ApplicabilityETBA StepsTypes of EnergyETBA ProceduresLimitationsBack

The energy trace and barrier analysis (ETBA)


The energy trace and barrier analysis (ETBA) is a professional level procedure intended to detect hazards by focusing in detail on the presence of energy in a system and the barriers for controlling that energy. It is conceptually similar to the interface analysis in its focus on energy forms, but is considerably more thorough and systematic. The Energy Trace and Barrier Analysis (ETBA) method can be used to develop a more detailed understanding of energy exchanges that occurred during a phenomenon. The technique helps investigators avoid oversights in behaviors that might not otherwise be noticed.

This technique approaches the development of Event Building Blocks (EBs) by tracing the flows of energy into, within, and out of a system or component involved in a phenomenon. It is based upon the premises that energy flows introduce changes in a system or component which, if understood, can be predicted and controlled. ETBA documents energy flows by methodically tracing energy movements within systems or components, and across interfaces, to identify behaviors that influenced the course of events being investigated.


The ETBA is intended for use by loss control professionals and is targeted against higher risk operations, especially those involving large amounts of energy or a wide variety of energy types. The method is used extensively in the acquisition of new weapons systems and other complex systems.

ETBA can be used at any stage of an investigation to explore changes and help develop hypotheses about what might have happened.

The procedure can accommodate any observed or documented data about energies involved in any occurrence. It requires knowledge about about energies, their attributes and behaviors; the energies present during an occurrence; the expected course of the energy flow through the system involved with the occurrence; and the energy flow out of the system.

The ETBA involves 5 basic steps. Step 1 is the identification of the types of energy found in the system. It often requires considerable expertise to detect the presence of the types of energy. Step 2 is the trace step. Once identified as present, the point of origin of a particular type of energy must be determined and then the flow of that energy through the system must be traced. In Step 3 the barriers to the unwanted release of that energy must be analyzed. For example, electrical energy is usually moved in wires with an insulated covering. In Step 4 the risk of barrier failure and the unwanted release of the energy is assessed. Finally, in Step 5, risk control options are considered and selected.

ETBA Steps

Step 1. Identify the types of energy present in the system
Step 2. Locate energy origin and trace the flow
Step 3. Identify and evaluate barriers (mechanisms to confine the energy)
Step 4. Determine the risk (the potential for hazardous energy to escape control and damage something significant)
Step 5. Develop improved controls and implement as appropriate

Types of Energy

Kinetic (moving mass e.g. a vehicle, a machine part, a bullet)
Potential (not moving mass e.g. a heavy object suspended overhead)
Chemical (e.g. explosives, corrosive materials)
Noise and Vibration
Thermal (heat)
Radiation (Nonionizing e.g. microwave, and ionizing e.g. nuclear radiation, x-rays)
Pressure (air, water)

Each type of energy may need to be considered individually from the perspective of the phenomenon being investigated if it is present during the process. Energies present also need to be considered in the context of any energy control strategy or strategies that may exist. The operation needs to be analyzed at the input /use /output level for each energy type to determine if energy barriers or controls address realistic potential control problems and satisfactorily control them.

ETBA requires detailed familiarity with the operation or system. ETBA often requires the services of someone who really knows the operation and who can trace energies and barriers /controls thoroughly.

This tool requires sophisticated understanding of the technical characteristics of systems and of the various energy types and barriers. Availability of a safety professional, especially a safety engineer or other professional engineer is important.

ETBA Procedures

The ETBA procedure relies on input-operation-output analytical thought processes. Someone or something introduces energy into the phenomenon being investigated (input.) After it is introduced, the energy does something in the system (operation.) After it does something in the system (output), left over energy may exit the system (output.) If the interaction(s) required all the energy available, it may leave behind evidence of its interactions. The residual effects of energy exchanges may be recorded as changes in things or on recordings of measurement devices, or as observations by people of motion or displacement, for example. These are the "tracks" that must be observed before EBs can be developed for an MES Matrix.

After identifying an energy source that was present or introduced into the system, and where it is present in the system, the procedure is to trace what the energy did or does during the phenomenon of interest. This requires identification of the "targets" of energy flows for each energy source. For each energy type, the flow must be traced to each transfer or use point, and then traced into any branches that flow from that point. Then each physical or procedural barrier to the energy must be considered to determine what changes occurred or might occur. When occurrences are being investigated, ETBA helps define EBs by asking certain questions about each energy type.

For an undesired outcome to occur, there must be an energy source with a released flow of energy to a target in the absence of adequate barriers. The flow or transfer of energy follows some path between the energy source and the target or component of the operation being protected.

Remember: the objective is to develop EBs, where the energy is the actor, what the energy did is the action, and what the energy acted on is included in the descriptor. The descriptor for an energy flow EB should include the pathway.


All mishaps involve the unwanted release of one kind of energy or another. This fact makes the ETBA a powerful hazard ID tool. When the risk stakes are high and the system is complex, the ETBA is a must have. However, the EFBA has the following limitations :Even after a thorough analysis, all hazards might not be discovered. Like the PHA, the EFBA fails to assess risks of combined hazards or co-existing system failure modes. This tool also fails to identify certain classes of hazards, e.g.: asphyxia in oxygen-deficient confined spaces. Because of design and performance requirements, it is not always obvious that energy may be reduced or redirected. A re-examination of energy as heat, potential vs. kinetic mechanical energy, electrical, chemical, etc. may aid this thought process.