Siemens Maxum II Manual page 67

Type X Pressurization (px)
A purged system where all external circuits including power are cut off whenever purge
pressure is lost.
Type Y Pressurization (py)
A purged system where an alarm is generated whenever purge pressure is lost. In addition,
any equipment which would exceed the T-Rating of the location upon loss of air flow (such as
the Maxum II air bath oven heater) must be de-energized when purge is lost.
Zone 1
An atmosphere where a mixture of air and flammable substances in the form of gas, vapor, or
mist is likely to occur in normal operation occasionally. This term is commonly used in
association with hazardous areas not located in the United States or Canada.
Zone 2
An atmosphere where a mixture of air and flammable substances in the form of gas, vapor or
mist is not likely to occur in normal operation but, if it does occur, will persist for only a short
period. This term is commonly used in association with hazardous areas not located in the
United States or Canada.
Explosion Protection Safety Standards
Manual, August 2017, A5E02220442001 Rev 8
Glossary
67