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CAN/CSA C22.2 No. 60079-31-15: Equipment Dust Ignition Protection by Enclosure ‘t’
A technical guide to the Canadian standard for equipment used in combustible dust atmospheres
Scope and Application
CAN/CSA C22.2 No. 60079-31-15 is the Canadian adoption of IEC 60079-31:2013, Explosive atmospheres – Part 31: Equipment dust ignition protection by enclosure “t”. It forms part of the C22.2 series of standards under the Canadian Electrical Code and specifies the requirements for electrical equipment that is protected by enclosure “t” for use in explosive dust atmospheres. The standard applies to equipment in which the ignition protection is achieved by limiting the maximum surface temperature and by restricting the ingress of combustible dust into the enclosure, thereby preventing ignition of an explosive dust atmosphere.
This standard is applicable to equipment intended for use in areas where explosive dust atmospheres may be present, classified as Zone 20, Zone 21, or Zone 22 according to the classification of hazardous locations. It covers three levels of protection: “ta” (very high protection for Zone 20), “tb” (high protection for Zone 21), and “tc” (normal protection for Zone 22). The standard addresses design, construction, testing, and marking requirements to ensure that equipment does not become an ignition source for surrounding combustible dust layers or clouds.
Note: CAN/CSA C22.2 No. 60079-31-15 is identical to IEC 60079-31:2013 with no national deviations regarding technical content. However, equipment sold in Canada must comply with the certification requirements of the applicable provincial or territorial authority.
Technical Requirements for Enclosure “t”
Key Protection Principles
Equipment protected by enclosure “t” relies on two fundamental protections:
- Dust Ingress Protection: The enclosure must prevent the entry of combustible dust in quantities that could cause ignition. This is achieved through specified IP (Ingress Protection) ratings per IEC 60529.
- Surface Temperature Limitation: The maximum surface temperature of any part of the equipment must not exceed the minimum ignition temperature of the relevant dust layer or dust cloud, considering safety margins.
Protection Levels and Zone Applicability
| Protection Level | Zone | Required IP Rating | Safety Level | Temperature Class Assignment |
|---|---|---|---|---|
| ta | Zone 20 | IP6X | Very high (EPL Da) | Txxx based on measured max. surface temperature |
| tb | Zone 21 | IP6X | High (EPL Db) | Txxx based on measured max. surface temperature |
| tc | Zone 22 | IP5X | Normal (EPL Dc) | Txxx based on measured max. surface temperature |
Temperature Classification for Dust Layers
In addition to the maximum surface temperature for a dust cloud, the standard requires that for dust layers, the permissible surface temperature is reduced as a function of layer thickness. Typical limits include:
- For dust layers up to 5 mm thick: Tmax ≤ T5mm (from standard tables).
- For layers up to 12.5 mm, 25 mm, and 50 mm: progressively lower temperature limits apply unless specific tests confirm higher values.
Warning: If the equipment is intended to operate with dust layers exceeding the tested thickness, the surface temperature must be reduced or the layer thickness physically limited. Failure to account for dust layers can lead to smoldering and fire.
Construction Requirements
- Enclosure materials must resist corrosion and be suitable for the environmental conditions. Non-metallic enclosures must pass thermal endurance and impact tests.
- Joint design must minimize dust ingress; flanged joints require gaskets and adequate compression.
- Fasteners must be captive or designed to prevent loss during maintenance.
- Cable entries and conduits must maintain the IP rating of the enclosure and be suitable for the ambient temperature range.
Best Practice: When selecting equipment for Zone 21, choose a “tb” rated device with IP6X to ensure maximum protection against dust ingress and surface temperature compliance under worst-case dust layer conditions.
Implementation in Hazardous Locations
Marking Requirements
Every piece of equipment must be marked with the following information as a minimum:
- Manufacturer’s name or trademark
- Type designation and serial number
- Year of manufacture
- Protection level (ta, tb, tc)
- IP rating (e.g., IP6X)
- Temperature class or maximum surface temperature (e.g., T85°C or T4)
- Standard reference CAN/CSA C22.2 No. 60079-31-15
Installation Considerations
The installation of enclosure “t” equipment must comply with the Canadian Electrical Code Part 1 (CE Code, CSA C22.1) and any local regulations. Key points include:
- Equipment must be installed in the zone for which it is certified.
