Barrier Analysis

Barrier Analysis as a Safety Tool

Barrier Analysis is the technique used for identifying the harmful or hazardous effects associated with the harmful sources of energy. Barrier Analysis provides an equipment to study the unwanted flow of energy sources to the potential targets, people or objects, through the assessment of various barriers in order to prevent the dangerous energy flow.

Barrier analysis is an effective and efficient system safety tool used to identifying the risks associated with the defined sources of energy. The successively organized paradigm of this analysis provides reliable, rationally reasoned and independent findings about various hazards and barrier controls as compared to many other methods available for the analysis purpose.

Barrier analysis came into the picture to help experts analyze accidents and risks. Talking in general terms, the main use of a barrier is to prevent an action from happening or in other words provide a shield to the people that are a part of that environment, from the consequences. This report will highlight the relation between accidents and the barrier analysis by providing a technique to thoroughly search or investigate the accidents and safety programs. An accident can be described as the set of barriers that have failed, although the reason of failure will be mostly not included in the list of suspected causes. A barrier, in this respect, can be a hindrance, an obstruction or a hurdle that prevents an action to take place or reduces the impact of the harmful consequences. Barriers are important to be analyzed for understanding and prevention of accidents in two ways –

  • The fact that accident has occurred implies that one, or more, of the defined barriers failed. This can be either because they were dysfunctional (Polet, 2002) or they did not serve the purpose properly. The search of such barriers is therefore considered an important part in understand the cause of the accident
  • Once the anatomy of the accident has been analyzed and casual ways have been identified, the defined barriers can be used in order to prevent similar kinds of accidents that take place in the future. For this, the pattern needs to be determined.

Hence, the barrier analysis provides an effective way to consider the events that are related to the failure of a safety system (Livingston et al., 2001). However, it is not a system that is comprehensive enough to act as the sole safety analysis of the system as it may miss a few points due to system failures or human errors (Reason, 1992) while producing the results.

According to the Energy Theory or the Barrier Analysis, whenever there is a chance that the person or an object is approaching the energy flow or trying to come in contact with the environment state that can cause harm to the person or the object, it is required to isolate such environmental state or the energy flow.

As the Barrier Analysis technique is quite different from others, with a limit scope of analysis, it doesn’t fulfill all the requirements completely. But at the same time the technique is most often used to provide support to the system design hazard analysis type, preliminary design hazard analysis type or detailed design hazard analysis type. The technique is also known as the Energy Trace and Barrier Analysis or sometimes the Energy Trace Analysis.

Quite often it is seen that even if the source of energy is harmful, it cannot be removed from the system as it is an essential element of that designed system. Now here comes the role of barrier analysis. The purpose of the barrier analysis here is to identify these sources of energy and evaluate if the potential harms in the designed system can be considerably reduced with the use of relevant energy barriers. The analysis provides a simple tool to separate the energy source from the target to prevent it from the hazards. It acts as a powerful tool in the game of accident analysis and prevention. It should be known at the time of evaluation of the system that the undesirable source of energy coming from a single source is capable of affecting multiple targets. In such cases, there might be a requirement to use multiple barriers to save these multiple potential targets from dangers and provide them optimal safety.

Barrier Analysis Safety
Barrier Analysis Safety

The Barrier Analysis technique is executed by evaluating the source of energy, the energy flow paths that may be harmful for the system, and then identifying and creating the right barriers that must be placed in order to prevent the flow of energy from harming the person or the target equipment (here the target can be objects or people). In general, there are various types and ways of energy barriers that can be used in a designed system. The commonly known barriers are – procedural barrier, physical barrier or a time barrier. These barriers are created with a purpose to counteract the harmful effects of the energy paths in order to reduce the likelihood and severity of system/object damage or a personnel injury.

