Explanations & Illustrations

Clause 7.4.1a.(1)&(2) : Provision

Section

Figure 7.4.1a.(1) & (2) : Atrium smoke control system

Before the use of engineered smoke control system is allowed in any proposal, the SCDF shall be satisfied that the compartment height of atrium is connecting more than 3 storeys below the habitable height of 24m;

Where more than 3 storeys are interconnected and the size and volume is relaxed with provision of atrium smoke control system, only the first basement is allowed to form part of the upper storey.

A smoke control system shall be provided to any compartment in a building or part of a building which has a total floor area greater than 5000m². Smoke from any fire in such compartment would easily find its way into escape routes leading to exits or exit staircases. The activation of the smoke control system would ensure that the smoke layer would not be lower than 1.8m from floor level to allow occupants to find their ways to the exits or exit staircases.

Explanations & Illustrations

Clause 7.4.1a.(3)(b) : Provision

Figure 7.4.1a.(3)(b)

Where the plant/equipment room is not greater than 250m², firefighters can fight a fire in that room from its doorway.

Explanations & Illustrations

Clause 7.4.1a.(3)(c) : Provision

Figure 7.4.1a.(3)(c)

Where floor area of the plant/equipment room is in excess of 250m², but not exceeding 2000m², provision of smoke vents in accordance to Cl.7.4.2 or smoke purging system in accordance with Cl.7.4.3 would be acceptable.

Cl.7.4.1a.(3)(c) is meant to grant relaxation over the general requirement as service rooms are usually of low occupancy load. Common areas outside the plant rooms/service rooms shall be provided with engineered smoke control system.

Explanations & Illustrations

Clause 7.4.1a.(3)(d) : Provision

Figure 7.4.1a.(3)(d) - 1

The above clause is mainly applicable to hotel building. Service areas such as laundries, stores and workshops that are restricted to staff only shall be compartmented. The total area of these compartments shall not exceed 2000m² (per storey basis). Each compartment shall be provided with smoke venting or smoke purging system.

Figure 7.4.1a.(3)(d) - 2

a. Service areas in basement storey used as laundry area are areas that are normally occupied.

b. Hence, smoke dilution of at least 9 air charges may not suffice.

c. Adequate level of visibility and smoke dispersal shall be maintained for these areas to facilitate escape.

d. Engineered smoke control system shall be provided.

Explanations & Illustrations

Clause 7.4.1b. : Provision

Figure 7.4.1b. - 1

Figure 7.4.1b. - 2

Total aggregate floor area of basement storeys = Area of car park + staircases + services area (telecommunication room, transformer room etc.) + plant/equipment room of basement 1 + area of whole basement 2.

If total aggregate area< 2000m² (see Cl.7.4.2). If total aggregate area>2000m² (engineered smoke control system or smoke purging is required), See also Cl.7.4.3 and Cl.7.4.1a.(3)(b) & (c)

Explanations & Illustrations

Clause 7.4.3a.-d. : Smoke purging system

Section

Figure 7.4.3a.-d. : Smoke purging system with ducted supply air intake

The reasons for locating the remote manual start/stop switch in the FCC or main fire alarm panel on 1^st storey (where FCC is not available) are:

a. to allow firefighting personnel to shut down the supply air system temporarily in the event that smoke is being drawn into the lobby through the outdoor air intake; and

b. to allow firefighting personnel to activate the supply sir system should the fire alarm system fail to automatically activate the supply air system.

Explanations & Illustrations

Clause 7.4.3e.-h. : Smoke purging system

Section

Figure 7.4.3e.-h. : Smoke purging system with natural opening for supply air intake

Exhaust fans shall be rated at minimum 250°C. Supply air part of the smoke purging system is provided via opening to the external air. The openings provided for supply air shall not be less than 2.5% of the floor area of each basement storey. Ramp openings, voids over car parking areas are considered acceptable openings for fresh air supply.

Where a smoke purging system consists of a supply and exhaust , both of which shall be designed such that each can operate in two sections.

The capacity of each section shall be sufficient to provide half the air changes required. Each section of the smoke purging system shall so constructed that in the event of failure of one section (exhaust part or supply part), the other section shall continue to operate. This can prevent failure of the system caused by failure of one single fan.

The exhaust and supply parts shall be electrically interlocked so that failure of any section of the exhaust part shall automatically shut down the corresponding section of the supply part, which can prevent total failure of the smoke purging system caused by the failure of one single fan.

