Electronics Guide

ATEX Directive Overview

Two ATEX directives govern equipment and workplaces in explosive atmospheres:

ATEX Equipment Directive (2014/34/EU): This directive establishes requirements for equipment and protective systems intended for use in potentially explosive atmospheres. It requires that equipment be designed and manufactured to prevent ignition of explosive atmospheres under normal operating conditions and under specified fault conditions.

ATEX Workplace Directive (1999/92/EC): This directive establishes minimum requirements for worker safety in workplaces where explosive atmospheres may occur. It requires employers to assess explosion risks, classify hazardous areas, and ensure appropriate equipment is used.

For EMC purposes, the Equipment Directive is most relevant. It requires that equipment meet essential health and safety requirements (EHSRs) that include provisions related to electromagnetic emissions and immunity. Equipment must not produce electromagnetic phenomena that could cause ignition, and must be immune to electromagnetic disturbances that could cause dangerous failures.

Equipment Categories and Groups

ATEX classifies equipment by group and category based on the intended environment and required protection level:

Equipment Group I: Equipment intended for use in underground mines and surface installations where firedamp (methane) and/or combustible dust may be present. Category M1 equipment must remain safe even with one fault present and during rare malfunctions. Category M2 equipment must be de-energized when explosive atmosphere is detected.

Equipment Group II: Equipment for use in other explosive atmosphere locations. Category 1 equipment provides very high protection level, suitable for Zones 0, 1, and 2 (gas) or Zones 20, 21, and 22 (dust). Category 2 provides high protection for Zones 1 and 2 or Zones 21 and 22. Category 3 provides normal protection for Zone 2 or Zone 22 only.

Equipment categories determine the extent of fault analysis required and the maximum allowable energy levels under fault conditions. Higher category equipment requires consideration of more simultaneous faults and provides greater safety margins.

ATEX Conformity Assessment

ATEX compliance requires conformity assessment procedures that vary by equipment category:

Category 1 (highest protection): Requires EU type examination by a Notified Body followed by production quality assurance or product verification.

Category 2: Requires EU type examination by a Notified Body followed by internal production control or production quality assurance.

Category 3: Allows internal production control with technical documentation submitted to a Notified Body for record keeping.

Conformity assessment includes evaluation of EMC characteristics as they relate to explosion protection. This is not the same as compliance with the EMC Directive, which applies separately to all electronic equipment. ATEX-relevant EMC assessment focuses on whether electromagnetic phenomena could compromise explosion protection.

EMC Directive Interaction

Equipment subject to ATEX must typically also comply with the EU EMC Directive (2014/30/EU), but with important considerations:

Parallel compliance: Equipment must independently satisfy both directives. ATEX compliance does not automatically provide EMC compliance or vice versa.

Conflicting requirements: Sometimes EMC protection measures could compromise explosion protection. For example, adding filter capacitors for EMC could exceed permissible capacitance for intrinsic safety. In such cases, explosion safety takes precedence.

Installation effects: Final EMC performance depends on installation conditions. ATEX equipment manufacturers must provide installation instructions that achieve both explosion protection and acceptable EMC performance.

IEC 60079 Series

The IEC 60079 series establishes requirements for electrical equipment in explosive gas atmospheres:

IEC 60079-0: General requirements applicable to all explosion protection methods. This standard includes provisions for electromagnetic compatibility relevant to explosion protection, particularly requirements for radiated and conducted emissions that could affect other explosion-protected equipment.

IEC 60079-1 through 60079-35: Standards for specific protection concepts including flameproof enclosures, increased safety, intrinsic safety, pressurization, and others. Each protection concept has specific EMC-relevant requirements.

IEC 60079-14: Installation requirements that include guidance on cable routing, grounding, and other EMC-relevant installation practices for hazardous area electrical systems.

IEC 60079-17: Inspection and maintenance requirements that address ongoing verification of explosion protection including elements that affect EMC performance.

IEC 61241 Series for Dust Atmospheres

Electrical equipment for use in combustible dust atmospheres was previously covered by IEC 61241, now largely incorporated into IEC 60079:

Dust-specific requirements: Combustible dust presents different ignition mechanisms than gases. Surface temperature limits are typically more restrictive because dust layers can ignite at lower temperatures. Enclosure sealing requirements prevent dust ingress that could accumulate and ignite.

EMC considerations: Dust atmospheres may be less susceptible to spark ignition than gases, but dust layer ignition from surface heating remains a concern. EMC-related heating effects must be evaluated for dust applications.

