IEC 60079-5 Explained: Powder Filling “q” Protection

Electrical equipment installed in hazardous areas must be designed so that it does not ignite the surrounding explosive atmosphere under the conditions for which it is certified. One method used for certain electrical equipment and Ex components is powder filling “q” protection.

IEC 60079-5 specifies requirements for the construction, testing and marking of electrical equipment, parts of equipment and Ex components using powder filling “q”. The protection method uses solid filling material around ignition-capable parts to prevent an internal ignition from igniting the surrounding explosive gas atmosphere.

This guide explains the operating principle, construction considerations, equipment limitations and documentation checks that engineers and procurement teams should understand when evaluating equipment using Ex “q” protection.

What Is IEC 60079-5?

IEC 60079-5 is part of the IEC 60079 series for equipment used in explosive atmospheres. It covers the specific requirements for the protection method known as powder filling “q”.

The standard supplements IEC 60079-0, which establishes general requirements for Ex equipment. Where the requirements of IEC 60079-5 conflict with the general requirements, the applicable provisions of IEC 60079-5 take precedence for this protection method.

Item	Description
Standard	IEC 60079-5
Protection method	Powder filling “q”
Primary application	Electrical equipment and Ex components for explosive gas atmospheres
General requirements	IEC 60079-0, supplemented and modified by IEC 60079-5
Protection level	Typically associated with EPL Gb or Mb, subject to the equipment design and certification

The applicable consolidated edition identified by the IEC is IEC 60079-5:2015+AMD1:2022, Edition 4.1. Project specifications and the equipment certificate should be checked to establish the edition applicable to a particular installation.

How Does Powder Filling “q” Work?

In powder filling protection, parts that could ignite an explosive gas atmosphere are fixed in position and completely surrounded by a specified solid filling material. The material is contained within a suitable housing.

The filling material used by this protection method is solid quartz or solid glass particles. The arrangement limits the free volume around electrical components and helps quench flame propagation through paths in the filling material.

An important point is that the surrounding explosive gas atmosphere may still penetrate the equipment. Internal circuits may even ignite a mixture within the equipment under certain fault conditions. The protection concept is designed to prevent that internal ignition from igniting the external explosive atmosphere.

What Equipment Can Use Ex “q” Protection?

IEC 60079-5 can apply to electrical equipment, parts of equipment and Ex components containing electrical circuits and components such as:

• Electronic circuits.
• Transformers.
• Protection fuses.
• Relays.
• Switches.
• Intrinsically safe apparatus and associated apparatus incorporated into a protected assembly.

These are examples of equipment that may use the protection method, not a list of products automatically suitable for Ex “q”. Suitability depends on the complete design, ratings, construction and certification.

Scope and Equipment Limitations

The IEC publication specifies the following rated limits for equipment within its scope:

• Rated supply current: not greater than 16 A.
• Rated supply voltage: not greater than 1,000 V.
• Rated power consumption: not greater than 1,000 W.

These are scope limits, not a substitute for checking the certified ratings of a particular product. Equipment that exceeds any applicable limit should not be assumed to fall within IEC 60079-5 without confirming the applicable standard and certification basis.

Construction Requirements

The protection depends on the complete construction of the filled assembly. The filling material alone does not establish compliance.

1. Container and Sealing

The container holds the electrical components and filling material. The assembly must be filled and closed using a permitted construction and sealing method.

Depending on the design, the container may be permanently sealed during manufacture or may use a sealing arrangement intended to allow repair and subsequent refilling. Any repairable construction must maintain the required sealing performance when correctly serviced.

2. Filling Material

The specified filling material is solid quartz or solid glass particles. The material specification and particle-size requirements must comply with the applicable edition of IEC 60079-5.

Substituting another granular material based only on its appearance or physical similarity is not acceptable unless the substitution is permitted by the applicable technical requirements and certification.

3. Complete Filling and Avoidance of Voids

The free space within the protected assembly must be effectively filled. The filling procedure must avoid unintended voids, for example by using an appropriate settling procedure where specified.

Voids or changes in the filling arrangement can affect the protection principle. Filling quantity, placement and assembly procedures are therefore controlled manufacturing considerations rather than ordinary packing details.

4. Container Integrity

The container must meet the applicable mechanical and pressure-test requirements. Its construction must also limit the escape of filling material through gaps and openings.

The required container design and tests must be established from the applicable standard and certificate. A visually robust housing alone does not demonstrate compliance.

5. Ingress Protection

IEC 60079-5 includes requirements for the ingress protection of the container in its normal service condition. The applicable minimum and any permitted exceptions must be checked against the relevant edition, equipment category and certificate conditions.

Where a breathing device or other specific construction is required, it must be part of the assessed design. The IP rating should not be inferred from the external appearance of the enclosure.

Ex “q” Compared With Other Protection Methods

Powder filling is one of several protection methods within the IEC 60079 series. The methods differ in how they control the ignition risk.

