Installation and Operation Safety 2
400/54 Premium Shielded NMR Magnet System Product Overview 21
quench gases by installing a passive vent opening directly
from the magnet room to the outside. Make sure that this
opening has, as a minimum, the same cross- sectional area as
a quench duct. An opening measuring 400mm x 400mm is
normally sufficient. To ensure that this passive vent is
fail- safe, do not include active control for the vent opening;
do not use fans or mechanical shutters.
Adequate ventilation during magnet installation
During the installation and cooling of superconducting
magnets, large volumes of nitrogen or helium gases are
sometimes generated. Although these gases are inert, if
generated in large enough quantities, they can create
dangerous circumstances if they displace the oxygen in the
room. The following table provides examples:
Oxygen monitor
The oxygen monitor sounds an alarm when the oxygen level
in the room rises above or falls below a safe level. This
alarm happens if the ventilation system malfunctions, either
during a quench or during a normal boil- off, and a large
Table 1 Examples of gas generation
Magnet
Type
Quantity of
liberated N
2
gas during
precool
Time taken to
liberate N
2 gas
during precool
Quantity of
liberated He
gas during
filling
Time taken to
evolve He gas
during filling
Quantity of He
gas liberated
during a
“quench”
Time to
liberate
He gas during
a “quench”
800/89 3400 m
3
40 hours 1750 m
3
14 hours 800 m
3
1 min
900/52 13600 m
3
160 hours 7000 m
3
56 hours 315 m
3
1.5 min
4T940 5400 m
3
48 hours 5400 m
3
72 hours 900 m
3
10 min
Adequate means of transporting evolved gases from the magnet
out of the magnet room and also good ventilation of the magnet
room is essential.
An oxygen monitor is recommended for the magnet room. See the Site
Planning Guide for recommendations. Make sure the audio/visual alarm
connected to an oxygen monitor is visible/audible outside the magnet
room as well as inside it.
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