Fire Safety Design for a 20-storey Building in Preston - Case Study Example

Fire Safety Design for a 20-storey Building in Preston Table of Contents Introduction 2 Part One: General Location and Layout Considerations 2 1.1 Location of the Building 2 1.2 Internal Layout of the Building 2 Part Two: Prevention of Internal and External Fire Spread 3 2.1 Measures to Prevent Internal Fire Spread 3 2.2 Measures to Prevent External Fire Spread 4 Part Three: Fire Alarms, Escape Routes, and Fire-Fighting Requirements 4 3.1 Types and Locations of Required Detectors and Alarms 4 3.2 Design and Location of Escape Routes 5 3.3 Fire-fighters’ Access and Building Fire-fighting Equipment 6 Conclusion 6 References x Introduction The developer of a 20-storey, mixed-use building planned for construction in Preston has wisely chosen to include a consultation on fire safety, which this report represents, in the design phase of the project. Because the design has not yet been produced to allow specific reference to construction features, this report will be somewhat generalised in nature. In keeping with the concept of an intelligent building as one which combines technical and practical innovations with skilful management to maximise return on investment (Coggan, 2008), the recommendations made in this report consider equally the multiple requirements of regulatory demands, comfort and flexibility for the occupants, and cost-effective construction. Part One of the report is a brief discussion of the general location and overall layout of the building with regard to fire safety considerations. Part Two addresses building construction details and materials with regard to making the structure as fire-resistant as possible. Part Three details fire detection and alarm systems, escape routes and rescue provisions, and fire extinguishing equipment and access for the fire services. Part One: General Location and Layout Considerations 1.1 Location of the Building Because of its commercial nature, it is assumed that the building will be located in a business area, possibly in central Preston in the vicinity of The Mall, along Fishergate, or perhaps along the Ring Way. Regardless of the location, due regard should be given to clear access on all sides of the building for the fire and rescue services. At 20 storeys the building would be the tallest structure in Preston, and already present an access challenge; locating it on a property which limits access to one side – along the river, for example, or with its back to the railroad – should be avoided. 1.2 Internal Layout of the Building The building plan calls for mixed-use design, with half the interior space used for offices and half for a hotel. This means that in use, the building will be occupied at approximately half-capacity at all times; the office areas will be occupied fully, or nearly so, during daytime business hours, while the hotel portion will be more likely to be occupied fully at night. The best arrangement for fire safety purposes would be to locate the hotel portion in the lower half of the building, minimising the distance needed for guests to escape and fire-fighters to access the building, particularly at night-time when fires are relatively more dangerous. This arrangement, however, might not be aesthetically or commercially desirable, making proper attention to fire safety requirements that much more important. Part Two: Prevention of Internal and External Fire Spread 2.1 Measures to Prevent Internal Fire Spread There are two aspects to the prevention of internal fire spread, linings and structure. Because the building is not yet designed, specific recommendations as to the suitability of wall and ceiling linings cannot be given, except to direct attention to Section B2 of Approved Document B, Volume 2 – Buildings other than Dwellinghouses (2007) of the Building Regulations 2000. (pp. 62-66) This clearly lays out the requirements that must be met by internal linings, that is, wall and ceiling linings. In general, most conflicts with the requirements can be avoided in this building if the following basic guidelines are followed: Linings for room spaces must meet a minimum National Class 3 standard, while linings in circulation spaces must meet a minimum National Class 0 standard. (Refer to Table 10, p. 64 of Approved Document B) Thermoplastic glazing or lighting diffusers should be, if at all practicable, of the TP(a) (rigid) classification. TP(b)-class thermoplastic materials are not prohibited, but their application is subject to specific limitations. (see Approved Document B, pp. 65-66) In terms of preventing internal fire spread through the structure, there are three key provisions that apply to this building. The first two are given by Paragraph 8.18 of Approved Document B (p. 72): Every floor of the building must be a separate compartment. This applies to buildings over 30 metres’ height, which a 20-storey building would surely exceed. If an atrium is planned, the regulations refer the builder to British Standards BS 5588-7 for guidance. (p. 73) The maximum floor area of uncompartmented space is 2,000 m2. In addition, Paragraph 8.18f requires that in Shop, Commercial, Industrial, or Storage premises, each space intended for separate occupancy must be compartmented. This