The LWF Blog

Fire Safety Engineering for Design – Quantitative Risk Assessment – Part 66

February 7, 2022 12:52 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 65, LWF looked at how the Cost Benefit Analysis (CBA) process may be used. In part 66, we discuss some of the pitfalls of the Quantitative Risk Assessment (QRA) process.

The QRA process is widely-used tool and can be highly appropriate for use in risk assessment for a fire engineered design. However, there are some codicils to its use and these should be understood before deciding on its usefulness in a given situation.

In terms of fire safety, where the prescriptive fire safety solution is appropriate for use and relevant to the circumstances, the use of QRA wouldn’t be appropriate.

When considering low-frequency potential events or any event that might have very serious consequences, such as a significant fire in most premises, it should only be used with caution.

Care should be taken when attempting to use historical data or statistics based on limited sample periods. Historical data may show, for instance, that it has been many years since a significant incident, however, this does not mean that it could never happen again. Current (and past) legislation is often based on the outcome of rare occurrences that may not have been predicable based on QRA.

The removal of any risk reduction measure based on potential cost saving as per a QRA is not acceptable, unless it can be shown that the level of fire risk is unchanged or improved by the use of other risk reduction measures.

It should be understood that numerical levels of probability generated by the QRA process are not fact. They are simply calculations which may have been based on some uncertain data. They should be viewed as indicators rather than certainties. It is important they are not given undue prominence when acceptable risk is being judged.

The figures generated by a QRA must be compared against a quantified ‘success criteria’. However, it can be difficult to establish at which level ‘acceptable fire risk’ is achieved. Levels of tolerable risk to individuals are fairly well-established numerically in available guidance and standards, however, where there may be multiple fatalities due to fire, society would be less tolerant of the risks. Societal concern is not easy to quantify.

Acceptability of risk should therefore be compared against accepted levels of risk as laid out in established and relevant good practice and equivalent to current legislation and recommendations in national government advice.

In part 67 of LWF’s series on fire engineering, we discuss societal concern regarding fire safety in more detail. 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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