Key Takeaways:
- Specifying ATEX-certified actuators is not optional in classified hazardous areas — using non-Ex electrical actuators or limit switches in a Zone 1 or Zone 2 area creates a potential ignition source that can trigger an explosion, and no insurance or regulatory authority will accept “we didn’t know” as a defence.
- The ATEX equipment category on the nameplate must match or exceed the zone of use: Category 2 for Zone 1 (Gas Groups IIA/IIB/IIC), Category 3 for Zone 2 — using a Zone 2 rated device in a Zone 1 area is non-compliant and unsafe.
- Pneumatic actuators with solenoid valves are the most common choice in hazardous areas because the actuator itself requires no electrical power at the valve — only the solenoid valve needs ATEX certification, significantly simplifying compliance.
Understanding Hazardous Area Classification
Hazardous area classification is a risk engineering methodology that identifies locations where flammable gas, vapour, or dust may be present in the atmosphere in quantities sufficient to require special precautions against ignition. The output is an area classification document — a series of zone drawings showing the extent and classification of each hazardous zone around each potential release source.
In the IEC/ATEX framework (the standard used in Europe and most of the world outside North America), flammable gas hazardous areas are classified into three zones:
Zone 0: A place in which an explosive atmosphere in the form of a cloud of flammable gas or vapour in air is present continuously, or for long periods, or frequently. Zone 0 areas are rare and are typically found inside open containers, storage tanks above liquid level, or the interior of vessels processing flammable liquids. Electrical equipment suitable for Zone 0 is very limited and expensive — intrinsic safety (Ex ia) is the primary protection concept available for Zone 0.
Zone 1: A place in which an explosive atmosphere in the form of a cloud of flammable gas or vapour in air is likely to occur in normal operation occasionally. Zone 1 typically includes the areas within 1–3 metres of equipment openings (valve glands, flanges, pump seals), areas within storage bunds, and pump rooms. Most process plant equipment requiring electrical components — limit switches, solenoid valves, position indicators, electro-pneumatic positioners — falls within Zone 1 at one point or another.
Zone 2: A place in which an explosive atmosphere in the form of a cloud of flammable gas or vapour in air is not likely to occur in normal operation but, if it does occur, will persist for only a short period. Zone 2 extends further from the source than Zone 1 and covers most of the outdoor process areas of a typical petrochemical plant. Electrical equipment for Zone 2 is less costly than Zone 1, and there is a wider range of protection concepts available.
For dust atmospheres, the analogous zones are Zone 20, Zone 21, and Zone 22, corresponding to the same frequency-of-occurrence definitions but for combustible dust rather than flammable gas.
ATEX Directives and IECEx: The Regulatory Framework
In the European Union, two ATEX Directives govern hazardous area equipment:
ATEX 114 (Equipment Directive, 2014/34/EU): Applies to manufacturers of electrical and mechanical equipment intended for use in potentially explosive atmospheres. Requires manufacturers to design, test, and certify equipment to specified protection concepts before it can be placed on the EU market. Equipment certified under ATEX 114 bears the Ex marking with the equipment category, gas group, and temperature class.
ATEX 153 (Workplace Directive, 1999/92/EC): Applies to operators of workplaces. Requires employers to assess the risk of explosive atmospheres, classify areas, and ensure that appropriate equipment is selected and maintained.
IECEx: The International Electrotechnical Commission’s international certification system for equipment used in explosive atmospheres. IECEx certificates are widely recognised internationally (outside Europe, where ATEX is not applicable) and follow the same technical standards as ATEX. Many manufacturers hold both ATEX and IECEx certifications simultaneously. For projects in non-EU jurisdictions (Middle East, Asia-Pacific, Americas), IECEx or locally equivalent certification (NEC/CEC in North America, INMETRO in Brazil) should be specified.
ATEX Equipment Categories and EPLs
ATEX equipment categories define the level of protection provided and the zones in which equipment can be used:
Category 1G: Very high protection level. Suitable for Zone 0, Zone 1, and Zone 2 gas atmospheres. Remains safe even when two independent faults occur simultaneously. Equipment Protective Level (EPL) Ga.
Category 2G: High protection level. Suitable for Zone 1 and Zone 2 gas atmospheres. Remains safe even when one fault occurs. Equipment Protective Level EPL Gb.
Category 3G: Normal protection level. Suitable for Zone 2 gas atmospheres only. Remains safe under normal operation. Equipment Protective Level EPL Gc.
The EPL concept (introduced in IEC 60079-0:2011) is preferred in modern specifications as it is more granular and directly comparable across different protection concepts. When specifying actuators for valve installations, the EPL required must match the zone classification of the installation location. An EPL Gc (Zone 2) actuator installed in a Zone 1 area is non-compliant, regardless of any commercial convenience.
