Principle of ASET & RSET with Regards to Means of Escape - Math Problem Example

Principle of ASET & RSET with regards to means of escape Student Name Professor’s Name Course Date Outline I Introduction II B1 Means of escape III ASET and RSET and how it is incorporated in to standard UK guidance IV Calculation of ASET and RSET V Discussion, Analysis V Conclusions References Introduction Fire outbreak in a building can cause devastating loss of human life if proper means of escape were not designed and implemented. Thus the British regulating agency have come up with principles that govern design of building to ensure life safety as well provides means of processes, assessing and calculating time to be used in saving life in the building. These regulations have taken into account people’s behaviour during stay in the building, escape or on hearing fire alarm or exposure to smoke, heat or fire affluent (Harold, Nelson and Mowrer, 2002). It has also considered human condition or state of mind for example the reaction of children is different from that of normal adults as well as the reaction of patients in a mental hospital will react differently from occupants of a flat. This paper is going to critically look at the principles of safe escape time (ASET) and required safe escape time (RSET) in relation to means of escape. In any design available safe escape time should be greater than the required safe escape time thus creating appropriate margin of safety which is considered to take into account possible fire scenarios. During the design process care should be taken to ensure that occupants have adequate escape space and escape routes are protected from fire effluent, smoke or heat which may impede escape or evacuation. It should be noted that escape routes are designed to enable occupants escape without getting into contact with fire or associated effect like heat and smoke as recommended by BS 7974. B1 Means of escape B1 of the Building Regulations is concern with the safety of occupants of the building. It requires designers of building to ensure that escape routes to be easy access to the building and be named fire exits, they should be not be the same place with normal entry route. This place should be lead to safety area and outward of the building and should have illuminated signs. In case of storey building they should be evacuation stairs or lobby which has fire proof walls. Before the house is constructed, the standard recommends that risky profiles of occupants should be considered in order to calculate the width of the escape route. For example the risky profile for a house whose occupants are expected to be awake throughout and familiar with building will require to a width of 3.3millimetres to 4.6 millimetres as minimum width per person for escape route. This is incomparable to participants who are not familiar with the building or are likely to be asleep in the building. However the risky profile is determined by the materials that are used for construction. Materials which are likely to ignite fire fast will require a larger width as compared to those that are slow in catching fire. Therefore the requirement of B1 of building regulation highlights clearly options that are available to designers of buildings in designing escape routes. The door should have proper colours indicating that it is escape or fire exit door and it should not be locked. In tall buildings doors that lead to protected escape routes should be constructed using fire resisting materials and they should be considered a place of relative safety once an occupant enters the stares. The same buildings should have places of ultimate security that is open air and is not restricted. This means escape routes are not supposed to lead to a closed room or yard unless it is so large to accommodate all the occupants of the buildings and it’s far away from measureable heat and smoke from the building. The aim of the standard is to provide a guideline that will enable quick and safe evacuation of occupants of a building. It also provides the width of fire escape routes required in any building. The standard states that when a building is expected to host 60 people it will require 750 millimetres of fire exit while 220 people and above with require 5millimetres per person. Tall buildings are also expected to have more than one fire exit because smoke, fire affluent, and heat may prevent people from using one. The following table shows clearly how the standard recommends escape route to be designed. Occupant characteristics Fire growth rate Risk profile Minimum width per person(mm) Occupants are awake and familiar with the building. Slow A1 3.3 Medium A2 3.6 Fast A3 4.6 Ultra-fast A4 - Occupants who are awake and unfamiliar with the building Slow B1 3.6 Medium B2 4.1 Fast B3 6.0 Ultra-fast B4 - Occupants who are likely to be a sleep or are unmoved because of state of mind Slow C1 3.6 Medium C2 4.1 Fast C3 6.0 Ultra-fast C4 - ASET and RSET and standard UK guidance Available Safe Escape Time and Required Safe Escape Time have incorporated in standard UK guidance through BS7974 to govern the design of buildings escape routes. The main purpose for principle of available safe escape time and required safe escape time is to provide necessary time that will enable occupants of a building escape from fire. The difference between the two is called margin of safety time which is necessary to enable the occupants to reach a place of safety. This guideline has been incorporated in UK regulations under standard BS 7974. In the standard, it provides that it is essential to have adequate evacuation time after taking into consideration travel time, alarm time, detection time and response time. The provision relating to the principle of ASET and RSET states that the margin of safety is the difference that is obtained when required evacuation time is subtracted from available time to escape from fire. This means that the principle which is incorporated in the standard ii useful in determining life