System safety precedence

The order of precedence for satisfying system safety requirements and resolving identified hazards is not unlike that which applies to general industrial safety considerations. There are five basic steps, as follows (MIL-STD-882)  

Design for Minimum Risk The system safety order of precedence dictates that, from the first stages of product or system design, it should be designed for the elimination of hazards, if possible. Unfortunately, in the real world, this is not always practical or feasible. If an identified hazard cannot be eliminated, then the risk associated with it should be reduced to an acceptable level of hazard probability through design selection. 

To clearly understand the relative importance of this element in the system safety order of precedence, consider the following example. 

Incorporate Safety Devices If identified hazards cannot be effectively eliminated or their associated risk adequately reduced to acceptable levels through system design, that risk should be reduced through the use of engineering controls and safety devices. These may include fixed, automatic, or other protective safety design and hazard limitation/control features or devices. Also, when applicable, provisions should be made for periodic functional checks and maintenance of any safety devices. 

In the above example, the management of this manufacturing plant has determined that many other comparable paints/lacquers available on the market also contain isocyanates or other equally hazardous commodities. The installation of automated technologies will be too cost prohibitive to operate a competitive enterprise. Therefore, the system safety order of precedence dictates that suitable safety devices should be installed to control the hazard risk posed by the toxic lacquer. This would mean that the management team must decide whether 

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It is not, however, always called the safety precedence sequence. It is also known as the system safety precedence, the hazard reduction precedence sequence, the hazard control precedence sequence, fhe risk control sequence, and several other names. The fifth step (accept residual risks) is not always included. 

The system safety requirements paragraph discusses program objectives, general design requirements, the system safety precedence (safety precedence sequence), and risk assessment descriptions of both severity and probability categories (Tables 3-1 and 3-2). 

Risks can be treated by the application of engineering and administrative controls to reduce the level of risk. It is done by application of systematic application of the system safety precedence (design, safety devices, warning devices, procedures, and training see Chapter 12). 

The CRC concept, believed to have been pioneered by Ludwig Benner of Events Analysis, Inc., applies RAC logic to hazard controls to develop a matrix to evaluate alternative control measures. It is used for selection and evaluation of hazard controls in conjunction with RACs. It is based on system safety precedence. The rules for use are... 

The energy controls that form one side of the CRC matrix roughly parallel and are consistent with the system safety precedence. 

Another means of improving overall system reliability is by application of the system safety precedence (or safety precedence sequence or hazard reduction precedence sequence). 

List the steps in the system safety precedence sequence. 

Risk Assessment 2 2B (see Tables 2.1-2.3). Liquid contact with parts is assessed as a critical occurrence, since the potential damage to the parts would most likely render them unusable. The likelihood of such a mishap is considered highly probable, based on the proposed system design. The risk assessment matrix (Table 2.3) indicates that a risk classification of 2B is unacceptable. Therefore, the system safety precedence tells us that such risk should be approached with the intention of elimination, or possible reduction to an acceptable level. 

System Safety Precedence An ordered listing of preferred methods of eliminating or controlling hazards (MIL-STD-882). 

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