Annex 2.C Additional guidance for enclosed shopping centres
Enclosed shopping centres can be extremely complex to design. There are large fire loads and large numbers of people all within a complicated series of spaces where most people only know one way in or out.
More complex shopping centres - the recommendations contained in this annex are in addition to the guidance to Standards 2.1 to 2.15 and are unique to enclosed shopping centres with malls on 1 or 2 storeys. The alternative approach described in clause 2.0.7 should be used where the enclosed shopping centre has malls on 3 or more storeys.
Uses other than shops - for the purposes of the guidance in this annex (other than in clause 2.C.3b), reference to a shop includes all building uses with a frontage to the mall, for example; cafes, banks or other use tenancies.
The compartmentation in an enclosed shopping centre is unlimited, provided an automatic fire suppression system is installed in accordance with clause 2.C.7.
Smoke and Heat Exhaust Ventilation Systems
SHEVS should be designed in accordance with the principles set out in the Building Research Establishment Report, BR 368, ‘Design methodologies for smoke and heat exhaust ventilation’ (1999), as read in association with CIBSE Technical Memorandum 19 (1995) and in accordance with the following where appropriate:
the underside of the mall roof should be divided into smoke reservoirs, each of which should be not more than 2000m2 in area and at least 1.5m deep measured to the underside of the roof or to the underside of any high level plant or ducts within the smoke reservoir or the underside of an imperforate suspended ceiling
the smoke reservoirs should be formed by fixed or automatically descending smoke curtains which are no greater than 60m apart, measured along the direction of the mall, and follow the guidance in BS 7346: Part 4:1990
smoke should not be allowed to descend to a height of less than 3m above any floor level
each smoke reservoir should be provided with the necessary number of smoke ventilators or extract fans to extract the calculated volume of smoke produced, spaced evenly throughout the reservoir
where mechanical extraction is used, there should be spare fan capacity equivalent to the largest single fan in the reservoir which will operate automatically on the failure of any one of the fans, or which runs concurrently with the fans
any fans, ducts and reservoir screens provided should be designed to operate at the calculated maximum temperature of the smoke within the reservoir in which they are located, but rated to a minimum of 300oC for 30 minutes, in accordance with BS 7346: 1990 or more detailed guidance can be found in the BS EN 12101 series of standards.
structures supporting any fans, ducts or reservoir screens should have the same performance level as the component to be supported
the fans or ventilators within the affected smoke reservoirs should operate:
on the actuation of any automatic fire suppression system, or
actuation of the smoke detection system within the reservoir, or
on the operation of more than one smoke detector anywhere in the shopping centre, or
following a delay not exceeding 4 minutes from initiation of the first fire alarm signal anywhere in the shopping centre
replacement air should be provided automatically on the operation of the ventilation or exhaust system at a level at least 0.5m below the calculated level of the base of the smoke layer
any power source provided to any elements of the smoke and heat exhaust ventilation system should be connected by mineral insulated cables or by cables which are code A category specified in BS 6387:1994 or by cables protected from damage to the same level
an automatically switched standby power supply provided by a generator should be connected to any fans provided as part of the smoke and heat ventilation system capable of simultaneously operating the fans in the reservoir affected and any of the two adjacent reservoirs
simple manual overriding controls for all smoke exhaust, ventilation and air input systems should be provided at all fire service access points and any fire control room provided
where outlets are provided with weather protection, they should open on the activation of the fan(s) or ventilators
smoke from areas adjoining the smoke reservoirs should only be able to enter one reservoir
where there is an openwork ceiling, the free area of the ceiling should not be less than 25% of the area of the smoke reservoir, or for natural ventilation, 1.4 times the free area of the roof mounted fire ventilator above (3 times where the height from floor to roof ventilator is more than 12m), whichever free area is the greater, and be evenly distributed to prevent an unbalanced air flow into the reservoir, and
when a natural ventilation system is used and the smoke reservoir includes a suspended ceiling, other than an openwork ceiling, the free area of the ventilator opening in the suspended ceiling, or any ventilator grille in the ceiling, should not be:
Width of mall - a separating wall is not necessary between a shop and a mall. However this exemption does not apply to shops having mall level storey areas more than 2000m2 that are located opposite each other. In such cases, at least 1 shop should be separated from the mall by a separating wall. Opposing shop frontages are those which make an angle of less than 80o with each other.
The mall width should at no point be less than 6m. However hard mall seating or similar controlled furniture can be ignored when measuring the minimum width of the mall.
An enclosed shopping centre should be so designed that:
from every part of the mall and from every mall level shop there should be at least 2 directions of travel leading to a place of safety without passing through any space in single occupation. However this does not apply to a kiosk of not more than 25m2 and in which either the general public are not admitted, or the depth the kiosk from the mall is not greater than 5m
the travel distances in the mall should be limited to 9m in one direction of travel and 45m in more than one direction of travel
The occupancy capacity is obtained by dividing the area in square metres by the relevant occupancy load factor. The calculation necessary to provide the occupancy capacity of a shopping centre with a mall should take account of sub-clauses (a) and (b) below:
Occupancy capacity of the entire shopping centre
When calculating the occupancy capacity of the entire shopping centre, all mall areas up to a maximum width of 6m should be calculated using an occupancy load factor of 0.7. All remaining areas beyond the 6m should use an occupancy load factor of 2.0. Food courts forming part of the mall should use an occupancy load factor of 1.0. An additional factor of safety is also applied when calculating the occupancy capacity of the entire shopping centre and a nominal occupancy loading is applied to all non-mall areas. For example, the occupancy load factor for shops and all other use tenancies should be taken as 4.0. Once established, all the figures should be added together to give the overall occupancy capacity of the entire shopping centre, and
Occupancy capacity of shops
When calculating the occupancy capacity of the individual shops (or other use tenancies) the occupancy load factors in the table to clause 2.9.2 should be used as appropriate.
