The Principle of ASET and RSET with Regards to Means of Escape - Coursework Example

Name Course title Task Date Introduction A crowded place is a great concern when dealing with human safety. There have been hazards in too crowded places. Even small accidental fire in a crowded space can be very serious. More damage would be created in case of a terrorist attack. Thus, evacuation in a building should be planned carefully to ensure safety of the occupants, especially in the presence of a crowd (Muckett and Furness, 2007, 83; Yung, 2008, 5). Evacuation time is important in escape process when determining the time needed for occupants to exit to safe place after recognizing the threat and starting to egress. The margin of safety can be used to calculate the life safety in a building. It is the difference between the required theoretical time for evacuation, Required Safe Egress Time (RSET), and the time available for evacuation, Available Safe Egress Time (ASET), for the occupants to move out from a building. The total evacuation time is the real time needed for all the occupants to be move out safely out of the building and to reach a safe place (Yung, 2008, 63). However, the total evacuation time can obtained through simulation using evacuation models. A study of evacuation time, ASET and RSET provides a better knowledge on the time components like recognition time, pre-movement time, response time, walking time, flow time and travel time used in evacuation. The objective of this study is to review the principle of ASET and RSET with regards to the means of escape (Muckett and Furness, 2007, 83). Discussion B1 – Means of Warning and Escape The provision of the means of warning and escape is the requirement of B1 of the Building Regulations. It requires suitable provisions for early warning of fire. This provision covers the measures needed to ensure that there are facilities that provide means of escape a fire incident, as well as structural fire safety measures where they are essential to maintaining escape routes (Muckett and Furness, 2007, 83). It is assumed that the occupants will include a number of people with disabilities, and therefore in during design of the building, there should be less reliance on the rescue by the fire brigade from the outside the building. The basis of the document is that the people who have occupied any part of the building can evacuate safely from the building in case of an emergency with no external support (Stephenson, 2013). The design of means of escape depends on the anticipated fire behavior that can begin at any part of the building and spreading to other parts of the building. Thus, the design of the building should be done carefully to determine the threat which may arise from fire. Fires usually begin in a small part before spreading to other parts of the building, which may be spread through movement routes in the building (Muckett and Furness, 2007, 83). Different measures are used in design to provide safe means of escape that include limiting the spread of fumes and smoke. The requirements of B1 document include: the sizes and number of routes are appropriate and can enable the occupants to evacuate to a safe place in case of an emergency, the routes should be protected enough in term of enclosure, and sufficient smoke control and alarm system to warn the people about the existence of fire and provide them with a means of escape depending of the height and size of the building (Billington, 2002, 66-80). Fire safety engineering approach is an alternative solution to technical guideline document. This is applied if certain provisions of the guidelines are not possible to be applied. There are different factors that should be considered (Waters, 2003). They include: The risk of fire occurrence The severity of fire The available safety measures The risk to the people in the building in case of fire occurrence Various consideration are made and techniques that may be suitable to specific circumstances which include sufficient provision of the means to prevent fires, early detection and warning, means of escape, smoke control systems, control of the fire growth, fire extinguishers, etc. Engineering fire safety technique provides a better solution compared to the prescribed method of fire safety. The design process for fire safety involves quality examination of the design through quantification and comparing with definite safety measures (Rasbash, 2004; Waters et al., 2003, 33). The assessment of the quality of fire safety design is based on the appropriate life safety measures using the following ways. A deterministic method, which determine the worst fire situation to be studied in detail, together with other safety factors. For the uncertainties in the design procedure and the initial assumptions used, there should be safety factors that can ensure adequate safety level. A comparison of the performance of the prescribed approach with the performance of the proposed approach. Inherent safety factors are used to ensure that the adopted design will provide safety that is comparable to the safety achieved with the prescribed approach. A probabilistic approach that involves life risk. The likelihood of the occurrence of event should be at acceptable low level. The analysis takes into account the likelihood of fire starting and smoke spreading to create untenable conditions in specific place in the building. An alternative risk assessment can be used to confirm that the fire safety design provide a safety equivalent to the prescribed design (Waters et al., 2003, 33). There are guidelines which provide principles for fire safety in engineering practice. Some of them include BS 7974: 2001 which is concerned with application of engineering fire safety approach in building design and in the related published documents and CIBSE guide E deals with introduction to fire safety engineering of buildings in London 2003. There are other guidance materials which contain codes of practice associated with fire safety (Muckett and Furness, 2007, 83: Great Britain, 2006). Due to the fact that fire is a complex phenomenon, there has been development in fire safety practice to increase knowledge in fire behaviour and the effects. Therefore, analytical models that are based on mathematical relationships required for some fire conditions to occur. Computer based models can also be used to predict fire behavior and it effects. When using these models for analysis, there should be an understanding of limitations, assumptions, parameters, proper application and accuracy of the data input and interpretation of the result (Peacock, et al., 2011). Flow rate In an emergency, occupants from various areas of the building converge in an exit. Therefore, congestion occurs due to reduction in the flow rate, because of the large number of occupants