Type pxb is a type of pressurised enclosure that provides an equipment protection level Gb (or Mb or Db).
This means that when a pxb enclosure is located in an area requiring Gb (e.g zone 1), it establishes non-hazardous conditions within the enclosure.
Type pyb pressurised enclosure provides equipment protection level EPL Gb (or Db) with EPL Gc (or Db) internal to the enclosure.
This means that normally, when a pyb enclosure is located in an area requiring Gb, it establishes conditions requiring Gc within the enclosure. The equipment inside must be suitably protected, but restricted breathing Ex nR is not allowed!
A type pzc pressurised enclosure provides equipment protection level Gc (or Dc)
This permits unprotected equipment within the enclosure.
The type of pressurisation to be used depends on
- The required EPL for equipment in the location concerned – Gb for Zone 1 or Gc for
Zone 2 (unless a risk assessment has determined otherwise), - The likelihood of an internal release of gas, and
- Whether the equipment within the pressurised enclosure is ignition capable.
From IEC60079-2: 2014, Table 1, the required pressurisation type for the enclosure in a gas atmosphere is as shown below. The shaded portion applies when there is no internal source of release.
| Flammable substance in containment system (C.S) | External Area EPL/CAT. | Equiv. Zone | Enclosure contains ignition-capable equipment | Enclosure does not contain ignition-capable equipment |
| No C.S. | Gb / 2 | 1 | Type pxb | Type pyb* |
| No C.S. | Gb / 3 | 2 | Type pzc | Type pzc |
| Gas or Vapour | Gb / 2 | 1 | Type pxb | Type pyb* |
| Gas or Vapour | Gc / 3 | 2 | Type pxb | Type pyb* |
| Liquid | Gb / 2 | 1 | Type pxb (inert gas)** | Type pxb (inert gas)** |
| Liquid | Gb / 3 | 2 | Type pzc (inert gas)** | Type pzc (inert gas)** |
For enclosures with no internal flammable release, the required type of protection can be summarised as shown below, from Iec60079-14: 2013, Table 16
| External EPL | Enclosure contains equipment not meeting EPL “Gc” requirements | Enclosure contains equipment that meets EPL “Gc” requirements |
| Gb | Type pxb | Type pyb |
| Gc | Type pxb or pzc | No pressurisation required |
