Risk Assessment

Machines pose various hazards. Therefore, it is necessary to understand the nature of such hazards in advance when considering machine safety at the design stage. This process of determining the level of hazard is called “risk assessment.”

The diagram below shows process of safety determination, or risk assessment, with the area of ​​the triangle representing the magnitude of risk.

The Goal of Risk Reduction

Procedure of risk assessment

Risk assessment of machinery is carried out according to the steps shown below. By repeating this procedure (risk assessment → risk reduction) enables us to eliminate hazards as much as possible and implement safeguards to ensure the required level of safety.

1. Determination of Limits of Machinery

The specifications for the limits of machinery involve determining three restrictions.

• Use limits: Consideration of intended use and reasonably foreseeable misuse
• Space limits: Consideration of a machine’s range of motion and the interface between an operator and the machine
• Time limits: Consideration of the life limits of the machine and its individual component

2. Hazard Identification

The aim is to identify potential hazardous situations in machinery and the possible causes that could lead to hazardous events. Examples of hazardous situations and events are listed below.

Hazard Classification and Events

3. Risk Estimation

After implementing the above-mentioned hazard identification, we estimate how dangerous the hazard is, by classing its ‘severity’ and ‘probability’. The required performance level (PLr) for the safety function is determined by estimating various risks which the machine involves.

Details about “Performance Level (PL) and Required Performance Level (PLr)”

PLr Determination Table for a brief risk assessment of your machinery products

4. Risk Evaluation

The results of the risk estimation are evaluated to determine whether risk reduction is necessary. If risk reduction targets are met, or if risk comparisons come to a positive conclusion, you can be confident that the machine is safe. Risk evaluation is based on two criteria: 1) achievement status of risk reduction targets, and 2) a comparison with the risks of similar machinery. Documentation is also required to demonstrate the last steps taken and their results.

5. Risk Reduction

As described and numbered 1 to 4 in the tree chart below, there are four ways to work on the safety measures in ISO 12100:

• Risk reduction through design (Safety measures)

This is a measure taken to ensure safety at the design stage of the machine itself, which is not supplemented by external safety measures such as guards or safety devices. It is also called “inherently safe design.”

• Safeguarding

This is a safety measure that uses protective fences/guards (and safety devices) to protect people, which is taken when safety cannot be sufficiently ensured by reducing risks through above-mentioned design.

• Complementary protective measures

This is a safety measure taken when the above-mentioned two safety measures are insufficient to avoid risk.

• Information for use

This is a safety measure taken to provide the following:
– Hazard indications and warnings for events such as ignition of the machine, speed limit exceeded
– Indications and signs for safe use
– Accompanying documents (instruction manuals) to inform users of residual risks

Terminology

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