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Building Standards technical handbook 2017: domestic buildings

The Building Standards technical handbooks provide guidance on achieving the standards set in the Building (Scotland) Regulations 2004 and are available in two volumes, domestic buildings and non-domestic buildings. This publication is available in html and also in PDF format (in 'supporting documents' ).

Building Standards technical handbook 2017: domestic buildings
2. Fire

2.9 Escape

Mandatory Standard

Standard 2.9

Every building must be designed and constructed in such a way that in the event of an outbreak of fire within the building, the occupants, once alerted to the outbreak of the fire, are provided with the opportunity to escape from the building, before being affected by fire or smoke.

2.9.0 Introduction

If a fire starts in a dwelling, occupants within the dwelling of fire origin should be provided with at least one route of escape through an exit door which leads to a place of safety outside the building. Occupants in dwellings may not be aware of the speed that fire can spread and if they are asleep are more likely to delay their escape. Therefore, it is important that a fire alarm is installed to provide occupants with early warning of fire (see Standard 2.11). In some cases, a fire alarm alone may not be sufficient and a protected route within the dwelling may be necessary due to the height that occupants are located above the ground. Occupants in dwellings located near the ground have the added benefit of access to windows to escape in an emergency.

Once outside flats or maisonettes, occupants may still need to escape through common areas within the building to reach a place of safety. This is termed an ‘escape route’. The building should be designed to inhibit fire and smoke spread into the escape route. Where occupants have only one means of escape from the building, automatic smoke ventilation is normally provided to help remove any smoke and heat that may enter the escape route.

Following the outbreak of fire anywhere in the building, there may be residents located in common lounges, communal laundry rooms and solid waste storage rooms. Service engineers may also be working in service spaces, plant rooms and lift machine rooms for example. These occupants should also be provided with the opportunity to escape from the building following a fire. The non-domestic Technical Handbook should be used for guidance on travel distances within ancillary rooms and for escape routes serving such rooms.

It is common practice for the fire and rescue service to intervene and commence fire-fighting and rescue operations before all occupants have made their escape to a place of safety. However compliance with Standard 2.9 should reduce the risk of occupants becoming trapped by fire and smoke.

If a fire has accidentally or deliberately been set in the common stair, the escape route may become impassable. In such cases occupants should be able to remain safely inside the building until the fire has burnt itself out or until the fire has been contained and it is safe to use the escape route.

Fire protection measures used to protect routes of escape and to provide a safe refuge include a combination of passive and active protection. Walls, floors, and doors can provide good passive fire protection. Active systems such as automatic detection, automatic smoke ventilation and automatic suppression are designed to activate in the earlier stages of fire development to provide early warning, control heat and smoke and inhibit fire growth. All escape strategies incorporate a combination of passive and active fire protection measures.

Exclusions and obstacles to escape - a lift should not be used for escape because there is a risk that the lift could malfunction during the outbreak of fire. Fire-fighters may use a fire-fighting lift to rescue injured occupants but this is matter for the fire and rescue service to decide, following a risk assessment at the incident.

Fixed ladders are considered to be too dangerous for residents to use for escape however a fixed ladder may be used from a lift machine room or a plant room provided it is not a place of special fire risk. These rooms will only be used intermittently by engineers who are likely to be familiar with and trained in the use of fixed ladders.

Locking devices on final exit doors and on escape windows should not prevent occupants escaping from the building. The intention is to assist escape, but not to exclude the use of locks or other safety devices (see Section 4 Safety). Permanent obstructions such as fixed security grills should not be used on final exit doors or escape windows.

Conversions - in the case of conversions,as specified in regulation 4, the building as converted shall meet the requirement of this standard (regulation 12, schedule 6).

2.9.1 Escape within dwellings - general principles

The time occupants need to escape varies enormously and is dependent on a number of risk factors including, early warning of fire, the occupant characteristics, the number of exit doors, the area of an individual storey within a dwelling, the height of the topmost storey above the ground or depth of the storey below ground.

Early warning of fire is one of the key fire safety measures to provide occupants with sufficient time to escape from the building before being overcome from the effects of fire and smoke. Sleeping occupants will react more slowly and it is important that they receive the earliest possible warning of the outbreak of fire within the dwelling. Guidance to Standard 2.11 provides recommendations for the installation of fire detection and alarm systems in domestic buildings.

The occupant characteristics in dwellings are wide ranging and therefore impossible to quantify in building standards. The guidance in the Handbooks assumes that the occupants are capable of moving or being moved to a place of safety. For dwellings that require to be licensed as a house in multiple occupation, or where a care service is provided for the occupants, additional fire protection measures may be required to satisfy other legislation (see 2.0 Introduction).

