18.104.22.168 Fuel Sensors. Ventilation should be designed to
eliminate the possibility of any accumulation of unburnt fuel.
Because fuel settles in low unflushed areas, careful crawl space
and facility ventilation design can preclude this. To monitor
this condition, the device includes fuel sensors located in the
crawl space and in the electrical rooms which contain burners.
These sensors sample their immediate location for fuel in excess
of a percentage of the LEL. If an excess is registered, they
sound an alarm. These sensor systems, installed by the device
contractor and maintained by the using activity, should be
located in strategic places.
Caution: Sensors and the ventilation system should be
kept in good working order to prevent an incident.
22.214.171.124 24-Hour Propane Alarm. If the trainer is not in
operation and 24-hour propane sensing is in effect, a means for
remote alarm activation should be provided (by device computer)
at the DTC. Any alarms or other indicators are the
responsibility of the facility contractor. The DTC will be the
interface where the facility contractor will receive the 24 Vdc
continuous signal. A 24-hour propane alarm from the DTC should
be provided at the 24-hour duty watch station. Refer also to
126.96.36.199 Fan Interlock. Another level of safety should be
provided to prevent the danger of accumulated unburned fuel in
the trainers. Danger from accumulated unburned fuel in the
trainer during the occupied period can be adequately eliminated
by a system of ventilation fans, sensors, and interlocks.
During unoccupied periods the risk is reduced by natural
ventilation and proper operation of the purge fan. Proper
operation during occupied periods requires flushing the crawl
space prior to energizing crawl space electrical circuits.
Crawl space electrical circuits therefore, should be interlocked
with main exhaust fans. At least one fan should be operating
during the maintenance period before training. Fans and dampers
as interlocked in the sequence in par. 188.8.131.52 should be
further interlocked to include a timer relay to energize
electrical circuits after a 3-minute delay from the key operated