ATEX Flow Meters: Hazardous Area Classification & Selection Guide

If your facility contains or could contain explosive atmospheres—crude oil vapour on a North Sea platform, flammable gas in a chemical plant, flour dust in a grain mill—you cannot use standard flow metres. You must specify equipment certified under ATEX (the Explosives ATmosphere Directive).

ATEX isn't optional. It's a legal requirement in the EU, UK, and EEA, enforced through national competent authorities. Non-compliance can result in facility shutdown, substantial fines, or worse—an explosion that kills workers.

This guide explains how zone classification works, what protection concepts are available, and how to select the right ATEX metre for your application.

What is ATEX? Legal Framework

ATEX (Directive 2014/34/EU) is the EU's legal framework for equipment and protective systems intended for use in explosive atmospheres. It has two key pillars:

• ATEX 2014/34/EU (Equipment Directive): Specifies how manufacturers must design, test, and certify equipment intended for hazardous areas
• ATEX 2014/35/EU (Workplace Safety Directive): Specifies employer obligations to classify work areas and prevent explosive atmosphere formation

The UK adopted ATEX post-Brexit; UKCA marking is required instead of CE marking for UK-only sales. Both ATEX and UKCA marking are typically obtained simultaneously.

Zone Classification: The Foundation

What is a Zone?

A zone is a classification of a work area based on the frequency and duration of explosive atmosphere presence. Zone classification determines which equipment is permitted and how it must be protected.

Gas Zones (Flammable Gases & Vapours)

Zone 0: Explosive atmosphere is present continuously or for long periods. Example: inside a storage tank during filling. Only intrinsic safety (Ex ia) is permitted.

Zone 1: Explosive atmosphere is likely during normal operation. Example: the pump room of an oil platform. Multiple protection concepts allowed (Ex ia, Ex ec, Ex d, Ex e, Ex n).

Zone 2: Explosive atmosphere is unlikely and, if it occurs, is for a short time. Example: the main platform deck during abnormal conditions. Simplified protection concepts allowed (Ex ec, Ex e, Ex n, Ex mx).

Dust Zones (Combustible Dusts)

Zone 20: Combustible dust is present continuously or frequently. Example: the interior of a grain silo. Only intrinsic safety (Ex ia) is permitted.

Zone 21: Combustible dust cloud is likely during normal operation. Example: grain handling facility. Multiple concepts allowed.

Zone 22: Combustible dust layer is possible but unlikely. Example: the exterior of grain handling equipment. Simplified concepts allowed.

Who Determines the Zone?

The facility operator (employer) is responsible for conducting a Zone Classification Study. This is typically performed by a competent engineer who reviews:

• Frequency and duration of explosive atmosphere presence
• Ventilation and containment
• Process hazards and failure modes
• Historical incidents or near-misses

Once zones are classified, the operator must document them in a safety case and ensure only ATEX-certified equipment appropriate for each zone is used.

Protection Concepts (How ATEX Works)

Ex ia (Intrinsic Safety)

The apparatus is designed so that even under fault conditions (short circuit, component failure), it cannot release sufficient energy to ignite the explosive atmosphere. This is achieved through limited current, voltage, and power.

• How it's achieved: Zener barriers or galvanic isolators limit electrical output; mechanical parts are designed to avoid sparks
• Zones permitted: 0, 1, 2 (gas); 20, 21, 22 (dust)
• Maintenance: Can be maintained while the apparatus is in situ under controlled conditions
• Cost: Premium; requires specialised design and component selection

Ex d (Flameproof Enclosure)

The apparatus is constructed with a rigid enclosure that can withstand an internal explosion without rupture, and any hot gases escaping are cooled below the ignition temperature of the external atmosphere.

• How it's achieved: Cast aluminium or ductile iron housing; tightly engineered flanged joints; cooling fins
• Zones permitted: 1, 2 (gas); 21, 22 (dust)
• Maintenance: Requires controlled conditions; repeated opening can degrade sealing surfaces
• Typical use: Coriolis metres, electromagnetic metres, pressure transmitters

Ex e (Increased Safety)

Equipment with increased safety measures to prevent arcing and spark generation during normal and anticipated fault conditions. No explosions are expected to occur inside the apparatus.

