Code of Practice for Fire Safety in the Design of Buildings - Report Example

The Use of natural and mechanical ventilation in corridors of apartments Name: Institution Name: Registration Number: Tutor’s Name: Date of Submission: Table of Contents Introduction 3 Design consideration in compliance with Approved Document B, BS 7974 and BS 9999 4 Mechanical Smoke Ventilations 8 Main types of mechanical ventilations used to control smoke 8 Mechanical Construction of the building 9 Design of fire-fighting and smoke control shafts 10 Conclusion 11 References 12 Introduction During the design process for natural and mechanical ventilations in a block of flats, rules set out in Approved Document B, BS 7974, BS 9999 should be followed in modeling the corridor or means of escape to ensure that the smoke is controlled efficiently in case there is fire. Performance criteria of these designs are based on tenability. The design and use of ventilations done in such a way that smoke is kept away as possible room occupants of the building. For instance, the air tightness that needs to be achieved within the escape may be affected by the corridor’s natural ventilation. In flats mechanical ventilations are often designed with an objective of overcoming the smoke movement forces of buoyancy, stack effect, thermal expansion and wind pressure during a fire thus any discrepancy in expected pressure differentials and airflow rates should be resolved. In fire safety strategy areas such as stairwells and corridors are considered strategic locations where air pressure should be maintained. While natural ventilations are intended for smoke and heat extraction depends on the air provided by the openings in a certain area, influence of wind and size of the openings, and the timing of their opening (in case of fire). In contrast, mechanical ventilation system extracts air (negative) in controlled manner in order to allow a defined volume of heat and smoke to escape. This means in laying out the building, a means of escape should be provided based on the nature and number of occupants at any given day in the building. Proper fire fighting facilities should be provided and placed in accessible area. There should be proper compartmentation of the building in terms of a number and size of ventilation, the internal height of the building and materials used in construction. Structural response of buildings ensures that the building can withstand fire without collapsing to give time to occupant’s to escape. The structure should be fire resistant in terms of structure supporting rooms, columns and stairs. It should be in a position to allow in air that will reduce the effect of smoke to the visibility of the occupants. This relates to the design and provision for ventilations. The purpose of this paper is to present mechanisms that can be used to control smoke in buildings with more emphasis on natural and mechanical ventilation. It provides an illustration of components that have to be included in order to design an efficient smoke control system in buildings. Design consideration in compliance with Approved Document B, BS 7974 and BS 9999 During the design of the natural and mechanical ventilations, there are certain codes that have to be complied with as enlisted by Approved Document B, BS 7974 and BS 9999. These are means of escape from the building and effective control of smoke in the design of ventilation systems must account for their proper designs. BS 7974 has procedures which are followed in the design of safety measures of a building. The principals that are highlighted in the standards include installation of pressurized and smoke control systems, installation of sprinklers as fighting equipments, provision of emergency stairs, increase of travel space within the building, provision for large volumes of people, restriction of access to fire services, and elimination of barriers from buildings. BS9999 introduces the use of tables as well as other factors in designing escape routes. It considers the population density and the type of occupants. The figure below shows how various buildings are designed to cater for occupants: Approved document B enlisted the inclusion of windows which can assist somebody to escape from fire, the inclusion of sprinklers, smoke alarms, inclusion of escape prude for disabled people, use of maximum compartment size for escape. During the design of corridors, the corridors that are used as a means of escape from the building should be constructed in such a way that it is partitioned so that it is smoke-retarding even in case where fire resistance is not required (Rapid Excavation And Tunneling Conference, Traylor and Townsend, 2007). In addition, opening rooms into corridors should be fitted with doors that should be fire resistant as well as close fitting to control the spread of fire into the building. In order to ensure corridors are not covered with smoke during exit from the building during fire, it should be subdivided into a number of sections by use of doors