The LWF Blog
Fire Safety Engineering for Design – Sprinkler Protection – Part 224
March 3, 2025 11:29 amLWF’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 223, LWF discussed exceptions to sprinkler protection throughout a building. In part 224, we look at hazard classification in relation to sprinkler systems.
Sprinkler systems should be chosen based on the type of hazard with which it will be expected to cope. Hazard classifications are based on three main divisions, each related to the expected fuel load of the occupancy and the rate of fire growth anticipated, as follows:
Light hazard – low combustible loading with a slow rate of fire growth
Ordinary hazard – low to moderate combustible loading with moderate to fast rate of fire growth
High hazard – high combustible content with fast to ultra-fast fire growth
Sub classifications of ordinary and high hazards are provided in order to further qualify the type of risk. These classifications are dependent upon the quantity and type of combustible materials present and the speed at which a fire is likely to develop. It also takes into account any processes which may produce severe circumstances for the fire propagation.
A building or multiple buildings within one premises might be comprised of a combination of different risk classifications. The allocation of correct classifications can be complex and therefore should be undertaken by an appropriately qualified professional. The final decision is often made by the fire insurer or other authority having jurisdiction.
Some risks, such as oil, flammable liquid and gas hazards, are unsuitable for standard sprinkler systems. The sprinkler system installed must be suitable for the hazards in place and, for instance, may involve a sprinkler system using a foam solution. Detailed guidance on these types of risk can be gained from the NFPA codes.
The hazard classification(s) identified as appropriate will instruct as to the minimum amount of water that should be provided at the fire in the form of spray. This figure is known as the design density and is normally expressed as ‘mm per minute or litre.m-2 per minute’.
The expected maximum area of the sprinkler system is also provided by the hazard classification and the ‘assumed maximum area of operation’ (AMAO) is expressed in square metres.
There are significant differences in the design approach between UK guidance and NFPA 13.
In part 225 of LWF’s series on fire engineering we will … 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 since 1986 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.