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Fire Risk Assessment
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From the Technical Director:
Fire Risk Assessment

By Morgan J. Hurley, P.E., FSFPE | Fire Protection Engineering

The theme of this issue is "fire risk assessment.” Fire risk assessment differs from other forms of fire safety analysis or design in how the probability of an event is considered. With most forms of fire safety analysis, the only consideration of the probability of an event occurring is in the context of whether or not the event is likely enough that it should be addressed. All events that are considered likely enough to merit protection are then considered equally.

This occurs in both performance-based designs (at least those that are not conducted on a risk basis) and within prescriptive codes. For example, many prescriptive codes contain requirements that are predicated on a single fire occurring at any time. That is not to say that more than one fire is not possible, only that the developers of these codes considered more than one fire happening at once to be sufficiently unlikely that it is not necessary to protect against this occurring.

Conversely, in fire risk assessment, the consequences of a fire event are weighted by the probability of the event occurring. The traditional way to do this is to multiply the consequences of an event (lives lost, cost of damage, hours of downtime, etc.) by the event’s frequency (e.g., once every 100 years) and then sum these products for all scenarios. The result is a measure of the risk associated with an activity, in units like dollars of fire loss per year.

Simpler methods of fire risk assessment are available as well. The viewpoint by Dr. John Hall on page 4 summarizes these approaches nicely.

Unlike other forms of fire protection analysis or design, rare events can’t be excluded from fire risk analysis solely on the basis that they are highly unlikely. Even extremely rare events must be considered, but their (usually extremely high) consequences are weighted by the low frequency at which these events would occur.

There are two major challenges associated with fire risk assessments: the time that they take to perform and the availability of data. For analyses with a large number of scenarios, the time necessary to conduct a fire risk assessment can be substantial. It can also be difficult to find data associated with the frequency of events occurring or the reliability of fire protection systems.

In some cases, it might be necessary to apply engineering judgment. When this is done, the uncertainty associated with the values used should be considered – such as by selecting conservative values or conducting an uncertainty analysis. Similarly, system reliability data can be hard to find. An article summarized sprinkler system reliability studies,1 which identified system reliabilities ranging from 81.3% to 99.5%; this shows that even published data can vary. For other types of fire protection systems, finding good reliability data can be a real challenge.

However, fire risk assessment can be a very powerful, cost-effective tool. If a few scenarios dominate the fire risk, then the fire risk can be reduced by focusing on ways to reduce either the frequency of the scenarios occurring or their consequences. This allows for resources to be applied in a very efficient manner.

With the exception of a few industries – like the nuclear industry and the petrochemical industry – fire risk assessment is rarely used in fire protection engineering design. The articles in this issue provide an excellent overview of the approaches that can be used to conduct a fire risk assessment and the references that are available to assist.


  1. Budnick, E. "Automatic Sprinkler System Reliability,” Fire Protection Engineering, Winter, 2001, pp. 7-12.

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