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

When electrical equipment has to operate inside a hazardous area, one approach is to prevent the surrounding explosive atmosphere from entering the equipment enclosure. This is the basic principle behind pressurized enclosure protection “p”.

The requirements for this protection concept are defined by IEC 60079-2, which specifies requirements for the construction and testing of electrical equipment using pressurized enclosures intended for explosive gas atmospheres or explosive dust atmospheres.

IEC 60079-2 works together with the general requirements of IEC 60079-0. Rather than creating a separate general framework, it adds the requirements needed specifically for pressurized equipment.

For engineers, EPC contractors, inspectors, manufacturers, and procurement teams, understanding IEC 60079-2 is important because Ex p equipment depends on maintaining the protective conditions inside the enclosure during operation.

This article explains what IEC 60079-2 is, how Ex p protection works, the main principles behind pressurization, and what engineers should understand when reviewing Ex p equipment.

Quick Answer

What Is IEC 60079-2?

IEC 60079-2 is the international standard titled Explosive Atmospheres – Part 2: Equipment Protection by Pressurized Enclosure “p”.

The standard specifies requirements for the construction and testing of electrical equipment using pressurized enclosures intended for use in explosive gas atmospheres or explosive dust atmospheres.

The basic idea is straightforward: a protective gas is maintained inside an enclosure under controlled conditions so that the external explosive atmosphere cannot enter the protected space in a manner that would create an ignition hazard.

Depending on the equipment design, pressurization can also be used where the enclosure contains a limited release of a flammable substance.

IEC 60079-2 does not replace IEC 60079-0. Instead, it supplements and modifies the general requirements of IEC 60079-0 for equipment using pressurized enclosure protection.

Why Is IEC 60079-2 Important?

An electrical enclosure located in a hazardous area can contain electrical components capable of producing ignition sources. One way to prevent an explosive atmosphere from interacting with those sources is to maintain a suitable protective environment inside the enclosure.

This is the fundamental role of pressurized protection.

The effectiveness of Ex p protection depends on more than simply putting a cabinet under pressure. The equipment must be designed, tested, installed, and operated so that the required protective conditions are established and maintained.

IEC 60079-2 therefore addresses the technical requirements associated with the pressurized enclosure and its protective system.

The standard is particularly relevant to equipment such as:

• Electrical control cabinets.
• Control panels.
• Analyzer systems.
• Instrumentation enclosures.
• Computer or electronic equipment enclosures.
• Large electrical assemblies.
• Equipment containing electrical components that cannot conveniently use another type of Ex protection.

How Does Ex p Protection Work?

The basic principle of Ex p protection is to create and maintain a controlled internal environment within an enclosure.

A protective gas is supplied to the enclosure and the internal pressure is controlled relative to the external atmosphere.

The protective gas can be air or another suitable gas depending on the application and design.

By maintaining the required protective conditions, the pressurized enclosure can prevent the external explosive atmosphere from entering the enclosure and reaching potential ignition sources.

Where the enclosure contains a limited release of a flammable substance, the protective system can also be used to control the concentration within the enclosure through the applicable pressurization or dilution arrangement.

IEC 60079-2 and IEC 60079-0

IEC 60079-2 should be understood together with IEC 60079-0.

IEC 60079-0 establishes general requirements for Ex equipment, including common requirements related to construction, testing, and marking. IEC 60079-2 then provides the additional requirements specifically associated with pressurized enclosure protection.

Standard	Role
IEC 60079-0	General requirements for Ex equipment and Ex components.
IEC 60079-2	Specific requirements for equipment protection by pressurized enclosure “p”.

This relationship is important when reviewing certification documents. An Ex p product is not normally understood by looking at IEC 60079-2 in isolation. The general requirements and the protection-specific requirements work together.

Scope of IEC 60079-2

IEC 60079-2 covers specific requirements for electrical equipment with pressurized enclosures used in explosive gas atmospheres and explosive dust atmospheres.

