Per API RP 521, if the equipment is located in an area where type and volume of the inventory and drainage system design is such that a sizable fire might occur:
The horizontal extent of fire zone should be a 65 ft diameter circle from a potential source of fire. A shorter fire zone could be assumed if equipment is segregated by firewalls or by a curbed area capable of containing or restricting the exposure to the spilled inventory.
Assume that all piping and equipment up to 25 ft above deck, ground, or any other fire-supporting surface is exposed to fire.
For air coolers with tubes located higher than 25 ft above grade or other surface at which a major fire could be sustained, the extent of fire should be as follows:
- For forced draft units (the tubes would be shielded from radiant heat exposure by the fan hood), wetted area should be taken as zero (no fire exposure).
- For induced draft units, the wetted area should be taken as the projected area (length multiply width) of the tube bundle.