that can be closed. For instance, Approved Document B provides a number of requirements for a flat, such as additional requirements for stair enclosures when a building goes beyond 4.5m and has a corridor more than 30m. the corridor should be designed in a such a way that the occupants are able to escape without external help. The following diagram shows a proposed flat plan The recommended corridors and escape routes for this flat according to BS 9999 In addition, corridors that are more than 30 meters long should have at least an exit on each end of the corridor in addition to another exit in the middle of the corridor. This ensures that people in the middle rooms do not have to move to the extreme ends of the corridor to exit the rooms before they are covered by smoke (Maevski, 2011). If the corridor has dead end it will lok as follows; During the design of tall buildings, there are certain design features that must be considered. One of these features is the stack effect. This is the tendency of air to move within the building resulting from variations of air density between the interior and exterior spaces in the building. Stack effect has the capability to create large pressure differentials that can result into dangerous smoke movement within the building and make it difficult to open doors and make control of smoke difficult (Johnson, 2001). During the design of tall buildings, stack effect can be reduced at regular intervals by use of mechanical shafts that are capped every often within the building. In addition, this effect can be reduced by use of shafts that are interrupted by use of transfer passageways or refuge areas. The effect of wind in very tall buildings can be reduced by use of wind tunnel testing or the use of computer modeling which assist in evaluation of impacts of pressure differentials during movement of smoke within the building and the effect of smoke control system. Windows which acts natural ventilation should be designed in a manner that ensures breakage cases are minimized during strong wind movements. Mechanical Smoke Ventilations Main types of mechanical ventilations used to control smoke The use of mechanical systems for smoke control includes such devices that use mechanical means during production of pressure differentials across barriers to ensure the spread of smoke is prevented. There are certain code trends that are relevant during design process for smoke control in tall buildings. The design of these mechanical smoke control systems are based on these codes. An example of a mechanical smoke control system is the atrium smoke control system. This is mainly used in tall buildings where two or more atria are fixed. According to the building code for smoke control, there is the need to design and construct a smoke management system for multiple-storey atria (Burton, 2000). During the design process for this form of mechanical smoke exhaust system to assist in extraction of smoke from the top of the atrium with low-level, low velocity make up, air at the rear section of the atrium to ensure a smoke layer is maintained above occupied areas and their related methods of egress for a particular time period. The other form of mechanical ventilation that can be useful in controlling smoke in building is stair pressurization system. According to the requirements of building codes, high-rise buildings should be provided with smoke proof exit stairs or stairs pressurization (Beard, 2005). Approved Document B requires that corridors, stair balconies; mechanically ventilate stair vestibules, and stair pressurization to be incorporated in tall building. The most popular form of ventilation is the mechanical pressurization system. This form of stem is mainly used during construction of high-rise buildings. Another form of smoke control system is the zoned smoke control system. This refers to a control system that partitions the building into control zones and develops pressure differentials that ensure the spread of smoke is inhibited. The use of mechanical exhaust is applied for areas that contain smoke and pressurization is done for additional contagious areas (The Fire Strategy Company, 2008). In high-rise buildings, the main components of zones may be entire floors, in addition to floors that are divided into a number of zones. An example of a pressure sandwich is the pressure ‘effect’ where the fire floor is exhausted and the floors are pressurized on either side. The disadvantage of these systems is that they are complex due to the required coordination between them and other HAVC equipment, controls and operational matrices. Mechanical Construction of the building During the design of buildings, heating, ventilation and air conditioning systems need to be included within the building to serve the purpose of spreading smoke by extracting and distributing smoke from the source of fire or creating pressure in the fire area and moving smoke into the nearby building areas (Ward, Ward and Leach, 2010). According to the building code that