How do you prove functional safety?

There are many steps to this process, and it requires a significant amount of technical assessment and documentation.

When machinery or an automated process requires functional safety, the manufacturer of the machine, robot or automated system must prove that the safety system they design meets the requirements of EU legislation.

The machinery directive specifically asks for a risk assessment which must be available to the owner of the machinery upon request.

There are many steps to this process, and it requires a significant amount of technical assessment and documentation. In some cases an independent test facility is required to confirm the manufacture of safety components. Generally, the process of proving functional safety is known as a conformity assessment procedure.

Conformity assessment

  • Proves that all relevant directives and laws are applied.
  • Declaration of conformity lists the standards and directives that are applied to the product and by signing the declaration, the manufacturer declares that the machine complies with the list standards

Risk assessment

  • Required by the machinery directive.
  • Proves that all risks have been identified and are sufficiently reduced.
  • Lists the hazards, measurements taken or to be taken and the performance levels before and after the defined measurements.

Conformity assessment procedure

When a control system is used to provide a safety function, it must provide an appropriate level of safety relative to the hazard it is protecting. In this case, systems requiring functional safety must be designed according to a risk assessment, explained below.

Fundamental to the concept of functional safety, a safety component or system of safety components used in safety related control system must be absolutely risk free. In the case that the control system or one of the components of the control system fails, the overall function of the system must remain safe. Normally, this requires that the hazardous equipment remains de-energized until the failure has been fixed.

Risk assessment

A risk assessment is mandatory for all devices that fall under the Machinery Directive. In case of an accident in connection with your machine at any stage of its product life cycle, the risk assessment will be taken into account. It is your most valuable document to prove you have taken all reasonable measurements to prevent hazardous situations.

You can complete your risk assessment in an excel file or use specific software developed to easily complete the task such as DOCUFY Machine Safety. If you are unsure how to complete the risk assessment, you can get help from a service provider. There are companies that offer training or can complete the risk assessment for you.

Risk assessment requirements

A risk assessment must include the following:

  1. Each possible hazard that is related to the use of your machine must be documented.
  2. For each hazard, define which person is affected and at what stage of the product life cycle the hazard appears.
  3. For each hazard, define the likelihood of the hazard and the severity of the harm.
  4. Combine the likelihood and the severity of the harm to evaluate the risk level and the performance level for your safety solution.
  5. Define the safety integrity level that the solution has to meet.
  6. Define the solution to reduce the risk and the new risk level with these solutions in place.
  7. Include technical drawings of the safety control systems, information relating to the control system components and calculations of the fault tolerance of the system.
  8. If the remaining risk is still too high, define further actions to be taken until your risk level is acceptable.
  9. Define the standards and directives that you’ve consulted for each risk.

There are two specific risk assessment diagrams applicable to functional safety:

EN 13849-1

EN 5150

The method for conducting machinery, robotic or automated process risk assessment is described in a number of international safety standards.

Selecting an appropriate standard that is accepted by the enforcement agencies in Europe provides a sure way of ensuring all elements of risk are identified and properly controlled.

The use of a recognised engineering standards allows the designer of a functional safety system a ‘presumption of conformity’.

Examples of safety standards useful in assessing automated processes, robotics and machinery include:

  • ISO 12100 – Safety of Machinery Basic Principles
  • ISO 14121 – Principles for Risk Assessment
  • IEC 61882 – Hazard and Operability Studies

Safety Integrity Level (SIL)

The SIL is the relative level of risk-reduction provided by a safety function. The IEC 61508 defines 4 SILs, with level 4 being the most dependable and level 1 being the least dependable. The safety integrity level for each safety function is usually defined during the risk assessment. It depends on the method and products you choose to reduce the hazard. There is a harmonised system used to provide a presumption of conformity under the machinery directive.

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