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

Review of the Principle of ASET and RSET with regards to Means of Escape Name: Lecturer: Course: Date: Table of Contents Table of Contents 2 Introduction 3 Background analysis 4 Requirements of B1 of the Building Regulations 4 ASET and RSET 5 Example calculations: British Standard 7974 7 Discussion 10 Analysis 12 Conclusion 13 References 14 Introduction In fire safety design, the application of engineering principles for purposes of understanding the effects and phenomenon of how people behave towards the fire in order to protect human life, property, and environment from the destructive effects of fire is critical (Billington et 2002, 2). Institutions like the British Standards Institute use the same underlying principle in setting up the required standards (Fire Protection Association 2014, 284). In most cases, this involves the modelling or calculation of scenarios that address all or several parts of the fire system. Using the same principle, this assessment bases its assumption on the premise that designing the protected routes is dependent on the designated use of the building and the risks of fire inherent in that particular use. In circumstances where the risks exceed the distances needed to travel to safety, the protected route has to be shorter (Billington et 2002, 2-3). This draws attention to the concepts of escape routes, means of escape and the required safe egress time (RSET) and available safe egress time (ASET). Basically, the escape routes include the range of components, such as stairways, lobbies and corridors, each of which need to be constructed from a desirable fire-resistant materials and detached from the adjoining areas using fires-resistant doors (Fire Protection Association 2014, 284). Means of escape comprise the assigned routes within a building that allow individuals to access a place of safety relatively fast without having to travel through expansive distances or delayed through jamming and to ultimately reach a safe place. Based on this backdrop, this paper reviews the principle of ASET and RSET with regards to means of escape. Background analysis Requirements of B1 of the Building Regulations Part B section B1 of the Fire Safety Building Regulations 1997 is concerned with the means of escape in the event of fire and requires that a building be designed and build in a way that it has sufficient means of escape in case of a fire, from the building to a relatively safe place outside the building, which can be used safely and effectively (Department of Environment, Heritage and Local Government 2006, 12-14). As a matter of fact therefore, B1 seeks to ensure that a building is provided with adequate standard of means of escape for the occupants in the event that fire occurs in the building. The performance requirements of the B1 are attainable when there are sufficient amount and size of routes that are well situated to allow people to escape to safe place when fire occurs. Second, when the routes are adequately protected from the effects of fire in regards to closure as well as in the application of materials in the routes. Third, when there the building has adequate lighting, alarm to warn the people in the building and smoke control mechanism to enable the people to escape safely (DEHLG 2006, 12-14). Hence, the underlying principle of the B1 requirement is that the occupants of a building should be able to make a safe escape during an emergency without necessarily an external assistance. Basing on the B1 requirement, emphasis is also drawn to the idea that alternative legislations may enforce certain provisions for means of escape in the event of fire that the building has to comply with and that operate when the building is in active human use. In this regard, the key legislations include the Fire Services Acts 2003 and the Safety, Health and Welfare at Work Act, 2005. The design of the building should therefore be carefully examined component by component in order to determine the risks of fire, where the fire originates, as well as other sections of the building that the fire may spread. As Grosshandler (2006, 11) comments, fires seldom start in two separate locations within a building simultaneously, as well as initially where a fire creates a hazard as well as in the section it starts and is not likely to involve in an expansive area. ASET and RSET When it comes to design fires, determining design fires is an integral task in fire-safety engineering design. According to Purser (2002, 91), the transitory fires that have a realistic growth phase are needed for reasonable calculation of time in order to ensure detection as well as the values of available safe egress time (ASET). At this rate, the concepts of required safe egress time (RSET) and available safe egress time (ASET) are significant. Fire Protection Association (2014, 284) defines ASET as the maximum time needed for occupants of a building to move to a safe place. ASET also refers to the calculated time that is available between when the fire is ignited and the time that is tenability (acceptable to a reasonable person) criteria are surpassed within a particular space inside a building. Indeed, the underlying principle of