External Fire Spread - Assignment Example

Running Header: External fire spread Student’s Name: Instructor’s Name: Course Code: Date of Submission: External fire spread The external walls of all the buildings should be build in such a way that they adequately resist any fire from spreading from one room or building to another through the walls. This is regardless of its use, building position and height of the wall. The building’s roof should also resist the fire spread over the roof from a building to another regardless of position or use of building. The B4 requirements are met when external walls are constructed in such a way that there is restriction of fire spread over the surfaces as well as restriction of ignition risk from an external source. This is through ensuring that they have low rates of releasing heats. The requirements are also met if the construction of the roof is such that it restricts the fire and flame spread from an external source (Communities and Local Government 41). External walls The chance of fire spread across a space that is open between the buildings as well as its impacts depends on various factors. Such include distance between buildings, intensity, and size of fire, fire protection that facing sides gives, and risk people are exposed to in other buildings. Relevant provisions should be made to have enough fire resistance towards fire spread prevention across the boundaries. The external walls are structure elements whose relevant period of fire resistance is dependent on the height, size, and use of the concerned building. Provisions are also put in place as an effort to restrict external walls combustibility of buildings that are less than 1000mm from the relevant boundary. Boundaries The distance use to a boundary other than to another building in separation distance measurement makes calculation for the proportion that is allowable of the unprotected areas. This is despite whether there is a building on an adjacent site and the extent of any unprotected area. If a wall makes an angle of 80degrees or less, then it is treated as facing a boundary as illustrated in figure 1. Mostly, only the distance towards the real boundary of the site requires to be taken into consideration. However, in some instances where site boundary is adjacent to a space with no more developments like a railway, then this is a relevant part of boundary as illustrated in the figure 1. Relevant boundary can be viewed as the boundary facing a wall whether it is the real boundary of the site or notional boundary (Communities and Local Government 44). Figure 1 Relevant boundary There is need to take into consideration the distance to other buildings within the same site. This is through an assumption that there is a boundary between those building; this is referred to as notional boundary. There are several rules that set the notional boundary. The setting of a new building or if both are new, should be checked to ensure it also conforms the relevant setting using notional boundary as the appropriate boundary for the second building. It is assumed that notional boundary exist in the two building space. It is usually positioned in such a way that one building complies with space separation provisions in regard to size of area protected. Figure 2 notional boundary An external wall is said to be unprotected area if it has more than 1mm of combustible materials as its external surface. This is because it totals to half of the actual area of combustible area. Figure 3 Status of combustible surface material as unprotected area There are some unprotected areas within the protected sections of the wall. However, these are seen to pose a fire spread risk that is negligible hence ignored. Such areas have some constraints in relation to one another as well as to lines of compartment within the building. The constraints usually vary to the unprotected area size. If a wall is found within 1000mm from any relevant boundary point with inclusion of a wall in coincident with boundary, it meets the space separation provisions in case the rest of the wall is resistance from fire from both sides. Provisions for separation of space are also met by a wall found at least 1000mm from any point within relevant boundary. This is only if the rest of the wall is fire resistance and that the extent of the area unprotected does not exceed method 1 used for small residential buildings and method 2 used for most compartments or buildings not suitable for method 1 (method 1&2 illustrated below). There two methods that are used in calculating the size of unprotected areas that is acceptable. This is for an external wall which is at least 1000mm from any point within relevant boundary. Method1: this is used to any building that is 1000mm or more from any relevant boundary point and meets some rules used in determining the maximum area that is unprotected and which can be found in the figure below. The building’s height should not be more than 3storeys excluding basements or more that 24m in length. The space separation provisions are met by every side of the building if side of the building distance from the relevant boundary and the range of unprotected section are within the confines in figure above. The side of building parts should be fire resistance in excess of the unprotected maximum region (Communities and Local Government 46). Method 2: it usually applies to any dwelling house whereby from any point within the relevant boundary, it is more than 1000mm. The table 1 shown below is for rules used in determining maximum areas that are unprotected. The rules say that the compartment or building should not be more than 10m in height (Communities and Local Government 46). Furthermore, every side of the building meets the space separation provisions in case the extents of areas that is unprotected and distance from the building’s side from the relevant boundary are within the suitable limits provided in table 1 below. Another rule for determining unprotected maximum areas is that any parts of building side in excess of maximum area that is unprotected must be resistance to fire. Table 1 Permitted unprotected areas for method 2 The unprotected area total percent is obtained by dividing the total area unprotected by the rectangle’s area enclosing areas unprotected and multiplying the result by 100. Roof coverings Roof covering refers to constructions having one or more material layers although it does not refer to the structure as a whole. They are some roof provisions that are part of means of escape. The minimum distance part of the roof or roof itself to the relevant boundary is referred to as the separation boundary. The separation distance varies according to building use, its size, and type of roof. Roof coverings uses are not restricted for the following selected classification: AB, AA, or AC (National class) or BROOF (European class) (Communities and Local Government 49). A rigid thermoplastic sheet product used in roof light can be regarded to have BROOF (European class) or an AA (national class) designation if it is made from un-plasticised PVC or from polycarbonate that attains a rating of Class 1 (national rating) for flame surface spread when tested to Class C-s3, d2 (European class) or BS 476-7:1997. Unwired glass of at least a thickness of 4mm when utilized in roof lights can be to have a classification of BROOF (t4) or AA designation (national class). In regard to thatch and wood shingles, in case are less than 30 minutes resistance to fire, they need to be overdrawn from the construction (Communities and Local Government 50). References Communities and Local Government 2006, Building Regulations 2000; Fire safety, Approved Document B-Volume 1; Dwelling Houses, Viewed 11 May 2011, from http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADB1_2006.pdf Read More