Hazardous
Area Classification
Nonhazardous
and / or Unclassified: An area, location, or atmosphere, which is
known to not contain any concentrations of ignitable or flammable
vapor, gas, liquid, and / or dust.
Division
2 and / or Zone 2: An area, location, or atmosphere, which is known
not to contain any concentrations of ignitable or flammable vapor,
gas, liquid, and / or dust during normal operation and if it should
occur will exist only during short periods, such as equipment failure,
breakdown, or service and maintenance.
Division 1 and
/ or Zone 1: An area, location, or atmosphere, which is known to
contain concentrations of ignitable or flammable vapor, gas, liquid,
and / or dust during normal operation and will exist frequently
because of equipment failure, breakdown, or service and maintenance.
Division 1 and
/ or Zone 0: An area, location, or atmosphere, which is known to
contain concentrations of ignitable or flammable vapor, gas, liquid,
and / or dust, which is present continuously or for long periods
of time.
Types of Purging
Definitions
Type Z - Purge:
Type Z purging reduces the classification within a protected enclosure
from Division 2 and / or Zone 2 to nonhazardous. Failure to maintain
pressure within the protected enclosure shall be detected by an
alarm or indicator. The dilution purge time can be a manual operation
and once the enclosure has been purged of ignitable or flammable
concentrations, only positive pressure is required to be maintained
within the enclosure and it is not necessary to remove power from
the protected equipment upon the loss of purge pressure.
Type Y - Purge:
Type Y purging reduces the classification within the protected enclosure
from Division 1 and / or Zone 1 to Division 2 and / or Zone 2. All
equipment in the protected enclosure shall be approved for Division
2 and / or Zone 2 locations. Failure to maintain pressure within
the protected enclosure shall be detected by an alarm or indicator.
The dilution purge time can be a manual operation and once the enclosure
has been purged of ignitable or flammable concentrations, only positive
pressure is required to be maintained within the enclosure and it
is not necessary to remove power from the protected equipment upon
the loss of purge pressure.
Purge Gas Inlet
Definitions
Continuous Dilution Purge Gas Inlet: Continuous dilution is a method of
maintaining pressure in an electronics enclosure in which after the electronics
enclosure has been diluted below the required lower explosive limit (LEL) the
protective gas is passed continuously through the electronics enclosure at a
pressure above that of the required 0.20 inches H2O (0.50 mbar) and discharged
to the outside atmosphere through an exhaust vent. The same volume of purge gas
is maintained during and after the dilution time cycle. Continuous dilution is
normally used for maintaining and controlling heat buildup from the electronics
within the pressurized enclosure by continuously exchanging purge gas through the
electronics enclosure to atmosphere.
Leakage Compensation Purge Gas Inlet:
Leakage compensation allows a higher volume of protective gas supply to be manually
or automatically selected to speed up dilution time of potentially flammable materials
to an acceptable level, permitting a more-rapid application of initial power, or restoration
of power to protected electrical equipment, after service. When the dilution cycle has elapsed,
the large volume of purge gas can be manually or automatically turned off, which allows a volume
of purge gas larger than the leak rate of the electronics enclosure to be introduced into the
now protected electronics enclosure to maintain at least 0.20 inches H2O (0.50 mbar). Leakage
compensation is normally used to conserve purge gas when utilities are at a premium.
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