Mall escape widths - the aggregate unobstructed width, of all escape routes from a mall should be at least 2.65mm multiplied by the occupancy capacity of the entire shopping centre as described above.
A shop of more than 1300m2 in area at mall level, where the means of escape has been designed independently of the mall, need not be included in this calculation. Similarly, a kiosk not exceeding 25m2 which is not accessible to the general public, or the depth the kiosk from the mall is not more than 5m, need not be included in the calculation.
The unobstructed width of each individual exit from the mall should be at least 1.8m wide. However the designer of the shopping centre should take account of localised areas where the occupancy levels will be higher than in other parts of the shopping centre. In such cases, a wider exit would be appropriate in those parts of the shopping centre. In addition, it is recommended that the entrances accessible to the general public are designed with the greatest escape route width as evacuees will tend to use the access and egress routes with which they are most familiar.
Shop escape width - the aggregate unobstructed exit width, from each shop and the unobstructed exit width of a route, or routes, which do not enter the mall should be at least 5.3mm x the occupancy capacity of the shop. An occupancy load factor of 2.0 should be applied to shops. In the case of all other use tenancies, the occupancy load factors in the relevant table to clause 2.9.2 should be followed.
A shop with a storey area at mall level more than 1300m2 where the means of escape has been designed independently of the mall need not be included in this calculation. Similarly, a kiosk not exceeding 25m2 which is not accessible to the general public, or the depth the kiosk from the mall is not more than 5m, need not be included in the calculation.
Where a service corridor is used for means of escape directly from a shop or shops, the unobstructed width should be based on the total number of occupants of the largest shop that evacuates into the corridor, plus (other than at column positions) an additional width of 1m to allow for goods in transit. Where a service corridor is used as an escape route, it should not be used for any form of storage.
Every crèche provided within an enclosed shopping centre should be designed so that it is:
An enclosed shopping centre should be provided with emergency lighting in all mall areas and all protected zones and unprotected zones. Emergency lighting should be installed so that it is not rendered ineffective by smoke filled reservoirs.
Automatic fire detection and alarm systems in enclosed shopping centres can increase significantly the level of safety of the occupants.
An enclosed shopping centre, should be provided with an automatic fire detection and alarm system, designed and installed in accordance with the guidance in BS 5839: Part 1: 2002 Category L1 and in accordance with the following recommendations:
the fire alarm should be activated upon the operation of the sprinklers, or
manual call points as specified in BS EN 54: Part 11: 2001 (Type A), or
on the activation of the alarm in a shop, evacuation may be restricted to the shop concerned for a grace period of not more than 4 minutes, unless during that time there is further detection in the mall, in which case the evacuation of the shopping centre should be commenced. Not withstanding this grace period, immediately upon activation of the alarm a message should be sent to an appropriate fire station or manned agency, or
in the case of the activation of the alarm anywhere other than in an individual shop, or on activation of sprinklers anywhere within the shopping centre, evacuation should be commenced immediately and there is no grace period, or
all areas of the shopping centre, including shops, should be alerted using a voice alarm system which follows the guidance in BS 5839: Part 8: 2008, however individual shops may use conventional sounders within the shop itself, or
the fire alarm system should be interfaced with other fire safety systems, to operate automatically in the correct zones. On the operation of the fire alarm:
all systems within the mall or shops which play amplified music are silenced
any smoke dampers installed to prevent the siphoning of smoke are activated
subject to the 4 minute grace period where appropriate, all air moving systems, mains and pilot gas outlets, combustion air blowers and gas, electrical and other heating appliances in the reservoir are shutdown, and
the main fire alarm system control panel is installed within the control room and indicator (or repeater) panels are provided at each of the fire fighting access points.
Fire control room - an enclosed shopping centre should have a fire control room:
have access points away from the discharge points for the general public, and
be provided with an alternative means of escape, and
be located adjacent to a fire and rescue service access point and accessible from the open air.
Horizontal dry fire main - every single storey enclosed shopping centre should be provided with a dry fire main with an outlet located not more than 5m from a fire service access point or points. However a dry fire main need not be provided where no point within the storey (not being a protected zone) is more than 60m measured along an unobstructed route for the fire hose, from the access point or points.
An automatic life safety fire suppression system should be installed in an enclosed shopping centre and cover the entire area, other than:
a mall or part of a mall with a ceiling height more than 10m, and
a stairway enclosure, and
a car park, and
every area where sprinklers would prove to be a hazard (e.g. main electrical switchgear).
The level of fire suppression should be appropriate to the occupancies within the enclosed shopping centre and should be determined on the basis of a risk assessment. The system should be designed and installed in accordance with the LPC Rules for Automatic Sprinkler Installations 2009, Incorporating BS EN 12845: 2004 including life safety recommendations where appropriate. The type of sprinkler head should be a ‘quick response’ type with a response time index (RTI) of not more than 50 (m.s)½.