire separation and for the protection of means of escape. The provision of fire-resisting doors offers protection to the escape route from a fire starting in a bedroom or other room. More modern premises may have fire doors fitted to the bedrooms in compliance with Building Regulations. In other cases existing doors may be suitable which, while not meeting the specification for a fire door, are of substantial construction and close fitting. Some existing doors may have the potential to be upgraded to the acceptable fire-resisting standard. However, existing domestic panel doors or doors which are warped, split or have substantial gaps around them may not be suitable for upgrading.
140. Where an exit door from a room, storey or a door across an escape route has to be secured against entry, it should only be fitted with a lock or fastening which is readily operated, without a key, from the side approached by people making their escape.
141. Security measures should not compromise the ability of the occupants to escape from premises in the event of fire, the emergency fire action plan, or any potential Fire and Rescue Service operations. However, it is not intended to prohibit the use of locks (including key operated locks) to secure a room or an area of premises, when that part of the premises is unoccupied.
Fire Spread Through Cavities
142. 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.
143. 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. Areas to consider are as follows:
144. Where it is identified that there may be a risk present in relation to the areas identified above, specialist fire safety advice should be sought.
Fire Spread On Internal Linings
145. 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. Table 1 gives benchmarks against which existing provision can be compared. Where it is not possible or practicable to achieve the benchmarks, consideration should be given to the provision of an automatic life safety sprinkler system as detailed in Chapter 11.
Table 1: Surface linings of walls and ceilings
146. 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.
Fire Spread On External Walls
147. 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.
Fire Spread From Neighbouring Buildings
148. 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. 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.