designing the building structure

Question 1

Fire protection and fire safety considerations affect the design of the building in the following areas, which are dealt with in more detail in the clauses referred to:

Answer 1

a) the fire resistance, in terms of load-bearing capacity, insulation, and integrity of elements of structure (see Clause 30);
b) compartmentation, including compartmentation of areas of ancillary accommodation (see Clause 31);
c) measures to prevent openings between different parts of a building offering routes for uncontrolled fire or smoke spread (see Clause 32);
d) measures to prevent fire and smoke spread via cavities (see Clause 33)
e) reaction to fire properties of roof covering, the external wall surface, the internal wall and ceiling lining materials used in the building and within certain voids where fire spread might pose a threat (see Clause 34);
f) the provision of fire-resisting elements in the external walls to reduce the risk of fire spreading from one building to another (see Clause 35).

Question 2

The life safety role of structural fire resistance is threefold?

Answer 2

a) to minimize the risk to occupants, some of whom might have to remain in the building for some length of time while evacuation proceeds (see also Section 5);
b) to reduce the risk to fire-fighters who might be engaged in search or rescue operations (see also Section 6); and
c) to reduce the danger to people in the vicinity of the building, who might be hurt by falling debris or as a result of the impact of the collapsing structure on other buildings.

Question 3

Buildings over 30 m high

Answer 3

Buildings having an occupied storey over 30 m above access level should be sprinkler-protected throughout in accordance with BS EN 12845 (new systems) or BS 5306-2 (existing systems).

Question 4

The structure of a roof, and the structure that supports only a roof, should have fire resistance if the roof:

Answer 4

a) forms part of an escape route; or
b) functions as a floor, e.g. as a car park; or
c) is part of a portal frame structure where the roof and the supporting stanchions form a single element of structure; or
d) is integral to the stability of a fire-resisting external wall

Question 5

The fire resistance performance of a fire-resisting glazed assembly is influenced by a number of factors, e.g.:

Answer 5

• type of glass and function;
• pane size and shape;
• glazing layout and number of panes;
• orientation of the glazed element;
• framing and framing junctions;
• glazing seal;
• beads and bead fixings;
• fixing of the assembly to the support structure

Question 6

there are four possible hazards to assess, even if the integrity of the glazed element as a flame and smoke barrier is maintained. These are:

Answer 6

• direct exposure to potentially high levels of radiant heat with the risk of burns to exposed skin;
• convective heating of the atmosphere in the escape way;
• smouldering smoke generation (before ignition) from floor coverings, fixtures and fittings in the corridor;
• secondary ignition and flaming of fixtures and fittings in the escape way

Question 7

A non-insulated fire-resisting glazed screen may be incorporated in the enclosure to a protected shaft between a stair and a lobby or corridor which is entered from the stair provided that the following conditions are met

Answer 7

a) the standard of fire resistance for the stair enclosure is not more than 60 min; and
b) the glazed screen: 1) has at least 30 min fire resistance in terms of integrity (E 30); and 2) meets the limits on areas of non-insulated glazing given in Table 27; and
c) the lobby or corridor is enclosed to at least a 30 min standard.

Question 8

Where sprinklers are provided together with a glazed assembly, intended to work together as a combined fire-resisting wall system, then the following conditions should be met.

Answer 8

a) The whole assembly should be designed as an integrated sprinkler-glass system, which should be installed in accordance with the manufacturer’s specific data sheet that applies for such a sprinkler-glazing arrangement
b) The sprinkler system should have a demonstrated capacity to deliver the required quantity of water throughout the full required period of fire resistance.
c) Either: 1) the glazed system should at least be classified for non-insulated fire-resistance performance, using a fire-resisting glass type that is not sensitive to water impingement failure under fire conditions; or 2) if not classified for non-insulated fire-resistance performance, the sprinkler array, when activated, should be able to wet the entire glazed surface of the assembly throughout the full period of any potential developed fire exposure, without the risk of dry spots caused by transoms and mullions or other obstructions during occupation of the building.

Question 9

On any one storey in a building, compartmentation can be necessary in the interests of occupant safety?

Answer 9

a) to meet travel distance limits;
b) to enclose a special fire hazard;
c) to support a progressive horizontal evacuation strategy;
d) to support a phased evacuation strategy;
e) to separate areas having different risk profiles if different standards of fire resistance, or different means of escape, apply;
f) if the compartment size would otherwise exceed the prescribed limit for the standard of fire resistance proposed; g) if there are occupants who need to stay in the building for as long as possible despite the fire, usually for operational safety reasons, e.g. an emergency services call centre.