guideline will not apply to the hotel portion of the building, but may affect the office portion, depending on the planned occupancy. The third provision addresses the installation of sprinklers as a means of fire suppression, and is covered by Paragraph 0.16 (p. 11) and Table 12 (p. 76) of Approved Document B. A sprinkler system is not strictly required by the regulations, but it has distinct advantages and is recommended because: Some regulations can be modified by the installation of a sprinkler system; where variation from the requirements is unavoidable, a sprinkler system may compensate. A sprinkler or other automatic fire-suppression system may be required by the building’s insurers, and even if not specifically required, the installation will certainly reduce insurance costs. (Fire safety risk assessment, 2006) The guidelines for the prevention of internal fire spread are complex and extensive, and are more easily understood with reference to an actual building plan. However, as a matter of general guidance, the following advice can be given: The objective is to prevent the spread of fire from one compartment of the building to another, thus special attention should be paid to any space which allows the uninterrupted passage of smoke or fire. This means that spaces above ceilings should be blocked above compartment walls, and that necessary passages connecting many compartments – such as elevator shafts, heating and ventilation ducts, shafts and passageways containing plumbing or electrical conduits, protected shafts for fire escape and fire-fighter access, and circulation spaces such as hallways – must be constructed in such a way that fire or smoke is prevented, as much as possible, from entering them. A significant exception to this, however, is that basement areas must be properly ventilated to remove smoke and gases in the case of a fire, as detailed in Section 18 (pp. 115-116) of Approved Document B. 2.2 Measures to Prevent External Fire Spread Given that a modern 20-storey tower is most likely to be built almost entirely of reinforced concrete or steel, the materials of which the building are constructed are of no special concern regarding external fire spread. However, attention must be paid to the use of non-flammable or fire-resistant insulating and sealing materials, such as would be used to fill expansion joints, and for the proper installation of cavity barriers. Another factor that must be considered is the separation distance of the building from surrounding buildings. The most onerous regulation for a building of this size is that the external walls be of a material meeting National Class 0 standard, if the distance of the building to the relevant boundary is one metre or less. The relevant boundary is in most cases a notional boundary, which is a line separating two buildings that represents the required minimum distance from each. Considering the likely construction materials to be used in this building, the probability is that the entire exterior will meet the standard for fire-safe materials. Assuming for planning purposes that it does not – for example, if the architect should have a mind to finish the outside of the building in thin wood shakes – odd though its appearance may be, the building will still meet separation requirements if it is placed at least 12.5 metres from the relevant boundary. (See Table 15, p. 101, Approved Document B) Proper separation distance not only satisfies the requirements for the prevention of external fire spread, but also helps in ensuring adequate access by fire and rescue personnel, as discussed below. Part Three: Fire Alarms, Escape Routes, and Fire-Fighting Requirements 3.1 Types and Locations of Required Detectors and Alarms The mixed-used nature of the building and its size presents some challenges in selecting a suitable detection and alarm system, and the best arrangement can only be determined with reference to the specific internal layout of the building. However, some general recommendations can be made at this point: The fire detection system should be automatic throughout the building, and connected to a central communication panel that is observed at all times. (Fire safety risk assessment, 2006) Because of the high occupancy of the building and the care required in evacuating a large number of people without panic from a high-rise, the alarm-sounding function could be semi-automatic, meaning that a brief delay between alerting the central communication panel and sounding the alarm could be provided to allow the building staff to investigate and prevent a false alarm. If no action is taken to forestall the alarm within the prescribed period of time, the alarm will sound to signal evacuation of the building. Regardless if an automatic or semi-automatic alarm system is used, the fire detection system must be integrated into the building’s other systems to immediately take actions to prevent the spread of fire and smoke and facilitate an evacuation. These would include such functions as stopping all lifts, closing dampers within ventilation shafts and ducts, and activating an emergency electrical supply for escape-route lighting and operation of any fire-suppression systems. If the detection of a fire is found to be false, these measures can easily be cancelled manually and the building returned to normal function, but the delay that would be required if they were to be manually initiated might allow fire and smoke to spread. 