being evacuated at the same time. Queuing would result which involves a number of steps that include approaching the queue, standing or waiting in the queue and moving through the exit. The effects of waiting in a queue would affect the movement of the occupants and will lead to lengthening of the time of evacuation. Waiting time in the queue has been studied extensively. Queue time is elaborated more in time to queue formation in BS 7974, which involves waiting and moving time. On the other hand, the occupants waiting time can be improved through changing crowd density, exit selection and the number and width of the exits (Muckett and Furness, 2007, 83) Preventive and protective processes in design The first step to ensure that the building is safe from the risk of fire is to design and maintain is to apply high level of fire safety for building and its occupants (Great Britain, 2006). The escape routes in a building in UK are designed based on the engineering approach or prescriptive approach. The prescriptive approach is based on the prescribed code of practice, notes from authorized person or other documents. The code of practice that deals with fire safety is provided by fire services department meant to include escape routes in building design (Peacock, et al., 2011). The numbers of occupants are specified for the designer to determine the building occupation density, the staircase width and travel distance, staircases in buildings with sprinklers or with no sprinklers, etc. The evacuation time to the protected area like staircase leading to the exit in a storey building should be within the calculated time of 2.5 minutes for building with no sprinklers. The building should be protected against fire including provision of escape routes and use of non-combustible materials that are resistant to fire (Great Britain, 2006). It is assumed that the building design following these codes should be sufficient to provide protection to the building occupants in fire incident. The engineers or designers makes building design based on these codes without questioning the performance of the actual evacuation routes (Leveson, 2011). However, some buildings with special features do not follow these requirements. The evacuation time is estimated, and the engineers consider the likely fire situations by studying the function and features of the building and nature of the occupants. The compliance to the fire safety design is checked alongside the codes of practice. Then the fire engineers determine the expected population and the means of escape for the design (Muckett and Furness, 2007, 83). Available Safe Egress Time (RSET) The ASET was introduced by Cooper (1983), as the time that elapses from the initiation of the alarm and the start of the hazardous conditions (Cooper, 1983, 133). The definition of ASET as adopted by BS 7974 is the time available from fire ignition time to the time the untenable conditions in the building are reached. This provide the maximum exposure time to hazard from the fire which may be tolerated with no one being incapacitated. All of the occupants in the building should be able to escape from threatened conditions before ASET is reached. ASET is calculated as follows. Where is the detection time, is the time for the onset of hazardous environmental conditions, and is the notification time (Great Britain, 2008). Required Safe Egress Time (RSET) RSET is the time taken by the occupants to move to a safe place after fire ignition, i.e. the target time for complete evacuation and includes the time the occupants remain safe within the time spent in the building (Schadschneider et al., 2009). BS 7974: 2002 is a comprehensive document which provides a systematic technique for calculating the escape time. The proposed formula for calculating RSET is shown below. Where is the time from the ignition to the detection time by automatic sensors, is the time duration between detection and the general alarm, is the pre-movement time which is the time from alarm to the time the occupants move out of the building. It includes the time the occupants recognize the alarm to the time they respond to the alarm and begin to move out. is the travel time for the occupants from the building to the a safe place, which can be determined using evacuation software simulation (Hasofer et al., 2007, 78-103). The travel time consist of parts, walking time and flow time. The walking time depends on the speed of the occupants during egress, while time is the times taken by the occupants to move through an exit which can be a downstairs or doorway. This includes the time taken to queue while waiting for to evacuate. The factors that affect the pre-movement time include recognition time,, response time, (Lataille, 2003, 33). Thus, pre-movement time,, is calculated from the equation: . The number of people moving through the exit will vary if they are moving at the same time or at different times. Jamming will occur if the occupants move at the same time and at the same speed, as they will arrive at the exit at the same time. The pre-movement time can be divided into three. a) Time between alarm and movement of the first occupants. b) The distribution of the occupants when exiting c) The time between the first alarms to the exiting of the last occupant (Lataille, 2003, 33-44). The travelling and waiting time can be ignored if the pre-movement time is long. Travel time has three components that include: Walking time, – This is the average time taken by the occupants from their locations in the building to the escape route. Queuing time, – The time required from the alarm to the time the queue is formed at the exit. At the exit, the occupants queue as they wait for room to move forward. The speed of occupants when passing through the exit is lower than the rate at which they are arriving. The queue can be bulk or orderly queue that is based on first come first serve (Rasbash et al., 2004). Flow time, – This is the time taken by the occupants to move through the exit, assuming that all he occupants are at the exit at a particular time (Hasofer et al., 2007, 78-103). Travel time is calculated from: Other Time Components Recognition time Recognition time in British Standards is the time taken by the occupants responds to alarm. They respond after accepting that they need to respond. Recognition time varies with the charateristics of the occupants and the alarm and organization management (Great Britain, 2006). Response time This is the time taken by the occupants to receive and interpret the emergency information and prepare to exit. Respond time can be reduced by providing prompt, accurate and clear information to the people. Other factors which affect response time are physical and mental state of the occupants, level of training on response to warning, role and responsibilities