Risk Matrix Calculations – Severity, Probability, and Risk Assessment

1. Severity

Severity is the amount of damage or harm a hazard could create and it is often ranked on a four point scale as follows:

• Catastrophic - 4: Operating conditions are such that human error, environment, design deficiencies, element, subsystem or component failure, or procedural deficiencies may commonly cause death or major system loss, thereby requiring immediate cessation of the unsafe activity or operation.
• Critical - 3: Operating conditions are such that human error, environment, design deficiencies, element, subsystem or component failure, or procedural deficiencies may commonly cause severe injury or illness or major system damage thereby requiring immediate corrective action.
•  Marginal - 2: Operating conditions may commonly cause minor injury or illness or minor systems damage such that human error, environment, design deficiencies, subsystem or component failure, or procedural deficiencies can be counteracted or controlled without severe injury, illness, or major system damage.
•  Negligible - 1 Operating conditions are such that personnel error, environment, design deficiencies, subsystem or component failure, or procedural deficiencies will result in no, or less than minor, illness, injury, or system damage.

2. Probability

Probability is the likelihood of the hazard occurring and it is often ranked on a five point scale:

• Frequent - 5: Likely to occur often in the life of an item
• Probable - 4: Will occur several times in the life of an item
• Occasional - 3: Likely to occur sometime in the life of an item.
• Remote - 2: Unlikely but possible to occur in the life of an item.
• Improbable - 1: So unlikely, it can be assumed an occurrence may not be experienced.

Risk matrices come in many shapes and sizes. For more information on how to build a risk matrix that's right for your project, see our more detailed guide.