3.2 Design and Location of Escape Routes Except for the ground floor of the building, it is presumed that the layout of each level will comprise, at a minimum, at least one hallway connecting to a circulation area where the lifts can be accessed, which either would be centrally-located or located at one side of the building. The hallway areas should be connected to two protected stairwells on opposite sides of the building, and the hallways themselves should be constructed as protected areas, i.e. with compartment walls. The hallway should be divided midway between the stairwells by a compartment wall and fire door, and should be separated in similar fashion from the circulation area around the lifts. This particular configuration would provide the maximum protection for the building occupants and the safest escape routes. In case of fire or smoke passing through the lift shafts, the lifts can be isolated from the hallways. And if one escape route through a hallway or one protected stairwell is compromised, these can be isolated while still providing one safe means of exit. Depending on the size of the building – which is not yet known – care should be taken to ensure that the maximum travel distance along any hallway to a protected stairwell should not be more than 18 metres for the shortest escape route from any point on any level. This is the general allowance given by the regulations. (See Table 2, p. 34, Approved Document B) The minimum width of the protected stairs must not be less than 1100 mm, as noted in Table 6 of Approved Document B. (p. 46) 3.3 Fire-fighters’ Access and Building Fire-fighting Equipment As noted above, proper location of the building and the appropriate configuration of protected stairwells and hallways will do much to ensure effective access to the building by the fire and rescue services. Street or other hardstand access must be provided on all sides of the building to allow the close approach of fire equipment, especially since the building is tall and will require the use of high-reach ladders or similar devices. Sufficient fire hydrant connections must also be provided, no less than one on each side of the building. Buildings over 18 metres in height, which this building obviously will be, require the installation of dedicated fire-fighting shafts to access the upper floors of the building; these are protected compartments separate from protected stairwells used for escape, although those too may be used by fire-fighters. Within the fire-fighting shaft, at least dry main access must be provided; if the building will be over 50 metres’ height, these must be wet mains, to ensure an adequate supply of water to fire-fighters in the upper part of the building. Regulations addressing the installation of mains and fire-fighting shafts are given by Sections 15 and 17 respectively of the Approved Document B. Within the building itself, systems to aid in fire-fighting must also be included. The use of a sprinkler system has already been noted; at a minimum, this should be installed throughout all protected hallways, circulation areas, and storage areas. In kitchen areas, a chemical fire suppression system installed above cooking equipment is also a prudent measure, and may be required. Another alternative that may be included in the fire-suppression system is the installation of fire hose reels throughout the building. These, however, require careful consideration and staff training, because well-meaning but inexperienced personnel might use these to fight a fire when it would be safer to evacuate, with potentially tragic results. (Fire safety risk assessment, 2006) Conclusion This paper has summarised the major considerations for fire safety that must be made during the design of a 20-storey, multi-use building to be located in Preston. These include preventing or limiting the spread of fire throughout the building, the installation of appropriate detection, warning, and fire-suppression systems, making provisions for secure escape routes, and providing sufficient access for fire and rescue personnel. While very detailed recommendations are not possible without a building design, the two most significant general recommendations that can be made now are to design the structure with a maximum amount of compartmentation, and to locate it in an area with wide access on all sides. References to the relevant sections of Approved Document B, which itself includes further references to other important regulations and standards, have been given throughout this report, as a guide to the designers in planning for a building that will both be useful and highly secure from fire risk. References Fire safety risk assessment: small and medium places of assembly. (PDF document) London: Department for Communities and Local Government, 2006. Available from: . Approved Document B, Volume 2 – Buildings other than dwellinghouses. (PDF document) London: Department for Communities and Local Government, April 2007. Available from: . Coggan, Donald A. (2008) Intelligent Building Systems. [Internet] Donald A. Coggan, PE, 2008. Available from: Read More