Fire Safety Design Requirements of UK Building Regulations - Case Study Example

CRITICAL REVIEW OF THE PRINCIPLES OF ASET AND RSET IN RELATION TO MEANS OF ESCAPE Table of Contents Contents Contents 2 REFERENCES/BIBLIOGRAPHY 19 List of Tables and Figures Tables Table 1- ADB Travel Distance Limitation 5 Table 2 BS 9999 Risk Profile Levels 8 Table 3 BS 9999 Travel Distance Limitations 9 Table 4- Floor space factors for Office 14 Table 5 ADB Min. Escape Routes and Exits 14 Table 6 - ADB Min. Width of Escape Routes and Exits 14 Table 7 Behavioural scenarios and occupancy types 15 Table 8 – Tenability limit based on temperature or heat 17 Figures Figure 1- Maximum Travel Distance in ADB 6 Figure 2- BS 9999 Timeline for Evacuation 8 Figure 3 Fire development and evacuation time relationship 10 Figure 4 One-Storey Office Building Means of Escape 12 Figure 5 CFAST Simulation of case study building showing surrounding temperature 16 1. INTRODUCTION/BACKGROUND Compliance to Building Regulations fire safety provisions is an important concern of building designers. For this reason, building designs often take into account the requirements in ADB’s B1 such as availability of means of escape from all points in the building, sizes of doors and stairways, the occupancy type and estimated number of occupants, travel time to place of safety in case of fire, human limitations, and the health and behavioural effects of smoke, heat, toxic gases, and other fire-related conditions. In Approved Document B for instance, provisions for alternative escape routes is a minimum requirement because of occupants travel limitations in relation to growth, spread, and associated harmful effects of fire. Since the safety of occupants is the main concern of building regulations requirements regarding means of escape, identification and evaluation of safety concerns during evacuation such as determination of available safe egress time or ASET and required safe escape time (RSET) is critical. This study critically reviews or examines the principles behind ASET and RSET in relation to Approved Document B means of escape provisions and BS 9999’s specifications for ASET and RSET calculation and application. The study also examine fire engineering’s principles and approach to ASET and RSET, the health and behavioural effects of heat and smoke, sample design calculation for one-storey office building specifications, analysis and discussion of findings, and conclusion/summary of this study . 2. ASET and RSET PRINCIPLES in B1 of APPROVED DOCUMENT In Section 1 or B1 of Approved Document B of the UK Building Regulation concerning Means of Escape, availability of alternative and safe escape route is a main requirement. This is because according to Section 3.5 of , occupants should be able to escape unharmed to a place of safety regardless of their location inside the building . Similarly, the term “safe route” in the definition of means of escape and superficially mentioned in Secton 3.2 of ADB demand several fire safety design requirements that include determination of building occupancy type and purpose group, appropriate height and width of escape routes including such as corridors, doors, stairs, exit signs and lighting, and so on. More importantly, as shown in Table 1, ADB is concern over the limitations in travel distance or the maximum travel distance that should be complied in safety design. Table 1- ADB Travel Distance Limitation The above limitation of distance of travel is indicative of ADB’s concern over the harmful effects of fire such as heat, smoke and toxic gases to a person escaping from fire and recommending design of shortest and fasters route to safety as shown in Diagram 22 and 33 below. Similarly, ADB contains many escape time and human ability related provisions such as the purpose group that in essence is a strategy accounting the effects of human health (i.e. affected by smoke and heat) and behavioural characteristics in travel time. Figure 1- Maximum Travel Distance in ADB The concept of maximum travel distance in ADB is somewhat related to ASET and RSET as evidenced by its emphasis on the practicality and usefulness of fire safety engineering approach in Section 0.30 where BS 7974 is specifically recommended for factors associated with human safety, adequacy of means of escape and others . Evidently, ASET (a function of fire growth and development) and RSET (a function considering occupants characteristics in relation to escape time) principles that were introduced by BSI or the British Standard Institute through BS 7974 are highly regarded in ADB as a viable approach to fire safety. Moreover, ADB recognised the positive effect of synchronising evacuation time with fire development in avoiding harmful effects of heat and smoke. For instance, since RSET takes into account the time from ignition to detection, and warning to tenability limit, it can greatly enhance evacuation planning by avoiding the tenability limit and creating a margin of safety for escaping occupants.. BS 7974-6 is generally concern over pre-movement and travel behaviours thus ASET and RSET is useful for ADB’s vertical and horizontal escape requirements in terms of travel distance limitations and provisions for alternative escape route . 