What is DSEAR and who does it apply to?

DSEAR (Dangerous Substances and Explosive Atmospheres Regulations 2002) is the UK legislation implementing the ATEX Workplace Directive (99/92/EC). It applies to all workplaces where dangerous substances — flammable liquids, flammable gases, explosive atmospheres from dusts — are present. DSEAR requires employers to: identify dangerous substances and assess the risks they present; eliminate or reduce those risks; classify areas where explosive atmospheres may occur into zones; ensure equipment in hazardous zones meets ATEX requirements; coordinate safety measures where multiple employers work in the same hazardous area; provide information, instruction, and training; and document the explosion protection measures in an Explosion Protection Document (EPD). DSEAR applies to refineries, chemical plants, petroleum storage facilities, gas terminals, and any site handling flammable materials.

What is the difference between ATEX and IECEx certification?

ATEX certification (from the ATEX Directive 2014/34/EU, retained in UK law as the UKEX Regulations) is the certification standard for equipment placed on the market in the UK and EU for use in potentially explosive atmospheres. IECEx is the international equivalent certification scheme administered by the International Electrotechnical Commission. ATEX/UKEX certification is required for equipment used in UK installations. IECEx certification from an IECEx-recognised certification body is widely accepted as equivalent and most Ex equipment carries both marks. Following Brexit, the UK has its own UKEX marking which applies to equipment placed on the GB market after 1 January 2022, though the technical requirements remain identical to ATEX.

What is CompEx and what units are required?

CompEx is the UK industry-recognised qualification framework for personnel working on Ex electrical installations, administered by Cogent. It comprises modular units covering different aspects of Ex work. For gas zone installation work, the core units are ExI01 (Fundamentals of Ex), ExI02 (Ex d flameproof enclosures), ExI03 (Ex e increased safety), and ExI04 (Ex i intrinsic safety). ExI05 covers Ex p pressurised enclosures. ExM01 to ExM04 cover inspection and maintenance of Ex installations. ExD units cover dust zone work. The CompEx Foundation certificate (ExI01-04) is the minimum required for most petrochemical electrical installation roles. Refresher assessment is required every five years.

What does BS EN 60079-17 require for Ex equipment inspection?

BS EN 60079-17 (the UK-adopted version of IEC 60079-17) defines the requirements for inspection and maintenance of Ex electrical installations. It specifies three grades of inspection. Visual inspection: a check for obvious defects without opening the equipment — checking the enclosure is intact, all bolts are present, the cable entry is secure, and there is no obvious damage. Close inspection: all visual inspection checks plus opening the enclosure (where accessible without live work) to check internally for moisture, damage, and correct assembly. Detailed inspection: all close inspection checks plus functional testing, insulation resistance testing, and verification of all aspects of the equipment condition against its certification documents. The frequency of each inspection grade is determined by the initial inspection interval (IEI), which is based on the installation environment and equipment type.

What are the main Ex protection concepts and where is each used?

Ex d (flameproof): the enclosure can contain an internal explosion and cool the products before they escape. Used for motors, switchgear, and junction boxes in Zone 1 and Zone 2. Ex e (increased safety): equipment that does not produce sparks in normal operation is enclosed to a higher standard. Used for terminal boxes, luminaires, and motors in Zone 1 and Zone 2. Ex ia/ib (intrinsic safety): electrical energy in the circuit is limited to safe levels. Ex ia is suitable for Zone 0 (two fault tolerance). Ex ib for Zone 1. Used for instrumentation. Ex p (pressurised): a protective gas at positive pressure excludes the hazardous atmosphere from the enclosure. Used for large control panels and analysers. Ex n or Ex ec (non-sparking/increased safety for Zone 2 only): simplified protection for Zone 2. Each protection concept has specific installation requirements defined in the IEC 60079 series.

How do I read Ex equipment marking?