• How it's achieved: Special winding patterns in coils; sealed connections; restricted temperature rise; robust terminal blocks
• Zones permitted: 1, 2 (gas); 21, 22 (dust)
• Maintenance: Can be serviced in-situ without special precautions
• Typical use: Motors, transmitters, solenoid valves

Ex n (Non-Sparking)

Equipment designed so that in normal operation, it will not produce sparks or surface temperatures that could ignite the explosive atmosphere, and fault conditions are anticipated but their occurrence is rare.

• How it's achieved: Non-sparking brushes in motors; spark-resistant materials; design limits on temperature rise
• Zones permitted: 2 (gas); 22 (dust) only
• Maintenance: Standard industrial maintenance procedures

Ex ec & Ex mx (Composite Classifications)

Ex ec: Intrinsic safety of the electrical circuit (usually control signals) combined with non-sparking (Ex n) for the mechanical/power components. Permits Zone 1 (gas) or Zone 21 (dust).

Ex mx: Equipment for measured use with monitored safety; typically restricted to Zone 2 hazardous areas with frequent inspection regimes.

Equipment Categories

Each ATEX certification is assigned a category (1, 2, or 3) indicating the severity of hazard the equipment is designed for:

Category 1

Very high level of safety. Equipment must continue to function safely even if two independent faults occur. Permitted in Zones 0 and 20 (continuous explosive atmospheres).

Category 2

High level of safety. Equipment designed to maintain safety under normal operation and reasonably anticipated faults. Permitted in Zones 1 and 21.

Category 3

Normal level of safety. Equipment designed for normal operation; safety is maintained under most conditions. Permitted in Zones 2 and 22 only.

For most industrial flow metre applications (oil & gas, chemical plants), Zone 1/2 (Category 2/3, Ex d or Ex e) is typical. Zone 0 applications requiring intrinsic safety are less common and more expensive.

Temperature Classes

ATEX requires that the equipment surface temperature not exceed the Auto-Ignition Temperature (AIT) of the gas/vapour present. Each ATEX certification includes a temperature class:

For most applications, T4 or T5 is sufficient. Your Zone Classification Study will specify the required temperature class based on the fluid's AIT.

Which Flow Metre Technologies Are Available in ATEX?

Coriolis Metres

Available in Ex d (flameproof) and Ex e (increased safety). Excellent for custody transfer and high-accuracy applications requiring ATEX. Limited intrinsic safety options.

Cost premium: +25–35% vs. standard Coriolis.

Electromagnetic Metres

Available in Ex d and Ex e. Popular for conductive fluids (water, aqueous chemical solutions, slurries). Limited availability in larger pipe diameters for ATEX.

Cost premium: +20–30% vs. standard EM.

Vortex Metres

Available in Ex d and Ex n (non-sparking). Good for steam, gas, and liquid applications. Intrinsic safety versions rare.

Cost premium: +20–25% vs. standard vortex.

Turbine Metres

Available in Ex d. Limited modern application due to superior alternatives, but still specified for legacy systems.

Ultrasonic Clamp-On

Non-intrusive measurement using Ex ia or Ex e transmitter (transducers are non-certified, external to hazardous zone). Excellent for temporary monitoring or retrofit in existing pipelines without breaking flanges.

Cost premium: +15–20% for Ex ia transmitter.

Orifice Plates (DP)

The plate itself is passive (no certification needed), but the differential pressure transmitter must be ATEX-certified. Rarely specified for new ATEX projects; Coriolis or EM preferred.

How to Specify an ATEX Flow Metre

When requesting a quotation, provide:

• Applicable Zone: Zone 1 or 2 (gas) / Zone 21 or 22 (dust)
• Required Protection Concept: Ex d, Ex e, Ex ia, Ex n, etc. (consult your zone classification study)
• Equipment Category: 2 or 3 (Category 1 is rarely needed for flow metres)
• Temperature Class: T1–T6 (from your fluid's auto-ignition temperature)
• Notified Body Number: The certification body's ID (e.g., 0197 for TÜV). Ensure the manufacturer is notified by a reputable body
• Fluid Type: Gas, liquid, steam, dust. If gas, provide name (methane, propane, hydrogen)
• Nominal Diameter: Size of pipeline; affects delivery time and cost

Typical delivery time for ATEX metres is 8–12 weeks (vs. 2–4 weeks for standard). Price premium is 20–40%.