In the event that any exhaust fan fails to run or is shut down for maintenance, the corresponding supply fan should not run so as to prevent fresh air from being pumped into the basement. The interlocking arrangement will not apply if smoke purging system consists of only the exhaust part. However, the exhaust system shall also be designed into two section as per the above.

Explanations & Illustrations

Clause 7.4.5a. : Engineered smoke control system

( No illustration )

BR 186 and BR 258 and subsequent revisions / amendments have been adopted as acceptable design guides for engineering smoke control systems. Other acceptable standards such as NFPA 92A may be adopted, taking into consideration that the basic requirements of smoke control system in the Fire Code should be strictly complied with. In the case of differences in requirement between BR 186 / 258 and NFPA 92A, e.g. classification of fire size, the clear height of smoke layer base, the QPs should consult the SCDF to determine which requirement to adopt before building plan submission. Other acceptable standards referred to from time to time will be evaluated and QPs will be informed through SCDF’s circulars.

Explanations & Illustrations

Clause 7.4.5d. : Engineered smoke control system

Section

Figure 7.4.5d. - 1 : Scenario A

Section

Figure 7.4.5d. - 2 : Scenario B

Section

Figure 7.4.5d. - 3 : Scenario C

The engineered smoke control system can be designed based on smoke control zones, provided the system is capable of handling the largest demand of smoke produced under the worst case scenario. The worst scenario would be scenario C where the fire size occurring at 1^st storey as shown in the figure above. As the smoke and hot gases rise through the upper levels, a very large quantity of smoke would be further generated through entrainment and greater cooling effect of smoke would occur.

Explanations & Illustrations

Clause 7.4.5e. : Engineered smoke control system

Section

Figure 7.4.5e.

The clear height below smoke layer (Y) = 2.5m minimum.

The main purpose is to permit occupants to evacuate in a clear breathable layer. The maintenance of this clear layer will aid the firefighting operations. The lowest  cceptable temperature of smoke layer to prevent loss of buoyancy is 20°C above ambient, i.e. 35°C (or 308K).

The highest temperature to prevent a radiation risk to people passing beneath the smoke layer should not exceed 200°C (or 473K). This temperature may appear high for areas such as means of escape, but it is considered acceptable.

Explanations & Illustrations

Clause 7.4.5f.(1) : Engineered smoke control system

Section

Figure 7.4.5f.(1)

Smoke reservoirs could be formed by using either the building’s geometry or by using smoke curtains/shutters/non-combustible downstands, such as fire resisting boards, glazing. The screens, which extend downwards from the roof or ceiling to form the smoke reservoir, should preferable be smoke tight. They should be resistant to the effects of the fire. The main reasons for restricting lateral spread of smoke by providing smoke reservoir are:

a. to prevent damage or even ignition to combustible parts of ceiling lining or service components if hot smoke layers are allowed to spread uncontrolled over unlimited areas; and

b. to prevent smoke layer (because of mixing with cold air in the course of lateral travel) become relatively cool and shallow. This will result in roof vents being unable to expel the smoke efficiently. Smoke vents would be most effective if the temperature of the smoke layer is high and that the layer beneath the vent is quite deep, thus developing a reasonable pressure differential to act to expel the smoke through the vent.

Explanations & Illustrations

Clause 7.4.5f.(2) : Engineered smoke control system

Section

Figure 7.4.5f.(2)

Room of origin includes atria, large shopping floor, rooms or spaces. Large reservoir will present a large surface area to the smoke layer, which can lead to considerable heat losses from it. Smoke control system is therefore designed with maximum specified smoke reservoir size to prevent excessive heat loss from the smoke layer, which leads to loss of its buoyancy for effective smoke venting or exhaust from the building.

Explanations & Illustrations

Clause 7.4.5f.(3) : Engineered smoke control system

Section

Figure 7.4.5f.(3) - 1 : Smoke extraction from atrium circulation space

Figure 7.4.5f.(3) - 2

Elevation A

Figure 7.4.5f.(3) - 3

For cases where smoke is allowed to spill into the circulation or atrium space before extraction takes place, the smoke reservoir sizes are halved. Individual smoke reservoir can be created for circulation or atrium space, subject to 1300m² for mechanical ventilation or 1000m² for natural ventilation.

The smoke reservoirs could be formed by using either the building’s geometry or by using smoke curtains/shutters/non-combustible downstands.

The depth of any screen used for subdivision shall be taken into account. Screens should terminate at a minimum of 500mm below the smoke layer base.

