Have you ever been trying to explain the safety life cycle for machinery, but some people don’t understand the importance of following this process to ensure safe machinery? Here’s a concept that might help… I call it “Bullet Proof Safety.”

Think of a Police Officer and apply the safety life cycle to that position….

First step…..”Risk Assessment” What is one of the “Tasks” that a police officer has? Pulling over a vehicle.

What is a “Hazzard” associated with that task? The person in the vehicle could have a firearm.

So how do police officers reduce the risk associated with that task? They implement some type of “Protective Measure“…for example, a bullet proof vest. In our world of machinery safety, this might be a light curtain.

Second Step….”Functional Safety Specification” So… if a bullet proof vest is the protective measure to reduce the risk, we should probably outline how the vest should operate, this example is pretty straight forward, it should stop the bullet. In our world, how is the equipment supposed to respond when the light curtain is interrupted?

Third Step….”Design and Implementation” If I were wearing the vest to reduce my risk, I would want to know that the vest had been designed properly and ensured my personal safety. Don’t we think that our machine operators rely on that same concept when they put their arms through a light curtain?

Someone would have to design the vest and take into account the “worst case scenario” that the vest would have to protect from, example, the largest caliber of bullet. In our world, this would be the PLr for the light curtain safety function to ensure adequate risk reduction.

Then someone would have to do the calculations of the energy dissipation to ensure (“Verify“) that the vest was designed to withstand the largest caliber bullet that it may exposed to. In our world, PL >= PLr, making sure the actual performance level of the light curtain safety function is greater than, or equal to the required performance level indicated by the risk assessment.

Fourth Step….”Validation” Before I put the vest on I would also want to know that it had been tested (“Validated“) by someone actually shooting a round into the vest and making sure the bullet did not penetrate the vest. In our world, we would interrupt the light curtain and make sure the safety function responded as required from our functional safety specification.  We would also inject faults to validate that the safety function responds as it should when exposed to faults.

Fifth Step….“Maintain and Improve” If we have put this much effort into providing a safe work environment, shouldn’t we re-apply this process if we make changes to our equipment that could involve the safety of the machinery?


Jeff Parish

Safety and Sensor Solutions Consultant

Functional Safety Engineer

with CED in Kentucky