Machine Safety: safety system validation and daisy divination

Take safety system validation seriously. Validation is substantiating that a required safety function is reliably achieved in a machine’s safety system. Validation is not the same as verification. Safety automation offers flexibility.

04/05/2014


Let’s not make light of the importance for a safety system validation. It’s not a game of choosing “is it safe or not” like pulling petals off a daisy. It’s also not a “divining stick” experience of supernatural powers which were thought useful for discovering future events. Validation is substantiating that a required safety function is reliably achieved in a machine’s safety system.

I have seen an increasing need for safety system validation in parallel with the application of more complex safety automation technology. Standards bodies also have seen this transformation, and to meet the needs of industry they’ve published ISO 13849-2: 2012, Safety of machinery -- Safety-related parts of control systems -- Part 2: Validation. This standard states: “Validation is a process that uses both static and dynamic testing, and other methodologies, to show that all parts interact correctly to perform the intended safety function, and that unintended functions do not occur.”

Validation and verification are not the same. Verification is also a required step which occurs before validation. Verification is performed during the design stage and is a design engineer’s analytical or mathematical effort to confirm that a safety circuit will achieve the risk assessment’s required performance level (PLr). Verification is not an actual live validation of a safety function on a completed safety system.

Safety automation: complexity and flexibility

Safety automation is much more complex today than earlier electromechanical relay technology. Safety systems today incorporate varying degrees of mechanical, pneumatic, hydraulic and electrical or electronic technology. They may also include other technologies such as safe sensors, safety bus communication, safe wireless and of course software. These are the kinds of complexities that make validation such an important step in the life cycle of functional safety.

Companies today are rapidly adopting safety automation over older safety technology because of the flexibility safety automation offers. These companies are accepting the need to perform validation even though it takes time, resources and money. With these complex systems, it is critically important to identify a fault that may not occur for weeks or months of continuous machine operation. In my opinion, if that fault does occur and the safety function operates correctly, validation just became an investment with a highly desirable return on investment.

Remember: Validation is substantiating that a required safety function is reliably achieved in a machine’s safety system. Safety functions should not be left to chance.

Has this presented you with any new perspectives? Do you have some specific topic or interest that we could cover in future blog posts? Add your comments or thoughts to the discussion by submitting your ideas, experiences, and challenges in the comments section below.

Related articles:

ISO 13849-2: 2012, Safety of machinery -- Safety-related parts of control systems -- Part 2: Validation.

The increasing role of functional safety in complex machine design by Mark Nehrkorn from Control Engineering

Machine Safety: How safe is safe enough? another Control Engineering Machine Safety blog post

Contact: http://www.jbtitus.com for “Solutions for Machine Safety”.



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