Ex equipment marking provides all the information needed to verify that the equipment is suitable for the intended hazardous area. A typical marking: II 2 G Ex d IIC T4 Gb. Reading this: II = Equipment Group II (surface industries, not mining); 2 = Category 2 (suitable for Zone 1); G = gas/vapour hazard; Ex = explosion protected; d = protection concept (flameproof); IIC = gas group (IIC covers hydrogen and acetylene — the most ignition-sensitive group; IIA and IIB are less stringent); T4 = temperature class (maximum surface temperature 135°C); Gb = Equipment Protection Level (suitable for Zone 1). For dust: II 2 D Ex tb IIIC T135°C Db would indicate dust zone equipment for Zone 21, suitable for the most ignition-sensitive dust groups.

What is an Explosion Protection Document and who must produce it?

An Explosion Protection Document (EPD) is a formal document required by DSEAR that describes the hazardous area zone classification, the measures in place to control explosive atmosphere risks, the competence requirements for persons working in hazardous areas, and the overall explosion protection strategy. The employer (or duty holder) is responsible for producing and maintaining the EPD. In practice it is typically prepared by a competent person — a hazardous area specialist or process safety engineer — with input from electrical engineers who provide information on electrical installation and Ex equipment. The EPD must be reviewed and updated when any significant change is made to the plant or process. Area classification drawings form a key part of the EPD.

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Petrochemical Electrical Installation UK: Refinery & Chemical Plant Guide

Everything UK electricians need to know about petrochemical electrical installation — DSEAR 2002 compliance, ATEX zone classification (Zone 0, 1, 2), Ex d/e/i/m/n protection concepts, area classification drawings, BS EN 60079-17 inspection requirements, and CompEx qualification.

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18 min readUpdated 2026-05-18Andrew Moore, Founder of Elec-Mate

Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.

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Key Takeaways

1DSEAR (Dangerous Substances and Explosive Atmospheres Regulations 2002) is the UK legislation that requires employers to control the risks from flammable liquids, gases, and dusts. It mandates hazardous area zone classification, appropriate equipment selection, and formal explosion protection documentation.
2ATEX zone classification (Zone 0, 1, 2 for gas/vapour; Zone 20, 21, 22 for dust) defines the likelihood of an explosive atmosphere. All electrical equipment in classified zones must be ATEX-certified for that zone and the appropriate gas group and temperature class.
3The main Ex protection concepts used in petrochemical installations are Ex d (flameproof), Ex e (increased safety), Ex ia/ib (intrinsic safety), Ex p (pressurised enclosure), and Ex n/ec (non-sparking, for Zone 2 only). Each has specific installation requirements.
4BS EN 60079-17 (IEC 60079-17) is the standard for inspection and maintenance of Ex electrical installations. It defines three categories of inspection: visual, close, and detailed — each with increasing levels of intrusion and frequency requirements.
5CompEx is the UK industry-recognised qualification framework for engineers and electricians working on Ex electrical installations. It covers both gas zone work (ExI units) and dust zone work (ExD units). Without CompEx, you cannot legally carry out Ex electrical work in petrochemical facilities.
6Area classification drawings are the definitive reference for zone boundaries on any petrochemical site. They are produced in accordance with IEC 60079-10-1 (gas) and IEC 60079-10-2 (dust) and must be consulted before any equipment selection or installation work.

01 · Specialist Sector

Petrochemical Electrical Installation in the UK

Petrochemical electrical installation encompasses electrical work on refineries, chemical plants, petroleum storage facilities, LNG terminals, and associated infrastructure. It is one of the most technically demanding and highly regulated areas of industrial electrical engineering in the UK — and one of the best paid.

The fundamental challenge of petrochemical electrical installation is the presence of flammable and explosive substances throughout the plant. Hydrocarbons, solvents, gases, and in some cases dusts create potentially explosive atmospheres across large parts of the facility. Every electrical decision — equipment selection, cable routing, earthing, protection — must account for the hazardous area classification of the area in which the work is carried out.