It also includes requirements for pressurized enclosures containing a limited release of a flammable substance.

However, the standard does not cover every possible application involving a pressurized room or enclosure.

For example, pressurized rooms and analyser houses are addressed by IEC 60079-13, rather than IEC 60079-2.

The standard also excludes certain specialized situations, including applications involving explosives or pyrotechnics and certain hybrid or pyrophoric conditions.

This distinction is important because “pressurized enclosure” and “pressurized room” are not automatically the same application.

What Is a Pressurized Enclosure?

A pressurized enclosure is an enclosure in which a protective gas is maintained at conditions intended to provide the required explosion protection.

The enclosure can contain electrical equipment that would otherwise require another form of protection if installed directly in the hazardous atmosphere.

The pressurization system is therefore part of the protection concept. It is not simply an accessory attached to an ordinary electrical cabinet.

The enclosure, protective gas supply, pressure control, monitoring, and associated protective functions have to work together as an engineered system.

Protective Gas

The protective gas is a critical part of Ex p protection.

Depending on the application and equipment design, the protective gas may be air or an inert gas.

The selection and supply of the protective gas must be appropriate for the equipment and the protection method being applied.

The purpose is to establish the required protective conditions inside the enclosure and maintain them throughout the relevant operating state.

The protective gas system therefore needs to be considered as part of the overall Ex p design rather than as a simple utility connection.

Pressurization and Internal Pressure

One of the defining characteristics of Ex p protection is the controlled pressure condition inside the enclosure.

The pressure inside the protected enclosure is maintained relative to the surrounding atmosphere so that the required protection is achieved.

The design has to account for the enclosure, leakage paths, doors or covers, cable and pipe entries, protective gas supply, exhaust arrangements, and other interfaces that can influence the internal protective condition.

This is why enclosure integrity and pressure management are important considerations when engineering an Ex p system.

Purging Before Operation

A pressurized enclosure may require a purging or flushing operation before electrical equipment is energized.

The purpose of this process is to establish the required internal conditions before potential ignition sources become active.

The exact procedure depends on the equipment design and the applicable protection arrangement.

In practical applications, this means that an Ex p system can have a defined startup sequence rather than allowing the electrical equipment to energize immediately after power is applied.

The control system can therefore be an important part of the overall protection arrangement.

Pressure Monitoring

Maintaining the required protective condition requires monitoring and control.

A pressure monitoring system can detect conditions in which the enclosure no longer maintains the required protective state.

Depending on the design, protective functions can include:

• Pressure monitoring.
• Alarm functions.
• Automatic shutdown.
• Control of the protective gas supply.
• Startup interlocks.
• Monitoring of the pressurization sequence.

The purpose of these functions is to prevent the equipment from operating in a condition where the intended protection is no longer maintained.

Pressurization System Components

An Ex p installation can contain significantly more components than a conventional electrical enclosure.

Depending on the design, the system can include:

• Pressurized enclosure.
• Protective gas inlet.
• Pressure regulator or control equipment.
• Pressure monitoring devices.
• Control valves.
• Exhaust or outlet arrangements.
• Purging control system.
• Alarms and indicators.
• Electrical interlocks.
• Protective shutdown functions.

The exact arrangement depends on the protection concept, equipment design, and application.

Limited Release of a Flammable Substance

One of the important applications addressed by IEC 60079-2 involves pressurized enclosures containing a limited release of a flammable substance.

In this type of application, the design has to consider the relationship between the internal release, the protective gas, and the resulting conditions within the enclosure.

The pressurization or dilution arrangement is therefore not simply intended to keep external gas out. It can also form part of the method used to control the internal atmosphere.

This is a more complex application than simply maintaining positive pressure around conventional electrical equipment.

Ex p and Hazardous Area Classification

The suitability of Ex p equipment still depends on the hazardous-area classification and the equipment's certified protection level.

The fact that equipment uses pressurized protection does not automatically mean that it can be installed in every hazardous area.