and how much they feel they are in danger (Great Britain, 2006; Muckett and Furness, 2007, 83). Margin of safety This is the difference in time between the ASET and RSET of the occupants. If the value of ASET is greater than RSET, the evacuation route will be considered to be suitable. The outcome will be forwarded to the authorities for approval (Hasofer et al., 2007, 78). From the formula, the delay before beginning evacuation would expose the occupants to vulnerability. The behavior of the occupants during evacuation would affect the movement of the occupants in case of fire and the response is affected by the psychological and the physical state of the occupants at the time of fire recognition, for example there severity of the threat due to fire, if the occupants are asleep or awake, firefighting devices available and the building design (Peacock, et al., 2011, 78-103). The occupant’s response after recognition of fire will be affected by their perception about the magnitude of the fire. Before exiting, most people have tendency to take preservative action like collecting valuable or important items. When estimating, it is important to take into account the occupant’s cognitive function ability. Some people may not take the seriously the audible fire warning, but they wait for further information for example clarification by the management through a phone call or notification from a neighbor before beginning to evacuate (Rasbash et al., 2004). Thus when fire engineering technique is used in designing the escape route, it is essential to recognize the behavior of the occupants in a fire incident such that can be included in calculating the egress time. Nevertheless, the value varies with uncertainties and accurate understanding of the occupants should be obtained. The determination of usually involves a lot of discussion by the engineers or designers with the authorities. Other considerations include the physical conditions and distribution of the occupants, the age, gender, and other conditions, are very important parameters used to estimate. There is however no universal guidelines for the determining this parameter by the fire engineering technique, which leads to arguments between the designers and the authorities (Hasofer et al., 2007, 78-103: Rasbash et al., 2004). Use of models The worst fire location and scenarios are envisioned by reviewing the operation and function of the building. A suitable fire size for the design is determined by the relevant parties. Fire engineers usually consider the effect of stack and wind that affect the development and movement of fire and smoke (Muckett and Furness, 2007, 83). Other factors will be used as parameters for calculating the spread of fir and smoke. Calculation may be based on the experimental equations provided in the design guidelines. Field simulation like fire dynamic simulator (FDS) or Zone simulations like CFAST can be used to determine the probable situations of the building in case of an emergency. The unsustainable situations can be found from thermal radiation, an enclosed temperature and the smoke layer. The time between the ignition and the beginning of the untenable situations will be considered to be the ASET for the people in the building (Peacock et al., 2011; Hasofer et al., 2007, 78-103). The use of Fire Dynamics Simulator (FDS) fire modeling tool enhances the accuracy and capabilities of implementation and management of the fire safety document. FDS involves enhanced accuracy and capabilities (Peacock et al., 2011, 447-460). Simulation Simulation can be done using various techniques such as Pathfinder. Pathfinder is an emergency egress simulator with a user interface provides a real time 3D visualization. It works like a video player such that it enables users to navigate through the model and make necessary changes that allow easier analysis of any complex structure. The system can be used in large models with a large number of occupants. Small portion of the building can be visualized with the help of data streaming. 3D visualization use human models which represent various ages, cultures and other occupants, which makes it possible to make a real portray of the various types of interest (Peacock et al., 2011, 447-460). When approximating the evacuation time for the occupants, the designers would begin by determining the ultimate place of safety. The evacuation software like EXODUS or SIMULEX can be used to estimate the travel time of the occupants. The dead ends, the prolonged traveling time by the occupants and the congested areas are identified. Conclusion The main components, terms and relationships in the evacuation time that include ASET and RSET has been reviewed, which has provided a clear overview of the process of evacuation. The development of these components has been discussed. Others factors which affect the evacuation that include the psychological effects of the occupants such as response and recognition time would affect the RSET. The human behavior including the actions taken by the occupants when evacuating would affect the movement of the occupants. Waiting time in a queue is the dominant factor in a crowded place. References Billington, M. J., Ferguson, A., & Copping, A. G. (2002). Means of escape from fire. Oxford: Blackwell Science, 66-80. Cooper, L. Y. (1983). A concept for estimating available safe egress time in fires. Fire Safety Journal, 135-140. Great Britain. (2006). Fire safety risk assessment: Educational premises. London: Department for Communities and Local Government. Hasofer, A. M., Beck, V. R., & Bennetts, I. D. (2007). Risk analysis in building fire safety engineering. Amsterdam: Butterworth-Heinemann, 78-103. International Conference on Pedestrian and Evacuation Dynamics, Peacock, R. D., Kuligowski, E. D., & Averill, J. D. (2011). Pedestrian and evacuation dynamics. New York: Springer, 447-460. Lataille, J. I. (2003). Fire protection engineering in building design. Amsterdam: Butterworth-Heinemann, p 33. Leveson, N. (2011). Engineering a safer world: Systems thinking applied to safety. Cambridge, Mass: MIT Press 33, 47, 61-71. Muckett M., Furness A., (2007). Introduction to Fire Safety Management, Routledge, 83, Stephenson J. and London District Surveyors Association, (2013). Building Regulations Explained, Routledge, 2013 Rasbash, D., & John Wiley & Sons (Firma comercial). (2004). Evaluation of fire safety. Chichester, West Sussex, England: J. Wiley. Schadschneider, A., Klüpfel, H., Kretz, T., Rogsch, C., & Seyfried, A. (January 01, 2009). Fundamentals of Pedestrian and Evacuation Dynamics. Waters, J. R., & Blackwell Publishing Ltd. (2003). Energy conservation in buildings: A guide to Part L of the Building regulations. Oxford: Blackwell Pub. Yung, D. (2008). Principles of fire risk assessment in buildings. Hoboken, N.J: Wiley, 63. Read More

