What Is a Hazard and Other Important Concepts

Over the years, there has been considerable confusion with the concepts of safety, risk, and hazard. The major problem is that many people tend to interchange the words as if they mean the same. On top of that, different industries often define the concepts differently. 

The most important thing to remember is that system safety engineering is a combination of management and systems engineering practices applied to the evaluation and reduction of risk in a system and its operation. The objective of system safety is to identify hazards resulting from the use or operation of a system and to eliminate or reduce the hazards to an acceptable level of risk. 

The system is the combination or interrelation of hardware, software, people, and the operating environment. In system safety engineering, you must look at the system from cradle to grave. In other words, the system life cycle is the design, development, test, production, operation, maintenance, expansion, and retirement (or disposal) of the system. A nuclear power plant is one large system with operators, pressure subsystems, electrical and mechanical subsystems, structural containment, safety systems, etc. A far simpler example is a boy riding his bike. The bike, the boy, the street (with all its traffic conditions), the weather, the time of day, and even other children make up the system of boy on his bike. 

A succinct definition is that a hazard is a condition that can cause injury or death, damage to or loss of equipment or property, or environmental harm (Roland and Moriarty, 1990). Some typical hazards in various systems are electrical discharge or shock, fire or explosion, rapid pressure release, and extreme high or low temperature. Chapter 5 discusses the different types of hazards. Appendix B is a generic hazard checklist. 

Hazard addresses only the severity or end result. Risk combines the concept of severity of the accident consequence and the likelihood of it occurring. In the simplest terms, risk is the combination of the probability (or frequency of occurrence) and consequence (or severity) of a hazard. There are always risks. There is a risk staying in bed and a different risk getting out of bed. As much as we would love to have zero risk, that is a practical impossibility. Because we cannot totally eliminate risk, we try to shrink it as much as possible. Lowering either the probability or the severity of the hazard or both can do this. So 

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