The type of analysis is generally used for all the types of systems with a goal that it is created to ensure consistent, effective, disciplined and efficient methods for the identification of hazards in the provided system. It is often used during the investigation of accidents in order to help understand the root cause of the incident and to study the damage conditions to ensure they do not occur in the future. The Barrier Analysis has fully devoted itself to overview the types of energy sources in the system, their attributes to understand if they are harmful; it is a tool to guide the discovery for the risks due to the energy sources that need more detailed analysis.

This tool is capable of fabricating detailed analysis report of risks in existing as well as new systems. By correctly and rationally identifying the energy flows into and out of the system, the Barrier analysis enables the growth of each of the sources of energy used in the system. A thorough knowledge and understanding of the sources of energy used in the system is important to get a clear picture of the complete system design and its behavior. The tool is pretty simple and easy to learn.

Barrier Analysis History

Although the concept was introduced more than 20 years ago, they have been only a few instances where the barrier concept was actually used. Haddon introduced the concept that the harmful effects of the flow of energy can be controlled by one of the provided barriers (Haddon, William Jr. 1973). The barriers can be listed as below:

  • Prevention of energy manufacturing or production
  • Reduction in the amount of energy like fuel storage, voltage
  • Preventing the release
  • Manipulating the rate of release, for example slow down the burning rate
  • Isolate in time or space, for example make the electric line go out of the reach
  • Strengthen the defined target, for example create earthquake proof buildings
  • Reorient persons and objects
  • Limit the extent of the damage caused, for example use of sprinklers

The barrier analysis is grounded on the concepts introduced by Haddon; these concepts were understood, adopted and improved by various other experts until the time this technique was used to give birth to a useful tool for the purpose of safety analysis.

Barrier Analysis Theory

The Barrier Analysis is based on the concept that when harmful and hazardous sources are present with in the environment, they act as a serious threat to certain targets. According to this theory, by placing effective barriers between these hazardous energy sources and the targets there is a chance to lessen the threat to these targets. In other words, when there is no isolation or a barrier between the source of energy and the target, it leads to disasters whereas placing a barrier between the energy flow and the target leads to a safe exit.  In situations where there is no barrier placed, effective safety requirement should be created to launch and implement effective barriers.

To understand the theory of barriers, there was work done on the barriers subject called Management Oversight and Risk Tree (MORT) programme. The MORT approach (Knox & Eicher, 1983) defines a method for a complete investigation of accidents as well as a method to analyze safety programmes. This MORT barrier analysis (Trost & Nertney, 1985) is capable of discriminating between safety barriers and control barriers. The difference between the two types of barriers is that the control barriers are related to the wanted energy flow path and the safety barriers are related to the unwanted energy flow paths.

MORT even offers distinguishing between various types of barriers like: physical barriers, warning devices, design of equipment, procedures, and skills. Hence, it provides a more detailed distinction as compared to that given by Svenson (1991) and Kecklund et al. (1996) into human, organizational and technical barriers.

The process that revolves around this tool called barrier analysis is a thorough analysis of the energy sources that are involved in the system and the possible effect these sources have on the attributes present in the environment; these attributes can be any equipment or any personnel. Experts mainly carry out the barrier analysis using a worksheet or some sort of a form to provide documentation, structure and nature of the analysis and the consistency. There is so specific format that is used by the experts as all that matters is the data contained in the worksheet.

Most of the times, the worksheets, that come with columns, are used to help maintain focus and structure in the analysis. The basic information that should be contained in these analysis worksheets should be as following:

  1. List of all the energy sources, present in the system, that provide a threat to the environment
  2. Targets that are a part of this system and are prone to damage, of any sort, from these energy sources
  3. Barriers, already in place, that are meant to control the energy sources to prevent targets from hazards
  4. Barriers, not there already, that should have been placed to control the energy risks
  5. Overall system risk for the energy sources – barrier risks.

While learning as a beginner to perform an analysis, following points should be considered in order to commit one or more problems:

  • Do not try to identify all the sources of energy present in the system
  • Do not evaluate the cascading outcome of the energy sources
  • Not understanding all the energy source paths
  • Not consider the entire system in one shot, rather take a narrow view of each of the energy paths.


