Initial and residual risk

Every risk in 4HSE carries two values.

• The initial risk is the risk of the activity as it would be without the measures: probability times damage, as you entered them.
• The residual risk is what remains once the mitigation actions are counted.

Why both are kept

A single number would answer “how dangerous is this?” and nothing else. Two numbers answer three questions:

• how dangerous the activity is in itself — the initial value, which does not change when you add protections, because the hazard has not gone away;
• how much the measures are worth — the difference between the two, which is the only evidence that what you are doing has an effect;
• what is left — the residual value, the one the activity retains after the measures, and what sets the priority for further action.

This is also why the initial risk must not be lowered to “reflect” the protections in place: doing that loses the measure of what those protections are achieving, and makes the assessment impossible to review.

The measures are actions, not notes

A mitigation measure in 4HSE is a prevention action: a course, a PPE assignment, a maintenance plan, a procedure. Giving it an impact on a risk connects two things that are usually kept apart — the assessment on paper and the activities actually carried out.

The consequence is practical: if the action expires and is not renewed, the measure you counted on is no longer in place, and the residual risk you calculated no longer describes reality. This is the link between the risk assessment and the scheduler.

Reviewing over time

Impacts can be changed as conditions change. The assessment is not a photograph taken once: it is a value that follows the operating conditions, and that has to be revisited when those conditions change — see Assess a risk.