IEC 60079-11 Explained: Intrinsic Safety "i"

Not all explosion protection techniques rely on heavy enclosures, flamepaths, or pressurized systems. Some of the safest electrical equipment used in hazardous areas operates on an entirely different principle: limiting electrical energy so that ignition simply cannot occur.

This principle forms the basis of Intrinsic Safety "i" (Ex i), one of the most widely used protection concepts in instrumentation and process automation systems.

The technical requirements for this protection concept are specified in IEC 60079-11 – Explosive Atmospheres – Part 11: Equipment Protection by Intrinsic Safety "i".

Unlike Ex d and Ex e equipment, which primarily rely on mechanical construction and design measures, intrinsic safety is based on controlling electrical and thermal energy to levels below those capable of igniting an explosive atmosphere.

Because intrinsically safe systems are extensively used in transmitters, sensors, analyzers, valve positioners, and field instrumentation, IEC 60079-11 has become one of the most important standards for instrumentation engineers working in hazardous areas.

This article explains what IEC 60079-11 is, how intrinsic safety works, and the key requirements that engineers, inspectors, and maintenance personnel should understand.

Quick Answer

What Is IEC 60079-11?

IEC 60079-11 is one of the most widely used standards within the IEC 60079 series because it governs the intrinsic safety protection concept used extensively in process instrumentation and control systems.

The standard applies to equipment, associated apparatus, and circuits that rely on energy limitation to prevent ignition of explosive atmospheres.

Unlike protection concepts that attempt to contain explosions or isolate ignition sources, intrinsic safety prevents ignition by ensuring that electrical energy remains below the minimum ignition energy of the hazardous atmosphere.

The standard works together with IEC 60079-0, which establishes the general requirements applicable to explosion-protected equipment.

Why Is IEC 60079-11 Important?

Many industrial instruments must operate directly inside hazardous areas while handling electrical signals and power.

Examples include:

• Pressure transmitters.
• Temperature transmitters.
• Level transmitters.
• Proximity sensors.
• Solenoid valves.
• Gas detectors.
• Field communicators.
• Portable instrumentation equipment.

Because these devices are frequently installed in the most hazardous locations, including Zone 0 areas, an extremely high level of protection is required.

IEC 60079-11 establishes the technical requirements necessary to ensure that these circuits remain incapable of causing ignition under both normal and specified fault conditions.

How Does Intrinsic Safety Work?

The principle of intrinsic safety is fundamentally different from most other explosion protection techniques.

Instead of preventing an explosive atmosphere from reaching the equipment or containing an internal explosion, intrinsic safety limits the energy available within the circuit.

The electrical energy is controlled so that even if:

• A short circuit occurs.
• A conductor becomes disconnected.
• A component fails.
• A spark is generated.
• A fault develops within the equipment.

The available electrical and thermal energy remains insufficient to ignite the surrounding explosive atmosphere.

What Types of Energy Are Controlled?

IEC 60079-11 establishes requirements that limit both electrical and thermal energy.

Examples of parameters that are controlled include:

• Voltage.
• Current.
• Power.
• Capacitance.
• Inductance.
• Surface temperature.

By controlling these parameters, intrinsically safe equipment can be safely used even in the highest-risk hazardous areas.

Where Is IEC 60079-11 Commonly Used?

Because of its high level of protection and suitability for low-power devices, IEC 60079-11 is extensively used in instrumentation and process automation systems.

Typical applications include:

• Oil and gas production facilities.
• Refineries.
• Petrochemical plants.
• Offshore platforms.
• Chemical processing facilities.
• Pharmaceutical manufacturing plants.
• Hydrogen production facilities.
• Tank farms and storage terminals.

For many instrumentation applications, intrinsic safety has become the preferred explosion protection technique because it combines a high level of protection with relatively simple installation and maintenance practices.

Scope of IEC 60079-11

IEC 60079-11 specifies the requirements for the construction and testing of intrinsically safe equipment, associated apparatus, and intrinsically safe systems.

The standard applies to electrical equipment that relies on energy limitation to prevent ignition in explosive atmospheres.

The requirements cover:

• Intrinsically safe apparatus.
• Associated apparatus such as safety barriers and galvanic isolators.
• Interconnecting wiring.
• Electrical parameters of equipment and circuits.
• Fault analysis and testing requirements.

The standard works together with IEC 60079-0 and, in many applications, also with IEC 60079-25, which addresses intrinsically safe electrical systems.

Major Requirements of IEC 60079-11

Although IEC 60079-11 contains extensive technical requirements, the main areas generally include:

• Energy limitation requirements.
• Fault analysis requirements.
• Entity parameter requirements.
• Separation distances.
• Component assessment.
• Temperature limitations.
• Construction requirements.
• Type testing and verification.

These requirements are intended to ensure that equipment cannot release sufficient energy to ignite the surrounding atmosphere.

Fault Analysis Requirements

One of the most important principles of intrinsic safety is that safety must be maintained not only during normal operation but also under fault conditions.

