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Hazard Analysis Methodologies

Hazards analysis can get pretty sophisticated and go into much detail. Where the potential hazards are significant and the possibility for trouble is quite real, such detail may well be essential. However, for many processes and operations — both real and proposed — a solid look at the operation or plans by a variety of affected people may be sufficient. The easiest and possibly most effective method is using the step-by-step process of the Job Hazard Analysis (JHA). JHA, sometimes referred to as a Job Safety Analysis (JSA), is covered in good detail in the Job Hazard Analysis, OSHA Publication 3071 [499 KB PDF*, 51 pages].

However, if you are faced with fairly sophisticated and complex risks with a reasonable probability of disaster if things go wrong, you may want some help with some of the other hazards analysis methodologies. What follows is a very brief look at the common ones. If you decide to try one of the approaches, check with your local OSHA Consultation office or call an engineering firm which specializes in hazards analysis.

WHAT - IF Checklist: The what - if checklist is a broadly-based hazard assessment technique that combines the creative thinking of a selected team of specialists with the methodical focus of a prepared checklist. The result is a comprehensive process hazards analysis that is extremely useful in training operating personnel on the hazards of the particular operation.

The review team is selected to represent a wide range of disciplines — production, mechanical, technical, safety. The team is then provided with basic information on hazards of materials, process technology, procedures, equipment design, instrumentation control, incident experience, previous hazard reviews, and so on. A field tour of the process is also conducted at this time, assuming the process is in operation.

The review team methodically examines the process from receipt of raw materials to delivery of the finished product to the customer's site. At each step the group collectively generates a listing of what - if questions regarding the hazards and safety of the operation. When the review team has completed listing its spontaneously-generated questions, it systematically goes through a prepared checklist to stimulate additional questions.

Subsequently, answers are developed for each question.The review team then works to achieve a consensus on each question and answer.From these answers, a listing of recommendations is developed specifying the need for additional action or study. The recommendations, along with the list of questions and answers, become the key elements of the hazard assessment report.

Hazard and Operability Study (HAZOP): HAZOP is a formally structured method of systematically investigating each element of a system for all of the ways in which important parameters can deviate from the intended design conditions to create hazards and operability problems. The hazard and operability problems are typically determined by a study of the piping and instrument diagrams (or plant model) by a team of personnel who critically analyze the effects of potential problems arising in each pipeline and each vessel of the operation.

Pertinent parameters are selected — for example, flow, temperature, pressure, and time. Then the effect of deviations from design conditions of each parameter is examined. A list of key words such as more of, less of, none of, part of, are selected for use in describing each potential deviation.

The system is evaluated as designed and with deviations noted. All causes of failure are identified. Existing safeguards and protection are identified. An assessment is made weighing the consequences, causes, and protection requirements involved.

Failure Mode and Effect Analysis (FMEA): The failure mode and effect analysis is a methodical study of component failures. This review starts with a diagram of the process that includes all components which could fail and conceivably affect the safety of the process. Typical examples are instrument transmitters, controllers, valves, pumps, and rotometers. These components are listed on a data tabulation sheet and individually analyzed for the following:

  • Potential mode of failure ... open, closed, on, off, leaks, etc..
  • Consequence of the failure.
    • Effect on other components.
    • Effect on whole system.
  • Hazards class ... high, moderate, low.
  • Probability of failure.
  • Detection methods.
  • Compensating provision/remarks.

Multiple concurrent failures are also included in the analysis. The last step is analysis of the data for each component or multiple component failure and development of a series of recommendations appropriate to risk management.

Fault Tree Analysis:

A fault tree analysis is a quantitative assessment of all of the undesirable outcomes, such as a toxic gas release or explosion, which could result from a specific initiating event. It begins with a graphic representation (using logic symbols) of all possible sequences of events that could result in an incident. The resulting diagram looks like a tree with many branches — each branch listing the sequential events (failures) for different independent paths to the top event. Probabilities (using failure rate data) are assigned to each event and then used to calculate the probability of occurrence of the undesired event. A simple example of a fault tree analysis chart is shown below.

This technique is particularly useful in evaluating the effect of alternative actions on reducing the probability of occurrence of the undesired event.

Other Hazard Evaluation Procedures:

Additional information on the hazard evaluation procedures outlined above and descriptions of other hazard evaluation procedures, as well as information concerning the selection of an appropriate procedure, are contained in Guidelines for Hazard Evaluation Procedures, prepared by The Center for Chemical Process Safety of the American Institute of Chemical Engineers.

Routine Hazard Analysis:

Even simple processes are complex — they are impacted by human behavior, workplace variables, other business and natural forces, raw material variables, normal wear and tear, and more.

It's a given — jobs once designed for safety may now have hazards or improper operations.

The hazards analysis process — called a Job Hazards Analysis (JHA) or Job Safety Analysis (JSA)— pulls processes back on the safety track periodically.

Done for every job, a JHA or JSA ensures safe steps, teaches new workers, eliminates or controls hazardous materials, and much more.

  • Some companies have work teams complete JHAs or JSA on every job or process and then use them as the guide for how to do the job

Accessibility Assistance: Contact the OSHA Directorate of Technical Support and Emergency Management at (202) 693-2300 for assistance accessing PDF materials.

*These files are provided for downloading.
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