There are four flammable gas detectors installed (one on top of the target,
one each on top of the hydrogen and deuterium gas panels, one on top of the gas
tanks)
to provide early detection
of hydrogen/deuterium leaks. These detectors are sensitive (and calibrated)
over the range from 0 to 50 
Lower Explosive Limit (LEL) of hydrogen.
The electro-chemical sensors were manufactured by Crowcon Detection
Instruments LTD and
the readout (four channels) was purchased from CEA Instruments, Inc.
(The Gas Master Four System). The readout unit provides two alarm
levels per channel. The low level alarm is tripped at 20 LEL
while 40 LEL activates the high level alarm.
Each channel has a relay output for both low and high level alarm
states and there is also a set of common relays for both alarm
levels (these common relays respond to the "logical or" of the sensor inputs).
The common relays will be connected to the Fast Shut Down System, FSD,
which removes the beam from the hall by disabling a grid bias at the
injector.