The number of exit doors from a dwelling is important. If every floor in every dwelling has 2 or more exit doors which lead to a place of safety, the risk that occupants could become trapped by fire and smoke would be low and the fire protection measures would be minimal. However this is not practical to achieve in the majority of cases and as a result, the guidance recommends that every dwelling should be provided with at least 1 exit door.

The area of an individual storey within a dwelling has an impact on the time occupants have available for escape from a fire originating in the dwelling. A dwelling with an individual storey more than 200m2 is outside the scope of the guidance (see 2.0 Introduction). In such cases, an alternative approach (see clause 2.0.8) based on the guidance contained in this handbook may be appropriate but the need for additional exits and additional fire protection measures would need to be considered on a case by case basis.

Height of storey above ground - increased height brings extra risk, both in the time needed for escape and the difficulties posed to the fire and rescue service in attempting to assist evacuation, effect rescue or fight fires. Therefore, the fire protection measures increase with the storey height of the building.

Dwellings on sloping sites may have certain rooms located deeper below or higher above the adjacent ground level than other rooms. In such cases, the storey depth below the adjacent ground or storey height above the adjacent ground from each room may be assessed individually and the guidance followed accordingly.

The scope of the guidance is limited to those storeys at a depth of not more than 4.5m below the adjacent ground level and to those buildings with no storey at a height of more than 60m (approximately 20 storeys) above the adjacent ground (see 2.0 Introduction).

2.9.2 Escape within dwellings - options

In the event of an outbreak of fire, every dwelling should be provided with at least one route of escape through an exit door which leads ultimately to a place of safety. The route within a dwelling will normally comprise a combination of rooms and circulation spaces. Where the dwelling has more than one storey such as houses and maisonettes, the occupants may be located on a storey where their only means of escape is by way of a private stair towards the floor of fire origin. The occupants would then need to negotiate the fire floor before reaching the exit door from the dwelling and therefore the guidance recognises the increased risk in multi-storey dwellings.

The following table summarises the recommendations for escape within dwellings. For example, a typical 2 storey house would normally have a topmost storey not more than 4.5m and from the following table should be provided with at least one route of escape through an exit door, early warning (smoke and heat alarms) and escape windows.

Table 2.3. Escape within dwellings (houses, flats and maisonettes)

Height of topmost storey of dwellings above, or basement depth below adjacent ground Summary of recommendations [1] [2]
Basement storey at a depth of not more than 4.5m (see clause 2.9.3)

1 route of escape, early warning [3], and:

Topmost storey not more than 4.5m

1 route of escape, early warning [3], and:

  • escape windows (see clause 2.9.4)

Topmost storey more than 4.5m but not more than 7.5m [4]

1 route of escape, early warning [3], and:

  • escape windows (see clause 2.9.4), and

  • protected enclosure (see clause 2.9.5), or

  • suppression and enhanced early warning (see clause 2.9.7)

Topmost storey more than 7.5m [4] but not more than 18m [4]

1 route of escape, early warning [3], and:

  1. for houses and maisonettes:

  2. for flats:

    • escape windows (see clause 2.9.4), and

    • protected enclosure (see clause 2.9.5), or

    • suppression and enhanced early warning (see clause 2.9.7)

Topmost storey more than 18m [4] but not more than 60m (see clause 2.9.1)

1 route of escape, early warning [3], and:

  1. for maisonettes:

  2. for flats:

    • escape windows (see clause 2.9.4)

    • suppression and enhanced early warning (see clause 2.9.7)


Additional information:

  1. No storey height more than 60m (see clause 2.0.3).

  2. No dwelling with a storey area more than 200m2 (see clause 2.0.3).

  3. See guidance to Standard 2.11 for early warning systems.

  4. See guidance to Standard 2.14 for explanation of 7.5m and 18m trigger heights and additional fire fighting facilities.

  5. See guidance to Standard 2.15 for suppression systems.

2.9.3 Escape within dwellings - basement storeys

A basement storey may have no windows or a limited number of ventilators which can cause a significant build up of heat and smoke. The fire may become suppressed as the oxygen is depleted however if the door to the basement storey (or room of fire origin) is opened, the sudden intake of air together with the release of hot fire gases can cause an explosive event known as a backdraught. This rapid fire spread places occupants on the ground or upper storeys at greater risk. Therefore, the private stair serving the basement storey should be separated at the ground storey by construction having a short fire resistance duration.

