Simplified Safety: Risk assessment improves reliability, performance, and compliance

Performing risk assessments regularly throughout the equipment life cycle is the best way to minimize costs, and keep people safe.

09/23/2011


Risk assessment benefits appear in four areas:

Improved machine design – Performing risk assessments in the design phase helps produce a safe design;

Reduced injuries – Risk assessments made at any stage in the machine life cycle identify hazards to life and limb existing in the design, installation, and use of the machine, and provide ways to mitigate the risks posed by those hazards;

Improved equipment salability – For OEM equipment manufacturers, sales largely hinge upon conformance to European standards;

Lower insurance cost – Having had a risk assessment done shows due diligence on the owner’s part, reducing potential litigation costs, and thus the cost to insure against those costs.

Conceptually, risk assessment is quite simple, as the accompanying sidebar (Quantitative risk assessment) shows. If there are a given number of ways the system can fail, and each failure has foreseeable consequences, it’s a simple matter of forming one vector representing the failure consequences, and another representing the probabilities of the failure modes. Taking the scalar product of the two vectors provides a quantitative measure of risk that machine represents.

You have to look at the outcome of each hazard. Will you have death by machine, amputation, cut, or nick? That is an important part of the risk assessment. You also have to look at the probabilities of those events occurring.

The biggest difficulty with older standards was assigning a level of danger to a hazard. With the older methodology, weighting of a hazard came out of the experience of the person doing the risk assessment. The more experience the person had with design and use of that and similar equipment on the floor, the more realistic that weighting would be.

Obviously, we don’t all have that kind of experience, making completing an accurate risk assessment difficult. Happily, there are now tools available that can help with estimating the probabilities and hazard levels on a machine. Recent ISO safety standards, notably ISO 13849, ISO 12100 and ISO 14121, bring in statistical data to help give identified hazards a weight. ISO 13849 does a particularly good job in that it provides statistical data on electromechanical machine components. That allows calculating, for example, component life spans in cycles of operation. Things like that can help you look at safety circuits and assign them a reliability and expected life span to help inform your risk assessment.

Most ANSI standards now being published include the requirement to perform a risk assessment. In Europe, it is a universal requirement, so if you are doing business overseas, it has to be done. In the U.S., where it is not yet a requirement, the fact that you do it can help in the sale of your product. If you show an understanding of these requirements and have a risk assessment done, it will show that you have risk under control and you are mitigating issues with the equipment. For an OEM, it demonstrates to your customers that you are sensitive to their needs for safely designed and constructed equipment, and have the competence to provide it.

Having had a risk assessment done shows due diligence on the machine owner’s part. Showing that you have identified and mitigated hazards will help in the event of an accident. It will also help diagnose the cause of the accident. Was there a hazard that was missed during the risk assessment? Was the accident caused by the employee bypassing the mitigation systems? All these bear strongly on the machine owner’s liability.

In my opinion, performing a risk assessment is the best way to keep people safe, protect your company from expensive litigation, and minimize overall cost of doing business.

RWD has helped many clients perform risk assessments and has conducted for the client, risk assessments. RWD Technologies, a div of General Physics has the staff to complete a risk assessment for you and your process or equipment. Our staff has many years of equipment and manufacturing experience to complete your risk assessment. Our goal is to help you and your customers reach compliance with the new standards that are being required now on a lot of your equipment. Safety is our goal for you. For those seeking online assistance with compliance and a better understanding of the new standards, help is available from a number of manufacturers. Siemens, for example, offers a free, TÜV-certified Safety Evaluation Tool to assist customers in checking their safety designs to determine compliance with SIL or PL requirements. For more information on this tool and other Siemens safety automation related products, visit the Siemens Industry website at www.siemens.com.

Another resource offered at no charge is the SISTEMA (Safety Integrity Software Tool for the Evaluation of Machine Applications) Software PL Calculation Tool developed by the German Institute for Occupational Safety and Health to simplify implementation of EN ISO 13849-1:2008. It allows functional safety data to be input manually or automatically using a manufacturer’s SISTEMA data library. For more information, go to www.dguv.de/ifa/en/pra/softwa/sistema/index.jsp.

- Scott Krumwiede is Manager of Manufacturing Performance Improvement Services, RWD Technologies, Division of General Physics Corporation.

This article was submitted for the custom newsletter, Siemens Simplified Safety. See other articles in the Siemens Simplified Safety newsletter. www.controleng.com/newsletter/siemens-simplified-safety.html 



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