Designed to be used by design engineers, safety professionals, consultants and machinery end users to enable Machinery Safety issues to be assessed and recorded to enable compliance with European legislation.
Risk Assessment – A History
Risk Assessment
Risk assessment is a key part of machinery safety. There are numerous methods of carrying out a risk assessment, the main issue is to identify the hazard and control or eliminate it. The method used in COMPLIANCE Risk Software is a tried and tested method, the history of it is below.
Risk Estimation – 25 years on
In June 1990, Safety Health Practitioner magazine published Chris Steel’s article on Risk Estimation which introduced Hazard Rating Numbers, by quantifying Probability and Frequency of Exposure to a hazard, Number of People at risk and Maximum Probable Loss. Numerical values were allocated to descriptive phrases as in table 1. The intention is to select the phrase that matches the hazard and multiply the values together. The resulting Hazard Rating Number, when viewed on the scale gives an estimation of the risk.
| PE Probability of Exposure | Frequency of Exposure | |||||||||||
| 0 | Impossible | Cannot happen | 0.1 | Infrequently | ||||||||
| 1 | Unlikely | Though conceivable | 0.2 | Annually | ||||||||
| 2 | Possible | but unusual | 1 | Monthly | ||||||||
| 5 | Even chance | could happen | 1.5 | Weekly | ||||||||
| 8 | Probable | not surprised | 2.5 | Daily | ||||||||
| 10 | Likely | to be expected | 4 | Hourly | ||||||||
| 15 | Certain | no doubt | 5 | Constantly | ||||||||
| MPH Maximum Probable Loss | NP Number of Persons at risk | |||||||||||
| 0.1 | Scratch or bruise | 1 | 1-2 persons | |||||||||
| 0.5 | Laceration or mild ill health effect | 2 | 3-7 persons | |||||||||
| 1 | Break of a minor bone or minor illness (temporary) | 4 | 8-15 persons | |||||||||
| 2 | Break of a major bone or minor illness (permanent) | 8 | 16-50 persons | |||||||||
| 4 | Loss of Limb, eye / serious illness of a temporary nature | 12 | 50 + persons | |||||||||
| 8 | Loss of Limbs, eyes / serious illness of permanent nature | |||||||||||
| 15 | Fatality | |||||||||||
| RISK | Negligible | Very Low | Low | Significant | High | Very High | Extreme | Unacceptable | ||||
| HRN | 0-1 | 1-5 | 5-10 | 10-50 | 50-100 | 100-500 | 500-1000 | Above 1000 | ||||
Table 1
A second table shows how quickly the risk should be resolved. If the HRN was less than one, it was tolerable, if greater than one, control measures should be implemented in the timescales given.
| Risk | HRN | Action Timetable |
| Acceptable risk | 0 – 1 | Accept risk/consider action |
| Very low risk | 1-5 | Action within 1 year |
| Low risk | 5-10 | Action within 3 months |
| Significant risk | 10-50 | Action within 1 month |
| High risk | 50-100 | Action within 1 week |
| Very high risk | 100-500 | Action within 1 day |
| Extreme risk | 500-1000 | Immediate action |
| Unacceptable risk | Over 1000 | Stop the activity |
Table 2
Chris explained that each organisation should select values and phrases according to its own needs.
A consulting organisation that was part of Longlands College in Middlesbrough adopted the method in their work assisting companies with CE marking of machinery, which was then new in 1993. The terminology was modified, changing ‘Probability of Exposure’ to ‘Likelihood of Occurrence’, and ‘Maximum Probable Loss’ to ‘Degree of Possible Harm’, the numbers were changed by removing the term ‘impossible’, as experience showed that nothing was impossible, if someone wants to override a safeguard, they will, often using ingenious methods! 0.1 almost impossible, possible in extreme circumstances, and 0.5 highly unlikely, though conceivable were added, to the Likelihood of Occurrence table. The remaining numbers stayed the same. In the original article, Chris stated that ‘If however backup safeguards, fail-to-safety devices, etc. are used then PE may be reduced to almost zero’.
In 1998 four consultants left Longlands College, to start Laidler Associates, which became one of the leading UK machinery safety consultancies, becoming the Machinery Division of TÜV SÜD Product Services in 2010. Laidler Associates developed software to assist companies with CE marking of machinery, and PUWER compliance, and the HRN method became widely used in industry. The software is no longer supported by TÜV SÜD.
On researching the system in 2015, the original article was found and is still considered relevant today. It meets the criteria in EN ISO 12100, the European Harmonised Standard for Risk Assessment, which states ‘The risk associated with a particular hazardous situation depends on the following elements:
- a) the severity of harm; (DPH)
- b) the probability of occurrence of that harm, which is a function of; (LO)
1) the exposure of person(s) to the hazard, (FE)
2) the occurrence of a hazardous event, and
3) the technical and human possibilities to avoid or limit the harm.’
The only area not directly addressed, is avoidance, although this should be considered within Likelihood of Occurrence. I believe that Likelihood of Occurrence is the main factor that can be changed. The others can rarely change realistically.
| LO Likelihood of Occurrence | Frequency of Exposure | |||||||||||
| 0.033 | Almost impossible | Possible in extreme circumstances | 0.1 | Infrequently | ||||||||
| 0.5 | Highly Unlikely | Though conceivable | 0.2 | Annually | ||||||||
| 1 | Unlikely | But could occur | 1 | Monthly | ||||||||
| 2 | Possible | but unusual | 1.5 | Weekly | ||||||||
| 5 | Even chance | could happen | 2.5 | Daily | ||||||||
| 8 | Probable | not surprised | 4 | Hourly | ||||||||
| 10 | Likely | to be expected | 5 | Constantly | ||||||||
| 15 | Certain | no doubt | ||||||||||
| DPH Degree of Possible Harm | NP Number of Persons at risk | |||||||||||
| 0.1 | Scratch or bruise | 1 | 1-2 persons | |||||||||
| 0.5 | Laceration or mild ill health effect | 2 | 3-7 persons | |||||||||
| 1 | Break of a minor bone or minor illness (temporary) | 4 | 8-15 persons | |||||||||
| 2 | Break of a major bone or minor illness (permanent) | 8 | 16-50 persons | |||||||||
| 4 | Loss of Limb, eye / serious illness of a temporary nature | 12 | 50 + persons | |||||||||
| 8 | Loss of Limbs, eyes / serious illness of permanent nature | |||||||||||
| 15 | Fatality | |||||||||||
| RISK | Negligible | Very Low | Low | Significant | High | Very High | Extreme | Unacceptable | ||||
| HRN | 0-1 | 1-5 | 5-10 | 10-50 | 50-100 | 100-500 | 500-1000 | Above 1000 | ||||
Table 3
It is sometimes difficult to achieve sufficiently low figures for the control measure, and it is difficult sometimes to demonstrate a reduced frequency of exposure. The Likelihood has been changed to 0.033, which allows a lower HRN to be achieved, once a suitable control is in place.
Risk assessment is subjective and people have varied perceptions. When using the method, the user should understand the ideas behind the numbers. Even so, it is not unusual for different people to get completely different HRN’s for the same hazard, it just demonstrates that there is no right or wrong answer, and the most important thing is to identify the hazard and do something about it!
There is the potential for ‘risk assessing the hazard out’, by manipulating the numbers to show that a hazard isn’t as bad as first perceived, and is acceptable, even though no control measures have been implemented. This is not the purpose of risk assessment, the intention in EN ISO 12100 is to Identify the Hazard, and carry out Risk Reduction.
EN ISO 12100 can be purchased from any EU Standards agency, currently Estonia is the most cost effective.