Ulvac CRYO-U Series Instruction Manual page 17

Ignition by static electricity
Ignition by liquid ozone
If a roughing pipe or and exhaust line is made of plastic such as vinyl chloride or etc., it
may produce static electricity.
On the other hand, ozone may generate under the process utilizing plasma with oxygen
or CO gas. Captured and condensed ozone in the pump liquefies in the warm-up process
X
of regeneration. Note here is the following. The liquid ozone is so unstable that it might
explode by impact or ignition resulting from the reaction with organic matter.
In case of a pumping flammable or explosive gas(es), appropriate safety precaution must
be taken with reference to "6. Regeneration after pumping flammable, explosive, or
combustion enhancing gas".
5. When pumping oxygen
The mixed gas of oxygen and flammable gas should be very dangerous.
Oxygen is the gas that enhances combustion. Use the cryopump after
confirming the safety precautions or measures when pumping the mixture of
oxygen and flammable gas into the cryopump. In particular, the mixture of oxygen
and hydrogen, which has a broad range of combustion/detonation, is extremely
dangerous.
The mixes gas with hydrogen of 4% or more and oxygen of 5% or more at atmospheric
pressure could cause explosion momentarily (refer to "4.When pumping flammable or
explosive gases").
Therefore, when oxygen is used as a process gas, the appropriate safety precautions
must be taken with reference to "6. Regeneration after pumping flammable, explosive, or
combustion enhancing gas".
Oxygen may generate ozone.
Ozone may be unknowingly generated in plasma production process (e.g.,
sputtering, etching, glow discharge, EB deposition). Captured and solidified ozone in
the pump liquefies in the warm-up process of regeneration. The liquid ozone at high
concentrations might explode by impact or ignition by the reaction with organic matter.
In case that a remarkable amount of ozone is generated in the process and accumulated
in the cryopump, the following phenomena could be occurred around the pump at the initial
stage of regeneration:
① Cracking/popping sounds (as in electrical arching) occurring within the first few
ULVAC CRYOGENICS INCORPORATED S-5