Engineers must consider the applicable:

• Hazardous area Zone.
• Gas or dust group.
• Equipment Protection Level.
• Ambient conditions.
• Equipment certification.
• Special conditions for safe use.

The hazardous-area classification itself is addressed by other standards in the IEC 60079 series, including IEC 60079-10-1 for explosive gas atmospheres and IEC 60079-10-2 for explosive dust atmospheres.

Ex p and Equipment Protection Level

Equipment Protection Level, or EPL, provides another important part of the equipment classification.

The applicable EPL depends on the equipment design and protection arrangement.

Therefore, engineers should not select pressurized equipment simply because the marking contains “Ex p”. The complete marking and certification documentation must be reviewed.

This is particularly important when equipment is being specified for Zone 0, Zone 1, Zone 2, or the corresponding dust hazardous areas.

Ex p Compared With Other Protection Concepts

Pressurized protection is fundamentally different from several other common explosion protection techniques.

Protection	Basic Principle	Standard
Ex d	Contains an internal explosion and prevents flame transmission.	IEC 60079-1
Ex e	Prevents ignition sources through increased safety design.	IEC 60079-7
Ex i	Limits electrical and thermal energy to prevent ignition.	IEC 60079-11
Ex p	Uses a controlled protective atmosphere inside an enclosure.	IEC 60079-2
Ex m	Uses encapsulation to prevent an explosive atmosphere from reaching ignition sources.	IEC 60079-18
Ex t	Uses an enclosure to prevent combustible dust from reaching ignition sources.	IEC 60079-31

The selection of protection concept depends on the equipment design, hazardous-area requirements, operating conditions, and certification basis.

Advantages of Ex p Protection

Pressurized protection can provide a practical solution for equipment that would otherwise be difficult to protect using conventional explosion protection techniques.

Some important advantages include:

• Allows certain complex electrical equipment to be used in hazardous areas.
• Can protect large control and instrumentation assemblies.
• Can accommodate equipment that generates internal heat or contains multiple electrical components.
• Can provide a controlled internal environment.
• Can be applied to equipment that is difficult to certify using a compact enclosure protection concept.

For large panels, analyzer systems, electronic assemblies, and other complex equipment, pressurization can therefore be an attractive engineering solution.

Limitations of Ex p Protection

Ex p protection also introduces additional engineering requirements that do not exist with some simpler protection concepts.

The system depends on maintaining the protective conditions during operation.

Potential considerations include:

• Continuous availability of protective gas.
• Pressure monitoring.
• Purging requirements.
• Control and interlocking systems.
• Correct operation of valves and regulators.
• Maintenance of enclosure integrity.
• Correct installation of associated equipment.
• Response to loss of pressurization.

This means that Ex p protection is not simply a product characteristic. It is often a complete engineered protection system.

Ex p Equipment in Engineering and Procurement

When an EPC contractor or procurement team evaluates Ex p equipment, reviewing only the equipment nameplate is not sufficient.

The technical review should consider:

• Applicable IEC 60079 standards.
• Ex protection marking.
• Equipment Protection Level.
• Gas or dust group.
• Ambient temperature range.
• Certification documentation.
• Protective gas requirements.
• Purging requirements.
• Pressure requirements.
• Alarm and shutdown functions.
• Installation requirements.
• Special conditions for safe use.

This information becomes particularly important when the Ex p equipment is integrated into a larger process control, analyzer, electrical, or instrumentation system.

Ex p Equipment and Installation

The installation of Ex p equipment requires consideration of more than the electrical connections.

The protective gas supply, enclosure interfaces, pressure monitoring, exhaust arrangements, control functions, and shutdown logic can all affect the protection system.

For Group II and Group III installations, the applicable installation requirements are addressed by IEC 60079-14.

This means the equipment certificate and manufacturer's installation instructions should be reviewed together with the project installation requirements.

