Skip to main content

Lund University Publications

LUND UNIVERSITY LIBRARIES

On the Use of Risk Concepts in Fire Safety Engineering

Nystedt, Fredrik LU (2018) 3rd European Symposium on Fire Safety Science, ESFSS 2018 In Journal of Physics: Conference Series 1107.
Abstract

Design for fire safety may be carried out by two generic approaches - a set of prescriptive rules or by a performance-based approach where analytical tools are used to verify fire safety towards a set of functional requirements and performance criteria given by the building code. Normally, these two methods are mixed when design fire safety within a building. The option to apply fire safety engineering to the design of buildings has been available during the last 20 to 40 years, depending on which aspect of fire safety being considered. Still, the fire protection of a building too often relies on general recommendations rather than scientifically-based solutions, due to a lack of standardised verification methods, acceptance criteria... (More)

Design for fire safety may be carried out by two generic approaches - a set of prescriptive rules or by a performance-based approach where analytical tools are used to verify fire safety towards a set of functional requirements and performance criteria given by the building code. Normally, these two methods are mixed when design fire safety within a building. The option to apply fire safety engineering to the design of buildings has been available during the last 20 to 40 years, depending on which aspect of fire safety being considered. Still, the fire protection of a building too often relies on general recommendations rather than scientifically-based solutions, due to a lack of standardised verification methods, acceptance criteria and procedures to ensure high quality fire safety design. The concept of risk, i.e. the combination of the probability of a fire and a quantified measure of its consequence, has been thoroughly investigated in several fire safety engineering applications over the last decades. Although there are techniques available that allow designers to evaluate fire risks, risk acceptance criteria are missing in general. Structural fire safety design is the exemption having defined target reliabilities. Although these criteria only address the likelihood of collapse of structural element and not explicitly the characteristics of the failure. Structural elements can be provided with fire resistance to control the spread of fire or to prevent structural collapse, or both and it is not uncommon to perform trade-offs between passive and active fire protection systems. But, very little effort has previously been made to understand the fundamental differences between these systems regarding their reliability and failure modes. Performance-based design of structural elements uses a heat exposure model to quantify the thermal load of the fire. The thermal load is characterised by the fire load (duration) and the intensity (air supply). Characteristic values of the fire load are found in various sources and commonly given in the building code, which ought to be used when designing for fire safety. A probabilistic approach was introduced in the 1980s where the probability of fire is expressed as a function of the probability of fire occurrence, the probability of a flashover and the probability of failure given a fully developed fire. Thus, the target probability of failure could be achieved by applying safety measures that alters the probability of any of these events. Currently, fire sprinklers do allow for a reduction in design fire load, but not other active safety system can be considered explicitly. Passive as well as active system for fire safety could both be considered as appropriate provisions to achieve sufficient safety. Even though there are support of trade-offs between passive and active provisions, current regulations, guidance as well as practise do not treat the different aspect of risk related to these systems. By only considering the probability of collapse, the design could deviate from overall societal requirements on avoiding catastrophes or principles of robustness stating that consequences should not be disproportionate to their cause. Traditionally, passive systems are assumed more robust. These findings are probably related to the concepts where target reliabilities are evaluated as the system is designed. Sprinklers are, on the other hand, assigned a probability of successful operation based on decades of statistics. This is an unfair comparison between the systems as a properly design sprinkler system always would prevent a fully developed fire, thus requiring no specific fire resistance on separating and structural elements. Naturally, this is not the path forward as the failure modes of both types of system must be treated and understood. Active systems could be argued to be more forgiven as the they do not care what mistakes are made to cause a fire, neither do they care if occupants act as planed or not. Passive systems are more sensitive to building use when e.g. doors are kept open. Future performance criteria and risk acceptance criteria should not focus solely on probabilities. Emphasis must be put on establish criteria that measure the risk of the unwanted event considering type of initiating event, number of barriers, expected consequence, possibility of damage control, etc. Not until such criteria are available the full potential of performance-based fire safety design cannot be utilised.

(Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Chapter in Book/Report/Conference proceeding
publication status
published
subject
keywords
active systems, building regulations, fire resistance, fire safety engineering, passive systems, performance-based design, risk analysis, risk assessment, statistics, structural design
host publication
3rd European Symposium on Fire Safety Science 12–14 September 2018, Nancy, France
series title
Journal of Physics: Conference Series
volume
1107
article number
042034
conference name
3rd European Symposium on Fire Safety Science, ESFSS 2018
conference location
Nancy, France
conference dates
2018-09-12 - 2018-09-14
external identifiers
  • scopus:85057545533
ISSN
1742-6588
DOI
10.1088/1742-6596/1107/4/042034
language
English
LU publication?
yes
id
1b5dffac-3e42-4aad-85f7-5f66c3b42290
date added to LUP
2018-12-11 13:12:05
date last changed
2021-09-29 02:28:07
@inproceedings{1b5dffac-3e42-4aad-85f7-5f66c3b42290,
  abstract     = {<p>Design for fire safety may be carried out by two generic approaches - a set of prescriptive rules or by a performance-based approach where analytical tools are used to verify fire safety towards a set of functional requirements and performance criteria given by the building code. Normally, these two methods are mixed when design fire safety within a building. The option to apply fire safety engineering to the design of buildings has been available during the last 20 to 40 years, depending on which aspect of fire safety being considered. Still, the fire protection of a building too often relies on general recommendations rather than scientifically-based solutions, due to a lack of standardised verification methods, acceptance criteria and procedures to ensure high quality fire safety design. The concept of risk, i.e. the combination of the probability of a fire and a quantified measure of its consequence, has been thoroughly investigated in several fire safety engineering applications over the last decades. Although there are techniques available that allow designers to evaluate fire risks, risk acceptance criteria are missing in general. Structural fire safety design is the exemption having defined target reliabilities. Although these criteria only address the likelihood of collapse of structural element and not explicitly the characteristics of the failure. Structural elements can be provided with fire resistance to control the spread of fire or to prevent structural collapse, or both and it is not uncommon to perform trade-offs between passive and active fire protection systems. But, very little effort has previously been made to understand the fundamental differences between these systems regarding their reliability and failure modes. Performance-based design of structural elements uses a heat exposure model to quantify the thermal load of the fire. The thermal load is characterised by the fire load (duration) and the intensity (air supply). Characteristic values of the fire load are found in various sources and commonly given in the building code, which ought to be used when designing for fire safety. A probabilistic approach was introduced in the 1980s where the probability of fire is expressed as a function of the probability of fire occurrence, the probability of a flashover and the probability of failure given a fully developed fire. Thus, the target probability of failure could be achieved by applying safety measures that alters the probability of any of these events. Currently, fire sprinklers do allow for a reduction in design fire load, but not other active safety system can be considered explicitly. Passive as well as active system for fire safety could both be considered as appropriate provisions to achieve sufficient safety. Even though there are support of trade-offs between passive and active provisions, current regulations, guidance as well as practise do not treat the different aspect of risk related to these systems. By only considering the probability of collapse, the design could deviate from overall societal requirements on avoiding catastrophes or principles of robustness stating that consequences should not be disproportionate to their cause. Traditionally, passive systems are assumed more robust. These findings are probably related to the concepts where target reliabilities are evaluated as the system is designed. Sprinklers are, on the other hand, assigned a probability of successful operation based on decades of statistics. This is an unfair comparison between the systems as a properly design sprinkler system always would prevent a fully developed fire, thus requiring no specific fire resistance on separating and structural elements. Naturally, this is not the path forward as the failure modes of both types of system must be treated and understood. Active systems could be argued to be more forgiven as the they do not care what mistakes are made to cause a fire, neither do they care if occupants act as planed or not. Passive systems are more sensitive to building use when e.g. doors are kept open. Future performance criteria and risk acceptance criteria should not focus solely on probabilities. Emphasis must be put on establish criteria that measure the risk of the unwanted event considering type of initiating event, number of barriers, expected consequence, possibility of damage control, etc. Not until such criteria are available the full potential of performance-based fire safety design cannot be utilised.</p>},
  author       = {Nystedt, Fredrik},
  booktitle    = {3rd European Symposium on Fire Safety Science 12–14 September 2018, Nancy, France},
  issn         = {1742-6588},
  language     = {eng},
  series       = {Journal of Physics: Conference Series},
  title        = {On the Use of Risk Concepts in Fire Safety Engineering},
  url          = {http://dx.doi.org/10.1088/1742-6596/1107/4/042034},
  doi          = {10.1088/1742-6596/1107/4/042034},
  volume       = {1107},
  year         = {2018},
}