LOPA alarm response as IPL

[RKJustice]

Hi,

In a LOPA for a certain scenario, a hazard is protected by the BPCS which closes a control valve. It is also protected against by a independent trip which closes a separate ESD valve. Can an operator response be credited as an IPL if the response is independent of the other IPLs EXCEPT that he/she can only close the control valve (which the BPCS will close) or the ESD valve (which the trip will close)?

I would say no, I just wondered if there are any other views?

 

[ajs1972]

I would say, like you, that is not an IPL, because the valves are common to another IPLs (common cause factor), normally the alarms are for operator´s awareness and the manual actions are required, for example, close manual valves or activate emergency buttons what close another final elements or activate another IPL´s or mitigation systems.

In this case this is another loop, the alarm is the sensor, the operator is the "controller" or "PLC" and the final element is a manual valve or activation of some organizational measures.

In the case of alarms, is necessary to consider the sensor of the alarm, the controller and the HMI. Talking about the operator, we need take in count of the time of response at least 20-30 minutes, the training and the operator must be free of stress.

Best Regards.

 

[EmmanuelTop]

Failure of an IPL means non-operability of the IPL, hence the operator intervention credit cannot be taken.

Dejan IVANOVIC
Process Engineer, MSChE

 

[georgeverghese]

Operator intervention ( in response to a DCS alarm ) credit is usually acceptable as mitigation ( I wouldnt call this an IPL, since human intervention is required to close this CV from the CR) only if the consequences of the failure of intervention are minimal - for example, if it results in

equipment damage : capital investment is low and there is no loss in production
AND
loss of containment : fluid released to the environment has no HSE concerns