IECEx Certification Process

IECEx provides a certification framework accepted in many countries:

ExTR (Test Report): Comprehensive test reports from IECEx-accepted test laboratories document compliance testing including any EMC-relevant tests.

ExCB (Certificate of Conformity): Certificates issued by IECEx certification bodies confirm equipment compliance with applicable standards.

QAR (Quality Assessment Report): Reports documenting manufacturer quality systems ensure ongoing production conformity.

IECEx certification facilitates international market access, as many countries accept IECEx certificates directly or as supporting documentation for national certification.

Relationship to EMC Standards

IECEx standards reference general EMC standards for certain requirements:

IEC 61000 series: General EMC standards provide test methods and limits referenced by explosion protection standards for immunity and emissions requirements.

CISPR standards: International standards for radio interference limits may apply to explosion-protected electronic equipment as radio interference sources.

Product-specific standards: Some products have specific EMC standards (such as IEC 61326 for measurement and control equipment) that apply in addition to explosion protection requirements.

Engineers must navigate the interaction between explosion protection and EMC standards to ensure complete compliance with all applicable requirements.

Gas and Vapor Zones

Zones for explosive gas atmospheres are classified based on occurrence probability:

Zone 0: Areas where an explosive gas atmosphere is present continuously, for long periods, or frequently. Examples include the inside of tanks containing flammable liquids, or areas around open-top processing vessels. Only the most restrictive protection methods (intrinsically safe "ia" or specially designed equipment) are permitted. EMC design for Zone 0 must ensure no single fault or combination of two faults can produce ignition-capable energy.

Zone 1: Areas where an explosive gas atmosphere is likely to occur occasionally during normal operation. Examples include areas immediately surrounding Zone 0 locations, or areas near points of potential release such as pump seals or valve packings. Most explosion protection methods are suitable for Zone 1. EMC design must ensure safe operation under single-fault conditions.

Zone 2: Areas where an explosive gas atmosphere is not likely to occur during normal operation, but if it does occur, will persist for a short period only. Examples include areas surrounding Zone 1 locations or areas with reliable ventilation. Less restrictive protection methods are acceptable. EMC design considers normal operation without fault tolerance requirements.

Zone classification affects not only the protection method selection but also the rigor of EMC analysis. Higher zone numbers (lower hazard) permit relaxed EMC requirements, while Zone 0 demands the most comprehensive EMC fault analysis.

Dust Zones

Combustible dust atmospheres are classified similarly:

Zone 20: Areas where a combustible dust cloud is present continuously, for long periods, or frequently. Similar to Zone 0 for gases.

Zone 21: Areas where a combustible dust cloud is likely to occur occasionally during normal operation. Similar to Zone 1 for gases.

Zone 22: Areas where a combustible dust cloud is not likely to occur during normal operation. Similar to Zone 2 for gases.

Dust zones also consider dust layer accumulation. Equipment surface temperatures must not exceed the dust cloud ignition temperature or the dust layer ignition temperature minus a safety margin.

Zone Extent Determination

Zone boundaries are determined through release source analysis:

Release source identification: Points where flammable materials may be released are identified, such as valves, flanges, pump seals, and vents.

Release characteristics: The rate and nature of potential releases (continuous, primary, or secondary) determines the grade of release and resulting zone classification.

Ventilation effects: Ventilation can reduce zone extent or even eliminate hazardous classification if sufficiently reliable and effective.

Zone extent affects EMC design by determining where different equipment categories are required. Proper zone classification ensures appropriate equipment selection without excessive restriction.

Equipment Selection by Zone

Equipment protection type must match the zone where it will be installed:

Zone 0/20 equipment: Only protection concepts providing protection under two faults are suitable. Intrinsically safe "ia" is the most common choice. EMC components must be carefully analyzed within the intrinsic safety assessment.

Zone 1/21 equipment: Equipment providing protection under single fault conditions is suitable. Multiple protection concepts are available, each with specific EMC implications.

Zone 2/22 equipment: Equipment suitable for normal operation without specific fault tolerance is acceptable. Standard industrial equipment with appropriate EMC design may be suitable if certified for Zone 2 use.

Division 1 and Division 2

The Division system has two classifications:

Division 1: Locations where hazardous concentrations of flammable gases, vapors, or combustible dust are present during normal operations, during frequent repair or maintenance operations, or where equipment breakdown could release hazardous concentrations while simultaneously causing electrical failure. Division 1 roughly corresponds to Zones 0 and 1 combined.

Division 2: Locations where hazardous concentrations exist only under abnormal conditions such as accidental rupture or breakdown of containers, failure of ventilation systems, or unusual operations. Division 2 roughly corresponds to Zone 2.