the UK’s B1 requirement is that the occupants of a building should be able to make a safe escape during an emergency without necessarily an external assistance. The requirement is consistent with the principle of ASET and RSET. ASET and RSET are two distinct measures used for assessing the effective of the evacuation plans, which are particularly consistent with the B1 requirements. In fact, RSET refers to the period of time that occupants of the building are likely to take in order to evacuate a building safety based on inherent human factors such as human behaviours and human perception (Fire Protection Association 2014, 284). On the other hand, ASET is the time likely to be taken for a worst-scenario fire to make it impossible to escape or evacuate a building safety based on evaluation of the risks. By comparing the RSET to the ASET, determining a viable escape is possible. Purser (2002, 91-92) argues that the ASET and RSET should both begin at the same time, such as the period when a fire is started and when it is detected. Additionally, they should both end when the occupants escaping have ultimately reached a place of relative safety. At this rate, the key assumptions should include the number or individuals within the building as well as how many need to be assisted. Based on the B1 requirements, a life-safety design should be contingent on the comparison between the time needed to escape from a building in the events of fire (RSET) and the time to the loss of tenability (ASET). The two factors include a number of stages or processes that call for a range of input date. A challenge for the design engineer however is that while these stages have to be addressed in order to acquire a realistic outcome required for analysis, several other aspects can be understood and measured, while other are overestimated and overlooked. Indeed, Billington et (2002, 2-3) suggests that comparing the time needed for escape (RSET) with the time available for escape before conditions become indefensible (ASET) is usually the starting point of life safety assessment. RSET is contingent on a sequence of processes that include the time from ignition to detection, the time from detection to providing warning to the occupants to evacuate, the evacuation time and the pre-movement time, which comprises the time the occupants are informed of the emergence as well as when they start to move to the exits and lastly, the travel time, which is the time needed for the occupants to travel to a relatively safe place or point (Fiona 2008, 234-36). For the purposes of warning, detection, response time and pre-movement, studies on human behaviour, such as that conducted by Purser (2002, 92-94), have basically been qualitative due to the complexity of the behaviours of the occupations in the events of fire emergencies and the significance of these behaviours relative to the escape time. They include the largest components of the time needed for escape. In spite of this, Fiona (2008, 234-36) reveals that there has been limited attempt to quantify the broad scope of behavioural phenomenon as well as the interactions between them. Hence, it is difficult to apply them in order to escape time calculations. As Grindrod (2014, iii) explained, when the evacuees move in different directions in a confused manner, the intended routes may lead to the increased possibilities of causing confusion. In the UK’s standards outline by B1, efforts have been made to link the type of alarm or the warning system to the pre-movement time. However, in some situations the characteristics of the occupants and the safety management system are critical. Therefore, there is a need to evaluate the time with a sufficient consideration of pre-movement time and the premovement time distributions. This comprises physically-based processes that are more open to the design calculation methods. Still, the travel time relates to the pre-movement times and is vulnerable to the behaviours of individuals, such as the choice or exits and routes for escape. Example calculations: British Standard 7974 In quantifying the fire behaviour and its effects on the property and human life, technical guidance of assessment of varied fire safety sub-systems becomes critical. The British Standard 7974 provides a guide on the main factors using mathematical relationships as well as some input data. BS7974 address the technical issues linked to fire-engineering approached design. The sub-systems necessary for quantifying the fire behaviour in buildings and its effects on property and life can be summated as: First is the process of initiating and developing fire in enclosure of origin. Here, the growth, and size of fire in the early stages of ignition and growth, to flashover and when the fire is fully developed. Next is the spread of smoke inside and beyond the enclosure. Here, the smoke control calculations are carried out combined with the effects of the exposure to heat and smoke. Next is the exposure of the structure and the spread further than the enclosure. Here, the heat and temperature influx are calculated. Next is the fire detection and activation of fire detection systems. Also to be calculated include the fire service intervention, where the calculation