The main ingredients of an accident are: the energy flow that causes the harm, the people who are the victim of this harm caused due to energy flow, lack of the barriers of failure of barrier system that are created to keep the accidents apart and the events that lead to the final accident situation.  If all these mentioned ingredients are present in a place, accident has to happen; failure of one leads to prevention of accident.

Hence, the generic constituents of barrier analysis are the energy sources, the barriers and the targets. The forms the basis of the barrier analysis and each of these components must be clearly understood and inferred with reference to the context. The first step in the analysis is the identification of the energy sources. Once these sources have been found out, a problem analysis should be done to nail done the questions which help in understanding the hazardous elements in the design. Some of these questions can be like:

Have the hazardous sources of energy been identified?

What are the energy paths?

What are the potential targets?

What are the safety barriers?

Have the safety barriers been thoroughly identified?

The answers to these questions can be provided after acquiring the knowledge on the system design and its operation, knowledge on the system environmental variables and energy sources.  The analysis process studies and verifies the authenticity of the engineered and the administrative barriers. Here the created safety attributes are considered as the hard barriers and the administrative controls like warning signs, safety procedures and the controlling checks are termed as the soft barriers. As it is difficult to deal with the hard barriers as compared to the soft barriers, the hard barriers are preferred over the soft option. But it doesn’t mean that soft barriers are not used at all; these may be used in certain conditions. Barriers can be categorized under various heads based on their location, function or type.

Barrier analysis Process

The technique that was used in the analysis of Barrier concept was to identify various tasks around the energy sources and the steps taken to achieve the goal.

  1. Identifying the energy sources – in order to achieve this, it is required to study the system and identify all the possible harmful sources of energy. In this step, energy quantity and location should also be identified, whenever possible, to create the list of energy sources. To quote some examples, we have electromagnetic radiations, electricity, explosives and so on.
  2. Identification of energy paths – all the potential energy flow path leading to the target should be identified that can act as a harmful source of energy. Target can be any object, environment or people.
  3. Finding the multiple energy paths – there can be multiple energy flows, more than one dedicated energy flow, leading to the target that can cause a mishap. For an instance, electrical and mechanical functions of a fuse.
  4. Defining targets – for each of the existing energy source, study its flow from the starting point till the end to identify all the possible targets that are likely to be harmed by the harmful energy sources.
  5. Finding out the vulnerability of the defined targets – the vulnerability of the target should be identified. For an instance, faulty equipment might have very little impact on human but can damage another device say microprocessor.
  6. Identifying of the safety barriers – this is the most important step in taking safety measures. All the probable barriers in the energy path from an energy source to the target should be identified. Also, study the effectiveness of all such barriers, the impact of the sudden failure of these barriers, reliability of the existing ones.
  7. Evaluation of the system risk factor study the effect and the extent of harm caused to the target due to the energy flow, or multiple energy flows, to evaluate the risk factor. This analysis should be done with the potential barriers and without the barriers.
  8. Determine the corrective measures – analyze if the barriers provided are effective and adequate for safety of target, else recommend the barriers that should be provided to reduce the risk factor and ensure the safety of the target from the energy sources. Also determine if there is a need to analyze the situation using other techniques to understand completely all the hazards and factors leading to accidents
  9. Identify hazards – determine and track the hazards using a tracking tool
  10. Document all the steps involved in the analysis and the findings

Advantages and Disadvantages

Barrier Analysis has provided huge contribution towards analysis of various energy sources and as a tool in preventing hazards.

Advantages of Barrier Analysis

  • In accident investigation, the tool has proved to be very useful in providing unbiased details on what went wrong which includes not only the physical barrier failures but also the failures of administrative controls. It also provides a visibility on the absence of barriers that should have been in place to avoid the accident.
  • In the field of safety analysis, it offers a common point for humans reliability experts, designers, safety analysts, so that they can all focus on one common goal towards achieving the effectiveness and failure of predicted accidental steps.