IEC 60079-11 therefore requires manufacturers to evaluate equipment under:

• Normal operating conditions.
• One fault conditions.
• Two independent fault conditions.

Depending on the required level of protection, equipment must remain incapable of causing ignition even after specified faults occur.

This approach provides a very high degree of confidence in the safety of intrinsically safe circuits.

Equipment Protection Levels and Fault Requirements

IEC 60079-11 establishes different levels of intrinsic safety depending on the number of faults that the equipment can safely withstand.

Protection Concept	EPL	Fault Requirement	Typical Zone
Ex ia	Ga	Two faults	Zone 0, 1, 2
Ex ib	Gb	One fault	Zone 1, 2
Ex ic	Gc	Normal operation	Zone 2

This classification explains why Ex ia equipment is commonly used in the most hazardous areas where explosive atmospheres are continuously present.

Entity Parameters

One of the most important concepts in intrinsic safety is the use of entity parameters.

Entity parameters allow engineers to determine whether field devices and associated apparatus can be safely interconnected.

Typical parameters include:

• Maximum input voltage (Ui).
• Maximum input current (Ii).
• Maximum input power (Pi).
• Internal capacitance (Ci).
• Internal inductance (Li).
• Maximum output voltage (Uo).
• Maximum output current (Io).
• Maximum output power (Po).

Proper verification of entity parameters is essential because an incorrect combination of devices could compromise intrinsic safety.

Associated Apparatus

Many intrinsically safe systems rely on equipment that is installed outside the hazardous area but limits the energy supplied to field devices.

Examples include:

• Zener barriers.
• Galvanic isolators.
• Isolated repeaters.
• Signal conditioners.
• Intrinsically safe power supplies.

IEC 60079-11 establishes requirements for these associated apparatus because they play a critical role in maintaining the safety of the entire intrinsically safe system.

Separation Requirements

Because intrinsically safe circuits contain limited energy, they must be protected from inadvertent contact with non-intrinsically safe circuits.

IEC 60079-11 therefore specifies requirements related to:

• Electrical separation.
• Creepage distances.
• Clearance distances.
• Insulation coordination.
• Isolation barriers.

These requirements help ensure that excessive energy cannot accidentally enter an intrinsically safe circuit.

Temperature Requirements

Although intrinsic safety focuses primarily on electrical energy limitation, thermal energy must also be controlled.

IEC 60079-11 therefore establishes requirements related to:

• Maximum surface temperatures.
• Temperature rise of components.
• Fault condition temperatures.
• Temperature classifications.

The standard works together with IEC 60079-0 to ensure compliance with the assigned temperature class and equipment marking.

Type Testing and Verification

Before equipment can be certified according to IEC 60079-11, manufacturers must demonstrate compliance through testing and engineering assessment.

Verification activities may include:

• Electrical spark ignition testing.
• Thermal ignition testing.
• Fault simulation.
• Separation verification.
• Temperature testing.
• Construction assessment.

These tests ensure that the equipment remains incapable of causing ignition under the operating and fault conditions specified by the standard.

Advantages of IEC 60079-11

IEC 60079-11 and the Intrinsic Safety protection concept offer several significant advantages compared with many other explosion protection techniques.

Because the protection method relies on energy limitation rather than heavy mechanical construction, intrinsically safe equipment is particularly well suited for instrumentation and low-power applications.

Key advantages include:

• Suitable for Zone 0 applications.
• Allows live maintenance and calibration under certain conditions.
• Typically lighter and smaller than Ex d equipment.
• No requirement for heavy explosion-proof enclosures.
• Reduced installation and maintenance costs.
• Well suited for instrumentation and control systems.
• Excellent safety performance for low-power circuits.
• Widely accepted internationally.

For these reasons, intrinsic safety has become the preferred protection concept for many field instrumentation applications in the process industries.

Limitations of IEC 60079-11

Despite its many advantages, intrinsic safety is not suitable for every application.

Because the protection concept depends on limiting available energy, it has several practical limitations.

• Generally unsuitable for high-power equipment.
• Requires detailed system design and verification.
• Entity parameter calculations can be complex.
• Requires careful segregation of wiring.
• Special attention is required during modifications and expansions.
• Associated apparatus may be required.

For these reasons, engineers must carefully evaluate whether intrinsic safety is appropriate for a particular application.

Relationship Between IEC 60079-11 and IEC 60079-25

A common misconception is that IEC 60079-11 alone governs every aspect of intrinsic safety.

In reality, the standard primarily addresses individual equipment and associated apparatus.

When multiple devices are interconnected to form an intrinsically safe system, additional requirements may apply under IEC 60079-25 – Intrinsically Safe Electrical Systems.

Standard	Purpose
IEC 60079-11	Requirements for intrinsically safe equipment and associated apparatus.
IEC 60079-25	Requirements for complete intrinsically safe systems.

Understanding the distinction between these standards is essential for instrumentation engineers responsible for system design and loop calculations.

Typical Applications of Intrinsic Safety

Equipment designed according to IEC 60079-11 is used extensively throughout the process industries.

