The LWF Blog

Fire Safety Engineering for Design – Quantitative Risk Assessment – Part 62

January 10, 2022 12:10 pm

LWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 61, LWF looked at qualitative risk assessment and how it is used to analyse and support design decisions. In part 62, we begin to discuss quantitative risk assessment and cost-benefit analysis.

While our previous blog looked at qualitative risk assessment, which relates to non-numerical and non-statistical techniques to assess fire risk, we begin now to look at quantitative risk assessment (QRA) which describes techniques to evaluate risk using numerical values. For example, the hazard in question (number of deaths or injuries or financial losses incurred) the probability the hazard will be realised and the resulting fire risk will be given numerical values which allow for comparison.

It allows the person undertaking the assessment to compare risk reduction measures, which may be vastly different to each other in quantitative terms, in a ‘like for like’ manner. QRA may also be used to ascertain whether risks are acceptable in absolute terms.

The QRA process is commonly used to determine if it is feasible and practical to make safety improvements under existing or altered conditions or to define safety objectives for new projects.

Some of the techniques that might be used when undertaking QRA include:

Hazards and operability study (HAZOPS)

Standard logical trees, such as fault tree analysis (FTA) and event tree analysis (ETA)

New logical trees

When using QRA techniques, the assessor may or may not also perform a Cost Benefit Analysis (CBA) as necessary or requested.

QRA and CBA may be used for other types of decision making and are not restricted to safety-related issues. They can be used to inform decisions relating to property and asset protection too. For example, when used to assess the probability of a significant fire during a given period of time, the projected consequences and possible financial loss may be estimated in terms of assets lost and/or lost revenue, and based on these figures a decision can be made as to investment in fire protection measures as a loss-control preventative measure.

While QRA and CBA may be used in relevant circumstances for life safety issues, it is more common for them to be used for asset protection. As in all cases, the risk to life safety should be as low as is reasonably practicable (ALARP) and so risks to life safety should be mitigated wherever possible unless the risk is low and the cost is prohibitively high.

In part 63 of LWF’s series on fire engineering, we will continue to discuss QRA and CBA. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.

Lawrence Webster Forrest has been working with their clients for over 25 years to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact the LWF office on 0800 410 1130.

While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.




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