The main reasons for limiting the size of reservoirs are:

a. smoke from a fire leaves a workshop and enters the smoke reservoir in the circulation or atrium space, it will encounter turbulence and greater mixing occurs which produces more smoke; and

b. the movement of smoke from workshop into the circulation or atrium space would cause the smoke to lose heat to the surrounding structure through conduction and further loss occurring due to downward radiation. This movement would cause the smoke to lose some of its buoyancy.

For factory, the circulation or atrium space serves as a means of escape for people escaping from the workshop, before exiting to a safe area outside the building. The circulation or atrium space is therefore an additional stage to the escape route, which requires to be protected from the effects of fire and smoke.

For warehouse, which is primarily designed for storage, the smoke ventilation system provided would be for the purpose of heat and smoke release from the building. Warehouse should be treated differently from factory.

For warehouse, which is used for palletised storage, consideration should be given to the possible collapse of stacks or radiated heat spreading the fire to adjacent stacks. In tall warehouse, which is used for high rack storage, the smoke layer temperature may not go beyond 35°C and therefore, the smoke layer could well go below the level of the storage. Consideration should be given to the existence of ceiling jet occurring in the smoke layer.

Explanations & Illustrations

Clause 7.4.5f.(4) : Engineered smoke control system

Figure 7.4.5f.(4) - 1 : Rectangle-shaped smoke reservoir

Figure 7.4.5f.(4) - 2 : Oval-shaped smoke reservoir

Figure 7.4.5f.(4) - 3 : Square-shaped smoke reservoir

Figure 7.4.5f.(4) - 4 : Circle-shaped smoke reservoir

Figure 7.4.5f.(4) - 5 : Rhombus-shaped smoke reservoir

Smoke reservoirs can be formed of different shapes. In order to prevent smoke from excessive heat loss, the length of an individual smoke reservoir within a mall, factory or warehouse spaces shall not exceed 60m.

Explanations & Illustrations

Clause 7.4.5f.(5) : Engineered smoke control system

Section

Figure 7.4.5f.(5) - 1

A stagnant region occurred in a long smoke reservoir when venting or extraction is not properly distributed or when circulation/atrium or mall has a closed end.

Section

Figure 7.4.5f.(5) - 2

A stagnant region could also be formed by physical obstruction in the smoke reservoir e.g. Beam. If a smoke layer is stagnant, it will cool down and will mix into the air below. If the air space under a smoke layer is stagnant, it will tend to fill up with hazy smoke of sufficient density to affect visibility. Venting or extraction should be well distributed in the smoke layer or smoke reservoir. The air inlets at low level should also be well distributed so that the air, which is being drawn in will purge as much of the low-level clear air as possible.

Explanations & Illustrations

Clause 7.4.5f.(6) : Engineered smoke control system

Section

Figure 7.4.5f.(6)

If the smoke reservoir incorporates a false ceiling, then the space above the false ceiling may be included in the depth of the smoke reservoir provided the screens forming the reservoir extend up to the structural ceiling, the perforations in the false ceiling are at least 25% of the total area of the reservoir, and the space occupied by services etc. above the ceiling is not greater than 50% of the volume above the ceiling.

Explanations & Illustrations

Clause 7.4.5g.(1) : Engineered smoke control system

Figure 7.4.5g.(1) - 1

The main purpose of controlling the max. floor area is to limit the distance to the circulation or atrium space as smoke and hot gases would tend to cool and lose its buoyancy if floor area becomes larger.

Where the workshop units are not larger than 1000m² (natural ventilation in the circulation or atrium space) or 1300m² (with powered extraction in the circulation or atrium space), smoke from these units are allowed to discharge into the circulation or atrium space. If the units are larger than the sizes mentioned above, the smoke layer from a fire in any of these units would lose temperature to a great extent thereby losing its buoyancy as it would be controlled by sprinklers located within the units. In addition, the smoke layer would also lose some heat to the building structures. Thus, the venting of smoke layer into the circulation or atrium space becomes not effective, as cooling of smoke takes place leading to dispersal of smoke and smoke logging.

Figure 7.4.5g.(1) - 2

The combined floor area of multiple shops should not exceed 1000m² or 1300m² (power extraction) fronting circulation or atrium space. It is acceptable to use screen to channel the smoke from the shop into the circulation or atrium space, subject to maximum 14m separation between channel screens.

Explanations & Illustrations

Clause 7.4.5g.(2) : Engineered smoke control system

Figure 7.4.5g.(2)

Where a large workshop is extracted separately from the circulation/atrium space, it can have ceiling reservoirs up to twice the area permitted in the circulation/atrium space; 2000m² (natural ventilation system) or 2600m² (mechanical ventilation system) as no smoke is allowed to spill into the circulation/atrium space.