safety of the building. The principle further explains that really evacuation time is the time that is taken to evacuate all occupants from the building. These times are obtained using simulation dynamics after obtaining occupant’s characteristics, fire management strategies and intervention effects as inputs (Spearpoint, 2004). The principle recognizes that, the condition of the fire and ability of the occupant to respond to fire either because they are familiar with the building or asleep will determine the size of width that will be used when designing. The building layer out and rescue facilities provided will determine the evacuation time. It provides guidance on escape and evacuation in case there no fire and when there is fire. The Simplified schematic of processes involved in escape time compared to available safe escape time is shown in the diagram below; (British Standards Institution, 2004) Required time for safely escape is summation of recognition time, detection time, travel time and response time while evacuation time is pre-movement time and travel time. This means that RSET will depend on ignition time, detection time, alarm time, response time, travel time and pre-movement time. The pre-movement time is time that one recognizes of fire incident and time taken to respond to fire alarm. From the figure there is detection time which is time taken to detect fire from ignition. This is done by equipment installed or a human being to help to raise an alarm. People learn about the fire when hearing an alarm and smoke or flame or even or reactions of other people are called recognition time. Travel time is usually variety because human behaviour and ability influences reactions. Some people may assume all warnings until they are reminded by colleagues. It is also determined by the characteristics of the buildings such as fire management strategies and warnings provided (Purser and Bensilum, 2001). Recognition time is time one takes to detect that it is fire from time the alarm went off or a warning issued. This time various from individual to individual since not all people may be at the place of fire. Using BS 7974 the following formulae is proposed to use to Estimate Required Time for Safely Escape RSET=++(+) Where is time taken to detect fire from the time it started while is the time take to raise an alarm from the time of detection. is pre-movement time. After estimating one need to estimate which time is taken to travel to within the building as one is escaping. presents time occupants of building travel to safety lounge. In the calculation of this time various things are taken into account like dead-ends, overcrowded areas, travelling time of people into and out of building. Thus it is important for one to consider cognitive functioning ability of the users of the building before estimating. Most will need to gather further information before beginning to evacuate from the building through phone calls, warnings from neighbours and management before evacuating. This time is determined by gender, population of the occupants, age and health of occupants. The factors that affect evacuation various which include Number of people and their distribution, Social connections, Ability to move, Role and responsibility, Location of escape routes, Directed and specific attention, Influence of smoke and Layout of escape routes. The number of people in the building as well as their distribution influences evacuation time taken; if the number of people is large and in one room a stampede may occur due to confusion. The occupants’ ability to move from one point to another safely will determine the evacuation; the children and disabled ability is different as compared to other individual (Purser, 2009). The location of the exit route is situated and its layout playing an important role in evacuation of individuals from a building. Thus the layout and location of the evacuation route should be in a position reachable by evacuees and other individuals involved in evacuation. The other factor that plays an important role in evacuation is smoke from the fire, smoke may affect visibility thus reducing ability to evacuate of escape from the building. Smoke can make decision of evacuation complicated to occupants by reduce visibility as well as ability of effective evacuation (McGlennon, Montgomery and Turner, 2009). Available safe escape time is time available to occupants to escape from the building. The main differences between required safe egress and Available safe escape time will determine whether will have causalities’ in case the fire breaks out. When the Available safe escape time is greater than required safe egress there will greater casualties this will require redesigning the escape routes according to the standard. To have a proper design ASET and RSET differences will be used as a criterion for safety measure. However these values will have to be approved by relevant authorities before the construction of the house continues. Calculation of ASET and RSET The figure below shows the process involved in escape from fire. It provides various time used in the escape. According to the figure, there is a margin of safety which is the difference between available safe escape time required safe escape times. Their formulas are as follows. Margin of safety =ASET – RSET RSET Is determined as follows RSET =+++ Where detection time is, is alarm time, is pre movement time and is travel time. Let me assume a two floor residential house with a population of 80 people but suppose to have 100 people. In this group you will find children, a sleep people, people with poor state of mind. We assume detection time is 42s and alarm time is 10s and ASET is assumed to 120s Evacuation time (+) = P/WN + Ks/V (Tzu-Sheng Shen, 2003) Where P = total number of occupants, W is the width of escape route in metres N is (persons/m/s) Ks is the distance to covered by the population to safety assumed to be 65m on average , V is the speed of the escapees which is assumed to