Requirement of B1 of the Building Regulations - Report Example

ASET AND RSET PRINCIPLES WITH REGARDS TO MEANS OF ESCAPE By Student’s name Course code and name Professor’s name University name City, State Date of submission Introduction Guidance B1 of the British Building Regulations was established in order to address early warning of occupants against fire in order to facilitate safe egress. This document guides design engineers in incorporating sufficient escape routes, suitably located as a boost for dwelling houses safety when dangers associated with fire erupt. In coming up with this guidance B1, it is clear that the incorporated codes conform with ASET(Available Safe Egress Time) and RSET (Required Safe Egress Time) principles methodologies which have been investigated over years thereby becoming important yardsticks for establishing levels of tenability. Although there are other equitable principles such as FAST (Model for smoke and toxic gases transport), ASET RSET has been given a wider coverage due to the consistency that it poses towards ensuring safe occupancy. As a result, guidance B1 has assimilated the ASET RSET principle in coming up with most of its clauses as shall be described in this article. Therefore, during practice, document B1 requires design engineers to deploy applicable methodologies as long as they ensure conformance to the set regulations that govern the British Building Regulations. These methodologies range from BS7974, FDS or CFAST modelling and evacuation simulations such as pathfinder among others. Therefore as part of analysis, this report uses BS7974 modelling example calculation in order to stage some of the facts that are usually applied in conforming to guidance B1. Requirement of B1 of the Building Regulations Document B1 of the building regulations is a detailed guide to provision of timely and sufficient fire warning to people residing within a dwelling as per the standard ASET RSET convention. It also details the fact that the escape routes provided by the designers should be located suitably in order for people to vacate with ease in case of a fire. It also highlights the importance of protecting the escape routes sufficiently in order to create enough grace period for the egress of occupants with respect to the time required to render a living space untenable. As a requirement, all buildings that already exist and those upcoming are mandated to embrace these codes accordingly (HM Government, 2013). The assumptions made while drafting this document put in consideration the fact that the external rescue may not be fully dependable and that the rescue service might also not be availed at all times. As such, the buildings should be designed in a manner that the occupants may be able to vacate without external assistance. Guidance B1 further clarifies that for single or double storey dwelling buildings, it is mandatory for the designers or builders to provide windows that can be easily opened in case of an emergency evacuation in order to increase the ASET time as compared to RSET (HM Government, 2013). Building engineers are required to bear in mind the means of escape that shall be incorporated in a building during the design phase. Smoke alarms for example should be installed in areas deemed risky to the people who shall be residing in a given building at the time of emergency. While conducting an assessment for the purpose of smoke alarm positioning, the document points out the important criteria as; the nature of the building, the purpose for which the building is constructed, the possibility of fire spreading in the building and the proposed fire safety management methodology. Apart from the smoke alarms placement, the building should be designed in such a way that ensures elimination of primary dangers associated with fire such as noxious gases. Therefore, the design should be made in such a way that limits quick spread of fumes and smoke (HM Government, 2013). Conventions listed in B1 also highlight positioning of heat and smoke alarms with regard to habitable spaces. Smoke alarms should always be positioned in areas where fires are most likely to occur such as bedrooms, living rooms and kitchens. Building designers are guided to have all dwelling houses furnished with at least one smoke alarm for every storey. In cases where the stairways or circulation spaces are not separated clearly, interlinked heat detectors and smoke alarms should be installed to cater for safe egress. For proper functionality, the smoke alarms must be mounted within a spacing of 7.5m in the circulation spaces (HM Government, 2013). The criteria applied in designing the means of escape is also set in the requirement list of B1. It is clearly stated that there should be alternative means of evacuation from the scenarios that may arise at any given time. This document requires building professionals to ensure that wherever direct escape is not viable, it is paramount to ensure that the building occupants reach the designated area of safety by any means possible. In so doing, the document details such means as protected stairways that lead to the exit