How to Design a Heating Plate for Explosion-Proof (ATEX/IECEx) Requirements

A conventional heating plate in an environment with flammable gases, vapours or dusts can be the ignition source. Designing for ATEX or IECEx explosion-proof certification involves a fundamental change in materials, structure, and testing to assure safety and conformity with tight industry standards.

Features of explosion-proof heating plate design
1. Encapsulated Heating Element
In explosion-proof designs, heating elements must be totally enclosed or cast-in to eliminate any danger of sparking or igniting. This is achieved using potted or encapsulated components, where the heating element is covered with an insulating substance that avoids direct contact with the atmosphere. This protects against exposure of live parts and minimises the risk of igniting flammable liquids.

2. Temperature Class (T-Class)
The temperature class (or T-rating) is the highest surface temperature of the heating plate. This must be carefully managed so as not to approach the auto-ignition temperature of the surrounding atmosphere. The T-rating is based on maximum permissible surface temperature, and extends from T1 (450°C) to T6 (85°C) depending on the combustible material in the area.

For most explosion proof applications T4 (135 °C) or T6 (85 °C) are common goals. In ATEX or IECEx situations, the lower temperature classes are required to prevent the heating plate from being an ignition source under normal operation.

3. Explosion Proof Enclosures
All electrical equipment, including junction boxes and wiring, shall be contained in flameproof enclosures. These enclosures are certified to contain any internal explosion and prevent the propagation of flame outside the enclosure. This safeguard ensures that any explosion or flame resulting from an electrical failure within the junction box will not escape to ignite the surrounding atmosphere.

Flameproof enclosures are tested under controlled settings to contain internal explosions and prevent danger to the surrounding environment.

4. Control circuits intrinsically safe
In the sensor-based system, sensors must be included into an inherently safe control circuit. An inherently safe circuit is one that limits the voltage and current to safe levels for the electrical components, hence limiting the risk of ignite from electrical defects. The circuits are designed to be safe in hazardous areas when explosive gases or dust are present.

The incorporation of inherently safe circuits allows the system to be non-sparking and low energy through the operation of Zone 1 or 2 areas.

Certification and Regulatory Requirements
The design and components of the heating plate shall meet the requirements of the appropriate ATEX directive 2014/34/EU and IEC 60079 series standards in order to obtain ATEX or IECEx certification. These regulations set out the safety criteria for electrical equipment for use in explosive atmospheres. Certification is a process of rigorous testing and validation by a Notified Body, to guarantee that the equipment satisfies all safety criteria.

ATEX and IECEx certifications are both recognised worldwide and are required in many industries, particularly those with explosive atmospheres such as chemical processing, oil and gas and pharmaceuticals.

Checklist for Designing Explosion-Proof Heating Plates
Design Consideration Description 
Heating Elements EncapsulationFully potted or cast-in parts for spark prevention
Temperature Class (T-Rating) T4 (135°C) or T6 (85°C) to avoid igniting
Flameproof Enclosures Certified enclosures for containment of internal explosions
Intrinsic Safety Control CircuitryElectric circuits for safe operation of sensors and controls
Conclusion of ATEX/IECEx Standards Compliance Certification by a Notified Body
In hazardous regions, explosion-proof design is a must and requires a holistic approach to eliminate ignition hazards. Heating plates should comply with ATEX or IECEx regulations for safety in areas containing flammable gases, vapours or dusts. The heating elements are encased. Flameproof enclosures and intrinsically safe circuits are used. A carefully built heating plate would not cause ignite and would be safe to use. Safety certification of equipment is a requirement for a number of businesses and is a necessity to achieve reliable and safe heat transfer in hazardous situations.