Solid floor: air coolers: fire zone increase due to??? 1

[jamesbanda]

Dear sirs,

On our plant we have several air coolers at an elevation above 10 meter and with solid floors (that self drain) below them. The solid steel floors were an insurance company requirement to prevent the coolers/condensers making a fire worse by induced draft.

However, it has been suggested these air coolers should be included in the fire case because the floor starts again. I've checked API521 and cannot find a specific case for solid floors in stuctures. But, it does not seem to make sense to be becaause liquid would not pool beneith the exchanger and any leak would self drain away to ground level in the structure. (via a drain path). The HX's dont contain much liquid anyhow. But as air coolers have large surface area including them in the fire case makes it very big.

Has anyone ever encontered this ?


I am not of the view that the larger the relief the safer it is. It just means the more flammable or toxic vapours you release when the relief valve lifts. My preference is approprately sized relief valves and with a good Instrument protection system IPS that is designed to prevent all but fire cases lifting relief valves.

 

[greenche]

For liquid coolers, see API STD521 (5th ed) section 5.15.7.4. It becomes a question of whether your solid floors qualify as a "surface at which a major fire could be sustained". If so then it requires relief. If your floors are designed so that the drainage is adequate then it does not.
If these are condensers, you may not need relief capacity if the requirements of section 5.15.7.3 are met.

 

[skearse]

I agree with greenche. I will typically include equipment above a solid elevated floor as a conservative measure, just because I know how well we (read don't)ensure that the strainers and caps on the floor drains are truly clean and free-draining. Also, I'll typically use 34,500 for the heat input coefficient rather than 21,000 unless it's an open sided structure (most of our stuff is in enclosed buildings which would make ERT response more difficult).