Protection Method	Basic Principle	Related Standard
Ex q	Solid filling material surrounds ignition-capable parts and limits flame propagation to the external atmosphere.	IEC 60079-5
Ex d	A flameproof enclosure withstands an internal explosion and prevents flame transmission to the external atmosphere.	IEC 60079-1
Ex e	Increased safety design reduces the likelihood of excessive temperatures, arcs and sparks under the conditions specified by the standard.	IEC 60079-7
Ex i	Intrinsic safety limits electrical and thermal energy to prevent ignition under the applicable conditions.	IEC 60079-11
Ex m	Encapsulation protects parts that could ignite an explosive atmosphere by enclosing them in a compound.	IEC 60079-18

These methods are not interchangeable. The correct choice depends on the equipment design, hazardous-area classification, gas group, temperature requirements, EPL and the conditions stated in the certificate.

Marking and Certification

Equipment using powder filling protection must be assessed and marked according to the applicable requirements. The marking and certificate provide information needed to determine whether the equipment is suitable for its intended installation.

When reviewing an Ex “q” product, engineers and procurement teams should check:

• The complete Ex marking and protection method.
• The gas group and equipment protection level.
• The temperature class or maximum surface temperature, as applicable.
• The permitted electrical ratings.
• The certificate number and issuing certification body.
• Any “X” suffix and associated specific conditions of use.
• The installation, operating and maintenance instructions.

Do not assume that a product is suitable merely because “Ex q” appears in a datasheet. The complete marking and certificate must match the hazardous-area and project requirements.

Engineering Review Checklist

For FEED, detailed engineering and procurement reviews, use the following checks as a starting point. The checklist does not replace the standard or the certificate.

Review Item	What to Verify
Application	Confirm the equipment is intended for an explosive gas atmosphere and is within the applicable standard scope.
Electrical ratings	Check current, voltage and power against the standard scope and certified product ratings.
Ex marking	Verify the protection method, gas group, EPL and temperature information against project requirements.
Certificate	Confirm the certificate applies to the offered model and its actual configuration.
Specific conditions	Review certificate conditions, including any conditions identified by an “X” suffix.
Enclosure and filling	Confirm the certified construction, sealing and filling arrangement are maintained.
Installation	Check terminal connections, mounting and other installation details against the manufacturer's instructions.
Documentation	Obtain the datasheet, certificate, instructions and required project documents.

Common Mistakes When Specifying Ex “q” Equipment

Assuming the Filling Material Makes Any Assembly Safe

Protection depends on the complete certified design, including the container, filling procedure, component positioning and sealing. Adding quartz or glass particles to an ordinary electrical enclosure does not create compliant Ex “q” equipment.

Ignoring the Certified Ratings

The scope limits in IEC 60079-5 do not establish the ratings of every certified product. Verify the specific equipment ratings and any limitations in the certificate.

Changing or Replacing the Filling Material

The filling material and its specified characteristics are part of the protection design. Unapproved substitution or incorrect refilling can compromise the intended protection.

Evaluating Only the External Enclosure

A housing that appears sealed or has a high IP rating does not, by itself, establish Ex “q” compliance. The complete assembly must satisfy the applicable construction, testing and marking requirements.

Confusing Ex “q” With Ex “d”

Both methods address the possibility of ignition inside equipment, but they use different construction principles and different standards. An Ex “q” assembly must not be evaluated as though it were an Ex “d” flameproof enclosure.

Frequently Asked Questions

What does Ex “q” mean?

Ex “q” identifies the powder filling type of protection. It uses specified solid filling material around ignition-capable parts to prevent an internal ignition from igniting the surrounding explosive gas atmosphere.

Which standard covers powder filling protection?

IEC 60079-5 covers the construction, testing and marking requirements for electrical equipment, parts of equipment and Ex components using powder filling “q”.

What material is used for Ex “q” filling?

The specified filling material is solid quartz or solid glass particles, subject to the requirements of the applicable standard edition.

Does Ex “q” prevent explosive gas from entering the equipment?

Not necessarily. The protection principle does not depend solely on excluding the surrounding atmosphere. It is designed to prevent an internal ignition from igniting the external explosive atmosphere.

Can Ex “q” equipment be repaired?

Only in accordance with the equipment design, manufacturer's instructions, applicable standard and certificate conditions. Reopening, refilling or resealing must not compromise the certified protection.

Can Ex “q” be used for combustible dust atmospheres?

IEC 60079-5 addresses equipment intended for explosive gas atmospheres. Suitability for a combustible-dust application must be established against the relevant dust-protection requirements and equipment certification.

Conclusion

IEC 60079-5 defines the requirements for powder filling “q” protection in electrical equipment and Ex components intended for explosive gas atmospheres. The protection relies on specified solid filling material, controlled internal construction and a suitable container to prevent an internal ignition from igniting the surrounding atmosphere.

For engineers and procurement teams, the essential checks are the complete Ex marking, certificate, electrical ratings, construction requirements and any specific conditions of use. Powder filling alone is not evidence of compliance; the complete equipment must meet the applicable requirements.

References

• IEC 60079-5:2015+AMD1:2022, Edition 4.1 — Explosive atmospheres – Part 5: Equipment protection by powder filling “q”.
• IEC 60079-0 — Explosive atmospheres – Part 0: Equipment – General requirements.
• IEC 60079-1 — Explosive atmospheres – Part 1: Equipment protection by flameproof enclosures “d”.
• IEC 60079-7 — Explosive atmospheres – Part 7: Equipment protection by increased safety “e”.
• IEC 60079-11 — Explosive atmospheres – Part 11: Equipment protection by intrinsic safety “i”.
• IEC 60079-18 — Explosive atmospheres – Part 18: Equipment protection by encapsulation “m”.