I have been doing a number of recent projects introducing the safety lifecycle to companies that are new to the field. As a result I have been playing with various ways to think about the overall safety lifecycle philosophy. As many of the more experienced readers are aware, the overall safety lifecycle ideas are not new. But, it is worth looking at these ideas in a variety of ways to ensure we are implementing them as effectively and clearly as possible.
Today’s blog supports this goal. It presents the safety lifecycle as a basic feedback and control loop to achieve a set point value for risk as shown in the figure.
In this risk management control loop, we start with a set point of the plant risk tolerance. Then we estimate the existing risk through our risk analysis to generate our initial measured value for safety. As with any standard feedback and control loop, we then compare our measured value for safety to the tolerance. The resulting error signal response is to specify anything we need to manage that risk down to our target set point for risk. Since the specification alone does nothing for us unless we apply it, we then design and build the specified safety instrumented system, check and validate that it works, and operate it accordingly. With our safety instrumented system in live operation, we now have a better opportunity to again measure the level of risk present based on real data. As a second iteration, we compare the field performance to our tolerance target and modify any equipment as needed to get back on target. So in effect, we make the actual plant risk/safety match our target plant risk/safety by adjusting the safety instrumented system design and applying other means of risk reduction.
So we have the safety lifecycle as a risk control loop to ensure that we get a level of risk we can live with. Also we have yet another way to understand the safety lifecycle and explain it to those who may not have as clear a picture of how it should work to give us what we need.