Typical applications include:

• Pressure transmitters.
• Temperature transmitters.
• Level transmitters.
• Flow transmitters.
• Gas detectors.
• Proximity sensors.
• Valve positioners.
• Portable communicators.
• Wireless field devices.
• Analyzer systems.

Many of these devices are installed directly in Zone 0 areas where other protection concepts may not be practical.

Associated Apparatus Commonly Used With Ex i Systems

Most intrinsically safe installations rely on additional devices that limit the energy supplied to field equipment.

Common examples include:

• Zener barriers.
• Galvanic isolators.
• Signal isolators.
• Intrinsically safe repeaters.
• IS power supplies.

The proper selection and verification of these devices are critical to maintaining the integrity of the intrinsically safe system.

Common Misunderstandings About IEC 60079-11

Intrinsic Safety Means Zero Electrical Energy

No. Intrinsically safe equipment still contains electrical energy. The energy is simply limited to levels below those capable of causing ignition.

Any Low-Voltage Circuit Is Intrinsically Safe

Incorrect. Low voltage alone does not guarantee intrinsic safety. Current, power, capacitance, inductance, and fault conditions must also be considered.

Ex ia, Ex ib, and Ex ic Provide the Same Level of Protection

No. The three protection levels have different fault requirements and are suitable for different hazardous area classifications.

Intrinsic Safety Eliminates the Need for Engineering Calculations

Incorrect. Entity parameter verification and system calculations remain essential parts of intrinsic safety design.

Any Barrier Can Be Used With Any Field Device

No. Associated apparatus and field devices must be evaluated together to ensure compatibility of entity parameters.

Why Engineers Should Understand IEC 60079-11

Instrumentation engineers encounter the requirements of IEC 60079-11 throughout the entire lifecycle of a project, from design and procurement to commissioning and maintenance.

A basic understanding of the standard helps engineers:

• Select suitable field devices.
• Understand Ex ia, Ex ib, and Ex ic markings.
• Perform entity parameter verification.
• Avoid unsafe modifications.
• Identify non-compliant installations.
• Improve hazardous area safety.
• Reduce commissioning and maintenance problems.

Because intrinsic safety is one of the most widely used protection concepts in instrumentation systems, IEC 60079-11 remains one of the most important standards for engineers working in hazardous areas.

Frequently Asked Questions (FAQ)

What is IEC 60079-11?

IEC 60079-11 is the international standard that specifies the requirements for equipment protection by Intrinsic Safety "i". The standard limits electrical and thermal energy to levels that cannot ignite a specified explosive atmosphere.

What is the principle of Intrinsic Safety?

Intrinsic Safety works by limiting voltage, current, power, and stored energy so that sparks or hot surfaces cannot ignite the surrounding explosive atmosphere, even under specified fault conditions.

What is the difference between Ex ia, Ex ib, and Ex ic?

Ex ia provides the highest level of protection and remains safe with two independent faults, making it suitable for Zone 0 applications. Ex ib remains safe with one fault and is suitable for Zone 1. Ex ic provides protection during normal operation and is intended for Zone 2.

Can intrinsically safe equipment be used in Zone 0?

Yes. Ex ia equipment is specifically designed for use in Zone 0 hazardous areas where explosive atmospheres may be present continuously or for long periods.

What are entity parameters?

Entity parameters are electrical characteristics such as Ui, Ii, Pi, Ci, Li, Uo, Io, and Po that are used to verify compatibility between field devices and associated apparatus in intrinsically safe systems.

What is associated apparatus?

Associated apparatus includes devices such as Zener barriers and galvanic isolators that limit the energy supplied to field equipment and help maintain intrinsic safety.

Conclusion

IEC 60079-11 is one of the most important standards within the IEC 60079 series because it governs the Intrinsic Safety protection concept that is extensively used in instrumentation and process automation systems.

Unlike other protection techniques that rely on mechanical construction or explosion containment, intrinsic safety prevents ignition by limiting electrical and thermal energy to safe levels.

Because intrinsically safe systems are widely used in transmitters, sensors, analyzers, gas detectors, and portable equipment, understanding IEC 60079-11 is essential for instrumentation engineers, inspectors, and maintenance personnel working in hazardous areas.

A solid understanding of the standard also helps engineers correctly apply entity parameter verification, select suitable associated apparatus, and avoid modifications that could compromise the safety of intrinsically safe systems.

Technical Review

References

• IEC 60079-11 – Explosive Atmospheres – Part 11: Equipment Protection by Intrinsic Safety "i".
• IEC 60079-25 – Explosive Atmospheres – Intrinsically Safe Electrical Systems.
• IEC 60079-0 – Explosive Atmospheres – Part 0: Equipment – General Requirements.
• IECEx System – International Certification System for Equipment Used in Explosive Atmospheres.
• International Electrotechnical Commission (IEC).
• EN IEC 60079-11 – Explosive Atmospheres – Equipment Protection by Intrinsic Safety "i".