IEC 60079-2 Explained: Pressurized Enclosure “p” Protection

A control cabinet may contain a PLC, HMI, power supplies, relays, network equipment, and other components that are not individually certified for installation in the surrounding hazardous area. One possible solution is to protect the assembly through a pressurized enclosure designed for that application.

This is the principle behind Ex p protection. Instead of relying solely on the construction of each component, the protection system maintains specified conditions inside an enclosure to prevent the surrounding explosive atmosphere from creating an unacceptable ignition risk.

IEC 60079-2, Explosive Atmospheres – Part 2: Equipment Protection by Pressurized Enclosure “p”, addresses this protection technique. It is used alongside the applicable general equipment requirements, including IEC 60079-0.

For engineers and procurement teams, the important point is that Ex p is not simply a cabinet with an air connection. The enclosure, protective gas supply, purging arrangement, monitoring devices, control logic, and protective actions must work as a suitable, documented system.

What Happens Inside an Ex p Enclosure?

An Ex p arrangement uses a protective gas, commonly air or an appropriate inert gas, to establish the conditions specified by its design. Depending on the protection method, this can involve maintaining overpressure, purging the enclosure, dilution, or other measures defined for the particular system.

The exact method matters. A system designed to prevent the external atmosphere from entering an enclosure is not automatically suitable for an application where flammable material may be released inside it.

A typical operating sequence may look like this:

1. The protective gas supply is made available under the specified conditions.
2. The enclosure undergoes the required purging or flushing sequence, where applicable.
3. The control system verifies that the required protective conditions have been established.
4. Equipment operation is permitted according to the certified design.
5. Monitoring and protective functions remain active during operation as required.

This sequence is illustrative, not a universal operating procedure. The actual purge requirements, permissive conditions, and responses to a fault must come from the equipment documentation.

What IEC 60079-2 Covers

IEC 60079-2 addresses equipment protection by pressurized enclosure “p” in explosive atmospheres. Its requirements must be considered together with the applicable general requirements, equipment marking, certification, and installation instructions.

Document or standard	Relevance to the review
IEC 60079-0	General requirements applicable to Ex equipment and components.
IEC 60079-2	Specific requirements for pressurized enclosure protection.
IEC 60079-10-1	Classification of areas where explosive gas atmospheres may occur.
IEC 60079-10-2	Classification of areas where combustible dust atmospheres may occur.
IEC 60079-14	Relevant requirements for the design, selection, and installation of electrical installations in explosive atmospheres.

Confirm the applicable editions and their status for the project. A standard reference by itself does not demonstrate that a particular product or installation complies with every project requirement.

Equipment Enclosure or Pressurized Room?

The distinction is important when reviewing vendor documents. IEC 60079-2 concerns equipment using pressurized enclosure protection. A pressurized room or a room protected through artificial ventilation is a different arrangement addressed by IEC 60079-13.

For example, a pressurized analyzer cabinet should not automatically be assessed using the same assumptions as a complete analyzer shelter. The protected boundary, air or gas supply, monitoring points, and safety functions may differ significantly.

Components That Need to Be Reviewed

There is no single component list that applies to every Ex p product. Depending on the design, an arrangement may include:

• Enclosure and seals: provide the physical boundary needed to maintain the specified conditions.
• Protective gas supply: provides the required gas at the specified quality and supply conditions.
• Pressure or condition monitoring: monitors the parameters required by the protection design.
• Purging controls: manage the required purge sequence where applicable.
• Exhaust and outlet arrangements: provide the specified gas discharge path.
• Alarms and interlocks: initiate the actions required by the system design.
• Protective shutdown functions: respond to loss of the required protective condition where specified.

During a technical review, identify which functions are included in the supplied equipment and which must be provided by the package integrator or installation contractor. Do not assume that every function is included simply because a vendor describes the product as an Ex p system.

Purging and Protective Gas Requirements

Purging is a critical part of many pressurized enclosure arrangements. Before equipment is permitted to operate, the specified procedure may need to displace the atmosphere inside the enclosure and establish the required protective condition.

The procedure depends on the equipment design. A generic purge duration, flow rate, or pressure value should not be copied from another installation and applied without verification.

When reviewing a vendor proposal, check the following:

• Specified protective gas and its required quality.
• Minimum and maximum supply conditions, where specified.
• Required purge or flushing procedure.
• How completion of the required sequence is determined.
• Conditions that permit energization or continued operation.
• Required action if the protective gas supply becomes unavailable or inadequate.