Fire safety engineering approach is an alternative solution to technical guideline document. This is applied if certain provisions of the guidelines are not possible to be applied. There are different factors that should be considered (Waters, 2003). They include: The risk of fire occurrence The severity of fire The available safety measures The risk to the people in the building in case of fire occurrence Various consideration are made and techniques that may be suitable to specific circumstances which include sufficient provision of the means to prevent fires, early detection and warning, means of escape, smoke control systems, control of the fire growth, fire extinguishers, etc.

Engineering fire safety technique provides a better solution compared to the prescribed method of fire safety. The design process for fire safety involves quality examination of the design through quantification and comparing with definite safety measures (Rasbash, 2004; Waters et al., 2003, 33). The assessment of the quality of fire safety design is based on the appropriate life safety measures using the following ways. A deterministic method, which determine the worst fire situation to be studied in detail, together with other safety factors.

For the uncertainties in the design procedure and the initial assumptions used, there should be safety factors that can ensure adequate safety level. A comparison of the performance of the prescribed approach with the performance of the proposed approach. Inherent safety factors are used to ensure that the adopted design will provide safety that is comparable to the safety achieved with the prescribed approach. A probabilistic approach that involves life risk. The likelihood of the occurrence of event should be at acceptable low level.

The analysis takes into account the likelihood of fire starting and smoke spreading to create untenable conditions in specific place in the building. An alternative risk assessment can be used to confirm that the fire safety design provide a safety equivalent to the prescribed design (Waters et al., 2003, 33). There are guidelines which provide principles for fire safety in engineering practice. Some of them include BS 7974: 2001 which is concerned with application of engineering fire safety approach in building design and in the related published documents and CIBSE guide E deals with introduction to fire safety engineering of buildings in London 2003.

There are other guidance materials which contain codes of practice associated with fire safety (Muckett and Furness, 2007, 83: Great Britain, 2006). Due to the fact that fire is a complex phenomenon, there has been development in fire safety practice to increase knowledge in fire behaviour and the effects. Therefore, analytical models that are based on mathematical relationships required for some fire conditions to occur. Computer based models can also be used to predict fire behavior and it effects.

When using these models for analysis, there should be an understanding of limitations, assumptions, parameters, proper application and accuracy of the data input and interpretation of the result (Peacock, et al., 2011). Flow rate In an emergency, occupants from various areas of the building converge in an exit. Therefore, congestion occurs due to reduction in the flow rate, because of the large number of occupants being evacuated at the same time. Queuing would result which involves a number of steps that include approaching the queue, standing or waiting in the queue and moving through the exit.

The effects of waiting in a queue would affect the movement of the occupants and will lead to lengthening of the time of evacuation. Waiting time in the queue has been studied extensively. Queue time is elaborated more in time to queue formation in BS 7974, which involves waiting and moving time. On the other hand, the occupants waiting time can be improved through changing crowd density, exit selection and the number and width of the exits (Muckett and Furness, 2007, 83) Preventive and protective processes in design The first step to ensure that the building is safe from the risk of fire is to design and maintain is to apply high level of fire safety for building and its occupants (Great Britain, 2006).

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