route but within a reasonable travel distance. Apart from this condition, it is also made clear that single direction escape i.e. one way can be accepted under conditions that the risks associated with fire in the building are low. The evacuation process singles out unacceptable means of escape which include portable ladders, lifts (unless designed for emergency purposes) and any other apparatus that requires manipulation (HM Government, 2013). The increasing height is diversely mentioned within the document due to complexity in provisions that may be required in emergency egress. The hazard associated with egress from the windows of storey buildings thereby calls for provision of a safe alternative towards the implementation of the emergency safety when need arises. The escape provisions are detailed in document B1 with the major issue at stake being the emergency egress to the dwellers. Ground storeys are required to have direct opening towards a suitable exit or be provided with a window whose dimensions are at least 450 x 450 mm and not greater than 1100 mm above the floor for quick accessibility. Buildings which are basically 4.5m above the ground should be furnished with two escape routes to say the least. Further, the separation medium between the lower and upper storey should be fire resistant in order to avoid any possibilities of fire spreading. Document B1 stresses the importance of having a protected stairways and sprinkler systems for buildings that are about 7.5 m above the ground level (HM Government, 2013). The means of escape are identified accordingly with their alternatives listed for further guidance. Galleries for example are expected to contain emergency egress windows as per the standard mentioned above for escape to be viable. The cooking facilities provided in such rooms are also required to be bounded in fire resistance enclosures. It is a requirement that all basements be furnished with external doors, windows and/ or protected stairways leading to the exit. If in any case the escape stairs are provided, the access doors should be made fireproof to eliminate any possibility of a fire. An air circulation system for dwelling houses that are built 4.5m above the ground level should have provisions to retard smoke and fire into protected escape stairways. A breakdown is given on enclosure protection for ventilation within the protected stairways. Mechanical ventilations are required to be designed in a manner that allows shutdown in cases of emergency. Thermostats should also be mounted at a height range of 1.37m to 1.83m with a maximum setting not exceeding 27°C. The only acceptable passenger lifts for emergency purposes should be protected from effects of fire. All these conventions are required for any dwelling whether existing or upcoming. It is further stipulated that existing buildings that do not meet the above conditions should be altered accordingly (HM Government, 2013). ASET RSET and How It Is Incorporated In to Standard UK Guidance Available Safe Egress Time ASET was hypothesized by Cooper (1983) as the time span between fire detection and the beginning of hazardous conditions also referred to as inhabitable conditions. Required Safe Egress Time (RSET) on the other hand refers to the amount of time that is required for safe evacuation of occupants during times of emergency (Grant & Pagni, 1986). The variables of these two principles have been found to be of utmost importance towards human habitat safety when it comes to fire and related catastrophes. Guidance B1of the British Building Regulations is one such beneficiaries of these principles owing to the incorporation of ASET RSET principles for the purpose of instilling order within the industry. To begin with, the performance guide in B1 is enough prove of ASET RSET incorporation within the British Building regulations. In order to provide sufficient means of warning in case of fire, the designers have to engage in calculations prior to implementation of a warning system. These design calculations are usually based on ASET RSET principle which is also responsible for the design of the fire alarm. RSET is calculated using the formula (1) below: 1 (1) Where = recognition phase, = coping phase, And = escape phase. ASET on the other hand is incorporated in BS7974 as time available for safe egress considering that fire leads to an untenable condition. In order to initiate an alarm when hazardous conditions commence, the available time is worked out basing on the volume of the dwelling and probable occupancy at the time of fire. Therefore all the notification systems installed in a building should conform to ASET time. ASET is calculated by the formula below: (2) Where, is the onset time for hazardous conditions. is detection time. is notification time. The variables above help designers in achieving guidance B1 abiding egress measures. The ASET RSET scheme has been found to be satisfactory enough especially when it comes to accommodating human activities that are of essence in safe evacuation. This methodology delivers maximum escape time that is pointed out by the first clause based on past