H azards are everywhere. Unfortunately, a hazard is not always identified until an accident occurs. It is essential to identify the hazards and reduce the risk well in advance of an accident. For each process in a chemical plant the following questions must be asked:
1. What are the hazards? 2. What can go wrong and how? 3. What are the chances? 4. What are the consequences?
The first question represents hazard identification. The last three questions are associated with risk assessment, considered in detail in chapter 11. Risk assessment includes a determination of the events that can produce an accident, the probability of those events, and the consequences. The consequences could include human injury or loss of life, damage to the environment, or loss of production and capital equipment. Question 2 is frequently called scenario identification. The terminology used varies considerably. Hazard identification and risk assessment are sometimes combined into a general category called hazard evaluation. Risk assessment is some- times called hazard analysis. A risk assessment procedure that determines probabilities is fre- quently called probabilistic risk assessment (PRA), whereas a procedure that determines prob- ability and consequences is called quantitative risk analysis (QRA). Figure 10-1 illustrates the normal procedure for using hazards identification and risk as- sessment. After a description of the process is available, the hazards are identified. The various scenarios by which an accident can occur are then determined. This is followed by a concurrent