Fire Safety Analysis for Two Storey Dwelling House - Term Paper Example

Fire Safety Report for Two Storey Dwellinghouse Table of Contents Contents Contents 2 1. Introduction There are a number of factors that should be considered when designing a fire safety system for buildings and these include the probability of fire occurrence, fire severity, the risk of fire to people in and around the structure, and the extent to which a structure can resist the spread of fire and smoke. Fire safety measures required by building regulation means of warning and escape, internal fire spread linings and structure, external fire spread, access and facilities (Approved Document B, 2006, p.8). Mr. & Mrs. Jones’ two-storey 250 square metres three bedroom house fire safety depends on the adequacy of incorporated safety facilities thus it is critical to determine the exact requirements. Following the guidance contained in Approved Document B Volume 1 (2006), this report determined the required safety facilities and other fire safety requirements for dwelling houses. 2. Required Safety Facilities 2.1 Means of Warning and Escape 2.1.1 Number of Exit Points As shown in the house’s floor plan below, the green arrows represents the emergency egress for each storey of a two storey dwelling house as indicated in section 2.1 of the Approved Document B (2006, p.17). Escape from the ground should be provided any habitable room except for the kitchen which in this case is the living room. In the upper floor, a window or external door should be provided since all rooms in the upper are only served by a single stair. Moreover, there should be a direct access to a protected stairway as indicated by a green arrow in the floor plan below. The large window located in ‘Bed 1’ or the small window in ‘Bed 3” can fill-in the requirements since both these windows can serve as alternative exit points. According to the provision, a single window can serve two rooms provided they have access to the stairs (Approved Document B Vol. 1(2006, p.17). However, since the stair is part of the primary escape route, it should be separated from the lower floor with fire resisting construction or a fire door with a 30 minute fire-resistance capability installed in the landing as indicated by the blue circle. In summary, there should be at least one primary and one emergency egress in the upper floor while the ground floor should have at least one final exit and one alternative exit. In total, for maximum fire protection, the house should be constructed with 5 exit points (4 – Alternative exit points plus 1 final exit point). 2.1.2 Minimum width of the exit As specified in Approved Document B Vol. 1 (2006, p.19) or section 2.8, windows that will be use for emergency egress should have an obstruction free area of at least 0.33 square metre. The minimum dimension on the other hand should be 450mm x 450mm and constructed with the openable area 1100mm above the floor. They should be fitted with lock and stays with release catch and should remain open during an escape. In general, the width of the door that will be use as emergency exit should allow unrestricted passage or escape. As detailed in Approved Document M (2004, p.28), the minimum effective clear width of these doors should be at least 800mm where the minimum is at 750mm with the door open at right angle to the frame. Alternatively, the calculation of effective exit width may be based on 2.5 minutes evacuation time at a flow rate of 40 people per minute as shown in the table below. Table 1- Emergency Exit Width (Source: North Yorkshire Fire and Rescue Service) Exit Capacity - number of people Per unit of exit width Maximum number for one exit (4 units=1950mm+) 1 unit (525mm) 2 units (1050mm) 3 units (1500mm) 100 200 300 400 However, the above table is more applicable to large areas with large occupancy rate such as assembly hall, restaurant, dance hall, and others. In Approved Document B (2006), the width of exit for 250 square metres residential house may be calculated using the following formula: W = ((N/2.5) + (60S))/80 Where: W= width of final exit in metres N = number of people served by the area S = stair width in metre Therefore; Using the maximum number of persons in Table 4 (Width of escape routes and exits) in Approved Document B Vol. 2 (2007, p.37), the calculation will be: W = ((60/2.5) + (1.2x60))/80 W= ((24) + (72))/80 W= 96/80 W= 1.2 metres (minimum width of exit) 2.1.3 Alarm and smoke detectors Mr. & Mrs Jones’ house is 250 square metres and according to the building regulation, this house should be classified as “large dwellinghouse” requiring Grade B category LD3 fire detection and alarm system conforming to BS 5839-6:2004. The regulation required at least one smoke alarm in each storey and it should be installed in circulation spaces, 7.5 metres from the door of every habitable room, ceiling mounted, 300mm from walls and light fittings, far enough from heaters or air-conditioning (Approved Document B Vol. 1 (2006, p.15). In this case, these devices should be positioned between ‘Bed 1” and “Bed 3” near the stair in the upper floor. In the ground, these devices should be placed in the kitchen and the living room where the fire is likely to start (Approved Document B Vol. 1 (2006, p.15) as shown by the orange dots in the floor plan below. These alarms should be linked so that all of them will respond when a smoke in one area of the house is detected. 