Design of protection measures

The choice and design of technical protection measures against runaway is in accordance with the risk level. This means that the consequences and controllability of the commencing runaway must be assessed. The criticality classes, based on four characteristic temperatures, are at the root of this assessment and serve in the design of protection measures. 

The systems not protected against DBEEs (i.e. EE-NC items) should be assumed to be operable or non-operable , depending on which status provides the more conservative scenario in the design of protection measures against the DBEE. 

Not suitable unless gas regime is reduced first and quantitative risk assessment carried out to assess design of protection measures in conjunction with foundation design. 

Comparison of E] q)losion Protection Design Measures In Table 26-24, comparison is made of the explosion protection design measures of containment, explosion venting, and explosion suppression. Regarding the effectiveness of the different explosion design measures, all three techniques are equal if the design of these measures is performed properly. 

A detailed knowledge of the runaway reaction, in particular the rate of runaway, is needed for the specification or design of protective systems. With the exception of (a), these measures are normally reliant upon control systems to operate, and the... 

This example shows that the design of protection systems must be careful and thought through, to be efficient in any emergency. Further, it also enhances the fact that technical measures may fail. Absolute reliability can never be guaranteed. 

Effective occupant restraints, safety systems, and protective equipment not only spread impact energy over the strongest body structures but also reduce contact velocity between the body and the impacted surface or striking object. The design of protective systems is aided by an understanding of injury mechanisms, quantification of human tolerance levels and development of numerical relationships between measurable engineering parameter, such as force, acceleration or deformation, and human injury. These relationships are called injury criteria. 

In common with using prevention as a basis of safety, it is essential that a full evaluation of the hazards of the process is carried out, before the type of protective measure is chosen and designed. The identification and definition of the worst case scenario is particularly important as, in contrast to prevention, any protective measure has to be able to cope with this worst case runaway reaction. In addition, the course of the runaway reaction has to be fully characterized and evaluated using the techniques described in Chapters 3 and 4. 

More important, over 90% of the guideline is generic. Thus, it is a basic document on hazard analysis and risk assessment providing guidance on reducing risks according to a prioritized procedure and on the selection of appropriate design and protective measures. When the process is complete, a tolerable risk level will be achieved. 

Once the site has been classified the scope of protection measures can be determined during the design process (described in Chapter 8). It should be noted that the classification system assumes there will be an underfloor ventilated void as the very minimum of protection (even for the green classification). 

Current UK construction practice adopts the concept of multiple gas protection measures, that comprise a gas control system, since no one protective measure is immune from factors unknown to or outside the control of tire designer. Typically, protection measures increase in number and robustness with the higher characteristic situations defined in Chapter 6. 

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