Major UK petrochemical sites — Grangemouth (Ineos) in Scotland, Fawley Refinery (ExxonMobil) in Hampshire, Pembroke Refinery (Valero) in Wales, Stanlow Refinery (Essar) in Cheshire, and the major chemical manufacturing complexes at Teesside and Merseyside provide the majority of petrochemical electrical contractor demand in the UK.
Shutdown and turnaround work — much petrochemical electrical contractor work is concentrated in planned shutdowns and turnarounds, when plant is taken offline for major inspection and maintenance. These intensive periods involve large numbers of contractors working around the clock to complete the work within the planned outage window.

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02 · Specialist Sector

DSEAR & ATEX Zone Classification

DSEAR (Dangerous Substances and Explosive Atmospheres Regulations 2002) is the UK legislation that drives hazardous area zone classification on petrochemical sites. Understanding DSEAR requirements and ATEX zone classification is the foundation of competent petrochemical electrical work.

Zone 0 — an explosive atmosphere in the form of a cloud of flammable gas, vapour, or mist is present continuously or for long periods. Zone 0 locations include the interior of storage tanks, process vessels, and pipework. Category 1G (Ga) equipment required. Very few electrical devices are installed in Zone 0 — instrumentation such as level transmitters is the main exception.
Zone 1 — an explosive gas atmosphere is likely to occur in normal operation. Typical Zone 1 locations include pump sumps, drain pits, areas within 1.5m of process flanges and valve glands, and the process deck area. Category 2G (Gb) equipment required. This is where the majority of petrochemical Ex electrical equipment is installed.
Zone 2 — an explosive gas atmosphere is unlikely to occur in normal operation but may occur in abnormal conditions. Zone 2 typically extends 3–5m from Zone 1 sources, and covers areas such as the wider process deck, pipe racks with potential for leakage, and areas below Zone 1 where heavier- than-air gases can accumulate. Category 3G (Gc) or better required.
DSEAR Explosion Protection Document — employers must produce and maintain an Explosion Protection Document (EPD) that records the zone classification, equipment selection criteria, personnel requirements, and overall explosion protection strategy. The EPD must be reviewed when plant or processes change significantly.

03 · Specialist Sector

Ex Protection Concepts: Ex d, e, i, m, n

The IEC 60079 series of standards defines the protection concepts (Ex types) that can be used to make electrical equipment safe for use in explosive atmospheres. Understanding the operating principle, application, and installation requirements of each protection concept is essential for CompEx-certified petrochemical electricians.

Ex d — flameproof enclosure (IEC 60079-1) — the enclosure is designed to contain an internal ignition and cool the products of combustion before they escape through gaps and joints. Used for motors, switchgear, and junction boxes in Zone 1 and Zone 2. Heavy, robust construction. Flameproof joints and thread engagements must be maintained — damaged flanges cannot be repaired without recertification.
Ex e — increased safety (IEC 60079-7) — additional measures are applied to equipment that does not normally produce sparks or hot surfaces to prevent ignition of the surrounding atmosphere. Applies to terminal boxes, luminaires, and motors in Zone 1 and Zone 2. Lighter than Ex d. Terminal tightening torques and creepage/clearance distances are critical.
Ex ia/ib — intrinsic safety (IEC 60079-11) — the energy in the circuit is limited to levels that cannot ignite the explosive atmosphere under defined normal and fault conditions. Ex ia (two fault tolerance) is the only protection concept suitable for Zone 0. Used exclusively for instrumentation and control systems. Associated apparatus (barriers, galvanic isolators) must be correctly selected and entity parameters matched.
Ex m — encapsulation (IEC 60079-18) — components that could cause ignition are encapsulated in a compound that excludes the explosive atmosphere. Used for certain instrumentation, solenoid valve coils, and electronic modules. No maintenance is possible on the encapsulated components — replacement of the complete unit is required on failure.
Ex n / Ex ec — non-sparking (IEC 60079-15) — simplified protection for Zone 2 only. The equipment is designed to not produce sparks or hot surfaces capable of igniting a Zone 2 atmosphere under normal operating conditions. Lighter and less expensive than Zone 1 protection concepts. Common for Zone 2 luminaires and small motors.