There is a risk that occupants in a basement storey could become trapped following the outbreak of fire. This is because windows are often positioned too high above the floor level to access with ease or they may lead to an enclosed space below the adjoining ground level from which there is no escape. Therefore, an alternative exit (see clause 2.9.6) should be provided from the basement storey unless escape windows are provided from every basement apartment.

2.9.4 Escape within dwellings - escape windows

Occupants in a basement storey or in an upper storey at a height of not more than 4.5m may have access to escape windows. The use of windows for escape should only ever be considered in an emergency situation as a last resort and should not form part of the principal route of escape. Where occupants are trapped on upper storeys, they can use the window to call for assistance or to supply fresh air whilst awaiting rescue. If conditions within the room become untenable, the occupant can use the window to escape and lower themselves to the adjoining ground. This inevitably involves some degree of risk and windows in a storey at a height of more than 4.5m are considered to be too high above the adjacent ground from which to escape. Therefore, an escape window should be provided in every apartment on an upper storey at a height of not more than 4.5m above the adjacent ground. However this is not necessary where there is an alternative route of escape from the apartment to other circulation spaces or to other rooms.

Occupants within an inner room can become trapped where there is an outbreak of fire in the adjoining access room. Therefore, every inner room on a storey at a height of not more than 4.5m above the adjacent ground level should be provided with an escape window unless the inner room has an alternative route of escape.

Escape windows should be large enough to escape through and should be situated in an external wall or roof. The windows should have an unobstructed openable area that is at least 0.33m2 and at least 450mm high and 450mm wide. The route through the window may be at an angle rather than straight through and the bottom of the openable area should be not more than 1100mm above the floor.

Conservatories - the location of conservatories also presents some difficulties in relation to escape windows. Where a conservatory is located below an escape window consideration should be given to the design of the conservatory roof to withstand the loads exerted from occupants lowering themselves onto the roof in the event of a fire. However the choice to construct a more robust roof and frame is a matter of preference and the decision to do this should remain with the owner.

2.9.5 Escape within dwellings - protected enclosure

Occupants in apartments (e.g. lounges, bedrooms etc) may be asleep during the outbreak of fire. Where they are located on a storey at a height of more than 4.5m above the adjacent ground there is a greater risk of becoming trapped by fire and smoke. For this option (see table to clause 2.9.2), every apartment on a storey at a height of more than 4.5m above the adjacent ground should provide direct access to a protected enclosure which leads to an exit door.

Protected enclosures should be designed and constructed to withstand fire in an adjoining room or space. The protected enclosure should form a complete enclosure having a short fire resistance duration. Every door in the wall of a protected enclosure (other than a door serving sanitary accommodation) should be a self-closing fire door with a short fire resistance duration. A cupboard door need not be self-closing unless there is an ignition source within the cupboard such as an electrical distribution board or a boiler.

2.9.6 Escape within dwellings - alternative exits

For this option (see table to clause 2.9.2), every upper storey in a house or maisonette at a height of more than 7.5m above the adjacent ground should be provided with an alternative exit. The intention is to reduce the risk that occupants could become trapped within their own dwelling and provide them with the opportunity to turn away from the fire on the floor of fire origin and make their escape in the other direction. Where the second route of escape is by way of another private stair, the stair should be enclosed in a protected enclosure which leads to an alternative exit.

2.9.7 Escape within dwellings - open plan option with suppression and enhanced early warning

Open plan layouts are becoming more popular with modern living styles. For this option (see table to clause 2.9.2), the following guidance should be followed for open plan layouts provided the kitchen is remote from the exit door.

Where the topmost storey height is more than 4.5m above the adjoining ground an automatic life safety fire suppression system and an enhanced early warning system should be installed to protect the occupants. In a slower developing fire, the early warning system should provide the occupants with sufficient time to escape and in those cases where the fire develops quickly, the suppression system should control the fire giving the occupants the opportunity to escape.

The automatic life safety fire suppression system should be designed and installed in accordance with BS 9251: 2005. For the purposes of satisfying Standard 2.9, the limit in the scope of BS 9251: 2005 to buildings below 20m in height can be ignored.

The enhanced early warning system should follow the guidance in BS 5839: Part 6: 2004 for a grade D, category LD1 system. Where this option is adopted in sheltered housing complexes, a grade C system should be installed (see Standard 2.11).

