Ulvac CRYOPUMP CRYO-U Series Instruction Manual page 14

KF25 flange is attached to the pressure relief valve for installing a duct.
Figure 1 Pressure Relief Valve (from ULVAC CRYOGENICS)
2. Check the safety of secondary-
generated gases in process
Some gases are generated in vacuum processes as by-products. They may include
flammable, oxidizing, explosive, or toxic gases.
For example, water in vacuum chamber, which comes from the atmosphere or the
substrate, dissociates into hydrogen and oxygen in plasma. Those gases may be also
discharged in large volume from some vapor or sputter materials. Oxygen is one of the
gases which helps combustion, hydrogen is flammable and explosive. At
atmospheric pressure, the mixed gas with hydrogen of 4% or more and oxygen of 5% or
more cause explosion momentarily if there is an ignition (refer to "2.Do not pump
flammable or explosive gases").
In addition, ozone might be secondarily generated when oxygen (O ) or carbon dioxide
2
(CO ) is resolved in plasma. Ozone is a toxic gas，and liquefied ozone is extremely
2
unstable and when in high density it may explode by reacting with organic substances or
any impact.
It is necessary to check the safety of the secondarily generated gases as well as gases to
be introduced in the vacuum chamber.
For handling flammable or explosive gases, refer to "4.When pumping flammable or
explosive gases" and "5.When pumping oxygen" in this chapter. Implement safety
precaution and preventive maintenance as necessary.
S-2 ULVAC CRYOGENICS INCORPORATED