Unwanted energy flow barriers

The sides of the accident triangle that are discussed in the MORT program are the unwanted energy flow, barriers that are less than adequate to prevent or control the energy flow, and targets (persons or objects) in the energy path (Fig. 13-1). This approach is the basis for ETBA, which systematically analyzes these three factors and their interrelations. 

Figure 18-9 Unwanted energy flow. Many accidents are the result of a series of unwanted energy flows, barrier failures, and vulnerable targets.

MORT conceives the accident occurred when an unwanted energy flow or environmental condition that results in adverse consequences reaches persons and/or objects. MORT combines this concept and others into a functional accident definition as follows An unwanted transfer of energy or environmental condition because of lack of or inadequate barriers and/or controls, producing injury to persons and/or damage to property or the process [p. 2]. 

After an accident occurs, the first step in the MORT process is to consider the adequacy of the amelioration process, their intent being to limit the severity of the consequences. Then MORT users would determine the unwanted energy flows or hazardous environmental conditions, whether barriers and controls were less than adequate, and whether vulnerable people or property were exposed. 

If controlling the hazards through improved design or engineering is impossible or impractical, the next course of action should be to use physical guards or barriers to separate potential unwanted energy flows or other hazards from potential targets. 

The HazOp study is also similar to the ETBA in that it traces energy flows through a facility, studies barriers to control energy flows, and identifies the targets of unwanted energy flows. 

Identify and evaluate the barriers that are in place to control the energy and the potential targets of any unwanted energy flow that could occur if the barriers fail. 

Column 5—Comments/Barrier Evoluation. Provide comments on the adequacy of the existing barriers to control potential unwanted energy flows at that particular location. If appropriate, include comments on compliance with applicable codes, standards, and regulations. 

For analysis purposes, the changes under the accident block make little difference. The three main branches on the specific control factors side continue to be the contributory events that allowed the unwanted energy flow (or hazardous environment), the LTA barriers, and the targets in the energy path (or vulnerable to the hazardous environment). 

A general approach to common cause failure analysis is to identify critical systems or components and then use energy trace and barrier analysis (ETBA) to evaluate vulnerability to common environmental hazards, unwanted energy flows, and barrier failures (see Chapter 13). 

Energy Trace and Barrier Analysis A system safety analytical technique used to evaluate the flow of energy through a system and analyze the effectiveness of existing barriers within the system which are intended to prevent unwanted transfers of that energy flow. 

Is the affected system/component designed to withstand the condition/situation without the barriers Why What design changes could have prevented the unwanted flow of energy Why ... 

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