2.9.8 Escape within dwellings - ducted heating and ventilation systems

Ducted heating or ventilation systems should not transfer fire and smoke from the room of fire origin to the remainder of the dwelling. Therefore, where a dwelling has a basement storey or a storey at a height of more than 4.5m and is provided with a system of ducts that connect rooms and circulation spaces:

  • transfer grilles should not be fitted between any room and the protected enclosure, and

  • supply and return grilles should be not more than 450mm above floor level, and

  • where warm air is ducted to a protected enclosure, the return air should be ducted back to the heater, and

  • where a duct passes through any wall, floor, or ceiling of a protected enclosure, all joints between the duct and the surrounding construction should be fire stopped, and

  • there should be a room thermostat in the living room, at a height more than 1370mm and not more than 1830mm, with an automatic control which will turn off the heater, and actuate any circulation fan should the ambient temperature rise to more than 35°C, and

  • where the system recirculates air, smoke detectors should be installed within the duct to cause the recirculation of air to stop and direct all extract air to the outside of the building in the event of fire.

Fire dampers should be installed where the ducts pass through fire resisting construction or alternatively fire resisting ductwork should be provided. In either case, the fire resistance duration of the construction should be maintained.

2.9.9 Escape routes - general principles

Once occupants have left the flat, maisonette or any other ancillary room or space, they should be protected from fire and smoke to allow them sufficient time to escape from the building in relative safety. Those occupants who are remote from the fire are more likely to be unaware of the outbreak and may delay their evacuation. People also move more slowly on stairs than they do on the level and will take longer to evacuate tall buildings with many flights of stairs.

The fire dynamics can be significantly different in high rise domestic buildings. The effect of the wind may be greater which could accelerate the speed, direction and intensity of the fire. For example, if a window is open or breaks under fire conditions or the door to the dwelling of fire origin is opened, the wind could accelerate fire growth to such an extent that the entire flat or maisonette becomes fully involved in the fire. The wind direction might also induce cross flows of fire and smoke that could endanger fire-fighters entering the dwelling and any occupants attempting to escape from adjoining dwellings. A further risk in high rise domestic buildings is the loss of smoke buoyancy in tall shafts such as stairs which may cause stratification of smoke before it reaches the smoke ventilator at the top of the stairwell.

2.9.10 Escape routes - options

The guidance assumes that in most cases, a fire will start inside a dwelling or other ancillary room or space within the building. Therefore, at least one escape route should be provided from every flat, maisonette and from the following ancillary rooms or spaces serving a domestic building:

  • communal room e.g. a communal lounge or laundry in a sheltered housing complex

  • plant room

  • solid waste storage room

  • store room

  • lift machine room, and

  • accessible service duct or cupboard.

The above list is not intended to be comprehensive and any other room or space should be provided with at least one escape route. The non-domestic Technical Handbook should be used for guidance on travel distances within ancillary rooms and escape routes serving such rooms. A parking garage is a non-domestic building but may be mixed use, see clause 2.9.17.

There are many options available to designers when considering escape routes in buildings containing flats and maisonettes. These options can be subdivided into 2 broad categories:

Where protected enclosures (see clause 2.9.5) or an automatic fire suppression system (see clause 2.9.7) are installed within a domestic building, there is no need to provide protected lobbies (see clause 2.9.13) between the dwellings and the escape stair. However there is a risk that the fire protection measures may not be maintained by the occupants of the building and as a result, the number of dwellings should be limited to 4 dwellings per storey and no storey is at a height of more than 7.5m above the adjacent ground level. The intention is to limit the size and height of a domestic building where some reliance is placed on fire precautions within a dwelling that also protects the common escape route.

The limitation on travel distance within protected lobbies is intended to reduce the time it takes occupants to escape and to reduce their potential exposure to fire and smoke. Automatic smoke ventilation should be provided within every protected lobby to improve tenability conditions within the escape route.

The following table summarises the recommendations when designing buildings containing flats and maisonettes.

Table 2.4. Escape routes (flats, maisonettes and ancillary rooms and spaces)

Height of topmost storey of dwelling above, or basement depth below adjacent ground Summary of recommendations [1]
Basement storey (see clause 2.9.11) at a depth not more than 4.5m (if applicable) and topmost storey not more than 7.5m [2]

at least 1 escape route:

at least 1 escape route, and:

at least 1 escape route, and:

at least 2 escape routes, and:

  • not more than 30m travel distance in protected corridor

Topmost storey more than 7.5m but not more than 18m [2]

at least 1 escape route, and:

at least 2 escape routes, and:

  • not more than 30m travel distance in protected corridor

Topmost storey more than 18m [2] but not more than 60m

at least 1 escape route, and:

  • protected lobbies (see clause 2.9.13)

  • smoke ventilation (see clauses 2.9.14 – 2.9.16)

  • suppression [3]

  • not more than 10m travel distance inside protected lobby, or

at least 2 escape routes, and:

  • suppression [3]

  • not more than 30m travel distance in protected corridor


Additional information:

  1. See diagrams for guidance on measurement of travel distance.

  2. See guidance to Standard 2.14 for explanation of 7.5m and 18m trigger heights and additional fire fighting facilities.