experiments and design experience. Other parameters such as human behaviour do not however feature in document B1 owing to the complexity that this might pose to designers (Grant & Pagni, 1986). The second clause in the B1 guidance document about the performance states that the egress routes should be of sufficient capacity to handle the population residing in a given building. The ASET RSET principle is applied critically when determining the number of routes in order to allow for safe egress to all occupants. The time aspect with regard to escape is also given importance when it comes to design of dwelling houses’ escape routes as evidenced in the means of escape section. It is noted that as the building continues to rise the distance of escape continues to increase thus alternative means should be considered by designers. Citing an example that is incorporated within the B1 guide further expounds the existence of ASET RSET principle as shown by section 2, provision 2.5. In this case the guidance document clearly states that for dwelling houses of more than 4.5m above the ground level, the escape routes should be protected so as to offer a conducive escape environment to the occupants. According to Klingsch et al. (2008), temporal factors of egress should be considered in coming up with a design for a building. The temporal factors such as the ones identified by guidance B1 are very important in industry regulation. The ASET RSET principle is utilized as an approach to egress safety and occupant assurance. Design and installation of fire detectors and alarm systems is given a wide coverage in guidance B1 owing to the contributions that ASET RSET have brought towards ensuring safe egress to occupants. Installing fire alarms and notification systems is expected to boost safe egress to the occupants and in places where risk is classified as special, additional detectors should be provided (Society of Fire Protection Engineers, 1999). Document BS9999:2008 also goes to detail about the allowable risk time and the principles of means of escape. Designers are given a breakdown of the pre-movement time, travelling time and actual evacuation all which are the major ASET RSET components as presented in the relationship chart below: Figure 1: A depiction of ASET RSET (BSI Standards, 2008). It is mandatory that all the alarm systems designed for the sake of fire should have timing that allows for RSET to be smaller than ASET. Ensuring that the notifications systems conform to this standard principle gives more confidence in buildings designed. Ensuring that the notification systems are positioned well gives the occupants safe egress by maximizing ASET. In the past conferences have been convened to offer a straight forward guidance to design and installation of notification systems with a rise of such conventions as BS 5839-6 and BS 5839-1 with regard to usage and maintenance (HM Government, 2013). Drills should however be carried out from time to time to ensure that alertness of occupants with respect to notifications timing for the purpose of ASET maximization and proper setup. Guidance B1 is stringent when it comes to external escape mechanisms provided by the design engineers. Apart from the fire notification systems, fire redundant materials have been designed to match the requirements of ASET RSET. Material design is performance based and should not be compromised by any means. The approach employed in order to eliminate doubts of whether a material can resist the fire beyond a given period is the fact that ASET should be greater than RSET in order to allow for safety (REAX Engineering: Expert Fire Consulting, 2013). Determining ASET RSET Time Using BS7974 Methodology The formulas used when deriving the design figures under document BS7974 “Application of fire safety engineering to the design of buildings” are contained CIBSE Technical Memorandum TM19: 1995. The most vital ones include: (3) Assuming a fast engulfing fire for safety purposes we have, (4) (5) (6) (7) (Tanaka, 1999). This example takes the form of a low-pitch portal building whose ridge is located 13 meters while the gutter is situated 12 meters from the ground. Assuming that the building dimensions are 60x40 meters for length and width respectively, a fire is ignited at the centre. The only ventilations designed for this building are located on the door and only open on occasion of fire. It is also assumed that there are no tangible heat losses apart from that radiated through the plume. The scenario for ASET and RSET time is initiated when the smoke fills down to a range of 5 meters and 2 meters respectively. During the design stage, the design engineer shall be required to determine whether the occupants are safe to egress within a period of 3 minutes after ignition. Consider that; the ambient air temperature is given as 15°C, density of air is 1.2kgm-3, specific heat of air is 1.92, fire growth parameter is 0.0444kWs-2 and virtual height above fire base is 0. Equation (3) below has been derived for standard BS7974 calculations. Substituting the above information in equation (7) and solving in a spread sheet, we have 