3. FIRE SAFETY DESIGN REQUIREMENTS OF UK BUILDING REGULATIONS AND BS 9999 IN RELATION TO ASET AND RSET ADB Section 1 or B1 requirements include means of escape related important provisions such as warning, design of vertical and horizontal escape, safe escape routes, travel time limits where ASET and RSET may be applied. ASET and RSET are not clearly stated in ADB but BS 7974 and use of fire engineering solutions is highly recommended. Note that ADB’s requirements are not compulsory thus building designers are allowed to use alternative methods for as long as they can meet Building Regulation functional requirements . BS 9999 requirements for means of escape follows include several important areas of common fire safety concern. These include provisions for structurally stable and safe means of escape, appropriate provisions for fire fighting access, fire safety management in the building . The difference between ADB and BS 9999 is the emphasis on occupants’ responses as shown below. These requirements are also evident BS 7974 means of escape design where early stages of occupant responses are considered in the calculation of available escape time. These include time when occupant detect or noticed the fire, pre-movement time, travel time, and movement to secondary place of safety such as protected stairs and refuge. In summary, BS 9999 recommend formulation of effective evacuation procedure, means of escape design that is concern with building and occupant type (see risk profile of high fire risk areas), use and storage of combustible materials, escape enclosed with fire resisting materials, maximum travel distance, and consistency of fire safety management . Figure 2- BS 9999 Timeline for Evacuation Table 2 BS 9999 Risk Profile Levels Table 3 BS 9999 Travel Distance Limitations 4. BS 7974 ASET and RSET PRINCIPLES FOR FIRE SAFETY DESIGN Fire safety engineering is concern over the effects of heat, smoke, and other fire effluents to the safety of those who will escape during a fire thus created a strategy that take advantage of time relationship between fire development and evacuation. The fundamental principle of this strategy is to create a margin of safety by lowering the amount of available time escape (RSET) in relation to ASET. Therefore, the greater the ASET and the lower the RSET, the longer is the safety margin thus tmargin = tASET- tRSET. Similarly, ASET time should be greater than the calculated to time to escape in a particular fire scenario thus ASET > ∆tesc. ∆tesc is the escape time from ignition to complete evacuation and calculated by adding estimated evacuation time or ∆tevac to the time of ignition or ∆tesc = ∆ta + ∆tevac as shown below. Figure 3 Fire development and evacuation time relationship The maximum level of exposure allowed to heat, smoke, toxic gases, and others is the time of tenability limit or the time from alarm to the end of margin of safety. This is the endpoint of ASET or the time when life cannot be sustained inside the building due to heat, smoke, and toxic gases. The occupant condition at this time is deteriorated due to breathing problems, blurred vision, pain from burns, and others. It is therefore necessary for evacuation time to be much lower than the tenability limit . By analysis, the principle of ASET takes into account the time relationship between fire growth and spread and evacuation in order to determine the maximum time available. In contrast, RSET take into account the fire detection, fire suppression capability of the building, fire safety management as well as likely occupant’s or human behaviour that extend their travel time during a fire evacuation . These include delays in detection due to lack of alarm system or rapid fire growth caused by ineffective fire safety management and absence of fire suppression capability, delayed human responses to alarms, and stressful condition caused by heat, smoke, and other fire effluents . . 5. THE BEHAVIOURAL AND HEALTH EFFECTS OF HEAT AND SMOKE The behavioural and physical effects of heat and smoke include optical limitations or visibility problems due to accumulation of thick smoke along the escape route. Impairments leading to inhalation of asphyxiant and toxic gases, pain due to high heat or extreme temperature, and death after hours or days due to inflammation of the lungs, blood contamination, and severe burns . In his study of fire-related deaths and injuries explains that exposure to fire, smoke, and fumes makes people confused and behave in irrational manner. High concentration CO and CO2 concentration can poison and occupants’ who are trapped and unable to reach a place of safety. Similarly, the lack of oxygen content in the air, burning sulphur, chlorine, and others can lead to breathing difficulty and death (p.188). High intensity heat in the form of actual flame or radiation is fatal due to serious burns of the skin and respiratory tract, hyperthermia, and various post exposure complications 6. CASE STUDY FOR ASET AND RSET SAMPLE CALCULATION 6.1 RSET DETECTION, WARNING, AND TRAVEL TIME ASET can be calculated through computer-based zone models and in this case CFAST was selected. ASET estimation based on requires time-concentration curves for smoke, heat, toxic gases and ASET endpoints specified in BS 7899-2. Value for RSET can be calculated through a given formula: where pre-movement and travel behaviours are taken into account as factors that may increase or decrease the value of safe escape time. As shown in Figure 3 ∆tdet is time from ignition to detection, while ∆ta is the amount of time spent from detection to activation of general alarm. The pre-movement time of occupants is represented by ∆tpre while the amount time for occupants to walk to exit is ∆ttrav. The selected case study to demonstrate ASET and RSET calculation is a one-storey office building with two possible escape routes. Figure 4 One-Storey Office Building Means of Escape The area of this office building is 30m x 20m or 160m2. The possible escape routes are shown by red arrows pointing to exits. The fire in this scenario originated in the lounge at the centre of the building. The green dashed line with pointed arrows indicates the origin of the occupant and the travel path and distance measuring about 16 metres (furthest route). The estimated travel distance from this point the nearest exit on the left of the plan is around 12 metres. RSET Calculation variables: Total Area = 160m2 Occupants capacity as per ADB formula T/FS = 160/6 = 26 persons ADB Minimum escape route for 60 persons as per ADB Table 3 is 1 (26 Read More