addresses this issue, when smoke has been detected it is required that HVAC fan should be shut down in the ductwork and fire barriers and smoke barriers should be installed as a method of reducing the spread of smoke. It is critical to integrate fully the HVAC system with engineered smoke control systems. Design of fire-fighting and smoke control shafts Shafts for fighting fire should be provided in buildings in the basements in areas that are 10m below the ground level while pressure differential systems should also be provided (Snow, 2003). In addition there should be pressure differential systems for all other fire-fighting shafts with the exception of natural ventilation where shafts for fighting fire can be located 10m below the ground level or up to a height of 30 meters above the level of the ground. Pressure differential systems are also used during smoke control by installing them in accordance with the British Standard 9999 and Bs 7974 for smoke control. Furthermore, all buildings must be provided with operable vents and smoke shafts (Maevski, 2011). Smoke shafts that go through fire compartments should be located at the same level of fire compartment as those that have been breached. Smoke shafts located in the basements should ensure direct discharge of smoke into the open air at the ground level where it is not possible to affect exits from the building while fire service access cannot be affected during discharge of smoke (Johnson, 2001). Smoke shafts should only be designed to serve a single basement level. Each smoke shaft must be covered by a metal grille designed to ensure the shaft is not blocked by rubbish, or materials that can break or easily accessible from the right fire service access level. For stairs located on external wall that serve top floor less than 30m above the ground, vents should be remotely operable at the head of the stairs while manual control can be used to control them. For a lobby located above the ground level on an external wall, the position of the vent should be near the ceiling direct to the open air while manual control should be used during its operation (The Fire Strategy Company, 2008). Smoke shafts that are designed to serve storey above the ground level have to be fully open to the outside air at the top and bottom. The opening at the top of the smoke shaft should be located in such a way that it is free from strong winds while the cross-sectional area of the smoke shaft must be designed at 3m2 while its dimensions should be 1 m minimum. Furthermore, the top part of the ventilation must be located in an area closer to the ceiling as possible and should be high enough at the top of the door that connects the stairway with the lobby. Conclusion All the standards for fire safety require buildings to have the means of escape, to have easy access to the building, the fire safety manual, and evacuation strategy. This is not possible by ensuring during construction the regulations made down are followed. More so, before constructing a house, the risk profile of resident is taken into consideration, that is, the escape or evacuation of a week occupants is different from sleeping occupants. Effectively constructed buildings should be those that comply with the British Standard 9999 and BS 7974, AD B for smoke control as well as ensuring safety of building occupants. In order to ensure proper protection of buildings and occupants from impacts of smoke and fire, buildings designers have to include mechanical and natural means of controlling smoke within the building. This involves installation of the right equipment such as fans and shafts that help in movement of smoke from one section of the building to another. It will also ensure building occupants are safe during fire outbreak while possibility of putting of the fire becomes high. References Beard, A. 2005. The handbook of tunnel fire safety. London, Telford. Burton, S. E. 2000. Energy efficient office refurbishment. London, James and James. Johnson, V. B. 2001. Laxton's building price book 2002 major and small works. Oxford, Butterworth-Heinemann. http://search.ebscohost.com/login.aspx?direct=true&scope=site&db=nlebk&db=nlabk&AN=199203. Maevski, I. Y. 2011. Design fires in road tunnels. Washington, D.C., Transportation Research Board. Rapid Excavation And Tunneling Conference, Traylor, M. T., & Townsend, J. W. 2007. Rapid Excavation and Tunneling Conference: 2007 proceedings. Littleton, Colo, Society for Mining, Metallurgy, and Exploration Inc. Snow, D. A. 2003. Plant Engineer's Reference Book. Burlington, Elsevier. http://public.eblib.com/EBLPublic/PublicView.do?ptiID=297095. Stationery Office (Great Britain). 2006. The Building Regulations 2000. London, TSO. Ward, J. P. T., Ward, J., & Leach, R. M. 2010. The respiratory system at a glance. Chichester, Wiley-Blackwell. The Fire Strategy Company, (2008). A Guide to BS 9999:2008- Code of practice for fire safety in the design, management and use of buildings. Available on from (accessed on 05 August, 2013) Read More