Practical fire safety guidance for existing premises with sleeping accommodation: consultation

Chapter 6: Restricting The Spread Of Fire And Smoke

156. To reduce the risk to persons from fire, it is necessary to consider how to restrict the spread of fire and smoke. The majority of people who die in fires are overcome by smoke. To evaluate the risk requires a basic appreciation of the way fires grow and how smoke can spread through a building. A fire in a building can generate smoke that is thick and black, obscures vision, causes difficulty in breathing, and can prevent persons from using escape routes. Smoke is a serious threat to life which should not be underestimated.

157. Fire is spread by convection, conduction and radiation. Convection causes the major proportion of injuries and deaths. When fire starts in 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. Some materials, such as metal beams can absorb heat 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. Combustible material close to a fire will absorb the heat until the item starts to smoulder and then burn.

Fire Separation and Compartmentation

158. The purpose of fire separation is to provide a physical fire-resisting barrier to restrict fire and smoke spread between different occupancies and between single occupancy parts and communal areas. Where premises adjoin or are part of a larger building, the potential for an outbreak of fire to spread to or from the neighbouring building or another occupancy should be considered.

159. A fire compartment is part of a building constructed to provide a physical fire-resisting barrier to prevent the spread of fire and smoke to or from another part of the building. The life safety objectives of fire compartmentation may be to:

• reduce the number of occupants who may be immediately at risk
• reduce the travel distance for persons
• restrict the size and growth of fire
• protect occupants where there may be delayed evacuation of premises

160. For the purposes of smoke control, corridors that have at least two directions of escape, and with more than 12 m in length between the exits, may be divided in the middle third of the corridor with a wall or screen with at least 30 minutes fire-resistance (for integrity) and the door in the wall or screen at least an FD30S self-closing fire door.

161. Bedroom corridors should be protected routes whereby the doors and walls forming the bedroom corridor, other than doors serving only toilets where the potential for fire is low, have at least a nominal 30 minutes fire resistance. The doors should be self-closing and have smoke seals (see paragraph 172). This offers protection to the bedroom corridor escape route from fire and smoke if a fire starts in a bedroom or other room, maintaining the tenability of the escape route to give maximum evacuation time. Figure 3 shows a floor layout with a protected bedroom corridor.

Figure 3 - Protected bedroom corridor

162. A lift well can be a route for vertical fire spread. A lift well which is enclosed by walls with fire-resistance will be a barrier to fire spread. A lift well which is totally within a protected area such as an enclosed stair, is already within a fire resisting enclosure. Where a lift well is not the full height of the building, the fire resistance of the floor and/or ceiling needs also to be considered.

163. Where services pass through any fire resisting structure, gaps should be sealed or fire stopped to maintain the fire resistance of the structure and prevent the passage of fire or smoke. Pipes should be fitted with a proprietary sealing system capable of maintaining the fire-resistance. A similar consideration exists for penetration by ventilation ducts.

164. Boiler rooms and plant rooms are a possible source of fire. To contain a fire, at least in its early stages, a room may be enclosed by walls with fire-resistance where it contains an appliance (solid fuel, oil or gas fired, or fuel oil tanks). Where the appliance or equipment uses liquid fuel, the room should be able to contain all the liquid plus 10%.

165. In situations other than in bedroom corridors, some rooms may need to be enclosed by floors, walls, doors and ceilings, to provide at least 30 minutes fire-resistance, in order to contain a fire in its early stages. Some examples are shown below.

• storage rooms and cupboards
• staff changing and locker rooms
• smoking rooms
• kitchens and laundry rooms
• day rooms
• rooms containing a lift drive mechanism (unless already within an enclosure)

Smoke Control

A hotel with an atrium may include an automatic smoke and heat exhaust ventilation system ( SHEVS). SHEVS are used in conjunction with automatic fire suppression systems; suppression limits the size of a fire therefore controlling the amount of smoke produced. Smoke control in this context is a specialist subject.

Doors

Fire doors

166. A ‘fire door’ is a fire-resisting door which is rated by performance to fire under test conditions. Fire doors are used to prevent fire spread and for the protection of means of escape. A self-closing device is a normal feature of a fire door, though there are some exceptions such as doors to small cupboards which are kept locked shut.

167. A fire door rated to 30 minutes is described as FD30 ^[8] or E30 ^[9] . A suffix is added to denote that the door has a smoke control function giving FD30S and E30Sa respectively. A 60 minutes fire door with smoke control is designated FD60S or E60Sa. The door rating is an indication of test performance and is not necessarily how a door will perform in a real fire.

168. The level of protection provided by a fire door is determined by the time taken for a fire to breach the integrity of the door assembly, together with its resistance to the passage of smoke, hot gases and flame. The gap between the door leaf and the frame is normally fitted with intumescent strips, in either the door or the frame (but not at the bottom of the door). The strips expand in response to heat from a fire, to seal the gap between the door leaf and the frame.

169. Smoke seals fitted to the door leaf gap prevent the spread of smoke at ambient temperatures, before an intumescent strip expands.

170. In determining the performance of a door in fire, it is necessary to consider the whole door assembly including the frame, glazing, side-panels, transoms and ironmongery. In the case of a new door assembly, the manufacturer’s installation instructions should be followed.

171. Some existing non-fire resisting doors may have the potential to be upgraded to nominal 30 minutes standard, but replacement of existing doors and frames is often preferable.

