Hazard Rating Numbers method

The Hazard Rating Numbers method is a system for quantitatively determining the risk level of hazards. Each hazard situation is assessed separately and a total risk factor is calculated to provide a better overview of the degree of danger. The method enables a systematic analysis and evaluation of risks, with the lowest occurring risk corresponding to a factor of 0.

S – Extent of damage, Severity of potential injury
Scratch / Bruise / Hematoma (First aid treatment)	0.1
Cut or minor injury (covered by accident insurance)	0.5
Minor fracture or mild illness (temporary)	2
Severe fracture or severe illness (temporary)	4
Loss of 1 limb, eye (permanent)	6
Loss of 2 body parts, eyes (permanent)	10
Death	15

F – Frequency of hazard exposure
Annually	0.5
Monthly	1
Weekly	1.5
Daily	2.5
Hourly	4
Permanent	5

N – Number of people simultaneously exposed to the hazard
1–2 people	1
3–7 people	2
8–15 people	4
16–50 people	8
> 50 people	12

O – Likelihood of the hazard occurring
Nearly impossible – possible under extreme circumstances	0.033
Very unlikely – though conceivable	1
Unlikely – but possible to occur	1.5
Possible – though unusual	2
Maybe – can happen	5
Likely – not surprising	8
Very likely – expected	10
Certain – no doubt	15

The risk assessment is quantified using the following formula:

Risk (R) = S · F · N · O

The calculated risk values can be interpreted as follows:

0 – 5	Negligible risk – remaining risk is acceptable
6 – 50	Low risk, but present – should be further reduced if possible
51 – 500	High risk – must be reduced
> 500	Unacceptable risk – must be reduced in any case
Maybe – can happen	5
Likely – not surprising	8
Very likely – expected	10
Certain – no doubt	15