be 2.5m/s . We use the following table to estimate RSET Occupants who are likely to be a sleep or are unmoved because of state of mind Slow C1 3.6 Medium C2 4.1 Fast C3 6.0 Ultra-fast C4 - Evacuation time = 80/4.1 x 3) + (65m /2.5) = 32.5s Thus RSET =+++ is 30s + 10s + 32.5s RSET =72.5s Marin of safety in this case is =120s – 72.5s = 47.5s Discussion, Analysis and Conclusions Fire outbreak in a building can be very devastating to occupants thus the need to have proper safety measures which are efficient, cost effective causes no or very minimal harm. Evacuation from such incidences will depend on fire detectors, escape routes, population in the building and their ability fast acting, to intelligently to sense fire before erupting hence sometimes provides an automatic safety (Chow, 2006). Human behaviour also is important determining evacuation from the building. The escape routes in most buildings in UK are regulated in BS7974 which requires fire escape means to be designed in a manner that ensures smoke does not spread across the route and choke occupants escaping. The standard requires exit routes to be wide to enable familiar and non-familiar occupants of a building to escape from fire when it breaks out. Escapes routes from fire should have fire fighting equipment as well be constructed with materials that are fire proof. The evacuation route should not take more than 2.5 minutes to reach in any place in the building. The materials of construction or finishing for the escape route should suitable non-combustible which possess fire resistance tendency. It also provides that stability, integrity and insulation of the exit stairs or routes are of paramount important. Any architects who follow this standard are assumed to provide enough protection to occupants of buildings while those who try to ignore are asked to repeat their work the relevant authorities. When there is too much smoke occupants will stumble, go different direction from exit route or hide in a certain corner depending his age, state of mind or level of education. Level of crowding can also affect evacuation from a building thus it is necessary to design with number of occupants to patronise the building in mind. How ever, some building will not use prescribed means of escape with approval from relevant authority because of the special features that it may posses in this case fire engineering approach is used where there are no standard figures for the design of escape route but what is determined from simulation and in this case timeline approach to estimate the evacuation time of the building occupants becomes very important. Conclusion The owners of the building are required to make provisions for fire escape routes that will be used by occupants during the time of fire outbreak. It is required that a building should have a wide travel space which will enable both familiar and non-familiar occupants of a building to escape from fire. There should be ideal heating and ventilation in the building to enable proper circulation of air and temperature. The door ways of a building should be labelled with proper colours or signs that indicate the escape routes in case of fire. When a place where the people has objects and the exit route is far then Available safe escape time to occupants to escape becomes too large as they have to negotiate the route with the object(Chow, Fong, Pang, Lau, and Kong, 2006). The factors that are considers in determining the time of evacuation or escape which include level of alertness, number of people in the house, mobility, mental tolerance, role and responsibility and level of education. The figure below shows time taken by humans in responding to emergencies. This affects significantly safer evacuation when it comes to effects of smoke, the presence of children and disabled people. Smoke will cause fear and decreased visibility among the occupants leading to fear and over reaction to the situation which may cause stumble. References British Standards Institution (BSI), 2004. BS 7974-6:2004, The application of fire safety engineering principles to fire safety design of buildings – Part 6: Human factors: Life safety strategies – Occupant evacuation, behaviour and condition, BSI, London,UK. Chow, W.K., Fong, N.K. Pang, E, Lau, F. & Kong, K., 2006. Case Study for Performance-Based Design in Hong Kong. Paper presented at Society of Fire Protection Engineers – 6th International Conference on Performance-Based Codes and Fire Safety Design Methods on 14-16 June 2006 by Professor W.K. Chow Chow, W.K., 2006. “Fire engineering approach and discussion on the design fire,” 6th International Conference on Performance-Based Codes on Fire Safety Design Methods, June 14-16, 2006, Tokyo, Japan – Paper to presented, June, 2006. Government of Ireland, 2006. Building Regulations 2006- Fire Safety. Dublin: Stationery Office Harold, E., Nelson B. & Mowrer, F.W., 2002. “Emergency movement”, The SFPE Handbook of Fire Protection Engineering, National Fire Protection Association and Society of Fire Protection Engineers, 3rd edition, Quincy,Massachusetts, USA, pp. 3-367 – 3-380. McGlennon, M., Montgomery, S. & Turner, B., 2009. Promoting Safe Egress and Evacuation for People with Disabilities. National Disability Authority Purser, D. 2009. Human Fire Behaviour - and Performance Based Design. Institution of Fire Engineers 2009 AGM Conference and Exhibition 1-2 July 2009< www.ife.org.uk/about/.../Purser_Human_Fire_Behaviour_24June09. >[ Accessed on 31st January, 2013] Purser D.A. & Bensilum, M., 2001. “Human behaviour in fire and other emergencies”, BRE Report 80893, Fire Safety Engineering Centre, UK. Spearpoint, M., 2004. “The effect of pre-evacuation distributions on evacuation times in the Simulex Model”, Journal of Fire Protection Engineering, Vol. 14, No. 1, pp. 33-53. Tzu-Sheng Shen, M. S, 2003. Building Planning Evaluations for Emergency Evacuation. A Dissertation submitted to the Faculty of the Worcester Polytechnic Institute [ Accessed on 31st January, 2013] Read More