Agilent Technologies 7890A GC Safety Manual page 10

Table 1
Mechanism
Mass spectrometer automated isolation
valves closed
Mass spectrometer manual isolation
valves closed
GC off
Power failure
10
Potential hydrogen accumulation mechanisms in GC/MSD (continued)
Results
Some mass spectrometers are equipped with
automated diffusion pump isolation valves. In these
instruments, deliberate operator action or various
failures can cause the isolation valves to close.
Isolation valve closure does not shut off the flow of
carrier gas. As a result, hydrogen may slowly
accumulate in the mass spectrometer.
Some mass spectrometers are equipped with
manual diffusion pump isolation valves. In these
instruments, the operator can close the isolation
valves. Closing the isolation valves does not shut
off the flow of carrier gas. As a result, hydrogen
may slowly accumulate in the mass spectrometer.
A GC can be shut down deliberately. It can also be
shut down accidentally by an internal or external
failure. Different GCs react in different ways. If a
7890A GC equipped with Electronic Pressure
Control (EPC) is shut off, the EPC stops the flow of
carrier gas. If the carrier flow is not under EPC
control, the flow increases to its maximum. This
flow may be more than some mass spectrometers
can pump away, resulting in the accumulation of
hydrogen in the mass spectrometer. If the mass
spectrometer is shut off at the same time, the
accumulation can be fairly rapid.
If the power fails, both the GC and mass
spectrometer shut down. The carrier gas, however,
is not necessarily shut down. As described
previously, in some GCs a power failure may cause
the carrier gas flow to be set to maximum. As a
result, hydrogen may accumulate in the mass
spectrometer.
7890A GC Safety Manual