325 seconds and 488 seconds for ASET and RSET respectively. The conditions are therefore tenable to the occupants for a period greater than the suggested 3 minutes (180 seconds). This in comparison with ASET gives a surplus time period of 145 seconds which is even 2 minutes greater than the initial anticipated period. The total egress time is 813 seconds after which the dwelling is rendered totally untenable. Discussion and Analysis Smoke is a very important phenomenon in estimation of the safe egress conditions within BS7974. Design example above establishes that smoke height in single compartment can be used to the advantage of the fire engineers and dwelling designers in order to better the egress conditions through the ASET RSET principle. One of the approaches applied in ASET RSET estimation is coming up with time based egress analysis through fire escape design, assessment of the time taken for evacuation and confirmation of the onset of hazardous condition (Tubbs & Meacham, 2007). A prediction of smoke build up is therefore one of the major variable that should be deployed when coming up with safe egress time from time to time. Smoke height prediction charts have also been derived by those championing for CFAST method of egress calculation. An example of smoke spread in a 4m high living space is shown in the graph below which was derived in a CFAST model as a basis for future design arguments (Chung et al., 2005). Figure 2: Predicted smoke levels in slow fire conditions (Chung et al., 2005). It can be noted from figure 2 above, the smoke effect cannot be of extreme danger in a slow spreading fire. It is established that it does not really matter which type of ASET RSET simulation or calculation methodology is applied between CFAST of BS7974 since they are all based on the same principles. In cases where mechanical exhaustion is simulated the egress conditions are worsened and may be catastrophic. According to guidance B1 (HM Government, 2013), the evacuation design should be well equipped with fire redundant material in order to establish safe egress conditions. With time BS7974 methodology of calculation of ASET RSET times has been incorporated in most design measurements that are carried out in the regulation other documents. Given chance and time, CFAST methodology shall also develop into one of the preferable ASET RSET approach for use for design purposes owing to its ability to determine the toxicity of emissions given in a bid to conserve mass and energy (Chung et al., 2005). Conclusion This report successfully depicts the requirements of guidance B1 and the incorporation of ASET RSET within BS999:2008 for successful building and construction industry regulation. Coming up with a design for a dwelling house requires clear calculations to be undertaken as a matter of establishing the conducive egress conditions for occupants to avoid fire danger in case of emergency. Actually, most of the fundamentals mentioned in this report reflect the British Building requirements in accordance to approved document B. The ASET RSET principle is approached using the BS7974 methodology to establish the required parameters through smoke circulation. This methodology establishes the inhabitable conditions on a dwelling based on the fact that the fresh air for human survival gets diminished as the smoke blanket gets thicker. List of References BSI Standards (2008) United Kingdom of Great, London: BSI. Cetegen, B.M., Zukoski, E.E. and Kubota, T. (1984) 'Entrainment in theNear and Far Field of Fire Plumes', Combustion Science and Technology, vol. 39, pp. 305– 331. Chung, K.-C., Tung, H.-S. and Wu, Y.-L. (2005) 'Applied Zone Model to Evaluate the Smoke Management in an Underground Structure', Journal of Fire Sciences, vol. 23, pp. 0099-0117. Grant, C. and Pagni, P.J. (1986) 'Towards an Integrated Egress/ Evacuation Model Using an Open Systems Approach', Fire Safety Science: Proceedings of the First International Symposium, Berlin, 581- 590. HM Government (2013) The buildings regulations 2010, London : HM Government. Klingsch, W.W., Rogsch, , Schadschneider, A. and Schreckenberg, M. (2008) Pedestrian and Evacuation Dynamics 2008, Wuppertal: Springer. Nakamura, N., Yamana, T., Matsushita, T. and Wakamatsu, T. (1992) 'Research on Smoke Control in Underground Structures', Tunnelling and Underground Space Technology, vol. 7, no. 4, pp. 325–333. REAX Engineering: Expert Fire Consulting (2013) Fire Protection Engineering, [Online], Available: http://reaxengineering.com/services/fire_protection_engineering.html [5 February 2014]. Society of Fire Protection Engineers (1999) 'Does Performance Based Fire Engineering Lead to Safer Designs for Hospitals?', Fire Research and Engineering, Third International Conference Proceedings, Chicago, Illinois, 123-149. Tanaka, T. (1999) 'Performance based fire safety design standards and FSE tools for compliance verification', International Journal of Performance-based Fire Codes, vol. 1, no. 3, pp. 104-117. Tubbs, J. and Meacham, B. (2007) Egress Design Solutions: A Guide to Evacuation and Crowd Management Planning, New Jersey: John Wiley & Sons. Read More