Also confirm that the proposed supply arrangement is suitable for the site utilities. A technically acceptable enclosure may still be unsuitable for the project if the required gas supply cannot be reliably provided under the intended operating conditions.

What Happens When Protection Is Lost?

Loss of pressure or another monitored condition can compromise the intended protection. The required response depends on the particular protection method, equipment design, and certification.

The vendor documentation should explain the relevant operating limits and what happens when a limit is exceeded. Depending on the design, this may involve an alarm, an interlock, automatic shutdown, or another specified protective action.

For engineering and commissioning, verify the actual function rather than accepting a general statement that the system has “low-pressure protection.” The review should establish:

• Which conditions are monitored.
• How the relevant limits are defined.
• What the system does when a limit is reached.
• Whether the required response has to be tested during commissioning.
• How faults, alarms, and protective actions are documented.

Do not assume that all Ex p systems use the same thresholds, alarm logic, or shutdown sequence. These details must match the applicable design and documentation.

Enclosure Integrity and Modifications

Pressurization performance depends on the enclosure and its interfaces. Doors, cable entries, pipe entries, seals, gas connections, exhaust paths, and other openings can affect the ability to establish or maintain the specified conditions.

This becomes especially important when a cabinet is modified after delivery. Adding a cable gland, drilling an entry, changing a door seal, or altering an exhaust arrangement may affect the original configuration or its performance.

Before approving a modification, check it against the manufacturer's instructions and applicable certification. Do not treat changes to a certified pressurized enclosure as ordinary cabinet work without assessing their effect on the protection system.

Applications Involving an Internal Release

Some applications may involve a limited release of flammable material inside the enclosure. These cases require specific consideration of the potential release, the protective gas arrangement, and the resulting internal atmosphere.

An enclosure intended for an application without an internal flammable release should not automatically be considered suitable for this service. Confirm that the actual process conditions and release scenario are covered by the design and certification.

For analyzer systems and process instrumentation, this check should be made early in the engineering stage. The process connection and the possible release of flammable material can influence the equipment arrangement and protection requirements.

How to Check Ex p Suitability for a Hazardous Area

The designation Ex p alone does not establish suitability for every hazardous location. Selection must be based on the complete equipment marking, certificate, intended application, and project requirements.

Before accepting a proposal, confirm:

• The hazardous area classification at the intended installation location.
• Whether the application involves gas, vapour, or combustible dust.
• The required equipment group and Equipment Protection Level (EPL).
• The complete Ex marking and the scope of the certificate.
• The permitted ambient temperature and relevant environmental conditions.
• Any special conditions for safe use stated in the certificate.
• The manufacturer's installation, operation, and maintenance instructions.

For background, see Hazardous Area Classification Explained and Equipment Protection Level (EPL) Explained.

Engineering note: Do not approve equipment based only on the protection concept named in a quotation. The complete certified configuration and its suitability for the specified location must be established.

Ex p Compared With Other Protection Methods

Protection method	Basic principle	Relevant standard
Ex d	A flameproof enclosure is designed to withstand an internal explosion and prevent flame transmission under specified conditions.	IEC 60079-1
Ex e	Increased safety measures reduce the likelihood of ignition under the conditions covered by the design.	IEC 60079-7
Ex i	Intrinsic safety limits electrical energy and other relevant ignition parameters under specified conditions.	IEC 60079-11
Ex p	A controlled protective environment is established within an enclosure.	IEC 60079-2
Ex m	Encapsulation protects potential ignition sources by enclosing them in a suitable compound.	IEC 60079-18
Ex t	An enclosure provides protection against combustible dust ingress and associated ignition hazards as specified by the design.	IEC 60079-31

These methods use different protection principles and are not interchangeable simply because they are used in hazardous areas. The appropriate solution depends on the equipment, installation conditions, certification, and project specification.

Ex p Review Checklist for RFQ and Technical Bid Evaluation

When evaluating a supplier, the main question is whether the proposed equipment meets the project requirements as a complete system. The following checklist can be used during technical bid evaluation (TBE).

