1 Jan 1970

Risk Assessment methods

It is always important that the most appropriate type of risk assessment is selected and used. But whichever approach is taken, the risk assessment procedure must be fully documented, including noting any assumptions and the reasoning behind them.

For simple situations it may be adequate to perform a qualitative risk assessment, such as that used in the controversial risk category chart in EN 954-1. However, with this method it is possible to make a major difference to the final outcome by making a borderline decision between two similar choices. For this reason, techniques such as the Hazard Rating Number system can be added to provide a quantitative element to a qualitative method. Nevertheless, qualitative methods still require judgements to be made, so the result might not be the same even if the exercise were to be undertaken by two different - but qualified and experienced - consultants.

It is often the case that there is sufficient data available to make a quantitative approach possible, or specific data can be sought if the hazards are severe and the additional effort is warranted. Failure Mode and Effects Analysis (FMEA) is a top-down technique often used within Pilz. First, the failures are identified and then, for each failure mode, the various possible causes are listed. Using data for the probability of the cause occurring, the severity of the injury, and the likelihood of the failure being recognised before injury occurs, an HRN (hazard rating number) can be calculated. On the basis of the resulting HRN scores, a decision can be made as to whether or not preventative action is required.

For the various risk assessment methods in use throughout Pilz, templates are commonly prepared as Microsoft Excel spreadsheets that can be completed by the consultants and printed for presentation to the client. But it is important to remember that machinery and processes seldom remain unchanged over time. Whenever procedures or processes change, in whatever way, the risks need to be reassessed. Although many clients will be diligent in carrying this out, others may not and it may be better to perform regular (perhaps annual) audits to check for any changes that will trigger a reassessment of the risks. And then, just as for the original risk assessment, the most appropriate method must be selected and used.

If you have any questions about risk assessment methods, please feel free to contact Pilz.


Pilz Automation Ltd
Pilz House, Little Colliers Field
Corby, Northants, NN18 8TJ
United Kingdom

Telephone: +44 1536 460766
E-Mail: sales@pilz.co.uk

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