- Dust accumulation on equipment must be minimized through orientation and location.
- Thermal management: free space around the enclosure to prevent dust buildup that could insulate and raise internal temperatures.
- Conduit seals are generally not required for dust-protected enclosures unless specified by the manufacturer.
Important: If the equipment is opened in service (e.g., for maintenance), the internal parts must not be exposed to the dust atmosphere unless the equipment is de-energized and the area is verified to be non-hazardous. The protection is lost once the enclosure seal is broken.
Compliance and Certification
Conformity Assessment
To be sold or used in Canada, equipment must be certified by a recognized certification body (e.g., CSA, UL, Intertek) to CAN/CSA C22.2 No. 60079-31-15. The certification process includes:
- Type testing (dust ingress test, thermal test, impact test)
- Factory production control assessment
- Surveillance audits
Differences from IEC 60079-31
As noted, this standard is identical to the international IEC version. However, compliance in Canada requires that the standard be referenced as a CSA standard and that the certification follows the rules of the applicable certification body. There are no additional technical deviations.
Tip: When sourcing equipment for Canadian projects, ensure the certificate explicitly references CAN/CSA C22.2 No. 60079-31-15 and not just IEC 60079-31, unless the local authority accepts the IEC certification.
FAQs
Q: What does the “t” in enclosure “t” stand for?
A: The “t” stands for “tested enclosure” — the original term from older European standards. In IEC/CSA context, it denotes the protection concept where dust is excluded by an enclosure that is tested for dust ingress and surface temperature limits.
A: The “t” stands for “tested enclosure” — the original term from older European standards. In IEC/CSA context, it denotes the protection concept where dust is excluded by an enclosure that is tested for dust ingress and surface temperature limits.
Q: Which zones does each protection level (ta, tb, tc) cover?
A: ta is for Zone 20 (continuous dust presence), tb for Zone 21 (likely in normal operation), and tc for Zone 22 (infrequent and short-duration presence). Ensure you select equipment with the appropriate EPL (Equipment Protection Level) for your zone classification.
A: ta is for Zone 20 (continuous dust presence), tb for Zone 21 (likely in normal operation), and tc for Zone 22 (infrequent and short-duration presence). Ensure you select equipment with the appropriate EPL (Equipment Protection Level) for your zone classification.
Q: How are the maximum surface temperatures determined?
A: The equipment is operated under worst-case conditions (maximum ambient temperature, normal and abnormal operation) and the hottest spot on the external enclosure is measured. This temperature is then compared to the minimum ignition temperature of the dust present. A safety margin is applied, typically 75% of the dust cloud ignition temperature for equipment without a layer risk, and lower for equipment that may accumulate layers.
A: The equipment is operated under worst-case conditions (maximum ambient temperature, normal and abnormal operation) and the hottest spot on the external enclosure is measured. This temperature is then compared to the minimum ignition temperature of the dust present. A safety margin is applied, typically 75% of the dust cloud ignition temperature for equipment without a layer risk, and lower for equipment that may accumulate layers.
Q: Are conduit seals required for enclosure “t” installations?
A: Generally, no — because the enclosure itself provides the dust-tight seal. However, if the enclosure is installed in a location where dust ingress through conduit entries is possible during maintenance, the manufacturer may require additional seals. Always follow the manufacturer’s instructions and the CE Code requirements for the specific environment.
A: Generally, no — because the enclosure itself provides the dust-tight seal. However, if the enclosure is installed in a location where dust ingress through conduit entries is possible during maintenance, the manufacturer may require additional seals. Always follow the manufacturer’s instructions and the CE Code requirements for the specific environment.
© 2026 HazardEx Resources. This article is for informational purposes and does not substitute for the full standard. Consult CAN/CSA C22.2 No. 60079-31-15 and the Canadian Electrical Code for complete compliance requirements.