Self-closing function

172. A fire door will only fulfil its function to provide a barrier to fire and smoke if it is closed at the time a fire occurs. A controlled self-closing device, complying with BS EN 1154, will be fitted to each fire door (other than to certain cupboard doors).The closing pressure of the self-closing device needs to be sufficient to overcome any latch mechanism. The force or speed of the self-closing action of a door could be a source of injury to some residents. It is inappropriate to rely on a procedure whereby staff will attend and close doors as an alternative to fitting self-closers.

Hold-open and door release devices

173. There are devices which hold self-closing fire doors in the open position until a fire detection system operates. They should not be used for a door to a room in which the type of automatic fire detector is solely a heat detector.

174. A self-closing fire door can be held open by an electromagnetic hold-open device (which complies, where appropriate, to BS EN 1155 or BS 5839: Part 3) or with electromagnetic hold-open door closers (to BS EN 1155). Electrically operated hold-open devices should deactivate and release the door on operation of the fire warning system or any loss of power to the hold-open device. Doors to a stairway that forms the only means of escape from an upper floor should close automatically in the event of fault in the fire warning system.

175. An alternative release is an acoustically-activated door release mechanism complying with BS EN 1155. Acoustic devices should not be used on fire doors to a protected stair that is the only stairway serving the building or part of the building. Acoustic devices actuate in response to the sound from the fire alarm sounders so will not be appropriate where the initial fire alarm activation does not activate the fire alarm sounders (such as a staff alarm).

176. A further type of self-closing device comprises a ‘swing-free’ arm ^[10] , allowing the door leaf to work normally and independently of the closing device in normal conditions. On the operation of the fire warning system or on power failure, the self-closer operates and closes the door. This type is particularly suitable for use on bedroom doors.

177. Radio-linked devices are available; these reduce the need for wiring. Some acoustic systems are battery powered.

178. BS 7273: Part 4 contains detailed guidance on conditions for use of door release devices.

179. The automatic closing of doors may take persons by surprise and the force of the closing mechanism could knock a someone over and be a source of injury. Consequently precautions should be taken to avoid injury, including during a scheduled test or action which will result in release of the doors.

Fire Spread through Cavities

180. Many buildings have cavities and voids, sometimes hidden from view, which may allow smoke and fire to spread. Examples are:

• vertical shafts. lifts and dumb waiters
• false ceilings, especially if walls do not continue above the ceiling
• voids behind wall panelling
• unsealed holes in walls and ceilings for pipe work, cables or other services
• a roof space or attic
• a duct or any other space used to run services

181. Potential fire spread through cavities and voids should be assessed and, where practical, examined to see if there are voids that fire and smoke could spread through.

182. Cavity barriers may be necessary to restrict the spread of fire in cavities, particularly for those cavities that could allow fire spread between compartments.

183. Certain modular construction buildings have hidden voids through which fire may spread. Modern timber frame buildings have cavities within the frame and these should have been installed with fire resisting cavity barriers between the external cladding and the timber wall panel at the time of construction.

184. Poor work standards during building work can result in cavity barriers (or the enclosure of escape routes) being breached and/or not being reinstated. This potential needs to be considered. The control of building work is covered in Chapter 5.

185. Insulated core panels (sandwich panels) normally consist of an insulated core sandwiched between an inner core and an outer metal skin. They are used in buildings as exterior cladding or for internal structures and partitions. Various materials have been used as a core. The existence of panels with a combustible core needs to be carefully considered since fire may spread through the combustible core.

Ventilation Systems

186. The potential for ventilation systems to allow the spread of fire and smoke should be assessed. A powered ventilation system may assist the spread of smoke unless it is designed to shut down automatically if fire is detected.

187. Ventilation ducts may provide a pathway for the spread of fire and smoke between compartments or into stairs. Where ventilation ducts penetrate the walls or floors of these enclosures, automatic dampers provided inside the ducts hold back fire and smoke. Dampers may need to be actuated by smoke detection. Specialist guidance on the use of dampers is contained in BS 9999.

Fire Spread on Internal Surfaces

188. Fire can rapidly spread on the surfaces of walls and ceilings, significantly affecting the rate of fire growth and smoke production. The potential for fire spread on surfaces in escape routes is important as this could prevent occupants from escaping. The internal surfaces may predominantly be:

• Category 0 for bedroom corridors, protected stairs and escape routes
• Category 1 for other corridors and large rooms

189. The grading system for surface spread of fire relates to performance against tests set out in certain British Standards. Examples of materials are:

Category 0 - brickwork, blockwork, concrete, ceramic tiles, plaster finishes (including rendering on wood or metal lathes), wood-wool cement slabs and mineral fibre tiles or sheets with cement or resin binding

Category 1 - timber, hardboard, blockboard and particle board, which have been treated to achieve this category

190. Additional finishes may be detrimental to the fire performance of the surface. Multiple layers of wallpaper or certain paints applied to the face of a wall or ceiling surface can increase surface flame spread.

191. The use of plastics for surface finishes is a complex issue and outwith the scope of this guidance document. Information on the suitability of plastic materials can be found in the Scottish Building Standards Technical Handbooks.

Fire Spread on External walls

192. If there is combustible external wall cladding or construction, 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 Spread from Neighbouring Buildings

193. An assessment should be made in respect of the potential for a fire to spread to the premises from any neighbouring buildings or structures and whether this could pose a risk to occupants.