  3. See guidance to Standard 2.15 for suppression systems.

Figure 2.4. Ground Floor - One Escape Route

Ground Floor - One Escape Route

Figure 2.5. Upper Floor - Two Escape Routes

Upper Floor - Two Escape Routes

Figure 2.6. Upper Floor with Dead Ends

Upper Floor with Dead Ends

A basement storey with insufficient ventilation can cause a significant build up of heat and smoke. If the door to the basement storey is opened, the sudden intake of air together with the release of hot fire gases can cause an explosive event known as a backdraught which can create significant flaming through the door opening. There is also a risk that disoriented occupants could continue their escape to the basement storey instead of escaping through the ground storey. In order to minimise these risks, a medium duration fire resisting wall or screen (including a self-closing fire door) should be provided in the protected zone at the ground storey to separate the basement storey from the remainder of the protected zone.

Protected zones are intended to provide a place of relative safety inside the building. Occupants using the escape stair should be safe from the effects of fire and smoke during their evacuation to a place of safety. The enclosing structure of a protected zone should have at least a medium fire resistance duration. In the case of a high rise domestic buildings the protected zone should have a long fire resistance duration. Self-closing fire doors in the enclosing structure of a protected zone need only achieve a short fire resistance duration and in the case of a high rise domestic building, a medium fire resistance duration.

External walls adjacent to protected zones - if a protected zone has an external wall that projects beyond the face of a building or is set back in a recess, the protected zone may be vulnerable if fire breaks out through an adjacent window, door or other opening. Radiated heat or flames from the fire may impede occupants using the protected zone to escape.

Therefore, where any part of an external wall of a protected zone is not more than 2m from, and makes an angle of not more than 135 degrees with any part of an external wall in another part of the building, the protected zone should be protected against fire for a distance of 2m by construction which provides a medium fire resistance duration. The designer can choose which wall should be fire resisting and may include fire resisting facades or other fixed glazing or any other opening protected against fire. However it is not sufficient to use the final exit door as a barrier between the occupants escaping and the fire. In such cases, the external wall adjoining the protected zone at the final exit should be protected against fire as described above.

2.9.13 Escape routes - protected lobbies

A protected lobby is located within a protected zone and is designed to inhibit the movement of fire and smoke from an adjoining room, storey or space into the escape stair or fire-fighting lobby. This is normally achieved by fire resisting construction together with at least 2 sets of self-closing fire doors between the fire and the escape stair or fire-fighting lobby. The wall between the protected lobby or fire-fighting lobby and the escape stair should have a short fire resistance duration and any door in the wall should be a self-closing fire door with short fire resistance duration. For high rise domestic buildings the wall between the escape stair and the protected lobby should have a medium fire resistance duration and any self-closing fire door should have a short fire resistance duration. See guidance to Standard 2.14 for fire-fighting facilities.

Protected lobbies in domestic buildings are used:

  • to inhibit fire and smoke spread to escape stairs

  • to help evacuees escape from the floor of fire origin

  • to provide protection and space for the fire and rescue service to set up a forward control point (see Standard 2.14), and

  • to provide a bridgehead from which to commence fire fighting and rescue operations (see Standard 2.14).

In order to inhibit fire and smoke spread to the escape stair and to help evacuees on the floor of fire origin reach the escape stair, automatic smoke ventilation should be provided and travel distance within the lobby is limited to 10m. Where flats or maisonettes are accessed from an open access balcony, there is no need to provide a protected lobby.

Protected lobbies should be designed that smoke entering one protected lobby should not spread to other protected lobbies. There should be no inter-connection between protected lobbies other than:

  • the escape stair

  • a smoke ventilation shaft

  • protected services

  • fire mains, or

  • passenger lift or fire-fighting lift.

Any gaps or imperfections of fit should be fire-stopped.

2.9.14 Escape routes - smoke ventilation

Although there are physical barriers to fire such as walls, floors and doors, there is still a risk of smoke spread into escape routes. Therefore, smoke ventilation should be provided in protected lobbies, fire-fighting lobbies and protected corridors to help maintain tenable conditions within escape routes.

