ISA RP12.4 : 1996

1 Scope
2 Purpose
3 Definitions
4 General requirements
5 Enclosure requirements
6 Components that protrude through the enclosure
7 Protecting hot surfaces and ignition-capable
    components
8 Protecting against enclosure rupture
9 Purging requirements
10 Tests
    10.1 Verifying ability of enclosure to limit internal
          pressure
    10.2 Maximum operating pressure test
    10.3 Purging test
11 Marking
12 Enclosure access for maintenance
Annexes
A - (normative) References
B - (informative) Comments on the text
C - (informative) Information for sizing pipes and ducts
Tables
1 - Clauses relevant to enclosure openings
2 - Impact levels for enclosure parts
C.1 - Pipe size as a function of flow and distance with a
      nominal 35 psi pressure source
C.2 - Pipe size as a function of flow and distance with a
      nominal 65 psi pressure source
C.3 - Duct size (diameter in inches) as a function of flow
      and distance with 6 in. H2O pressure source

Deals with equipment made suitable for using in hazardous (classified) locations by use of a pressurizing system. Covers equipment with and without an internal release of a flammable gas or vapor.