Question 10

Elements that have a fire-separating function include:

Answer 10

1) enclosures protecting means of escape (see Clause 17); 2) compartment walls and floors (see 31.3); 3) walls common to two buildings (see 31.3.1.2); 4) ground floors over basements (see 31.3.1.3); 5) basement floors, other than the lowest, in any building with a floor at more than 10 m below ground level (see 31.3.1.3); 6) any part of a roof forming an escape route (see 16.3.12 and 31.4.5); 7) elements provided to separate areas occupied by different owners or tenants in the same occupancy characteristic other than in occupancy characteristic A buildings (see 6.2 and 31.3.1.5); 8) elements separating areas occupied for different purposes (unless the different purpose is ancillary to the main one) (see 17.3.4); 9) floors in occupancy characteristic Ci, Cii and Ciii, and in any building with a floor at more than 30 m above ground level (see 31.3.3 and 31.3.4); 10) elements separating dwellings from the common parts of a block of flats (see 31.3.3); 11) enclosures to protected shafts (see 31.4.6.2); 12) elements enclosing a fire-fighting shaft (see 31.4.6.2, Clause 32 and Clause 33); 13) elements such as doors that protect openings in compartment walls (see Clause 32); 14) fire dampers (see Clause 32); 15) fire-resisting ductwork (see Clause 32); 16) cavity barriers (see Clause 32 and Clause 33); 17) fire-resisting ceilings (see Clause 30 and Clause 33); 18) fire-protected air transfer grilles (see 32.5.6); 19) parts of external walls forming protected areas for space separation purposes

Question 11

Each basement storey should be a separate compartment if there is a basement floor more than

Answer 11

10 M below Ground

Question 12

The ground floor over a basement should be a compartment floor unless?

Answer 12

a) the building is in occupancy characteristic Ci;
or b) the building comprises one basement storey and not more than two other storeys, and no storey is more than 280 m2 in area; or
c) the basement and ground storeys are part of a small shop having no more than three storeys, none of which is more than 280 m2 in area; or
d) the ground floor is penetrated by an atrium that meets the relevant recommendations of Annex B.

Question 13

Buildings designed for a phased evacuation strategy should have?

Answer 13

Floors in a building designed for a phased evacuation strategy (see Section 5) should be constructed as compartment floors

Question 14

The following walls and floors should be constructed as compartment walls and compartment floors:

Answer 14

a) every wall needed to subdivide the building to observe the size limits on compartments in multi-storey buildings given in Table 28;
b) every floor above ground level, if the building, or separated part of the building, has a storey with a floor at a height of more than 30 m above ground level;
c) the floor of the ground storey, if the building has one or more basements (with the exception of small basements and shops; see 31.3.1.3);
d) the floor of every basement storey, except the lowest floor, if the building or separated part of the building has a basement depth of more than 10 m below ground level.

Question 15

Every compartment wall and floor should:

Answer 15

a) form a complete barrier to fire spread between the compartments; and
b) have the appropriate fire resistance indicated in Table 23 or Table 24.

Question 16

The following areas are not deemed to be a high fire risk and do not need to be enclosed in fire-resisting construction

Answer 16

a) kitchens (cold preparation/reheat);

b) water storage tank rooms; c) plant rooms with air handling units only.

Question 17

Fire doors have at least one of two functions:

Answer 17

a) to protect escape routes from the effects of fire so that occupants can reach a final exit;
b) to protect occupants, fire-fighters and the contents and/or structure of a building by limiting the spread of fire.

Question 18

The failure of doors under fire conditions usually occurs at one of the following places:

Answer 18

• at the gap between the door and the frame;
• at the meeting point between two door leaves in double door assemblies;
• at one or more of the points where building hardware is fixed (particularly at the hinges or lock positions);
• in the case of glazed doors, at the line of the junction between the glazed area and the rest of the door.

Question 19

Doors forming part of the means of escape from, and within, the building should:

Answer 19

a) be fitted only with simple fastenings that can be operated from the escape side of the door without the use of a key;
b) be hung clear of any change of floor level;
c) be hung such that they do not reduce the effective width of any escape route across a landing;
d) if opening into a corridor, be recessed to the full width of the door;
e) where hung to swing both ways (double swing), or subdividing corridors, be provided with a minimum of a vision panel; NOTE 3 For further information, see BS 8300. f) open to an angle not less than 90°.

