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Term Safety System operating as intended

Term Safety System operating as intended

Term Safety System operating as intended

What term do you guys use for a safety system that is activated under a unsafe condition? Example: The rupture disk had rupture/failed during an over pressure situation.

What term do you guys use for a piece of equipment that has failed during operation outside design envelope? Example the boiler exploded under 10,000 PSI load.

I am wondering this to help communicate to management that these reliability issues are process related and not equipment related.


I've got a PHD is Broscience

RE: Term Safety System operating as intended

There are are several classes of failure modes in which the equipment operated as designed and the safety system did its job. I might put them in the terms below with easy analogies for a non-tech. I think it's important to clearly state that the boiler performed as it was designed to perform.

Try to keep it at an 8-year-old's level of communication for management types. Drop down to 5-year-old language if the recipient has an MBA on his wall and asks for the 50,000-foot view.

"Operator error, not a machine failure."
Somebody accidentally asked the boiler to make 10,000 PSI steam instead of 1000 PSI. The boiler operated as it was designed to do, releasing the pressure through its safety valve instead of blowing us all to kingdom come.

"Controller flaw, not a machine failure."
Our control system was not programmed properly. We experienced heavy demand and the controls asked the boiler to do more than it was designed to do. The boiler reacted properly and vented the excess pressure to prevent disaster.

"Process upset, not a machine failure."
Our last delivery of reagent X was mislabeled, which created a very cold process stream that we would never experience otherwise. The control system tried to compensate by raising the boiler pressure beyond its limits. The boiler's safety system kicked in to prevent an explosion.

"External event, not a machine failure."
Lightning glitched our control system. It called for all equipment to go to maximum and stay there. The boiler's overpressure safety features acted to prevent collapse.

An easy analogy: If you stop the air flow through your hair dryer at home, its insides will get too hot and catch the plastic on fire. You can do this by leaving it turned on and covering the warm air outlet with a towel. No fire will start, though, because there is a thermostat safety switch in there that cuts off the power when the temperature gets too high. Our boiler did the same thing.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

RE: Term Safety System operating as intended

1) the designed safety features performed as expected to the off-spec situation. the over-pressure protection (rupture disc) failed as designed (venting the pressure vessel), protecting the pressure vessel from catastrophic over-pressure. This over-pressure occurred because ...

2) sadly the over-pressure protection features failed to protect the pressure vessel from a catastrophic explosion. The reason the rupture disc didn't rupture is ...

Quando Omni Flunkus Moritati

RE: Term Safety System operating as intended

Please let a 'non-native' in English try his hand (head? mouth? smile). I generally agree with rb1957:

1. The installed safety device, rupture disc (no. xx, see technical details below ) performed as designed, ruptured and released the occuring overpressure at vessel (no. yy, see technical details below)

2. Recommended actions:
a) All details and causes of overpressure occurence to be clarified. Actions to be taken to avoid repetition. (Time limit?) Safety device solution to be checked against current state of the art and possible new additional equipment and control procedures. (Time limit)
b) Depending on consequences and possible damage: New rupture disc to be installed and process restarted (Time limit?)

RE: Term Safety System operating as intended

"over-pressure protection failed as designed" sounds like an oxymoron to me. I would say "operated as designed." Certainly systems can be designed so that failure occurs in a safe way, but the rupture disk is an individual component in such a system and it operated properly. If it had failed, the consequences would be much worse.

RE: Term Safety System operating as intended

I'd save "failed" for the boiler explosion event, and used "ruptured correctly" for the expected behaviour of the protective device.


RE: Term Safety System operating as intended

Maybe an analogy to the air bags in the car?

The car didn't fail -- the driver did. But the air bag saved his life.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

RE: Term Safety System operating as intended

it's awkward but starting with SNAFU you'd get
... SUEWF ??

Quando Omni Flunkus Moritati

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