The Division system's broader Division 1 category encompasses situations that would be separately treated as Zone 0 or Zone 1 under the IEC system. This affects equipment selection and EMC requirements differently than Zone classification.

Class and Group Designations

The Division system further classifies hazardous locations by material type:

Class I: Flammable gases, vapors, or liquids. Groups A through D designate specific gas families based on explosion characteristics, from most hazardous (Group A, acetylene) to least hazardous (Group D, propane and similar).

Class II: Combustible dust. Groups E through G designate dust types from most hazardous (Group E, metal dusts) to least hazardous (Group G, agricultural dusts).

Class III: Ignitable fibers or flyings such as cotton lint or wood chips. No group subdivisions.

Class and Group affect equipment design requirements including maximum surface temperatures and explosion containment requirements. EMC design must consider the specific ignition characteristics of the designated group.

Equipment for Division Locations

Equipment suitable for Division locations is designated by approval agency listing:

Division 1 equipment: Must use protection methods that prevent ignition under normal and fault conditions. Explosion-proof (similar to flameproof), intrinsically safe, and purged/pressurized equipment are common choices.

Division 2 equipment: May use non-incendive equipment or other methods that prevent ignition under normal operation. General-purpose equipment may be suitable if it does not produce arcs, sparks, or high temperatures during normal operation.

Non-incendive concept: The North American non-incendive concept (similar but not identical to IEC "nA") provides a protection method for Division 2 that has specific EMC implications. Non-incendive circuits must not produce ignition-capable energy under normal operation, but need not consider fault conditions.

Zone vs. Division Comparison

Both classification systems address the same fundamental hazards but with different approaches:

Hazard stratification: The Zone system provides finer gradation with three levels versus two for Divisions. This allows more precisely matched equipment requirements but requires more detailed hazard analysis.

Equipment availability: Zone system equipment following IECEx is increasingly available worldwide. Division system equipment may have broader availability in North American markets.

Regulatory acceptance: Jurisdictions determine which system is acceptable. Some allow either system; others mandate specific approaches.

EMC engineers must understand both systems to work effectively in international markets. Equipment may require certification under both systems for global deployment.

Intrinsic Safety

Intrinsic safety limits energy in hazardous area circuits to levels incapable of igniting the specified atmosphere:

Energy limitation principle: Circuit voltage, current, capacitance, and inductance are controlled so that spark energy and thermal energy cannot reach ignition thresholds even under fault conditions.

EMC component restrictions: Capacitors and inductors used for EMC filtering must be accounted for in intrinsic safety calculations. Their stored energy contributes to the total available spark energy. This often forces trade-offs between EMC performance and intrinsic safety margins.

Cable capacitance: Long cable runs in hazardous areas add distributed capacitance that consumes allowable energy storage. Little margin may remain for EMC filter capacitors.

Associated apparatus: Barriers and isolators interfacing between hazardous and safe areas must maintain intrinsic safety while providing any required EMC isolation. Galvanically isolated barriers generally offer better EMC characteristics than simple zener barriers.

Intrinsic safety is the most common protection method for process instrumentation and has significant interaction with EMC design that requires careful coordination.

Flameproof Enclosures

Flameproof (explosion-proof) enclosures contain any internal explosion and prevent propagation to the surrounding atmosphere:

Enclosure design: Heavy metal enclosures with specially designed joints and cable entries contain explosion pressure and cool escaping gases below ignition temperature.

EMC shielding: Flameproof enclosures provide inherent electromagnetic shielding due to their robust metal construction. However, the flame paths required for explosion protection may affect high-frequency shielding effectiveness.

Cable entry EMC: Flameproof cable glands must maintain both explosion protection and EMC integrity. Cable shield termination may be constrained by explosion protection requirements.

Internal EMC: Equipment within flameproof enclosures requires EMC design appropriate for the internal environment, considering both external interference and internally generated interference.

Increased Safety

Increased safety prevents ignition by eliminating ignition sources through enhanced design:

Design enhancements: Increased safety equipment uses improved insulation, larger clearances, and controlled temperatures to prevent ignition under normal conditions and specified abnormal conditions.

Surface temperature limits: Maximum surface temperatures are controlled to remain below ignition temperatures. Power dissipation from EMC components must be considered in thermal analysis.

Terminal design: Increased safety terminals must prevent loosening and maintain good contact. This affects how EMC ground connections can be implemented.

Cable selection: Increased safety installations have specific cable requirements that may affect EMC cable selection options.

