Relance on operator responce API521 to discount a case
Relance on operator responce API521 to discount a case
(OP)
Dear all,
I've noted in API 521 page 24: 5.4 Effect of operator comments are made regarding allowance for operator responce. It stated along the lines that you dont need to size for a case if an operator responce time is 10-30 minutes and they can reasonably be expected to take the right respoce. It has room for interpretation - which makes sense.
Has anyone actually used this argument? not to size for a process case or even calculate the relief rate
Note: I dont want to prejudge or bias peoples responces by explaining my perpsective.
I would appeciate candid comments on this:
I've noted in API 521 page 24: 5.4 Effect of operator comments are made regarding allowance for operator responce. It stated along the lines that you dont need to size for a case if an operator responce time is 10-30 minutes and they can reasonably be expected to take the right respoce. It has room for interpretation - which makes sense.
Has anyone actually used this argument? not to size for a process case or even calculate the relief rate
Note: I dont want to prejudge or bias peoples responces by explaining my perpsective.
I would appeciate candid comments on this:





RE: Relance on operator responce API521 to discount a case
RE: Relance on operator responce API521 to discount a case
I have used this criteria for the following 2 scenarii:
- Fire case: if the amount of wetted surface area in a pressure vessel is totally vaporized by fire before operator response, one should treat the vessel as a gas-filled vessel.
- Liquid blocked outlet: when the liquid filling time is less than the time for operator response, then the scenario is credible.
In any case, be conservative and use 30 min. It highly depends on the location of the equipement however...
"We don't believe things because they are true, things are true because we believe them."
RE: Relance on operator responce API521 to discount a case
RE: Relance on operator responce API521 to discount a case
RE: Relance on operator responce API521 to discount a case
"We don't believe things because they are true, things are true because we believe them."
RE: Relance on operator responce API521 to discount a case
I felt strongly that it is inapprorpate to take credit for operator responces without a proper consideration of the risks. I believe this can be done effectively if you document your basis in your risk assessment or hazard study.
Otherwise i would not take credit for it in rv sizing,
RE: Relance on operator responce API521 to discount a case
We have standardized on LOPA for simple risk analysis of most scenarios. We have more complex tools for complicated scenarios.
In my training and experience, an operator response alone does not justify making a scenario non-credible. It also does not justify reducing the severity of a scenario or extending the protection level of another layer of protection; you add enough independent protection layers (IPLs) to balance the full scenario, which is evaluated assuming NO controls (i.e. no operator). Severe consequences need many IPLs, and an operator response that requires a 10-30 minute response time qualifies for only 1 IPL credit. Under the duress of an emergency situation, well-trained operators have a fairly high failure rate; thus only the 1 credit.
Good luck,
Latexman