Hazard vs Risk vs Harm

Hazard, risk, and harm are related but distinct terms. Confusing them leads to incomplete risk analysis — understanding the precise meaning of each is essential for CQE and safety engineering work.

Definitions

Term	Definition	Example
Hazard	Potential source of harm	Electricity flowing through a conductor
Hazardous situation	Circumstance in which people are exposed to the hazard	An uninsulated conductor within reach of an operator
Harm	Physical injury or damage that actually occurs	Electric shock causing injury
Risk	Combination of probability of harm × severity of harm	High voltage + high operator exposure = high risk

The hazard sequence (ISO 14971)

Hazard → Hazardous situation (if exposure occurs) → Harm (if a triggering event occurs)

Risk control breaks this chain: remove the hazard, reduce exposure to the hazardous situation, or add protective measures that prevent the triggering event.

Risk = Probability × Severity

Risk level is a function of two dimensions: P1 = probability of the hazardous situation occurring P2 = probability of harm given the hazardous situation S = severity of harm Risk ∝ P1 × P2 × S

CQE exam tips

A hazard that is not exposed to people is not a hazardous situation — the exposure step is required in the chain.
Harm has occurred; risk is the potential for harm — distinguishing past from future is tested.
ISO 14971 defines these terms for medical devices; ISO 31000 uses similar but broader terminology for enterprise risk.

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