The LWF Blog

Fire Safety Engineering for Design – Risk Assessment & Fire Engineering – Part 61

January 4, 2022 12:44 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 60, LWF looked at qualitative risk assessment and how it is used to analyse and support design decisions. In part 61, we continue looking at qualitative risk assessment.

The risk profile for a building can be adjusted by the addition of risk reduction measure. The measures taken are commonly active fire protection measures, such as sprinkler systems and/or enhanced fire detection and alarm systems. The ability to alter the risk profile in this way allows flexibility of design in terms of other risk reduction measures and may prove less costly or intrusive to the overall design than that which would be necessary when following a prescriptive solution.

For more information on variation of risk profile, see BS 9999 Fire safety in the design, management and use of buildings – Code of Practice.

Another method of qualitative risk assessment is a risk matrix technique, also known as a qualitative risk assessment/analysis matrix. The basis is a table of data to allow comparison, showing the likelihood and consequences of a risk occurring, relative to each other as a qualitative ranking.

The value given for level of risk in each cell of the table can be expressed as a colour, code or letter indicating risk level, (e.g. H = high risk, M = moderate risk, L = low risk etc.). The tables are also seen used with nominal values to likelihood and consequence, which gives an overall risk factor of likelihood multiplied by consequence (or added… as long as the calculation is consistent and only used in comparison to other risks in the same matrix, it doesn’t matter how the number is reached).

Although a risk matrix can be useful as a technique to compare risk for fire safety management purposes, it is not to be relied upon as a sole method of defining design solutions. The process requires subjectivity and it can be hard to agree acceptability criteria.

For example, is something classed as ‘medium’ risk ever to be considered an acceptable level of risk? If something is considered ‘low’ risk, should improvements that could be made in a simple and un-costly manner be ignored?

Whatever methods are used to analyse risk, the results should be documented in a manner that illustrates how the assessment was undertaken and should include the rationale for concluding that the risks are acceptable.

In part 62 of LWF’s series on fire engineering, we will begin to look at quantitative risk assessment (QRA) and cost-benefit analysis (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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