Controls hierarchy, safety practice

The Department of Defense s Standard Practice for System Safety, MIL-STD-882, was originally issued in 1969. It was a seminal document at that time, and three revisions of it have been issued over the span of 31 years. This standard has had considerable influence on the development of risk assessment, risk elimination, and risk control concepts and methods. Much of the wording on risk assessments and hierarchies of control in safety standards and guidelines issued throughout the world is comparable to that in the various versions of MIL-STD-882. 

Much was made in Chapter 12, Hierarchy of Controls The Safety Decision Hierarchy, of the need to design work methods so that they were not error-provocative or overly stressful. Safety design reviews should not be Umited to the facility, equipment, and processes, that is—the hardware. They should also limit the hazards and risks in the work methods prescribed, taking into consideration the capabilities and limitations of the workers so that the risks of injury and damage are at a practicable minimum. 

A hierarchy is a system of persons or things ranked one above the other. The hierarchy of controls in ZIO provides a systematic way of thinking, considering steps in a ranked and sequential order, to choose the most effective means of eliminating or reducing hazards and the risks that derive from them. Acknowledging that premise—that risk reduction measures should be considered and taken in a prescribed order—represents an important step in the evolution of the practice of safety. 

To provide guidance to those applying The Safety Decision Hierarchy, we here reproduce General Design Requirements A Thought Process for Hazard Avoidance, Elimination, or Control, as it appeared in our earlier On The Practice Of Safety. This guideline is my extension of the incident and exposure prevention aspects of Haddon s work. 

The actual control measures should be selected on the basis of their effectiveness, applicability, practicability and, finally, cost. Some controls may be dictated by legal requirements, e.g. equipment guards. In most cases, however. It Is usual to apply a hierarchy of measures such as that given In the publication Successful Health and Safety Management (HS(G)65). 

The PtD focus is to achieve workplace safety by levels 1-3, thereby avoiding reliance on levels 4-6. While the optimal approach is complete elimination of a hazard, there may be limitations because water industry facilities have some inherent hazards that cannot be completely designed out. Therefore the PtD goal is to use the hierarchy of controls to modify the design within practicable limits, reducing the hazards as low as is reasonably possible. 

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