# Risk Index Method--A Tool for Building Fire Safety Assessments
## 1 Introduction  
### Fire Safety Engineering and the Use of A Performance-Based Approach  
Fire safety engineering is generally recognized as a unique branch of engineering [1]. Whereas other engineering disciplines make use of known laws, fire safety engineering is rarely absolute in its science and application. Therefore, traditionally, a strongly prescriptive approach has been applied for the fire safety and protection requirements of buildings by the use of national codes, such as British Standards [2]. Most nations make use of the application of fire safety regulations to ensure that minimum standards are applied. These laws are often supported by national or international codes or standards, which typically provide specific details that should be followed. However, such an approach has often restricted advances in building design British Standard DD 240-1 [3]. The concepts behind a performance-based approach were introduced from the 1970s onwards to allow greater flexibility in designing and applying fire safety and protection systems. From the 1990s, standards were introduced to provide guidance regarding the application of a performance-based approach. The UK is acknowledged as an early pioneer in standardizing this more flexible approach. However, in later years, many other countries have followed up with their own ideas and codes. An early alternative approach (1997) developed within the UK is a standard, referred to as a \"Draft for Development\", introduced by British Standards Institution (BSI) in 1997 (British Standard DD 240-1) [3]. The scope of the standard highlighted that it provided a framework for an engineering approach to the achievement of fire safety in buildings by giving guidance on the application of scientific and engineering principles to the protectionof people and property from fire. A second supporting standard, British Standard DD 240-2 [4] was also published to provide commentary on the equations given in Part 1 [3]. This Draft for Development was seen as a breakthrough in allowing building designers the option of applying fire safety to a building based upon performance objectives determined for that building. The idea was that one or more meetings would be held involving relevant stakeholders who would set these performance objectives. These meetings were described as \"qualitative design reviews\", in that the qualitative decisions made would guide the subsequent quantitative analysis described in British Standard DD 240-1 [3]. The key concepts of DD 240 were developed further by BSI when, in 2001, British Standard BS 7974 [5] was published to supersede DD 240. The Standard used the same framework for an engineering approach as described for British Standard DD 240-1 [3]. It also provided a \"rational methodology for the design of buildings\". The main standard was supported by eight \"Public Documents\", PD 7974 parts 0-8, which allowed fire safety engineers to create effective and relevant performance-based fire strategies [6; 7; 8; 9; 10; 11; 12; 13; 14]. At the time of the publication of BS 7974 (5), a series of prescriptive British Standards were still in force and referred to as the BS 5588 series [2]. These standards supported the UK Building Regulations and specifically Approved Document B (volumes 1 and 2), which covered fire safety (2010) [15; 16]. BSI determined that the restrictive nature of these standards should be replaced by a standard that allowed for some flexibility in applying fire safety, even if it did not apply the methodologies adopted by the performance-based standards. The British Standard BS 9999:2017 [17] was first published in 2008. This allowed variation in the specification of aspects of fire safety, such as travel distances for evacuating persons, based upon the building's risk profile. The risk profile was made up of two factors: the potential rate of fire growth and the occupancy profile (e.g., occupants' knowledge of the building and the potential for not being awake during a fire).