What is a HAZOP Safeguard?

For every hazardous consequence analyzed as part of a HAZOP, the HAZOP team has to identify what safeguards or mitigating factors exist to reduce the risk of the event. Simply put, safeguards are anything that will effectively prevent or mitigate the hazardous consequence. Some different types of safeguards include:

• BPCSs - Basic process control systems

• Pressure safety valves

• Secondary containment

• Alarms with operator actions

• Operator rounds

• Conditional modifiers

Safeguards must always be at least 90% reliable in order to be used in a HAZOP to reduce the likelihood of a consequence.

How do we know if a safeguard is effective?

In order to be considered as a protection layer and credited for risk reduction, a device, system or action must have the following four characteristics:

1.      Specificity – the protection layer is designed to prevent or mitigate the consequences of one potentially hazardous event

2.      Independence – there is no potential for common cause or common mode failure with any other claimed protection layer for the same scenario. For example, multiple alarms that all go to the same operator cannot be taken as independent. The action of all the alarms is for the operator to bring the process to a safe state, and if the operator is fatigued or absent, it won't make a difference if there are one or 100 alarms that go off.

3.      Dependability – both random failures and systematic failures have been addressed during the design

4.      Auditability – the protection layer’s protective functions are designed to be validated regularly.

Conditional modifiers are another form of a mitigating factor that can be considered as part of the HAZOP. These modifiers are most often used when there is a low likelihood of personnel being in the area (must be less than 10% of the time to reduce the likelihood by a factor of 10) or a low likelihood of a source of ignition in cases such as a flammable liquid or gas release in a classified area.

In order to identify all the safeguards present in a particular scenario, it’s imperative to have a collaborative discussion with your HAZOP team and analyze the scenario from both a technical and operational standpoint.