Machine Safety Verification and Validation

Verification and validation of a machine’s risk reduction measures are two independent steps. They are critical for any machine’s safety performance prior to putting it into production. A machine’s design (schematics, controls, etc.) of its risk reduction measures first go through verification. Validation begins after the design is verified and the machine is ready to run.

• The verification checks that the design is following the risk assessment requirements and the PLr. 
• The validation checks that the risk reduction measures are functioning up to their expected and needed reliability/performance via analytical and functional tests. 

There are three steps to verify your functional safety circuit.

1. The first verification step includes reviewing the risk assessment, safety requirements specification, operator/technical documents for the machine, electrical schematics, fluid drawings, bill of material, proper application of risk reduction measures, etc. 
2. When machines have a safety PLC or a safety controller or a programmable safety device (robot safety parameters, safety drive parameters, programmable safety devices, etc.), the second verification step consists of reviewing the safety related application software (SRASW). Reviewing the software allows us to ensure that proper programming principles were used, input /output parameters are well set and that the SRASW meets the minimum reliability or performance requirements required by the risk assessment. 
3. The third verification step, includes calculating the probability of dangerous failure per hour for each safety function to meet or exceed the required reliability of performance level. It as well provides you the mission time for each safety device that you are using as part of your safety function. Completing the calculations can be done manually, by following the calculations within ISO 13849-1; or less manually by using software tools, such as SISTEMA and others. The convenience of using software tools is that most manufacturers of safety-related devices used within safety functions, have their reliability data published within their technical documentation and within SISTEMA, which makes the data very easy to transfer.

The validation includes checking the following:

• Each safety function meets the requirements of the risk assessment
• Each safety function meets the performance level required via checking:
  • the requirements of the category.
  • avoidance of systematic failures via checking:
    • suitable materials and adequate manufacturing
    • correct dimensioning and shaping
    • selection and installation of components
    • failure modes
  • ability to perform a safety function under environmental conditions.
• The ergonomic design meets the requirements so that the operator does not act in a hazardous manner.

In order to conduct a validation, the risk reduction measures have to be installed, wired, programmed, powered, integrated into the machine, and the machine should be ready to run. The validation can be performed both via testing and analytically. The purpose of the validation step is to ensure that design of the safety function and implementation of the safety related devices is in accordance with the requirements for the safety function and risk assessment. 

In summary, both verification and validation are important to be performed at various stages in the machine design, build, installation and operation. Together they ensure that the machine’s functional safety reliability is achieved, tested and documented.