Risk Rating and Assessment

Overview

Risk is the probability that a hazard will result in an adverse consequence. Assessing risk of potential hazards helps to determine the proper mitigation strategy and priorities. Risk ratings and scaling can show where additional resources are required.

In our discussion, we'll focus on rating risks using probability of occurrence and severity of consequences scales.

Because risk identification and rating establish priorities, this assessment should be incorporated early in the experimental process. A higher degree of user training is required to consistently and accurately rate probability of occurrence and severity of consequences among users and operations. It's recommended to have a principal investigator or experienced lab workers lead risk assessments and confirm accuracy of risk ratings.

Applying appropriate control measures to your highest risks should reduce the probability of occurrence and severity of consequences.


Calculate Risks Using Probability of Occurrence and Severity of Consequences Scaling

Many risk assessments use “probability of occurrence” and “severity of consequences” scales to rate risks associated with laboratory experiments. They are comprehensive assessment tools and provide greater differentiation of risks based on actual laboratory operations.

Using this kind of scaling, laboratory hazard risk rating is calculated as follows:

Risk Rating (RR) = Probability of Occurrence (OV) x Severity of Consequences Value (CV)

As the formula indicates, the higher the assessed probability of occurrence and severity of consequences, the greater the risk rating will be.


Probability of Occurrence

Probability of occurrence explores the likelihood that an identified risk could occur. Probability of occurrence uses a rating and value scale ranging from Not Present (0) to Almost Certain to Certain (4).

Examples:

  • A laboratory is measuring the pH of ground water and handles hundreds of samples daily. In this case, the likelihood that a container could spill and expose an employee to ground water would be high.
  • A laboratory is conducting research on electroplating with cyanide baths and only uses the bath monthly. The probability of an occurrence happening would be low.

The following Probability of Occurrence with Standard Linear Scaling chart includes a percent probability an issue will occur. Note: This chart is arbitrarily scaled 1 to 4, with 4 being the highest probability.

Probability of Occurrence with Standard Linear Scaling

Probability of Occurrence with Standard Linear Scaling table

Severity of Consequences

Severity of consequences assigns a rating based on the impact of an identified risk to safety, resources, work performance, property, and/or reputation. Each rating is then assigned a value. (E.g., a "No Risk" may be assigned a value of 1; a "High" rating may be assigned a value of 4.) The numerical values from the severity of consequences will contribute to other types of risk rating tools, like the hazard risk rating with standard linear scaling.

Examples:

  • The severity of consequence for a laboratory measuring the pH of ground water samples would likely be No Risk (0) in the event of a “failure” that caused an employee to be exposed to the ground water.
  • The severity of consequence for a laboratory conducting electroplating research with cyanide baths would be High (4) in the event of a “failure” that caused an employee to be exposed to cyanide.

This Severity of Consequences with Standard Linear Scaling chart assesses impacts to personnel safety, resources, work performance, property damage, and institutional reputation associated with each rating. Note: This chart is arbitrarily scaled 1 to 4, with 4 being the highest severity.

Severity of Consequences, Standard Linear Scaling

The primary goal of risk rating is to differentiate between an institution's high-risk activities and low-risk activities. Therefore, it may be necessary to weight your consequences value scale to meet your institution's existing priorities and protocols.

For example, using the standard linear scaling, an activity with a certain probability (4) with no risk (1) would produce an overall risk rating of 4. An activity with a rare probability value (1) with potentially lethal consequences (4) would also result in a risk rating of 4. Since any activity with the potential of being lethal would not be considered low risk, regardless of how low the probability, the scale needs to be weighted to reflect the severity of potential consequences.

The Weighted Consequence Value Scale demonstrates how you might assign consequence values to achieve risk ratings more reflective of the impact of moderate and high consequences.

Severity of Consequences, Weighted Value Scale

Consequence Value (CV) Impact to...
Rating Value Personnel
Safety
Resources Work
Performance
Property
Damage
Reputation
No Risk 1 No injuries No impact No delays Minor No impact
Minor 5
Minor injuries
Moderate impact
Modest delays
Moderate Potential damage
Moderate 10 Moderate to life impacting injuries
Additional resources required Significant delays Substantial Damaged
High 20 Life threatening injuries from single exposure Institutional resources required Major operational disruptions Severe Loss of confidence

Let's look back to our previous example. Using this weighted scale, an activity with a certain probability (4) with no risk (1) would still produce an overall risk rating of 4. But, an activity with a rare probability value (1) with potentially lethal consequences (20) would result in an overall risk rating of 20.

Every institution should determine the scaling and assignment of risk levels that best suits its priorities and available resources.


This collection of methods and tools for assessing hazards in research laboratories is based on the publication, Identifying and Evaluating Hazards in Research Laboratories. The guide was published in 2015 by the Hazard Identification and Evaluation Task Force of the American Chemical Society’s Committee on Chemical Safety in response to a recommendation from the U.S. Chemical Safety Board.