The fire and rescue service will normally be in attendance before all flats or maisonettes have been evacuated. Therefore, it is important that the smoke ventilators (including powered systems) are capable of being opened, closed or shut off by fire and rescue personnel to assist them with their fire-fighting and rescue operations (see Standard 2.14).

Smoke ventilation of escape routes can be provided by:

  • natural smoke ventilation, or

  • mechanical smoke ventilation.

The merits and limitations of each system should be assessed by the designer before deciding which system to choose.

2.9.15 Escape routes - natural smoke ventilation

Natural ventilation uses external openings in the roof or walls of the building to remove smoke using its own buoyancy. The efficiency of a natural smoke ventilation system depends upon the location of the ventilator and the direction and velocity of the prevailing wind. Under certain conditions, the smoke flow through ventilators may be enhanced whilst under other conditions, it may be impaired. Ideally the location of ventilators should be positioned on the building in negative pressure zones and inlets in positive pressure zones however this is difficult to achieve for all wind directions. Natural smoke ventilation can be provided by either:

Automatic opening external wall ventilators - every protected lobby should be provided with natural smoke vents on an external wall which have an area of at least 1.5m2 that discharges smoke direct to the external air. The ventilators should be actuated automatically by means of smoke detectors in the common space.

A natural smoke shaft uses the natural buoyancy of the smoke together with the effect of the wind passing over the top of the shaft to help draw the smoke through the shaft to the outside air. The design of natural smoke shafts is based on a fire providing a heat output of not more than 2.5 megawatts through an open door of 780mm wide. This scenario simulates a fully developed (flashover) fire condition in a room within the flat or maisonette. Where the fire produces cooler smoke (e.g. a smouldering fire), the smoke might not escape so readily when subject to adverse wind or stack effects. The inlet/outlet configuration will vary depending wind direction and designers should take this into account. For example, a vent cowl could be installed on the top of the smoke shaft to help draw the smoke out of the shaft for all wind directions. The full research report ‘Smoke ventilation of common access areas of flats and maisonettes (BD 2410) – Final Factual Report (BRE, 2005)' can be accessed on the BRE website http://www.bre.co.uk/.

The shaft should be closed at the base and replacement air is provided from the automatic opening ventilator in the adjacent stairwell to help the efficiency of the shaft system. The smoke shaft should have:

  • a minimum cross-sectional area 1.5m2 (minimum dimension 0.85m in any direction), opening at roof level at least 0.5m above any surrounding structures within a horizontal distance of 2.0m, and

  • the minimum area of the ventilator from the protected lobby into the shaft and at the opening at the head of the shaft and at all internal locations within the shaft (e.g. safety grilles) should be at least 1m2, and

  • the smoke shaft should have at least a medium fire resistance duration and all ventilators should have a short fire resistance duration, and

  • the shaft should be vertical from base to head but may have not more than 4m at an inclined angle not more than 300 from the vertical plane, and

  • on detection of smoke in the protected lobby, the ventilator on the fire floor, the ventilator at the top of the smoke shaft and the 1m2 ventilator at the head of the stairway should all open simultaneously. The ventilators from the protected lobbies on all other storeys should remain closed.

2.9.16 Escape routes - mechanical smoke ventilation

Mechanical smoke ventilation using pressure differentials may be used to inhibit smoke spread into escape routes by means of:

  • depressurisation systems, or

  • pressurisation systems, or

  • heating and ventilation systems.

For more detailed guidance on the design of smoke control systems using pressure differentials is available in BS EN 12101: Part 6: 2005.

A depressurisation system is based on the principle of extracting smoke to the outside air. This creates a negative pressure in the space relative to the adjacent spaces. Where a smoke ventilation depressurisation system is used, replacement air should be provided for the system to operate effectively. The volume of air and smoke removed should be replaced with the equivalent volume of replacement air at a sufficient rate in order to ensure a smoke flow out of the building. Reducing the rate of replacement air can result in the smoke ventilation system becoming less efficient whereas increasing replacement air and extraction at high velocities can produce air pressure conditions which make doors difficult to open. The system should be balanced to ensure that the forces required to open doors are not greater than those specified in Section 4 Safety.

A pressurisation system is based on the principle of forcing air into the escape route which helps to keep smoke out. Forced air can be used to maintain a positive pressure in the escape route which produces an air flow through gaps around doors preventing the smoke from entering. The system design should take account of likely pressure reduction when occupants open doors to escape or when fire-fighters open doors to access the fire. The system should be balanced to ensure that the forces required to open doors are not greater than those specified in Section 4 Safety.

