crawl space is purged. In addition, the crawl space will
contain propane detectors (provided by the device contractor)
which will prevent the introduction of propane if 10 percent of
the lower explosive limit (LEL) of propane is detected in the
crawl space or burner rooms.
should normally be deenergized and can be energized only after
the above interlocks are satisfied.
d) The crawl space exhaust fan and power enable
controls should include the following features:
Detect fan run status via a differential
(2) Detect a closed damper (with fan running) via
a differential pressure sensor.
(3) Transmit the analog fan differential pressure
to the device computer.
Turn off fan upon detection of failure or
Indicate when fan fails to respond to a
(6) Latched fan start circuit in hand control
mode (upon restoration of power after a failure, fan will be
(7) Use the fan status in purge timer interlock
with crawl space power. Timer interlocks should be provided
with adjustable settings from 0 to 30 minutes, and set at 3
(8) Indicate when crawl space power enable fails
to respond to a control action.
Crawl space power indicator light.