ATEX Protection Concepts for Valve Actuators
Multiple protection concepts are available under the IEC 60079 series of standards. For valve actuator applications, the most relevant are:
Flameproof (Ex d): The electrical components are enclosed in a robust housing that can withstand an internal explosion without propagating it to the external atmosphere. The enclosure joints are designed with long, tortuous flame paths that cool any escaping combustion products below the ignition temperature of the surrounding atmosphere. Ex d is the classic protection concept for electric motors, switchgear, and solenoid valve coils in Zone 1. The enclosures are typically cast iron or aluminium alloy, substantially heavier than equivalent non-hazardous equipment. Common for electric actuator motors, gearbox limit switches, and position transmitters.
Increased Safety (Ex e): Prevents the occurrence of sparks, arcs, or excessive surface temperatures under normal operation and under defined fault conditions by enhanced construction standards — higher IP rating, better terminal connections, temperature class verified with additional margin. Used for junction boxes, terminal boxes, and non-sparking equipment where no arc-producing components are present in normal operation.
Intrinsic Safety (Ex ia, Ex ib): Limits the electrical energy in circuits to levels too low to cause ignition, even under fault conditions (Ex ia: two simultaneous faults; Ex ib: one fault). Intrinsic safety is the preferred concept for instruments and sensors — 4–20 mA position transmitters, thermocouples, pressure sensors. The signal cables and instruments can be installed with lighter-weight construction but require certified IS barriers or galvanic isolators at the safe-area boundary. Ex ia is the only concept suitable for Zone 0.
Pressurisation (Ex p): A purge-and-pressurisation system maintains the interior of an electrical enclosure at a pressure slightly above the surrounding atmosphere using inert gas (nitrogen) or clean air. The positive pressure prevents the entry of flammable gases. Used for control panels, VSD enclosures, and motor control centres that must be installed in Zone 1 or Zone 2 without the weight penalty of Ex d construction. Requires a continuous purge supply and an automatic shutdown of electrical power if purge pressure is lost.
Non-Sparking (Ex nA), Energy Limiting (Ex nL): Zone 2-only concepts that provide a cost-effective means of using simplified construction for equipment that does not generate sparks in normal operation and has limited energy storage. Widely used for Zone 2 junction boxes, limit switches, and simple instrumentation.
Gas Groups and Temperature Classes
The Ex marking on ATEX equipment includes both the gas group and the temperature class, which together define the specific flammable atmosphere the equipment is safe to use with:
Gas Groups (Group II for surface installations): IIA — propane and similar gases (least energetic, easiest to protect against). IIB — ethylene and similar (intermediate). IIC — hydrogen and acetylene (most energetic, hardest to protect against — requires the most robust construction). A Group IIC-certified device can be used with all Group II gases; a Group IIA device is only safe with Group IIA gases. Always specify the most severe gas group present at the installation location.
Temperature Class (T-class): Defines the maximum surface temperature the equipment can reach during operation, which must be below the ignition temperature of the flammable gas in the atmosphere. T1 (≤450°C) through T6 (≤85°C). Most flammable hydrocarbons have ignition temperatures above 200°C, making T3 (≤200°C) adequate for most oil and gas applications. Hydrogen ignites at approximately 500°C, requiring T1 class equipment. Always verify the T-class against the auto-ignition temperature of the most easily ignited gas present.
Specifying ATEX Actuators: Practical Engineering
When specifying electric actuators or electro-pneumatic actuators for classified hazardous areas, the purchase specification must explicitly state:
Zone classification and EPL required for each valve location. Gas group (IIA, IIB, or IIC) based on the worst-case flammable substance at each location. Temperature class required. Ambient temperature range at the installation (affects T-class verification). Protection concept acceptable for each electrical component (motor, limit switches, solenoid valves, position transmitters). Certificate type required (ATEX, IECEx, or both). Certification body acceptable.
For pneumatic actuators with solenoid valve control, the solenoid valve is the only electrical component that requires ATEX certification — the pneumatic actuator body itself is a non-electrical, non-ignition-capable component. This is why pneumatic actuation dominates in hazardous areas: simplicity of compliance, high reliability, and spring-fail-safe operation. The solenoid valve must be certified to the appropriate EPL; the supply air system, actuator body, and linkage are not subject to ATEX requirements but must meet process containment and mechanical integrity requirements.
For electric actuators in Zone 1, the entire actuator — motor, gearbox, limit switches, local controls, position transmitters, and terminal boxes — must be ATEX-certified. This means substantially heavier, more expensive construction than an equivalent non-Ex unit. Always check the actuator’s certification details against the specific installation zone, gas group, and ambient temperature before approving for purchase.