International Journal on Engineering Performance-Based Fire Codes, Volume 6, Number 2, p.78-86, 2004 78 A NEW METHOD OF ASSESSING UNCERTAINTIES IN DESIGNING BUILDING FIRE SAFETY PROVISIONS W.W. Yuen Department of Mechanical & Environmental Engineering, University of California at Santa Barbara California, USA W.K. Chow Department of Building Services Engineering, The Hong Kong Polytechnic University, Hong Kong, China (Received 11 May 2004; Accepted 5 June 2004) ABSTRACT New architectural features and special usages of modern buildings can lead to difficulties in complying with prescriptive fire codes. Engineering performance-based fire codes (EPBFC) and application of the fire safety engineering approach (FEA) are important alternatives to prescriptive code in the design of fire safety provisions for those new buildings. However, there are uncertainties associated with these approaches. The uncertainties must be assessed systematically prior to the acceptance of the proposed fire safety provisions design and to assure that public safety is achieved. A new method, using a probability based Monte Carlo approach, is shown to be effective in providing a quantitative assessment of the uncertainties. A general three- step probability based approach is proposed for fire safety provisions design. 1. INTRODUCTION Fire safety provisions, both passive construction designs and active fire protection systems (known as fire services installation in Hong Kong) are required in buildings as described clearly in the prescriptive codes [e.g. 1,2]. Those codes were developed over a period of many years, as it took time to pass the necessary monetary procedures, such as reading for three times in the Legislative Council of the Special Administrative Region. In recent years, however, there are increasing difficulties for big construction projects with new architectural features [3] or special use of the buildings, to comply with prescriptive fire codes. Upon smooth reunification of Hong Kong to Mainland, more ‘open’ approach was adopted. Design similar to engineering performance-based fire codes (EPBFC) [4-7] in overseas known as fire safety engineering approach (FEA) [8] has been accepted since 1998. Views from academics were respected in approving those designs. In applying EPBFC or FEA for designing fire safety provisions, the system characteristics should be studied carefully. For a given design objective with a specific system characteristics, standard procedures are available. An example is the calculation of the required spacing of ceiling-mounted thermal detectors in designing fire detection system [9] if prescriptive codes [10,11] are not complied. Most of the design procedures are deterministic and generally used without an assessment of the uncertainty. Uncertainties, however, are known to exist in the safety system characteristics and they can have a significant impact on system performance in a fire. Currently, the standard design approach to “minimize” the fire risk associated with such uncertainties is to depend on the fire engineer to provide subjectively the appropriate conservatism in the design. For example, a longer response time index might be used in the design of a thermal detection system to eliminate unwanted fire alarm. A bigger heat release rate is used for designing static smoke exhaust systems. The current “subjective” approach to account for the uncertainty of a fire safety provisions design has many difficulties. First of all, this approach provides no systematic assessment on what “appropriate conservatism” is and how fire risk is “minimized”. For example, the “slowest” response time index chosen by a one fire engineer might not be considered as the “slowest” by another. Since both engineers make his/her decision subjectively, it is difficult, if not impossible, to resolve the difference between two “expert opinions”. Without a quantitative approach in the assessment of risk, it is also difficult to convince stakeholders (owners, government officials and the general public) that the design has met his/her expected level of risk. There is no systematic approach to determine a level of “conservatism” which is acceptable to different stakeholders. Indeed, the lack of a systematic and quantitative approach to address uncertainties in fire safety provisions design is probably the most significant obstacle preventing