Question 20

Where lift landing doors need to be fire doors, one of the following conditions should be met. ?

Answer 20

a) The lift landing doors should achieve the appropriate level of fire resistance in terms of integrity (see Table 22 and Table 30) when tested in accordance with BS EN 81-58.

b) Imperforate steel panel lift landing doors may be used provided that all of the following criteria are met: 1) they are not directly exposed to the effects of fire through a fire-resisting lobby doorway to the accommodation; and
2) the structure of the lift lobby, including its floor, is of non-combustible construction; and
3) the lobby contains no significant fire load and its wall and ceiling linings are classified as Class 1 when tested in accordance with BS 476-7 or European Class C-s3, d2; and 4) the lift car is of substantially non-combustible construction as specified in BS EN 81-20

Question 21

with the exception of lift landing doors, should be fitted with a self-closing device (other than rising-butt hinges) that should:

Answer 21

a) be of a type that cannot readily be disconnected or immobilized and does not embody a mechanical hold-open facility unless it automatically releases the door in a fire situation (see 32.1.6.2); and
b) override any latches fitted to the door, or in the absence of a suitable latch or other positive device for holding the door shut in its frame,
c) for swing doors, conform to BS EN 1154; and
d) for fire curtain barriers, conform to BS 8524

Question 22

. If a hold-open device is to be used, it should be:

Answer 22

a) a fusible link or heat detector (unless the door is fitted in an opening provided as a means of escape, or to protect a means of escape); or
b) an automatic release mechanism actuated by an automatic fire detection and fire alarm system; or

c) a delayed closing device with the delay adjusted not to exceed 25 s. The automatic release mechanism should allow the door closing device to resume its self-closing function in the event of one or more of the following:
1) the detection of smoke by suitable automatic apparatus;
2) the detection of heat or smoke by any in-built sensing device;
3) failure of the power supply;
4) operation of the fire detection and fire alarm system; 5) local manual operation;
6) if the facility is provided, a manual operation at a central control point

Question 23

A fire door that is needed to resist the passage of smoke at ambient temperature conditions, should?

Answer 23

have a leakage rate not exceeding 3 m3/h per metre, when tested in accordance with BS 476-31.1 with the threshold taped and subjected to a pressure of 25 Pa; or

meet the classification requirement of Sa when tested in accordance with BS EN 1634-3.

Question 24

All fire doors other than lift doors should be marked with the appropriate fire safety sign conforming to BS ISO 3864-1 according to whether the door is

Answer 24

a) to be kept closed when not in use;
b) to be kept locked when not in use; or
c) held open by an automatic release mechanism.

Fire doors to cupboards and to service ducts should be marked on the outside. All other fire doors should be marked on both sides.

Question 25

Active fire curtain/barrier assemblies in buildings should be self-closing under gravity (gravity fail safe). They should be tested and installed in accordance with BS 8524-1 and BS 8524-2 respectively, and should?:

Answer 25

a) be initiated by an appropriate automatic fire detector;
b) be capable of multi-stage deployment to act initially as a smoke barrier relevant to the risk, where deemed necessary;
c) have emergency retract controls relevant to the risk;
d) have obstruction warning devices or floor markings dependent upon the location;
e) have controls and associated wiring that is appropriate to the risk and type;
f) have deployment speeds ranging between 0.06 m/s and 0.15 m/s;
g) achieve the same standard of fire resistance and smoke separation as the element of structure being replaced;

h) have monitoring of the battery condition;
i) have display panels having visual and audible provision to: 1) indicate any faults; and 2) indicate if the batteries (for emergency retract) need replacing

Question 26

When fire curtain barriers are used to protect a means of escape route

Answer 26

1) the escape route width should be increased by the stated deflection zone; and
2) the maximum length of an uninsulated barrier forming the protected route should not exceed 5 m.

NOTE 1 BS 8524-2 allows uninsulated barriers over 5 m with a fire safety engineering approach, which is outside the scope of BS 9999

Question 27

mechanical ventilation and air con should ?

Answer 27

Any system of mechanical ventilation should be designed to ensure that, in a fire, the ductwork does not assist in transferring fire and smoke through the building and put at risk the protected means of escape from the accommodation areas. Any exhaust points should be sited so as not to further jeopardize the building, i.e. away from final exits, combustible building cladding or roofing materials and openings into the building.

