Inherent safety principles

Bayer (Pilz, 1995) uses a procedure based on hazard analysis, focusing on the application of inherent safety principles to reduce or eliminate hazards. 

Reducing and eliminating hazards and their associated risks is the second major objective. Applying inherent safety principles early in the product/process development effort provides the greatest opportunity to achieve the objectives of the inherent safety review process for the project at hand. If these principles are applied late in the effort the results may have to be applied to the project after next as the schedule may not permit implementation of the results. 

Operations and human factors specialist involvement is important to find optimum solutions to human factors/ergonomics issues. Applying inherent safety principles to ergonomics/human factors issues can reduce risks associated with ... 

There are a variety of process safety risks one needs to assess with chemical processes. In general, these risks will lead to an evaluation of the potential for the process to have precipitous changes in temperature and or pressure that lead to secondary events such as detonations, explosions, over pressurizations, fires, and so forth. The most cost-effective way of avoiding these sorts of risks is through the adoption of inherent safety principles. Inherent safety principles are very similar to and complementary to pollution prevention principles, where one attempts to use a hierarchy of approaches to avoid and/or reduce the risk of an adverse event. The reader is referred elsewhere to a more complete treatment of this important area of process design. ... 

In practice the main purpose of the process plant design is to minimize the total process risk for the limitation of effects. Here risk is the product of the probability of an incident to happen and the possible consequences of that incident. In this thesis the limitation of effects by the means of inherent safety principles is evaluated. 

Human error is the most frequent cause of the loss of containment. Training and certification of personnel on critical procedures are permanent considerations. Also some other inherent safety principles, like ease of control, making status clear, tolerance and making incorrect assemply impossible, come into play here. 

An inherent safety design should contain the mentioned principles. They should also cover the whole design process. In the early stages of process design these principles help to choose the safest materials, process conditions and even process technology. The difficulty at the moment is the lack of rutines to implement these inherent safety principles into reality. 

From Table 6 it can be seen how the selected parameters have a connection to the basic principles of inherent safety. For instance the subindices of equipment safety and safe process structure contain several characteristics of inherent safety such as limitation of effects or tolerance to maloperation. It is practical to include several characteristics into few parameters, since the inherent safety principles are both very broad and overlapping. The philosophy behind them cannot be described just by one process parameter. The selected parameters are discussed in more detail on the following pages. 

In the Chapter 7 the selected inherent safety parameters for conceptual process design were presented. From these parameters an inherent safety index is formed in this Chapter. There is a straight link between inherent safety principles and the inherent safety index as discussed earlier (see Figure 5). 

Their final inherent safety index (12 SI) shows the potential applicability of the inherent safety keywords to the process. The index value greater than unity means positive response to inherent safety principles. The larger index indicates better response. A less than unity I2SI indicates that the equipment does not respond to inherent safety guidelines which is a weakness of the process route containing that equipment. 

Codes and standards should, therefore, be used to provide a foundation for a safe and reliable design. But their use is not enough— PSM and inherent safety principles should also be applied if the final facility is to meet high standards of safe and reliable operations. 

The safety of a process can be achieved by inherent (internal) and external means. Inherent safety focuses on the intrinsic properties of a process and attempts to design out hazards rather than trying to control hazards through the application of external protective systems. Inherently safer processes rely on chemistry and physics (properties of materials, quantity of hazardous materials) instead of control systems (interlocks, alarms, procedures) to protect workers, property, and the environment. It would be inappropriate to talk about an inherendy safe process, as an absolute definition of safe is difficult to achieve in this context since risk cannot be reduced to zero. However, one can talk about a process or chemical being inherently safer than other(s). For instance, water can be an extremely hazardous chemical under certain conditions (e.g., floods), but in the context of a chemical process, water is an inherently safer solvent than other chemicals. Trevor Kletz has postulated some basic principles of inherent safety [79,80] that process systems engineers can follow when designing or retrofitting chemical processes. Kletz s inherent safety principles can be summarized as follows ... 

Hazardous substances released from plants could cause serious problems to plant employees as well as to the nearby public. The release could be due to accidents (human error), instrument failure, control failure, and natural calamities or through deliberate acts of vandalism, terrorism, or sabotage. The application of inherent security can help in two ways (1) by reducing the likelihood that a facility will be targeted and (2) by minimizing the severity of an incident should an attack occur. Similar to inherent safety principles, one can consider a set of guidelines for inherent security ... 

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