Safety barriers

It has developed a real time method to compare successive non-destructive inspections of the steam generator tubes in nuclear power plants. Each tube provides a safety barrier between the primary and secondary coolant circuits. Each steam generator contains several thousands of tubes whose structural integrity must be ensured through the lifetime of the plant, Therefore, Laborelec performs extensive nondestructive tests after each plant outage. 

Warning Signs Displayed Y/N Safety Barriers Erected Y/N... 

Evaporative cooling is very unlikely to be a safety barrier. Only dumping or quenching can be used. Reduce concentrations, optimize operating conditions in order to minimize accumulation, change to continuous operation, etc. 

That would have brought the Drain end of the Primary winding right next to the safety barrier, with the Secondary ground end (which is usually connected to the chassis) directly across the isolation boundary. With this winding arrangement, we would have a healthy dose of CM noise injected directly into the chassis/earth. 

Electrical Isolation. These two circuits are integrated to create one circuit through a safety barrier. The purpose of this safety barrier or protective interface is to ensure electrical isolation so that the higher levels of energy available in the non-hazardous circuits cannot be transmitted to and through the circuits in the hazardous area. 

Safety Barriers. Figure 1 illustrates an application employing intrinsically safe electrical circuits for the demilitarization of ammunition. Three separate areas are required for this application - one area, classified as non-hazardous, to serve as the control and loading area a second area, classified as hazardous, where the actual demilitarization is accomplished and a third area, classified as non-hazardous, is required for the hydraulic pump due to the level of noise produced. 

For this application, Zener safety barriers were selected as the protective interface. Further, every circuit going into the hazardous area is connected to a separate Zener safety barrier. 

The case studies revealed a lack of overview regarding precursors, their underlying organizational root causes (the latent conditions) and their possible effects on safety barriers. This lack of overview created the opportunity for safety risks in the operational process, despite the presence of many safety indicators and measures. 

When these latent conditions create an unfolding situation, the safety barriers present in an organization can be seriously affected. Svenson (Svenson, 2001) identifies three functional categories of safety barriers, e.g. technical, human, organizational. These safety barriers can be activated by different safety barrier systems, such as the closure of a valve automatically by a computer or manually by an operator. Moreover, a safety barrier system can (simultaneously) operate more than one safety barrier, like an operator who can close a valve, connect a hose, or a computer which closes down a machine and alerts an operator, etc. 

A technical safety barrier represents technical equipment, whose function it is to arrest the accident/incident evolution so that the next event in the chain will not be realised. The human safety barrier is the suitable people, whose function it is to intervene and arrest the accident/incident evolution so that the next event in the chain will not be realised. The organizational safety barrier is the procedures, rules, guidelines, etc. present, which function to arrest the accident/incident evolution so that the next event in the chain will not be realised. In this thesis the latent conditions and precursors in an unfolding situation are considered to have three possible effects on the safety barriers negative, positive or none at all. 

If the safety barriers are ineffective or missing, the precursor present can pass through a hole in a safety barrier and if a sequence of safety barriers are ineffective or missing, eventually an accident can occur. To explain the foregoing, an example is given ... 

C By maintaining an overview of effective and ineffective safety barriers,... 

In practice the presence of all three ways of intervening are needed. It is not possible to eliminate all latent conditions and there will always be conditions leading to possible ineffective safety barriers and ineffective control elements, which subsequently lead to precursors. Therefore, recovery is necessary, to intervene and arrest the precursors and ineffective safety barriers from evolving into a possible accident. Finally, because not all precursors can be effectively recovered, finally an overview of affected safety barriers is necessary to prevent an alignment of ineffective safety barriers and the presence of precursors that can escalate into an accident. 

Using this case study, the concepts derived in the previous Chapter will be enhanced to retrieve a structured way of analysing which in turn will be developed to retrieve the operational control structure of the company and the way safety barriers (measures) are affected by the control process in daily use. 

In the following sub-Sections the practical approach derived in the previous Chapter will be applied on this case study. Therefore, the precursors present inside the operational process are identified. Then, the control of the operational process will be modelled and analysed to find the ineffective control elements. Furthermore, the latent conditions causing the ineffective control will be retrieved and their impact on the existing safety barriers will be identified. Finally, improvement opportunities for the company will be indicated, together with some recommendations and enhancements for the applied concepts and the proposed practical approach. 

The next sub-Section will discuss how the latent conditions, that cause the identified ineffective control elements, affect the current safety barriers in the pesticide company. 

In this sub-Section the ineffective control elements are further analysed to retrieve the conditions causing their ineffectiveness. By checking all six types of conditions for their contribution to the ineffectiveness, the causal conditions can be identified. These causal conditions are the latent conditions. Subsequently, these latent conditions are used to explain why certain safety barriers are affected in the pesticide company. 

Once both latent conditions and precursors are identified in the company s control process and operational process, the effects on the company s safety barriers can be retrieved. Therefore, the safety barriers present around the transformation process will be identified, i.e. technical, human, and organizational safety barriers. Subsequently, the identified types of latent conditions are used to check if they affect the identified safety barriers either positively, negatively, or not at all (as discussed in the previous Chapter). How safety barriers are affected is illustrated by the example of the re-... 

The ineffective observation element of the extrusion sub-process enables the reoccurring product purity problem, which had no effect on any safety barrier present. It appears that the focus of the analysis so far should be more on safety relevant precursors and processes, to avoid results that do not affect any safety barrier. This problem will also be discussed further in Section 5.2. 

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