Encapsulation and Potting

Encapsulation embeds electrical components in compound to prevent explosive atmosphere contact:

Complete encapsulation: All live parts are covered by compound with defined properties. This prevents sparks from contacting explosive atmosphere.

Thermal considerations: Encapsulation affects heat dissipation from enclosed components. EMC component power dissipation must be evaluated for thermal effects within encapsulation.

EMC implications: Encapsulation compounds have dielectric properties that affect capacitive coupling and component behavior. High-frequency EMC performance may differ from non-encapsulated designs.

Pressurization and Purging

Pressurization maintains positive pressure with protective gas to exclude explosive atmosphere:

Enclosure requirements: Pressurized enclosures maintain specified overpressure with protective gas (typically air or nitrogen). Loss of pressure triggers protective actions.

Internal environment: The internal atmosphere is non-hazardous, allowing use of non-explosion-protected equipment inside. Standard EMC design approaches apply to internal equipment.

Cable entry considerations: Cables entering pressurized enclosures must maintain pressure integrity while providing EMC continuity. Specialized fittings address both requirements.

Purge cycles: Pressurized equipment requires purging before energizing to ensure any explosive atmosphere has been displaced. EMC systems must accommodate purge cycle timing requirements.

Cable Selection and Routing

Cable selection for hazardous areas considers multiple requirements:

Intrinsic safety cables: Intrinsically safe circuits require cables with defined capacitance and inductance per unit length. Cable selection must balance IS parameters with EMC shielding requirements.

Cable segregation: Intrinsically safe cables must be separated from non-IS power cables to prevent energy transfer. This separation often aligns with EMC cable segregation practices.

Shield requirements: Cable shielding for EMC must not compromise IS parameters. Shield grounding practices must be compatible with both IS and EMC requirements.

Routing in hazardous areas: Cable routes through hazardous areas must minimize exposure while maintaining required separation from interference sources.

Grounding and Bonding

Hazardous area grounding addresses both safety and EMC needs:

Equipotential bonding: All metallic parts in hazardous areas must be bonded to prevent static discharge and ensure fault current paths. This bonding system can serve as an EMC reference if properly implemented.

IS ground isolation: Some intrinsically safe systems require ground isolation to prevent ground loops that could compromise safety. This affects EMC grounding options.

Shield grounding: Cable shield grounding must address both EMC and explosion protection requirements. Shield currents must not flow through hazardous areas in ways that could create ignition sources.

Lightning protection: Lightning protection in hazardous areas must safely conduct lightning energy without creating ignition sources. Surge protective devices must be suitable for the hazardous classification.

Equipment Mounting

Equipment mounting affects both explosion protection and EMC:

Enclosure integrity: Equipment enclosures must maintain explosion protection integrity when mounted. Mounting methods must not create paths for flame or gas transmission.

EMC bonding: Equipment mounting should provide EMC bonding to facility ground structure. Contact surfaces may require treatment to ensure low-impedance connection.

Vibration considerations: Industrial vibration can affect both explosion protection seals and EMC connections. Appropriate mounting addresses both concerns.

Multi-Hazard Installations

Many facilities have areas with multiple hazard classifications:

Zone boundaries: Cable runs crossing zone boundaries require appropriate protection for the most hazardous zone traversed.

Combined gas and dust hazards: Some areas may have both gas and dust explosion hazards. Equipment must be suitable for both, with EMC design addressing the specific requirements of each.

Interface locations: Intrinsic safety barriers and other interface equipment are typically located in non-hazardous areas. These locations must still address EMC for the connected hazardous area circuits.

Initial Inspection

Before energizing new installations, initial inspection verifies correct implementation:

Documentation review: Inspection verifies that installed equipment matches design documentation and is appropriate for the classified location.

Installation verification: Physical inspection confirms that installation follows manufacturer instructions and applicable codes. This includes cable routing, grounding, and EMC-related installation details.

Circuit parameter verification: For intrinsically safe systems, circuit parameters (capacitance, inductance, cable lengths) must be verified against safety analysis.

Functional testing: Equipment operation is verified, including any EMC-sensitive functions.

Periodic Inspection

Regular inspection maintains protection throughout equipment life:

Visual inspection: Regular visual inspection identifies obvious problems such as damaged enclosures, deteriorated cable jackets, or loose connections.

Detailed inspection: More thorough periodic inspection opens enclosures to verify internal condition, check connections, and assess component status.

Inspection frequency: Inspection frequency depends on equipment type, environmental conditions, and facility requirements. More hazardous classifications generally require more frequent inspection.