2.2 Fire Sprinkler Sprinklers installed in dwelling houses generally reduced the risk to life and property thus it should be incorporated with Mr. & Mrs. Jones new house. Moreover, the building regulation as detailed in Approved Document B Vol. 1 (2006, p.17) section 2.7, houses with more than one floor should be fitted with a sprinkler system designed in accordance with BS 9251:2005. However, although it is a safer practice to have sprinkler protection throughout the house, it is acceptable to protect an area of the house (as compensatory feature) where a fire will likely to start (Approved Document B Vol. 1 (2006, p.9). Therefore, this report recommends the installation of automatic fire sprinkler only in the kitchen and the living room marked by red blocks in the floor plan below. 3. Internal Fire Spread (Linings) Along with an effective means of escape, the material that should be use to construct the house should conform to building regulation as specified in Approved Document B Vol. 1 (2006, p.25). The house circulation spaces should be constructed with fire-resisting lining materials to allow occupants sufficient time to escape. There is no provision for floor surfaces and stairs since they are not involve in early stages of fire spread. Similarly, although furniture and fittings can greatly affect fire spread, it is impossible to control them through regulations and therefore no provision is provided in Approved Document B (2006, p.25). However, the house and the garage should be separated by fire-resisting wall (brown line in the ground floor plan) as the garage contained highly combustible materials (see B3 Section 5 – Compartmentation on page 32 regarding separation requirements). Since internal fire spread linings can reduce the rate of fire spread, inner walls separating the living room and the dining area where one of the proposed alternative escape is located must be constructed with fire resisting lining (black line inner wall). The same should be done with other inner walls (yellow line). 4. Internal Fire Spread (Structure) Fire safety requires walls of two separate building constructed with fire-resisting materials (as in the wall separating the house and the garage mentioned earlier) and installation of automatic fire sprinkler. Fire resisting capability include withstanding the effects of fire, collapse, fire penetration, and transfer of excessive heat (Approved Document B Vol. 1 2006, p.29). The fire resisting capability of these materials should be at least 30 minutes as provided in BS 476. The floor plan below contained the recommended points of fire-resisting walls (brown line). As building regulations generally recommend maximum fire protection, this report additionally propose construction of at least 30 minute fire-resisting walls around the stair area (purple line). This is to help ensure that the primary escape route is safe from spreading fire. 5. External Fire Spread Similar to internal linings and structure, the external walls and the roof of the house should be able to resist fire and prevent fire spreading to another building. This is to reduce the risk of ignition from external source or thermal radiation being generated by the fire. Since the external wall (as there is no indicated neighbouring structure) is more than 1000mm from the relevant boundary, the Mr. & Mrs. Jones’ house only need internal fire resistance provided by internal linings and structure (Approved Document B Vol.1 2006, p.43). The blue-grey line surrounding the structure represents the beginning of the house external boundary line which as required should be built with fire-resisting materials in case there are nearby structures 1000mm or less away. 6. Access and Facilities for the Fire Services Providing access and facilities for the fire service is an important requirement of Building Regulation 2000 and as specified in Approved Document B Vol. 1 in B5, the house should have reasonable facilities to assist the fire fighters in dealing with fire and rescuing people. At the minimum, the following should be provided: a. Means of external access for fire appliances A road with a minimum width of 3.7m between kerbs and carrying capacity of at least 12.5 tonnes (see Figure 6.1 below). Gateways with minimum width of 3.1m Turning circle of at least 16.8 m between kerbs or 19.2 m between walls There should be an available clearance height of 3.7 m Note: the house does not need high reach appliances and therefore not included. b. Means of access to and from the house for effective search and rescue Provide internal fire mains if possible and other facilities necessary to assist fire fighters. 7. Conclusion/Summary Mr. & Mrs. Jones’ house at the minimum requires all recommended fire protection facilities. However, an alternative method of fire safety may be adopted provided it is conforming to building regulation’s requirements. The number of exit points including the alternative means of escape is recommended for maximum safety. Similarly, locations of internal fire spread linings and structures are recommended to provide maximum fire growth and spread protection as well as safer escape routes for the house occupants. 8. Reference list Approved Document B Vol. 1, Fire Safety: Dwellinghouses, Communites and Local Government, 2006 Approved Document M, Access to and use of buildings, Office of the Deputy Prime Minister, 2004 North Yorkshire Fire and Rescue Service, Assessing Maximum Safe Occupancy, NFRS, 2003 Read More