Question 28

general comments of ventilation and ducting ?

Answer 28

Ventilation ducts supplying or extracting air directly to or from a protected stairway should not also serve other areas. A separate ventilation system should be provided for each protected stairway.

Where the ductwork system serves more than one part of a subdivided escape route, a fire damper should be provided where ductwork enters each section of the escape route operated by a smoke detector or suitable fire detection system.

The fire dampers should close when smoke is detected. In the case of a system which recirculates air, smoke detectors should be fitted in the extract ductwork (see 32.5.5).

Non-domestic kitchens, car parks and plant rooms should have separate and independent extraction systems and the extracted air should not be recirculated.

Where smoke control systems such as pressure differential system is installed, ventilation and air-conditioning systems in the building should be compatible with it when operating under fire conditions

Question 29

Where air handling ducts pass through fire-separating elements such as compartment walls or the enclosures to protected escape routes, then the integrity of those elements should be maintained, using one or a combination of the following four methods:

Answer 29

• Method 1: thermally actuated fire dampers;
• Method 2: fire-resisting enclosures;
• Method 3: protection using fire-resisting ductwork;
• Method 4: automatically actuated fire and smoke dampers triggered by smoke detectors.

Question 30

what air handling methods should not be used in Kitchen extract ?

Answer 30

• Method 1: thermally actuated fire dampers;
• Method 4: automatically actuated fire and smoke dampers triggered by smoke detectors

NOTE 1 This is due to the likely build-up of grease within the duct which can adversely affect the effectiveness of any dampers

Question 31

HVAC Methods for Protected escape routes ?

Answer 31

Method 1 should not be used where ductwork passes through or serves an escape route, as large volumes of smoke can pass through without activation of the thermal devices and E-rated fire dampers have no performance rating in terms of smoke resistance.

Methods 2 and 3 should be used only where ductwork does not serve the escape route it passes through.

Method 4 may be used for extract ductwork passing through the enclosures of protected escape routes, both where the ductwork does and does not serve the escape route (

Question 32

Occupancy characteristic C

Answer 32

In occupancy characteristic C buildings, Method 4 should always be used where ducts pass through compartment walls or floors. Methods 1, 2 and 3 may be used in other suitable locations but should not be used in the locations given in 32.5.2.2 and 32.5.2.3.

Question 33

Extract ductwork systems serving the following appliances or parts of a building should be entirely independent of each other and of any ventilation ductwork serving other parts of the building:

Answer 33

a) non-domestic kitchens;
b) deep fat fryers;
c) boiler chambers;
d) areas containing oil-immersed electrical plant;
e) car parks.

Question 34

Recirculating distribution systems

Answer 34

In any system of air conditioning where vitiated air is recirculated from one part of the building to another, smoke detectors should be installed, linked to the ventilating system controls.

One or more smoke detectors should be fitted in the extract ductwork before the point of separation of the recirculated air and the air to be discharged to the open air, and before any filters or other air cleaning equipment. Such detector(s) should, if the smoke reaches an optical density of 0.5% per metre, be capable of either:

a) causing the system to immediately shut down; or
b) switching the ventilation system from recirculating mode to extraction to open air, so as to divert the vitiated air containing any smoke to the outside of the building.

Question 35

Air transfer grilles

Answer 35

Whilst air transfer grilles in walls, partitions, doors, etc. are not part of ventilation ductwork, they can form essential components of an air distribution system in a building.

Air transfer grilles fitted in any construction or door that needs to be fire-resisting should be of the intumescent type or fitted with fire dampers. Where these grilles are within the enclosure of protected escape routes, they should incorporate fire and smoke shutters operated by adjacent automatic smoke detectors

Question 36

In general, the installation of air transfer grilles should be avoided in any construction required to be fire-resisting, particularly those forming compartment boundaries.

Air transfer grilles should not be installed in:

Answer 36

a) elements of construction enclosing compartments or protected shafts;
b) enclosures to protected stairways, protected lobbies, protected corridors, fire-fighting stairways or fire-fighting lobbies;
c) bedroom walls or doors

Question 37

The controls for the ventilation system should be located adjacent to the fire detection and fire alarm control and indication panel. The following should be clearly marked, where applicable:

Answer 37

• “Fire and rescue service ventilation control”;
• “Automatic”;
• “Off”;
• “Extract only”.