IECEx: International ATEX Equivalent

Outside the EU/UK, ATEX certification is not required. However, many countries follow the IECEx (International Electrotechnical Commission System for Certification to Standards) scheme, which provides mutual recognition of ATEX certificates.

If you operate globally (e.g., oil platforms in multiple regions), requesting an ATEX-certified metre with IECEx reports ensures broader market acceptance.

Cost Impact: Why ATEX Is Expensive

ATEX-certified metres cost 20–40% more than equivalent standard units. Why?

• Engineering: Specialised design for temperature limits, intrinsic safety, or flameproof enclosures
• Testing: Third-party Notified Body testing (type examination, surface temperature verification, explosion testing)
• Documentation: Detailed technical files, materials traceability, test reports
• Certification: Notified Body review and issuance of EC Type-Examination Certificate
• Manufacturing: Quality control, traceability, batch testing
• Small volumes: ATEX equipment is typically lower-volume, so unit cost is higher

If you can avoid a hazardous area designation (through ventilation, process design, or containment), standard equipment is cheaper. However, safety always comes first—never cut corners on ATEX compliance.

Common ATEX Pitfalls

Pitfall 1: Assuming Your Area Isn't Classified

Many facilities skip zone classification, assuming their process is safe. However, ATEX applies to ANY location where explosive atmospheres COULD form, even occasionally. Conduct a proper zone classification study.

Pitfall 2: Specifying Over-Engineered Equipment

A Zone 0 (Category 1, Ex ia) metre is overkill for a Zone 2 application and costs significantly more. Specify the minimum protection that matches your actual zone.

Pitfall 3: Ignoring Maintenance Implications

Some ATEX protection concepts (Ex d flameproof) require controlled maintenance. Repeated opening of flanged joints can degrade sealing surfaces. Plan your maintenance strategy before purchase.

Pitfall 4: Buying from Uncertified Suppliers

Ensure the manufacturer is notified by a recognised Notified Body. Check the EC Type-Examination Certificate number. Counterfeit ATEX certificates exist.

Real-World Application Example

North Sea Oil Platform: Custody Transfer Metre Selection

Scenario: A North Sea crude export platform needs a custody transfer metre to measure export to the floating production, storage & offloading (FPSO) vessel. The crude stream is wet (free gas present) and hot (60 °C). Process pressure is 30 bar.

Zone classification: Zone 1 gas hazard (explosive atmosphere likely during normal operation; the export line passes through the open-air platform deck).

Requirements:

• ATEX 2014/34/EU certification: Ex d Category 2, Zone 1, T4
• IECEx for potential international recognition
• Coriolis metre for accuracy (±0.1%–0.2%, multi-phase capable, mass-based)
• Material certification for crude oil (potential sour service, H2S-bearing)

Metre selection: Emerson Micro Motion ELITE or Endress+Hauser Promass 200 in ATEX Ex d flameproof enclosure, stainless steel construction, with integrated electronics module certified separately.

Cost: GBP 8,000–12,000 (vs. standard Coriolis GBP 5,000–8,000).

Delivery: 10–12 weeks (long lead time due to ATEX certification and customisation).

Next Steps

1. Conduct zone classification: If not already done, engage a competent engineer to classify your hazardous areas. This is the foundation for all ATEX decisions.

2. Define your specification: Based on zone, determine protection concept, category, and temperature class required.

3. Select your metre: Use our selector tool to compare ATEX-certified flow metres from leading manufacturers. Filter by technology, protection concept, and zone.

4. Plan delivery and cost: Budget extra time (10–12 weeks) and cost (+20–40%) for ATEX equipment. Engage with the manufacturer early if customisation is needed.