1Introduction
5975/5977 Series MSD Operating Manual 21
Precautions
Take the following precautions when operating a a GC/MSD system or GC/MS
system with hydrogen carrier gas.
GC off 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 7890 Series GC equipped with Electronic Pressure Control (EPC) is shut
off, the EPC stops the flow of carrier gas. If a GC’s 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.
Power failure If the power fails, both the GC and mass spectrometer shut down. The carrier gas, however, is not necessarily
shut down. 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.
Table 4 Hydrogen accumulation mechanisms (continued)
Mechanism Results
Once hydrogen has accumulated in a mass spectrometer, extreme caution
must be used when removing it. Incorrect startup of a mass spectrometer
filled with hydrogen can cause an explosion.
After a power failure, the mass spectrometer may start up and begin the
pumpdown process by itself. This does not guarantee that all hydrogen has
been removed from the system, or that the explosion hazard has been
removed.
You must remove the plastic cover over the glass window on the front of a
5977B Series MSD. In the unlikely event of an explosion, this cover may
dislodge.
You MUST make sure the top thumbscrew on the analyzer side plate is
fastened finger-tight. Do not over tighten the thumbscrew; this can cause air
leaks.
Failure to secure your MSD as described above greatly increases the chance
of personal injury in the event of an explosion.
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