Fire Solution: External Fire Spread between Buildings - Assignment Example

Student Name: xxxx Tutor: xxxx Title: Fire Solution Date: xxxx ©2016 Part A: External Fire Spread between Buildings The control and protection of external fire spread between buildings can be assessed by looking at three major aspects, namely;- i. External walls ii. Roof covering iii. Space separation External Walls The Building Regulation (Approved Document B) dictates that external walls to a building shall be constructed in a manner so as to adequately resist the spread of fire over and/ or through the walls from one building to another, making due consideration for the height, use and position of the building [The10]. This requirement is only said to be met if the external walls are constructed so that the risk of ignition from an external source, or the spread of fire over their surface is restricted by having provisions which limit their rates of heat release. However, the construction of the external walls may provide adequate protection from external fire spread only to be compromised by the presence of unlimited unprotected areas along their surfaces, such as windows. The Building Regulation states that there should be adequate restriction on the amount of unprotected area on the side of the building, in an effort to limit the quantity of thermal radiation passing through the external wall, with due consideration to the free distance between the wall and the boundary. The combustibility of external walls should be restricted in order to reduce the susceptibility of the surface to ignition and reduce the danger from fire spread up the external surface of the building. These provisions are made for external load bearing walls to maintain their load bearing functionality even in the occurrence of a fire outbreak. These provisions are mandatory for all walls less than from the relevant boundary, and all external walls of high buildings and those used for assembly or recreation, irrespective of the distance to the relevant boundary. Cavities and filler elements in high buildings, such as gaskets and sealants, used in external wall construction should have provisions that restrict their combustibility, so as not to compromise the structural integrity and fire spread resistance of the wall. Roof Covering The Building Standards dictate that the roof of the building shall adequately resist the spread of fire over the roof and from one building to another, having due regard to the use and position of the building. Therefore, the mode of construction of the roof should limit the risk associated with fire spread by providing adequate protection from fire spread and/ or ingress of fire from an external source. The space separation between rooflights in any direction is determined to be a minimum of 3m. Additional distance is required () when plastic rooflights are used. The requirements of roofs are limited as buildings do not border each other with roofs. However, it should be noted that, if the roof is erected with a pitch greater than 700, it is considered an external wall and the requirements dictated for external walls apply in this scenario. Space Separation Modern architecture leans towards buildings with larger windows for aesthetic value. As a result, the risk of external fire spread is increased due to the large sections of unprotected areas. To maintain such constructions and prevent fire spread, space separation has become a very integral part of the design and location of modern buildings [Fir91]. The provisions for space separation detailed in the Building Regulations are based on assumptions that allow a reasonable standard to be specified. Due to the lack of boundaries between roofs, these provisions do not apply, except in the case where the roof is erected at a pitch is greater than 700. These assumptions are;-[The10] a. The compartmentation of the building will determine the size of the fire, so that the fire may engulf an entire compartment but not spread to other compartments b. The use/ purpose of the building, and hence the components stored therein will determine the intensity of the fire. Nonetheless, the intensity of the fire can be reduced/ moderated by the installation of a sprinkler system c. There is a greater risk to life in buildings used for residential, assembly and recreational purposes than other uses d. The elevation and distance from the common boundary of the adjacent building are identical to those of the building in question e. The amount of radiation passing through any part of the external wall installed with adequate fire protection may be discounted The use of distance to a boundary in the measurement of separation distance, as opposed to the actual distance between the buildings, allows for the calculation of allowable proportion of unprotected areas regardless of the properties of the building on the adjoining site. When the adjoining site’s land use makes it unlikely that there will be additional development, such as a road or railway, part of the adjoining space may be regarded as being within the relevant boundary. If the angle between a wall and a boundary is 800 or less, the wall is taken as facing the boundary. In the case where two buildings are within the same site and are used for residential, assembly or recreational purposes or are managed by different authorities, a notional boundary is introduced. The location of this boundary is determined by the provisions of one building to adhere to the requirements of space separation. The location of the second building will be determined using the notional boundary as its relevant boundary to determine the distance to conform to space separation requirements. The distance between the building and the relevant boundary is determined by the fire load intensity of the building, as well as the compartmentation under consideration (is it ‘normal’ or ‘low’) [Fir91]. It is very rare for actual flame contact or flying brands to ignite a building on an adjacent site that is cold. However, the possibility of ignition of a secondary fire becomes a real danger should the building be heated by radiation from the primary fire, due to the heat of radiation bringing the building close to its ignition point. Therefore, it is important to determine the level of radiation being produced by a burning building and the amount of radiation necessary to ignite the exposed surfaces of the building on the adjacent site. Fire spread by radiation from building to building is dependent on;- [BSI08] a. The distance between the building of origin and the neighbouring structure and their orientation (configuration factor) b. The extent of building surface capable of transmitting heat to the neighbouring building. Heat transfer is ignored for structures whose external walls have sufficient fire protection c. The intensity of the source radiation Unprotected areas on the surface of external areas may be regarded as negligible when considering space separation if;- 1. The area is less than or has two or more small unprotected areas () within a area and is separated from another such area by at least 4m 2. The distance between small unprotected areas is more than 1.5m Several experiments were carried out by the Fire Safety Team of the Building Research Establishment (BRE Global) concluded that the spread of fire between buildings was facilitated by various factors, such as narrow streets, combustible building materials, hazardous activities involving combustible materials and the poor enforcement of regulations [Chi15] Methods of Determining Boundary Distance 1. Enclosing Rectangles (Geometric Method) In this method, the elevation is viewed and a rectangle drawn around the unprotected areas, and the minimum boundary distance for this size of rectangle determined from a table. The process is repeated for all elevations to obtain a trace in plan. If the relevant boundary falls outside the trace, no action is required; otherwise, further analysis of the problem is necessary to determine possible solutions. This method is used for external enclosures in a single plane without significant recesses or setbacks 2. Notional Areas (Protractor Method) In this method, the building is viewed from a series of points on the boundary and the effective areas of the visible ‘unprotected areas’ calculated. The further an unprotected area is from the boundary, the smaller the effective area. The distance factors used in calculation of the area are obtained by placing a ‘protractor’ made to the same scale as the plan and noticing which zones the unprotected areas fall. The sum of all the effective areas of ‘unprotected areas’ should not exceed a prescribed limit. This method is employed for buildings that have complex plan shapes. 3. Small Residential Buildings [BSI08] Table 37 is used to determine the appropriate boundary separation distance when the building is intended for residential use only. The building should be less than 3 storeys high and less than 24 m in length 4. Fire Engineering Calculation This method is described in BS 7974 [BSI01] Part B: Determination of Unprotected Areas Methods of Enclosing Triangles This method is chosen as the two buildings in question have an external enclosure (nominal) in a single plane, without any significant setbacks or recesses. Assumptions 1. The Maudland Building is classified under Residential, Assembly or Recreational buildings, being relatively fully occupied during most times of the day 2. The Maudland Building’s external walls are constructed with provisions to prevent fire spread 3. The Maudland Building’s walls do not have any combustible material more than 1mm thick on their external surfaces (unprotected percentage Read More