1Introduction
Dangers unique to GC/MSD operation
5977B Series MSD Operating Manual 25
Dangers unique to GC/MSD operation
Hydrogen presents a number of dangers. Some are general, others are unique to
GC or GC/MSD operation. Dangers include, but are not limited to:
• Combustion of leaking hydrogen
• Combustion due to rapid expansion of hydrogen from a high-pressure
cylinder
• Accumulation of hydrogen in the GC oven and subsequent combustion (see
your GC documentation and the label on the top edge of the GC oven door)
• Accumulation of hydrogen in the MSD and subsequent combustion
Hydrogen accumulation in an MSD
All users should be aware of the mechanisms by which hydrogen can
accumulate and know what precautions to take if they know or suspect that
hydrogen has accumulated. (See Table 4.) Note that these mechanisms apply to
all mass spectrometers, including the MSD.
The MSD cannot detect leaks in inlet or detector gas streams. For this reason,
it is vital that column fittings should always be either connected to a column or
have a cap or plug installed.
The MSD cannot detect leaks in the valves for the optional JetClean system. It
is possible that hydrogen can leak into the MSD from this cleaning system.
Always turn off the JetClean system, close the manual hydrogen shutoff valve
to the JetClean MFC, and ensure good vacuum before venting the MSD.
Table 4 Hydrogen accumulation mechanisms
Mechanism Results
Mass spectrometer
turned off
A mass spectrometer can be shut down deliberately. It can also be shut down accidentally by an internal or
external failure. There is a safety feature that will shut down the flow of carrier gas in the event of a foreline
pump shut down. However, if this feature fails, hydrogen may slowly accumulate in the mass
spectrometer.
MS automated
shutoff valves
closed
The mass spectrometers are equipped with automated shutoff valves for the calibration vial, optional
JetClean system, and the reagent gases. Deliberate operator action or various failures can cause the
shutoff valves to close. Shutoff valve closure does not shut off the flow of carrier gas. As a result, hydrogen
may slowly accumulate in the mass spectrometer.
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