LOPA is a Layer of Protection Analysis and is a type of PHA that looks at the actual layers of protection a particular scenario would have. As you know, process safety is built upon the fundamental concepts of prevention, threat, and mitigation. Hence, we want to prevent the scenario from even starting, but if we can’t, then we want to protect our assets (including people), and then we want to mitigate the consequences of the event. In NH3 systems you would be doing ALL three!