Common Misunderstandings About IEC 60079-2

Ex p Means the Enclosure Is Simply Pressurized

Not necessarily. The protection concept involves a controlled protective condition and the associated requirements for establishing and maintaining that condition. The complete protection system must be considered.

Any Pressurized Cabinet Can Be Called Ex p

No. A conventional cabinet that happens to operate under pressure is not automatically certified as Ex p equipment. The equipment must satisfy the applicable requirements and certification basis.

Ex p Equipment Can Be Used in Any Hazardous Area

No. The complete equipment marking, EPL, certification, hazardous-area classification, and installation requirements must be compatible with the intended application.

IEC 60079-2 Replaces IEC 60079-0

No. IEC 60079-2 supplements and modifies the general requirements of IEC 60079-0 for pressurized equipment.

Pressurized Rooms Are Covered by IEC 60079-2

Not generally. Pressurized rooms and analyser houses are addressed separately by IEC 60079-13.

Loss of Pressure Has No Effect on Equipment Safety

Incorrect. Maintaining the required protective condition is fundamental to Ex p protection. The equipment and protection system therefore require appropriate monitoring and protective responses to loss of the required condition.

Frequently Asked Questions (FAQ)

What is IEC 60079-2?

IEC 60079-2 is the IEC standard covering equipment protection by pressurized enclosure “p”. It specifies requirements for the construction and testing of electrical equipment using pressurized enclosures in explosive gas and explosive dust atmospheres.

What does Ex p mean?

Ex p is a type of explosion protection in which a protective gas is used to establish and maintain a controlled protective condition inside an enclosure.

What is the difference between Ex p and Ex d?

Ex d uses a flameproof enclosure designed to contain an internal explosion and prevent flame transmission to the surrounding atmosphere. Ex p uses a protective gas and controlled pressurization to prevent the formation of an explosive atmosphere within the protected enclosure or to control the internal atmosphere as applicable.

Does IEC 60079-2 apply to dust atmospheres?

Yes. IEC 60079-2 includes requirements for pressurized electrical equipment intended for explosive gas atmospheres and explosive dust atmospheres.

Does IEC 60079-2 cover pressurized rooms?

No. Pressurized rooms and analyser houses are addressed by IEC 60079-13.

Does Ex p require a protective gas supply?

Yes. The protection principle relies on a protective gas being supplied and the required protective conditions being established and maintained within the applicable enclosure.

What happens if the pressurization condition is lost?

The protection system must respond according to its certified design and applicable requirements. Depending on the equipment, this can involve alarms, shutdown, or other protective functions.

Can Ex p equipment be used without purging?

The applicable purging or flushing requirements depend on the specific equipment and protection arrangement. The manufacturer's certified instructions and the applicable IEC 60079 requirements must be followed.

What standard covers Ex p installation?

Installation requirements for Group II and Group III equipment are addressed by IEC 60079-14, together with the equipment manufacturer's instructions and applicable project requirements.

Conclusion

IEC 60079-2 provides the specific technical requirements for equipment protection by pressurized enclosure “p”.

Unlike protection concepts that rely primarily on enclosure construction, encapsulation, energy limitation, or flame containment, Ex p protection depends on maintaining a controlled protective environment within the equipment enclosure.

This makes the pressurization system itself an important part of the explosion protection arrangement. Protective gas supply, pressure control, monitoring, purging, interlocking, and protective shutdown functions can all form part of the overall system.

IEC 60079-2 should also be read together with IEC 60079-0 and the other applicable IEC 60079 standards. The complete Ex marking, certification documentation, hazardous-area classification, EPL, and installation requirements must be considered before equipment is selected or installed.

For engineers and procurement teams, the key point is simple: Ex p is not merely a pressurized cabinet. It is a certified protection system whose effectiveness depends on maintaining the required protective conditions.

Technical Review

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 – Part 14: Electrical Installations Design, Selection and Erection.
• IEC 60079 Series – Explosive Atmospheres.
• IECEx System – International Certification System for Equipment Used in Explosive Atmospheres.