is for designing the response time, and the evacuation and control. Lastly is the evaluation, where the evacuees’ responses are assessed (Fiona 2008, 234-36). For instance, in a scenario, the rate at which the compartment will become filled with smoke and to determine the time the smoke takes to fill at the flow level to within 5 meters and 2 meters, it can be determined whether the occupants are safe and can leave the building within 8 minutes after the fire starts. For instance, in calculating the time smoke takes to fill a portal framed compartment by assuming that a t2 grows fires while there is no roof ventilation. Additionally, the 2-bay building has a valley gutter is at 12 meters while the floor level is 13 meters at the flow level. In addition, the building has a width of 50 meters and length of 60 meters. At the same time, it has an exhibition item within the centre that when ignited will burn away at t2 fire. In the scenario, it is assumed that there are no vents within the roof while there are doors that open once smoke is detected, to allow air. Additionally, two-thirds of the total heat that is released is transmitted as heat in the plume. From the above data, it can first be supposed that under the worst scenarios, the height of the plumes is kept constant as time advances. Once the above data is substituted, the results is: Time the smoke layer takes to reach 5 meters from the flow level = 352 seconds. Time the smoke layers takes to circulate down to 2 meters from the flow level = 455 seconds. Once it is assumed that the air entrainment manages to reduce, the smoke layer rises in thickness, which means that z reduces. What is obtained is: time for the smoke layer to reach down to 5 meters from the floor level = 534 seconds, time for the smoke layer to circulate to 2 meters from the floor level = 700 seconds Hence, it could be concluded that the smoke will take between 488 seconds and 700 seconds to reach the 2 meters of the floor level. In which case, is the evacuees evacuate the building within 700 seconds, they would be safe. The situation would therefore be tenable. Discussion Critically, the principle objectives of BS 7974 and FDS are to protect human lives instead of the building and the property inside the buildings or to maintain business continuity. Indeed, B1 requirements are also contingent on this objective. Ultimately, focus is placed on human behaviour. In respect to comparing ASET and RSET, it is reasoned that the behaviour of the occupants who are involved in escape are dependent on the varied factors, such as the characteristics of the building (including the method of fire detection, the type of occupancy and the layout of the building), the characteristics of the occupants (including the number of the occupants and the alertness of the occupants), and the situations where the evacuees are exposed to fire (Purser 2002, 92-94). Because the fire scenarios are tremendously changeable, design fire scenarios are usually applied to depict varied typical fire behaviours. The methods of measuring evacuation and escape time are applied to represent the design behavioural scenarios. Examples of the methods used for quantifying or measuring evacuation and escape time include the British Standard 7974 and the Fire Dynamics Simulator with Evacuation (FDS+Evac). In using the methods, the main qualitative aspects of the behaviours of the occupants are determined to design data for comparing ASET and RSET (Fiona 2008, 239). Purser (2002) however explains that the limitation of evaluation time is that most methods of calculation assume no interaction between the fire seepage and the occupants. For instance, when the evacuees become exposed to the irritant smoke, the speed of their movement is likely to become reduced. Fire Protection Association (2014, 284) showed that the waking speed is likely to be reduced by non-irritant smoke relative to the smoke density and that the effect is likely to become considerably high in the event of irritant smoke. In such a situation, a calculation method to be used should be that that predicts the travel speed relative to smoke and irritant levels (Grindrod 2014, 157). For instance, the toxic product brings up equivalent ratios for using in calculating ASET. In the case of the ASET time line, the tenability is misplaced when occupant incapacitation is forecasted from exposure to fire affluent. This is contingent on the time concentration curves for the fire effluents that are toxic, hence calling for inputs on smoke and toxic products, which are brought under different conditions. When it comes to spread of smoke and control of smoke, Purser (2002, 91) comments that RSET and ASET are not distinct deterministic values although they have probability distributions linked to them. A review has to take the safety of the occupants into consideration rather than the principle that the ASET has to be greater than the RSET. The two have to account for the time delay between when the fire is ignited and when it is first detected. Regarding RSET timeline, greater emphasis is place on the component of the travel time, which represents the evacuees’ physical movement through the escape routes. Despite this, the time needed for the