EMC-relevant items: Inspection should include EMC-relevant items such as cable shield connections, ground bonds, and filter component condition.

Inspection Records

Documentation of inspection activities provides evidence of ongoing compliance:

Inspection logs: Records of inspections performed, findings, and corrective actions provide audit trail for regulatory compliance.

Equipment records: Individual equipment records track inspection history, modifications, and any issues identified.

Change documentation: Modifications to installations require documentation showing that changes do not compromise explosion protection or EMC performance.

Work Permit Systems

Work in hazardous areas requires appropriate permits and procedures:

Hot work permits: Activities that could create ignition sources (welding, grinding, etc.) require specific authorization and precautions.

Electrical work permits: Electrical work in hazardous areas must follow procedures that prevent ignition during work activities. This includes considerations for EMC testing and troubleshooting activities.

Isolation procedures: Equipment isolation for maintenance must address both electrical safety and explosion protection requirements.

Repair and Replacement

Repairs must maintain original protection integrity:

Like-for-like replacement: Replacement components should match original specifications for both explosion protection and EMC characteristics.

Certification implications: Modifications may affect equipment certification. Significant changes may require recertification or manufacturer authorization.

EMC component replacement: EMC components (filters, suppressors, etc.) must be replaced with equivalent types that maintain both EMC performance and explosion protection.

Calibration and Testing

Routine calibration and testing must be conducted safely:

Test equipment: Test equipment used in hazardous areas must be suitable for the classification or used with appropriate precautions.

EMC testing in hazardous areas: EMC troubleshooting may require special procedures when conducted in hazardous locations. Signal generators and other test equipment must not create ignition sources.

Calibration gases: When calibrating gas detectors with test gases, procedures must address the temporary presence of flammable gases.

Risk Assessment

Comprehensive risk assessment addresses EMC-related ignition risks:

EMC failure modes: Assessment identifies potential failure modes where EMC events could create ignition sources. This includes both equipment failures and operational scenarios.

Probability and consequence: Risk assessment evaluates both the likelihood of EMC-related ignition events and their potential consequences.

Mitigation measures: Identified risks inform selection of protection methods, installation practices, and operational procedures.

Management of Change

Changes to facilities or equipment require systematic evaluation:

Change identification: All changes that could affect hazardous area classification, equipment suitability, or EMC environment must be identified for review.

Impact assessment: Changes are evaluated for impact on both explosion protection and EMC. This includes addition of new equipment, modifications to existing equipment, and changes to facility operations.

Authorization and documentation: Approved changes are documented, and installations are verified before returning to service.

Training and Competency

Personnel working in hazardous areas require appropriate training:

Hazardous area awareness: All personnel must understand hazardous area classifications and general precautions.

Technical competency: Personnel performing installation, maintenance, and inspection must be competent in both explosion protection and relevant EMC practices.

Continuing education: Training must be updated as standards, technologies, and facility conditions change.

Incident Investigation

When incidents occur, investigation must consider EMC factors:

Root cause analysis: Investigation should consider whether EMC-related failures contributed to the incident.

Lessons learned: Findings should be communicated to prevent similar incidents and improve practices.

Industry sharing: Significant findings may warrant sharing with industry organizations to improve general practice.

Wireless in Hazardous Areas

Wireless technologies offer benefits but require careful implementation:

RF energy concerns: Radio frequency transmitters generate electromagnetic energy that could potentially cause ignition. Maximum transmit power and operating frequencies must be evaluated.

Approved wireless devices: Wireless devices for hazardous areas must be specifically certified, with RF emissions evaluated as potential ignition sources.

Network planning: Wireless network design must consider both RF coverage and hazardous area boundaries.

Higher Power Equipment

Increasing power levels present challenges for hazardous area EMC:

Variable frequency drives: High-power VFDs in hazardous areas generate significant EMI that could affect explosion-protected equipment.

Power electronics: Advanced power electronics with fast switching create high-frequency emissions requiring careful management in hazardous environments.

Mitigation requirements: Higher power levels may require enhanced filtering and shielding beyond typical industrial practice.

Digital Instrumentation

Digital instrumentation offers enhanced capabilities with EMC considerations:

Digital communication: Digital protocols in hazardous areas must maintain communication integrity despite EMI while meeting explosion protection requirements.

Smart devices: Intelligent field devices with enhanced processing capabilities require EMC protection for complex electronics while maintaining intrinsic safety or other protection.

Integration challenges: Integration of digital instrumentation with legacy analog systems may create EMC interfaces requiring careful design.