# The LWF Blog

## Fire Safety Engineering for Design – Quantitative Risk Assessment – Part 63

January 17, 2022 12:02 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 62, LWF began to discuss quantitative risk assessment and cost-benefit analysis. In part 63, we continue to discuss QRA and CBA.

When considering the use of quantitative risk assessment (QRA) and cost-benefit analysis (CBA) as a loss control measure, the cost of a form of fire protection may be offset against the reduction in the cost of probable damage to premises. For example, the use of fire resistance in compartmentation (or an increase in duration) may reduce the probability of the fire spreading outside the compartment and therefore reduce the probable damage area.

PD 7974:7 – Application of fire safety engineering principles to the design of buildings – Probabilistic risk assessment (Current, 31 Jan 2021) contains a modelling system based on statistical studies, used to calculate the probability of a fire starting that has a ‘power relationship’ with the building area. Additionally, the probable damaged area can be calculated based on building area and ‘power’ constants derived from real fire statistics and data. The constants are modified for compartments with or without sprinklers.

When the premises are of a high value, the potential cost of a maximum loss scenario will far exceed the cost of a sprinkler system installation. The cost of a sprinkler system installation can be further minimised by the consideration of such at a very early stage in a new build.

In the majority of cases, the commercial case for installation of sprinklers can be made easily when compared to the potential losses due to fire.

The likelihood or probability of fire occurring can be estimated through QRA by using statistical or historic data, or expert input may be sought to estimate probabilities for the hazards involved.

When looking at losses due to fire, no loss is so great as that of life. It might seem inappropriate to talk about the value in currency that is put on saving one life, but such quantification can be necessary. In some industries – transport being one example, there is guidance on the value that society is willing to place on the prevention of a fatality. The Value of Preventing a Fatality (VPF) can be used in a CBA, where the cost of the risk reduction is measured against the risk reduction achieved. It should be noted that in no way does this indicate the value of a life, it is merely an indication of the cost society is willing to pay to achieve an assessed reduction in risk to life in that particular industry.

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.