Page 137 - CHEF Guide

Hazard Evaluation Techniques

• Hazard Identification is part of the Hazards Identification and Risk Analysis (HIRA) method in which the material and
energy hazards of the process, along with the siting and layout of the facility, are identified so that a risk analysis can
be performed on potential incident scenarios.
• Impact is a measure of the ultimate loss and harm of a loss event. Impact may be expressed as the number of injuries
and/or fatalities, the extent of the environmental damage, or the magnitude of the loss, such as property damage,
material loss, production loss, market share loss, and recovery costs.
• Incident is an event, or series of events, resulting in one or more undesirable consequences, such as harm to people,
damage to the environment, or asset/business losses. Such events include fires, explosions, releases of toxic or
otherwise harmful substances, runaway reactions, etc.

• Incident Outcome is the physical manifestation of the incident: for toxic materials, the incident outcome is a toxic
release, while for flammable materials; the incident outcome could be a boiling liquid expanding vapor explosion
(BLEVE), flash fire, vapor cloud explosion (VCE), etc. For example, the incident outcome for a leak of chlorine from a
railcar is a toxic release.

• Initiating Cause (Initiating Event), in the context of hazard evaluation procedures, is the operational error, mechanical
failure, or external event that is the first event in an incident sequence and marks the transition from a normal situation
to an abnormal situation.
• Loss or Hazardous Event is the point in time in an abnormal situation when an irreversible physical event occurs that
has the potential for loss and harm impacts. Examples include release of a hazardous material, ignition of flammable
vapors or ignitable dust cloud, and overpressurization rupture of a tank or vessel.

• Scenario is a detailed description of an unplanned event or incident sequence that results in a loss event and its
associated impacts, including the success or failure of safeguards involved in the incident sequence.

8.13 What-If Analysis

The What-If Analysis technique is a qualitative brainstorming approach in which a group of experienced people familiar
with the subject process ask questions or voice concerns about possible undesired events. It is a common Hazard
Evaluation technique and questions often start with Initiating Events. It is particularly effective at identifying “Cause-
Consequence” pairs for scenario development.

What-If Analysis is not as inherently structured as some other techniques such as a HAZOP study. The concept
encourages the hazard evaluation team to think of questions that begin with “What-If.” However, any process safety
concern can be voiced, even if it is not phrased as a question. The technique can also be used to evaluate hazards in a
safety review.

Ideally “What if” questions represent potential Initiating or Loss Events in a Scenario. For example, “What if the
unloading connection comes apart when the transfer begins?” represents an Event which could be caused by mechanical
failure or human performance issues. The team would brainstorm process deviation scenarios and identify inherent safety
improvements for reducing or eliminating the potential for the scenario to develop. The strategies of substitution,
minimization, moderation and simplification can be used to determine the safety improvement.

8.14 What-If Checklist

What-If Checklists provide the team with a list of thought-provoking issues to help reduce the time commitment to
identify scenarios while improving the quality of the analysis (Figure 8-3).

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