All design considerations presented on this page are intended for basic applications only.

1. All windows should be shatterproof and sized as small as possible.
2. All NFPA 496 required markings should be placed on or near all doors and covers, and should be easily visible.
3. The enclosure should withstand an internal pressure of five (5) inches of water without sustaining permanent deformation and resist all corrosive elements in the surrounding atmosphere.
4. All lightweight objects in the enclosure, such as paper or insulation, should be firmly secured.
5. The enclosure should be constructed from materials such as metal or polycarbonate to meet NEMA 4 or 12 performance requirements, but does not require 3rd party approval.
6. The installation of obstructions or other barriers which block or impede the flow of protective gas should be avoided.
7. The creation of air pockets or other areas which trap flammable gases within the enclosure should be avoided.
8. The enclosure should be located in an area where impact hazards are minimal.
9. A pressure relief device should be used if it is required to protect the enclosure against pressurization system control failure or to allow proper purging system operation.
10. If the enclosure is non-metallic and contains equipment which utilizes or switches power loads greater than 2500 VA, it should be constructed from substantially non-combustible materials, such as materials designed to meet or exceed ANSI/UL94 ratings of 94 V-0 or 94 5V.
11. The enclosure should have no surface area that exceeds 80% of the flammable or ignitable substance's auto-ignition temperature.
12. If the enclosure is protected by a Type X System and can be opened without the use of a tool or key, the door should be equipped with a Division 1 rated power interlock switch to de-energize all equipment that is not suitable for Division 1 areas.

1. The total volume of all pressurized enclosures, devices and wireways should be considered.
2. All enclosure, device and wireway volumes should be calculated without consideration of internally consumed space.
   

   Exceptions: motor starters, rotors, field coils, etc.

3. Cubical device volumes should be calculated as follows:
   Height x Width x Depth - in inches ÷ 1728 = ft³

   - in feet = ft³

4. Cylindrical device volumes may be calculated as follows:
   pr² x Cylinder Length - in inches ÷ 1728 = ft³

   - in feet = ft³

1. All internal enclosures (within the protected enclosure) should be protected by one of the following means, if the free volume of the internal enclosure exceeds 1.22 cubic inches (20 cm3).
2. Internal enclosures should be ventilated on the top and bottom sides with at least one (1) square inch (6.5 cm3) of opening for each four hundred (400) cubic inches (6560 cm3) of volume within the internal protected enclosure, with a minimum size of one quarter (1/4) inch diameter (6.3 mm); or,
3. Adjacent and internal enclosures should be purged in series with the protected enclosure or be purged separately; or,
4. Equipment within adjacent and internal enclosures should be protected by other means; e.g. explosion proof enclosures, hermetically sealed housings or intrinsic safety barriers.

1. All pressure relief devices should be designed to minimize air leakage, unless intended for dilution or ventilation.
2. All pressure relief devices should be constructed from flame, shatter and ignition proof substances. They should also be designed to prevent the escape of sparks and burning materials.

Captive screw and cage nut assemblies can be used to provide multiple point fasteners, and improve enclosure appearance and pressure seals.	Some enclosure manufacturers utilize clamping fasteners to meet TYPE 4 performance requirements.