evacuees to behave in certain ways before the pre-movement time usually represents the greater constituent of the total time of escape. The pre-movement time distributions are contingent on several features, including the type of occupancy, the warning, the characteristics of the occupants, the fire safety management strategies in place and the complexity of the building (Purser (2002, 92). Hence, a practical solution for the engineer is applying pre-movement time distributions measured from the monitored evacuations, the events of fire, as well as through the behavioural models. Still, the main problem with evaluation time is that most methods of calculation used assume there is lack of interaction between the effluent fire and the occupants. As outlined above, if the occupants become exposed to irritant smoke, then the speed of occupant’s movement is likely to reduce (Fiona 2008, 234). The ASET time-line, on the other hand, ends when the incapacitation of the occupants is calculated from exposure to the effluent fire. This is contingent on the time concentration curves for the high level toxic effluents, which requires the inputs of smoke and the other toxic elements produced from diverse conditions (Fire Protection Association 2014, 245). Analysis Basing on the principle of ASET and RSET and the requirement of the B1, within the context of UK, it can be reasoned that when accidental fire occurs, it is critically essential that a building has to be evacuated rapidly, safely and efficiently (DEHLG 2006, 12-14). At this rate, providing sufficient means of escape is critical to the design of a new building as well as to the changes in the use or the need to extend a building. In the case of the United Kingdom, the enacting of the Fire Precautions Regulation in 1997 has made it mandatory for the employers to assess the fire risks at the workplace, including the means of escape. As expressed by (Billington et al 2002, 2-3), for maximum efficiency, the means of escape need to be anchored in the standardised circulation routes within the building. Hence, a building that has a well-designed means of escape needs to function effectively and efficiently. In which case, the means of escape design principles need to be considered in the early stages of the project when the basic design decisions are being made that relate to the positions of entrances and exit, the patterns of the corridors and their widths, and the number of staircases and their location. Conclusion Designing the protected routes is contingent on the designated use of the building and the risks of fire inherent in that particular use. When the risks exceed the distances needed to travel to safety, the protected route needs to be shorter. It is based on this backdrop that attention is drawn to the means of escape when it comes to required safe egress time (RSET) and available safe egress time (ASET). Ultimately, focus is placed on human behaviour. At this juncture, it is concluded that in quantifying the fire behaviour and its effects on the property and human life, technical guidance of assessment of varied fire safety sub-systems becomes critical. The BS 7974 provides a guide on the main factors using mathematical relationships as well as some input data. FDS modelling also provides a means of calculating these factors. Critically, the principle objectives of BS 7974 and FDS are to protect human lives instead of the building and the property inside the buildings or to maintain business continuity. Indeed, B1 requirements are also contingent on this objective. In respect to comparing ASET and RSET, it is reasoned that the behaviour of the occupants who are involved in escape are dependent on the varied factors, such as the characteristics of the building Basing on the principle of ASET and RSET and the requirement of the B1 within the context of UK, it is concluded that when accidental fire occurs, it is critically essential that a building has to be evacuated rapidly, safely and efficiently. At this rate, providing sufficient means of escape is critical to the design of a new building as well as to the changes in the use or the need to extend a building. References Billington, M, Ferguson, & Copping, A 2002, Means of Escape from Fire, A Blackwell, Oxford Department of Environment, Heritage and Local Government (DEHLG) 2006, Building Regulations 2006: Technical Guidance Document B, viewed Jan 4, 2015, Fiona, T 2008, A Critical Study on Performance-based Fire Safety Design in Hong Kong with Timber Perforrate Ceilings as an Example, The Hong Kong Polytechnic University, Hong Kong, viewed 4 Jan 2015, Fire Protection Association 2014, Fire Safety and Risk Management: For the NEBOSH National Certificate in Fire Safety and Risk Management, Routledge, New York Grindrod, S 2014, Information Driven Evacuation System (I.D.E.S.), The University of Edinburgh, viewed Jan 4, 2015, Grosshandler, W 2006, Forum Workshop on Establishing the Scientific Foundation for Performance-Based Fire Codes: Proceedings - NIST Special Publication 1061, U.S. Department of Commerce Purser, D 2002, ASET and RSET: addressing some issues in relation to occupant behaviour and tenability, International Association for Fire Safety Science, Watford Read More