How do you Rank or Prioritize the Risk?

Ranking for prioritizing hazards is one way to determine the level of seriousness of the hazard. Once you have observed a condition you should be able to place it in a context of its seriousness. There are many factors that enter into the assigning a priority to hazards. Many are site-specific. Others vary according to the stage of construction. In either case ranking and prioritizing risk takes into the probability and consequence of events. This relationship has been charted as follows.

This is known as the “Risk Model”

The left-hand axis of this chart is the probability is something is likely to occur. The bottom row of this model is the potential consequence of what happens if it does occur.

High probability

Low consequence

Probably going to happen, but it does not cause much damage

Low probability

Low consequence

Never going to happen, and if it does not one cares

High probability

High consequence

Probably going to happen and it will cause a lot of harm

Low probability

High consequence

May not happen very often, but when it does the results are catastrophic


When it comes to talking about probability there is a chart for that also. The British Standard organization has produced a table that illustrates this nicely.

Risk assessment probabilities and severity of harm
Likelihood of harm
Severity of harm
Slight harm Moderate harm Extreme harm
Very unlikely Very low risk Very low risk High risk
Unlikely Very low risk Medium risk Very high risk
Likely Low risk High risk Very high risk
Very likely Low risk Very high risk Very high risk

This chart is supported by the definitions of these terms: very likely means that a person is typically going to experience this type of an event once every six months.

Likely means that a person may not experience this is except about once every five years.

Unlikely means that they would typically only experience this type of it in once during their working lifetime.

And very unlikely means that you have less than a 1% chance of an individual having an experience of this nature during their working lifetime.

One interpretation of this chart is that individuals are likely to have slight or moderate harm occur to them on a fairly frequent basis, but a really serious incident is not likely to happen very often. The analysis of that observation is that people do not expect extreme harm to come to them frequently. Depending upon their attitude toward safety the behavior of an individual towards removing hazards really begins with their understanding that severe events sometimes have relatively insignificant causes and they must be prepared.

This results in a need to prioritize risk and hazard using some form of definition that is separate from the idea of frequency and consequence. The following definitions might be used in defining how priorities can be identified.

Very Low – these are risks that are considered to be perfectly acceptable. No further action is required except to comply with the provisions of fire, building codes and NFPA standards.

Low – there are no additional controls required unless they can be implemented easily. Easily means limited time money and effort is required. To reduce these risks would be a low priority. They would still be expected to be in compliance with the provisions of fire, building codes and NFPA standards

Medium – this is when a set of conditions exists where risk reduction measures should be taken into account. Medium priority means attention to detail. The use of specific tools, or processes, such as salamanders and heating appliances might qualify as a medium risk. Risk reduction measures should be specific rather than generalized

High – this is a situation where substantial efforts have to be made to reduce risk. These risks should be looked at with respect to win the condition begins and when it will end. This is the level of risk where there is a strong need for personal commitment to compliance with fire codes, building codes and NFPA standards.

Very High – these risks are simply unacceptable. They are conditions in which work activity may have to be halted or altered until adequate risk mitigation measures are implemented this type of risk may result in work activity being prohibited.

Once the person assigned to do risk assessment has completed this profile should be able to rank the various elements of risk into groupings that can be used to guide day-to-day activities.