Disadvantage of Barrier Analysis

The only drawback of this tool is that while doing a predictive analysis for future, they might assume more amenability with the barriers than actually tends to happen.


A useful example of how barrier analysis was used to save the target from the hazards:

At the French Cadarache nuclear power plant, barrier analysis was used to evaluate the events that led to the release of various water contaminants in the environment. Sequence of events can be described as mentioned below:

  • Somebody forgot to turn off the tap after using the water to rinse his/her eyes
  • After a certain amount of time, water overflowed from the basin and spilled into the tank used for storage.
  • Tank slowly got filled up but the overflow alarm of the storage tank failed to function
  • When the storage tank also overflowed, the low level radiation tank also overflowed but the alarm for this one also failed.
  • As a consequence, a great quantity of water spilled on the flour and flowed into the sump
  • The pump of the sump was unfortunately connected to the rainwater tank rather than the industrial waste tank so the contaminants flowed in the wrong place.

Analyzing the system for energy source path flows, the barriers and the target, it can be clearly seen that although there were two barriers provided in the system they both failed to function. The first step was the omission of an action, which led the energy source, water in this case, reaches the target. This seems to be a failure of a symbolic barrier that could have been the instructions for using the tap. Although there were no functional barriers involved in this step, use of one could have saved the target. To suggest one, a timer that automatically turns off the tap after a time could have done the task for us.

Although the next two steps involved functional barriers, both failed. These could have been replaced with alternative barriers like having difference types of fittings in the two tanks and so on.

Likewise, there are many other applications and examples that used the Barrier Analysis to study the sources, the barriers and the targets in the provided system to ensure use of effective barriers.


The report contains an overview of the Barrier concept as applied by various experts and researchers. The aim of the report is to have an understanding of how the Barrier Analysis can be used to understand the various elements of a system to evaluate the nature of the barrier that is used or should have been use. By identifying the energy sources flow and the target, evaluation of barrier can be studied.

The process can be considered as the comprehensive hazard analysis and its effect on the various element of the environment like the objects and the personnel. The analysis is very simple and can be easily used to find out various threats to the system especially the targets that are at the receiving end. Barrier Analysis provides a pictorial view that helps many analysts and researchers to visualize the risk factor involved in the system. Moreover it is pretty inexperience, which makes it excel over other tools. Barrier analysis has the capability to easily recognize most of the energy sources and their flow path; to quote examples it can recognize sources like electricity, compressed gas and so on.

This combined with the accident analysis can be very helpful in learning the pattern of the accident which happened either because of failure of the existing barrier or because of the missing barrier. The retrospective analysis can be used as an effective tool for the predictive use so that the target can be prevented from the hazards.


Livingston A D, Jackson G and Priestley K; “Root causes analysis: Literature review. HSE Health & Safety Executive”, 2001

Polet P “Modélisation des Franchissements de Barrières pour l’Analyse des Risques des Systèmes Homme-Machine. Ph.D. thesis presented at Université de Valenciennes et du Hainaut-Cambrésis”, 2002

Reason, J. T. (1992). The identification of latent organisational failures in complex systems. In J. A. Wise, V. D. Hopkin & P. Stager (Eds.), Verification and validation of complex systems: Human factors issues. Berlin: Springer Verlag.

Trost, W. A. & Nertney, R. J. (1985). Barrier analysis (DOE 76-45/29). Idaho Falls, Idaho: EG&G Idaho, Inc.

N. W. Knox and R. W. Eicher, MORT User’s Manual, ODE 76/45-4, SSDC-4 (Revision 2), May 1983

Haddon, William Jr.; “Energy Damage and the Ten Counter-Measure Strategies,” Human 2 Factors Journal, August 1973.

Kecklund, L. J., Edland, A, Wedin, P. & Svenson, O. (1996). Safety barrier function analysis in a process industry: A nuclear power application. Industrial Ergonomics, 17, 275-284

Svenson, O. (1991). The accident evolution and barrier function (AEB) model applied to incident analysis in the processing industries. Risk Analysis, 11(3), 499-507.

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