Ducted heating and/or ventilation systems, including air conditioning systems, that serve all dwellings in the building should not transfer fire and smoke to or from any dwelling to any other dwelling, common space, roof space or concealed space. Fire dampers should be installed where ducts pass through fire resisting construction unless the ducts have a medium fire resistance duration or in the case of a high rise domestic building, the ducts have a long fire resistance duration.

The system installed to maintain interior environment conditions in a building should not compromise the function of the mechanical smoke ventilation system. Therefore, in the event of an outbreak of fire, the system should automatically either shut off or its function integrated with any smoke ventilation system that serves the escape routes. For more detailed guidance refer to BS 5588: Part 9: 1999.

2.9.17 Escape routes - mixed use buildings

In a mixed use building the fire in the non-domestic part of the buildings could remain undetected for some time and reach a severe intensity (due to fire load) before the occupants in the flats or maisonettes get warning. Therefore, where a protected zone is shared with a non-domestic building, a protected lobby should be provided between the non-domestic building and the escape stair to provide additional time for the residential occupants to escape. For additional guidance on protected lobbies including ventilation, see clauses 2.9.13 - 2.9.16 and clause 2.9.24.

Where flats or maisonettes have only one escape route and share a protected zone with a non-domestic building, the height of the topmost storey of the domestic building should be limited to 7.5m to reduce the number of occupants who might be affected by a fire originating in the non-domestic building.

2.9.18 Escape routes - fire hazard rooms and services

Fire hazard rooms and services can present a potential source of fire ignition and fire spread into common escape routes.

The following fire hazard rooms and service spaces adjacent to escape routes should be separated from the escape route by a construction that provides a medium fire resistance duration:

  • communal room e.g. a communal lounge or laundry in a sheltered housing complex

  • plant room

  • solid waste storage room

  • store room

  • lift machine room, and

  • service duct or cupboard.

Even if the room does not contain an ignition source, the potential for a fire to be set accidentally or deliberately should be assessed. For example, the door to a solid waste storage room might be left unlocked. For this reason, any door accessing a fire hazard room should be a self-closing fire door with a short fire resistance duration. A fire door to a service duct or service cupboard should be locked to prevent unauthorised entry therefore does not need to be fitted with a self-closing device.

Fuel pipes conveying fuel inside protected zones and protected lobbies could accelerate fire growth and under certain conditions, create an explosive atmosphere within the building. Oil and liquefied petroleum gas can produce pool fires (i.e. a turbulent fire burning above a horizontal pool of vaporising hydrocarbon fuel). The pool fire can either be static, where the pool is contained, or a ‘running’ pool.

Fuel pipes carrying oil (other than a pipe conveying oil supplying a hydraulic lift) should be located outside protected zones and protected lobbies.

Fuel pipes carrying natural gas or liquefied petroleum gas (including associated meters) may be located inside protected zones or protected lobbies provided:

  • the installation is in accordance with the requirements of the Pipelines Safety Regulations 1996, SI 1996 No 825 and the Gas Safety (Installation and Use) Regulations 1998 SI 1998 No 2451, and

  • any pipe in a protected zones is constructed of screwed steel or welded steel construction, and

  • the pipe or pipes are contained within a service shaft having a medium fire resistance duration, and

  • the service shaft is ventilated at high and low level in accordance with BS 8313: 1997.

Escape stairs should be protected from the outbreak of fire to allow occupants to escape and fire-fighters to access the fire. Therefore, every part of an escape stair (including landings) and the floor of a protected zone (including the floor of protected lobbies), should be constructed of non-combustible products.

However this does not apply to:

2.9.20 Escape routes - openings

Fire and smoke can easily pass through openings in escape routes which could prevent the occupants from escaping in the event of an outbreak of fire within the building. For this reason, the openings should be designed to inhibit the spread of fire and smoke into the escape route. Where fire shutters or dampers are installed as part of a ducted system, they should be activated by localised smoke detectors.

In order to inhibit the spread of fire and smoke, openings in separating walls and floors and openings in protected routes of escape should be protected and fire-stopped in accordance with the guidance to Standard 2.2.

2.9.21 Escape routes - junctions

The junctions between escape routes and other parts of the building are vulnerable to fire and smoke. This is because fire and smoke can penetrate weaknesses at junctions which could compromise the escape route. The designer should consider detailing at junctions to inhibit fire and smoke spread into escape routes.

