Review of the Process Hazard Analysis cont'd

D0E-HDBK-1100-2004

INCIDENT CAUSES.

Incident causes or initiating events should be readily identifiable in any

PrHA method. Reviewers should use their experience to assure that all initiating events,

including hardware failure modes, operator errors, administrative errors, and loss of utilities, are

considered. If the process is in a location subject to external events, the PrHA should include

relevant events such as earthquakes, traffic, weather, or accidents at an adjacent process.

CONSEQUENCE EVALUATION.

Anomalies are most often found in the consequence section of

the PrHA. A common mistake is to use the successful actuation of a protection device as a

consequence, thus omitting the true consequence. For example, if a pressure vessel can be over-

pressured due to a system failure, the consequence is damage/destruction of the vessel, not

opening of the relief valve. It is also necessary to assure that all consequences are listed for

every cause. For example, a pipe break and spill of vessel contents could result in a runaway

reaction due to loss of the chemical and a fire if the chemical is flammable. Finally, the

consequence must be developed assuming all protection fails. A common mistake is to assume

"No Consequences," if protection was successful.

IDENTIFICATION OF PROTECTION.

Protection reduces the probability of the consequence

occurring given that the cause has occurred. There are two key questions to ask when reviewing

the protection portion of a PrHA. First, is the protection capable of preventing the consequence

if it functions correctly? Second, will the protection function, given the cause? For example, a

normally open electric solenoid valve will not close after loss of electrical power and, therefore,

cannot function as protection under that circumstance. A motor-operated valve also will not

operate after loss of electrical power. However, a normally closed electric solenoid valve will

automatically close upon loss of power.

DECISION FOR ACTION.

A PrHA reviewer needs to know the team's criteria for determining if

additional effort is warranted to review a specific scenario or provide risk reduction. After

reviewing the criteria, the reviewer should spot check the PrHA to see how the criteria were

applied to several scenarios.