Explanations & Illustrations

Clause 7.4.5h. : Engineered smoke control system

( No Illustration )

1. It has commonly been found that very large exhaust rates, typically larger than about 175 kg/s, become impractical as
large and heavy fans or ventilators would be required. Large and heavy fans or ventilators required additional
structural supports.

2. A minimum design temperature is required to maintain stability of the smoke layer. Smoke layers which have temperatures approaching that of the replacement air will have a tendency to mix with this air rather than to float above it.

The stipulated minimum design layer temperature is intended to be high enough to allow safe operation of the system for fires which are smaller than the full design size.

Explanations & Illustrations

Clause 7.4.5j. : Engineered smoke control system

( No Illustration )

All the associated systems/mechanisms, like the door venting actuators, are to be back-up by secondary power supply. This is necessary, as these devices are not incorporated with “standby” batteries that can operate the mechanisms to function as required in the emergency mode.

Explanations & Illustrations

Clause 7.4.5k.(1)(a) : Engineered smoke control system

Section

Figure 7.4.5k.(1)(a)

Scenario A :

A fire occurring at 3^rd storey failed to activate the smoke detector at that level owing to its poor location. Instead, smoke is allowed to spill into the atrium void and smoke control system for the building is activated. This would release all the smoke curtains overlooking the atrium void, including the fire floor, which is not correct. As a result, smoke and heat will be retained in the fire floor. The correct sequence of events should be that the smoke detectors at the fire floor should be activated first, thereby locking the smoke curtain, while releasing all smoke curtains in other parts of the building.

Scenario B :

A fire occurring at the atrium floor caused smoke to spill and activate the smoke detector in 2^nd storey. The smoke
curtain will remain locked but at other floors, the smoke curtains will descend down. As a result, part of 2^nd storey will be smoke logged.

Smoke control system reacts to the first signal sent by the detector. To overcome the above problem, it is recommended that closer spacing of smoke detectors, closer than the permitted limit in SS CP 10, be adopted and that the detectors should be placed correctly in close proximity of the atrium void.

Explanations & Illustrations

Clause 7.4.5k.(1)(b) : Engineered smoke control system

( No Illustration )

The smoke ventilation system shall operate automatically upon detection of smoke by smoke detector placed strategically at the smoke control zone. The layout of smoke detectors shall comply with SS CP 10.

Explanations & Illustrations

Clause 7.4.5l. : Engineered smoke control system

( No Illustration )

Mechanical ventilation to the following room or space should not be affected:

a. exit staircases and exit passageways;

b. smoke-stop and fire lift lobbies;

c. areas of refuge within the same building;

d. basement car parks;

e. fire command centres;

f. flammable liquid/gas storage room;

g. emergency generator; and

h. engine driven fire pump.

AHUs serving the affected smoke zone are to be shut down automatically upon activation of the smoke ventilation system, while the rest may continue to function.

Explanations & Illustrations

Clause 7.4.5m.(1) : Engineered smoke control system

Section

Figure 7.4.5m.(1)

Explanations & Illustrations

Clause 7.4.5r. : Engineered smoke control system

Section

Figure 7.4.5r.

The combination of natural exhaust ventilation and powered smoke exhaust ventilation in a building would create complications on the design of the distance between the bottom of the smoke reservoir and the floor and also the extent of the depth of the smoke reservoir.

Explanations & Illustrations

Clause 7.4.5t. : Engineered smoke control system

Section

Figure 7.4.5t.

Upon activation of smoke detector, the smoke curtain is automatically unfurled from its roller under gravity fall to impede smoke flow. The dropped curtains limit the area of smoke spread, maintain visibility and tenable conditions for escape purposes.

Smoke curtain in operation should not obstruct the escape routes. The clear height of smoke curtain across the escape routes should not be lower than 1.8m from its finished floor level.

Explanations & Illustrations

Clause 7.4.5u. : Engineered smoke control system

Figure 7.4.5u. - 1

Wired glass or tempered glass could be used as smoke screen to form smoke reservoir, provided they are able to meet the designed highest temperature. Glass walls or panels acting as smoke screen shall not be of sliding, louvers or openable type.

Section

Figure 7.4.5u. - 2

Smoke screens, which are to meet the designed highest temperature, could be used to form smoke reservoirs to limit lateral spread. Smoke channelling screens are used to channel smoke away from the origin of fire to smoke reservoirs where extraction can be carried out, or away from the building entrance canopies to the external open space as shown above.

It is recommended that the spacing between channelling screens should not be more than 14m so as to prevent lateral spread of smoke and excessive cooling.