External fire and failure of plant compressed air supply - is this a fair assumption?
External fire and failure of plant compressed air supply - is this a fair assumption?
(OP)
Hello all,
I am writing a pressure relief case and making an assumption that plant compressed air supply will fail [stopped] in case of external fire.
Do you think this is the fair assumption? I believe, in case of fire, to stop the air supply would be one of the emergency actions. For example, failure of air supply will close all the raw material supply valves [if they are air fail close] and open cooling water supply valves [if they are air fail open valves]?
Please share your experience.
Thanks
KS
I am writing a pressure relief case and making an assumption that plant compressed air supply will fail [stopped] in case of external fire.
Do you think this is the fair assumption? I believe, in case of fire, to stop the air supply would be one of the emergency actions. For example, failure of air supply will close all the raw material supply valves [if they are air fail close] and open cooling water supply valves [if they are air fail open valves]?
Please share your experience.
Thanks
KS





RE: External fire and failure of plant compressed air supply - is this a fair assumption?
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat
RE: External fire and failure of plant compressed air supply - is this a fair assumption?
Thanks,agree with you. All make sense.
RE: External fire and failure of plant compressed air supply - is this a fair assumption?
It's also important to remember that a diaphragm-actuated control valve may lose its ability to remain in the fail position during prolonged fire. This is one of many reasons that control valves are often backed up with firesafe rotary on/off actuated valves in failure critical applications, i.e. isolating a source of fuel. The rotary valve's aluminum actuator may melt off eventually, but he valve will long ago have been taken to the failure position- and unlike a rising stem valve actuated with a diaphragm, the fluid provides no driving force to change the valve's position even once the actuator is removed.
RE: External fire and failure of plant compressed air supply - is this a fair assumption?
Another plant may take the position that it is not credible for the entire plant to ignite at once and retaining control gas gives them a better potential to minimize the extent of damage through control actions. This would also be a valid foundation for a design philosophy.
I guess my point is that long before you get to the point of specifying plant equipment you need to have thought about these things and made some foundational decisions. You are not going to get a one-size-fits-all answer from a free web site.
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat
RE: External fire and failure of plant compressed air supply - is this a fair assumption?
Thanks very much for your input, much appreciated.
RE: External fire and failure of plant compressed air supply - is this a fair assumption?
So I would write it up stating that you take failure of instrument air in one scenario and the external fire case in a separate scenario.
RE: External fire and failure of plant compressed air supply - is this a fair assumption?
I could see where they were coming from. Most of the time we don't design the instrument air lines other than the main supply header and maybe some sub-lines. The final lines, 1.5" or smaller are run by the field contractor and these valves were all in a similar area that a single line could be the common supply point. If you don't like the idea of a fire, someone closes a root valve or a forklift takes out the air line, the result is the same. In an existing facility knowing how the lines are actually run, this might not be the case you could decide this case was no longer credible.
Another factor is how large of a fire circle are you using? A 2500 ft2 circle is about 56' diameter. 5000 ft2 is 80 ft2 which just makes more things possible to be caught up in the fire.