In order to inhibit the spread of fire and smoke, junctions in separating walls and floors and junctions in protected routes of escape should be protected and fire-stopped in accordance with the guidance to Standard 2.2.

2.9.22 Escape routes - external escape routes and escape stairs

Protection of external routes of escape - escape routes will normally lead to the final exit door of the building, which leads to a safe place in the outside air from which occupants can freely disperse. An exit can also lead to an external escape stair giving access to a place of safety.

In some cases it may not be possible to freely disperse away from the building (e.g. where the final exit door discharges to an enclosed outdoor space). In such cases, where there is only 1 route of escape, the external wall of the building within 2m of the route of escape should have a short fire resistance duration for integrity up to 1.1m above the adjoining ground. This does not apply to sub-floor vents.

An external escape stair is an unenclosed escape stair which is open to the external air and provides occupants with an escape route which leads to a place of safety. External escape stairs present additional hazards to people escaping from buildings in the case of fire. This is because the escape stair may be exposed to inclement weather during the evacuation. For this reason, an external escape stair should not serve a building where the topmost storey height is more than 7.5m above the adjacent ground.

In order to protect the occupants from fire and smoke during evacuation, the external escape stair should be protected against the outbreak of fire from within the building. Where the escape stair has a total rise of more than 1.6m, every part of the external wall including fixed windows or glazing, self-closing fire doors (other than a door opening from the top storey) or any other opening not more than 2m from the escape stair, should have a short fire resistance duration. Fire protection below an escape stair should be extended to the lowest ground level.

An external escape stair with a total rise of not more than 1.6m from which occupants can freely disperse, is considered to be low enough above the ground to present minimal risk to occupants leaving the building and as a result, fire protection need not be provided.

2.9.23 Escape routes - open access balconies

An open access balcony can be used as an escape routes from flats or maisonettes. Fire and smoke should ventilate more freely than an enclosed escape route. The balcony should be open to the external air and have an opening that extends over at least four-fifths of its length and at least one third of its height.

Where only one direction of escape is available, the travel distance along an open access balcony should be not more than 40m. However where the balcony provides 2 directions of escape, the travel distance can be unlimited.

Flames and smoke from a fire may emanate from a window or other opening in the external wall of a flat or maisonette. Therefore, where an open access balcony provides escape in 1 direction only, the external wall up to a height of at least 1.1m above the level of the balcony should be provided with a short fire resistance duration to allow evacuees to pass below the level of windows in relative safety. Any door in the external wall should be a self-closing fire doors with a short fire resistance duration.

In order to protect occupants escaping from flats or maisonettes on storeys above the fire floor, every open access balcony should have a medium fire resistance duration from the underside. Openings in the floor of the balcony should be fire-stopped in accordance with the guidance to Standard 2.2.

Wide balconies above the floor of fire origin could present a risk to occupants escaping on the fire floor. This is because lateral fire and smoke spread along the underside of the balcony may compromise the escape route. Therefore, in order to inhibit lateral fire and smoke spread, every balcony more than 2m wide should be provided with smoke channels or down-stands at 90 degrees to the face of the building on the same line as the separating wall between each dwelling. The depth of the smoke channel or down-stand should be at least 300mm below the soffit of the balcony.

2.9.24 Escape routes - refuge within buildings

Research and fire investigation reports from fire and rescue services show that the incidence of multiple fire deaths and injuries beyond the dwelling of fire origin is uncommon. This is because:

However there are occasions where the common escape routes serving flats and maisonettes may be compromised by fire and smoke. For example, where a fire has accidentally or deliberately been set in the protected zone or protected lobby.

Where a domestic building and a non-domestic building share a protected zone (see clause 2.9.17), the occupants in the domestic building should be provided with additional protection. A protected lobby is necessary between an escape stair and every:

Occupants who are confronted by fire and smoke in the common space may retreat back into their flat or maisonette and contact the emergency services. Control room personnel will provide helpful advice and attempt to keep callers calm whilst awaiting arrival of the fire and rescue service.

Occupants should be able to remain safely inside the building until the fire has burnt itself out or until the fire has been contained and it is safe to use the escape route. In most cases, the fire and rescue service will intervene and commence fire-fighting and rescue operations before all occupants have made their escape to a place of safety (see Standard 2.14).

Although a rare event, if the spread of fire and smoke is significant, it may be necessary to evacuate the entire building as a precaution. This will normally be co-ordinated by the fire and rescue service with assistance from the other emergency services such as the police and ambulance services.