Review point	Evidence to request or verify
Protection concept	Confirmation of the proposed Ex p arrangement and applicable standard.
Hazardous area	Compliance with the specified zone, gas or dust group, and EPL requirements.
Equipment marking	Complete Ex marking consistent with the intended application.
Certification	Certificate number, scope, applicable conditions, and any restrictions.
Protective gas	Gas type, quality, supply conditions, and utility requirements.
Purging	Specified procedure and conditions for permitting operation.
Monitoring	Required parameters, monitoring arrangements, and operating limits.
Protective actions	Alarm, interlock, and shutdown functions required by the design.
Enclosure interfaces	Doors, seals, cable and pipe entries, gas connections, and exhaust paths.
Documentation	Installation instructions, operating procedure, maintenance requirements, and relevant drawings.
Project deviations	Documented exceptions against the RFQ, datasheet, and project specifications.

For a large control panel or analyzer package, also confirm the division of responsibility between the equipment manufacturer, package integrator, and site contractor. This helps prevent gaps in the supply of utilities, control interfaces, and protective functions.

Installation and Commissioning Considerations

Installation is not complete simply because the enclosure has been mounted and connected to the protective gas supply. The system must be installed and checked according to its certified design and the applicable project requirements.

Depending on the equipment, the verification process may include:

• Checking the protective gas supply and connections.
• Inspecting enclosure seals, entries, and exhaust arrangements.
• Confirming monitoring devices and control connections.
• Testing specified alarms, interlocks, and protective actions.
• Verifying the purge procedure and conditions for operation.
• Recording test results and outstanding deviations.

IEC 60079-14 is relevant to the design, selection, and installation of electrical installations in explosive atmospheres. Apply the edition and requirements relevant to the project, together with the equipment certificate and manufacturer's instructions.

Common Errors During Ex p Selection

• Equating pressurization with certification: a pressurized cabinet is not automatically suitable for a hazardous area.
• Reviewing only the product name: the complete marking, certificate scope, and application must be checked.
• Ignoring the site gas supply: the required protective conditions must be achievable at the installation.
• Assuming a standard purge procedure: purge requirements are equipment-specific.
• Overlooking protective functions: alarms and shutdown responses must match the documented design.
• Changing enclosure entries without review: modifications can affect the original configuration or its performance.
• Confusing equipment enclosures with protected rooms: these are different applications with different assessment requirements.

Frequently Asked Questions

What is IEC 60079-2?

IEC 60079-2 specifies requirements for equipment protection by pressurized enclosure “p” in explosive atmospheres.

What does Ex p protection do?

It uses a controlled protective environment within an enclosure to address ignition hazards under the conditions defined by the equipment design and certification.

Is every pressurized cabinet suitable for a hazardous area?

No. The equipment must meet the applicable requirements and be suitable for the intended installation. Pressurization alone does not establish Ex compliance.

Does every Ex p system use the same purge time and pressure?

No. Required values and operating sequences depend on the specific design. Use the manufacturer's documentation and certified equipment requirements.

What happens if the protective condition is lost?

The required response depends on the design. It may include an alarm, interlock, shutdown, or another specified action. Verify the actual response in the equipment documentation.

Does IEC 60079-2 cover pressurized rooms?

Pressurized rooms and related artificially ventilated room applications are addressed separately by IEC 60079-13.

Conclusion

Ex p protection is useful for certain electrical assemblies that require a controlled protective environment inside an enclosure. Its suitability depends on more than the enclosure itself: the protective gas supply, purging requirements, monitoring, protective actions, interfaces, and certified configuration all matter.

For engineering and procurement, review the complete equipment marking and certification, confirm the required site utilities, and establish how the system maintains its protective condition. Resolve deviations before accepting the proposal, and ensure that installation and commissioning follow the applicable documentation.

Related Reading

• IEC 60079 Series Explained: A Complete Guide to Explosion Protection Standards
• IEC 60079-1 Explained: Flameproof Enclosures “d”
• IEC 60079-7 Explained: Increased Safety “e”
• IEC 60079-11 Explained: Intrinsic Safety “i”
• What Is Ex p Pressurized Protection?
• Equipment Protection Level (EPL) Explained
• IEC 60079-14 Explained: Design, Selection and Installation
• Hazardous Area Classification Explained

References

• IEC 60079-2 – Explosive Atmospheres – Part 2: Equipment Protection by Pressurized Enclosure “p”.
• IEC 60079-0 – Explosive Atmospheres – Part 0: Equipment – General Requirements.
• IEC 60079-13 – Explosive Atmospheres – Equipment Protection by Pressurized Room “p” and Artificially Ventilated Room “v”.
• IEC 60079-14 – Explosive Atmospheres – Electrical Installations: Design, Selection and Installation.