04 · Specialist Sector

Area Classification Drawings

Area classification drawings are the definitive reference for zone boundaries on any petrochemical site. They are produced in accordance with IEC 60079-10-1 (for gas and vapour) and IEC 60079-10-2 (for combustible dust) and form a key part of the site's Explosion Protection Document.

What they show — area classification drawings show the boundaries of Zone 0, Zone 1, and Zone 2 areas on plan and elevation views. Zone boundaries are shown as dashed or coloured lines with the zone designation clearly marked. The drawings also identify the source of hazardous release (grade of release) that defines each zone.
How they are used — before selecting or installing any electrical equipment on a petrochemical site, the electrician or engineer must consult the area classification drawings to determine the zone applicable to the intended equipment location. Equipment must be certified for the zone in which it is installed — installing Zone 2 equipment in a Zone 1 area is non-compliant and potentially dangerous.
Maintaining drawings — area classification drawings must be updated when plant layout, process conditions, or substance inventories change. Out-of-date drawings present a serious hazard — equipment may have been installed to the wrong zone specification. Document control is a critical aspect of area classification management.

05 · Specialist Sector

Ex Equipment Selection & Marking

Selecting the correct Ex equipment for a petrochemical installation requires understanding of the zone classification, the hazardous substance properties (gas group and ignition temperature), and the protection concepts available. Equipment must be certified to a standard compatible with the zone and must bear the correct marking.

Gas groups — Group IIA covers propane, acetone, and most common hydrocarbons (minimum ignition energy >180µJ). Group IIB covers ethylene and hydrogen sulphide (45–180µJ). Group IIC covers hydrogen and acetylene (<45µJ) and requires the most stringent equipment. Equipment must be rated for the same or a higher gas group than the hazardous substance on site.
Temperature classes — T1 (450°C maximum surface temperature) through T6 (85°C). The temperature class must be below the auto-ignition temperature (AIT) of the flammable substance by an appropriate margin. For petrol (AIT ~280°C), T3 equipment (200°C surface temperature) is appropriate. For hydrogen sulphide (AIT 260°C), T3 or T4 is required.
Equipment Protection Level (EPL) — Ga, Gb, Gc (for gas zones) or Da, Db, Dc (for dust zones). EPL must match or exceed the zone requirement: Ga for Zone 0, Gb or Ga for Zone 1, Gc or better for Zone 2.

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06 · Specialist Sector

Ex Equipment Inspection & Maintenance: BS EN 60079-17

BS EN 60079-17 (the UK adoption of IEC 60079-17) is the standard for the inspection and maintenance of electrical installations in explosive atmospheres. It is mandatory reading for anyone responsible for maintaining Ex electrical equipment on petrochemical sites, and CompEx ExM units are based directly on its requirements.

Grade 1 — Visual inspection — a check for obvious defects without the need to open equipment or use tools. Checks include: enclosure integrity (no cracks or damage), all bolts present and tightened, cable entry condition, no unauthorised modifications, warning labels in place, and equipment type and marking match the area classification. This grade can be performed by persons with basic Ex awareness.
Grade 2 — Close inspection — all visual inspection checks plus opening the equipment (where it can be done safely without live work) to check internally. Checks include: internal condition (moisture, damage, contamination), correct cable type and cross-sectional area, correct gland type and installation, correct terminal tightening, and earth continuity. Requires CompEx-qualified personnel.
Grade 3 — Detailed inspection — all close inspection checks plus more detailed examination including verification against certification documents, measurement of Ex d flameproof gaps, insulation resistance testing, verification of intrinsically safe circuit entity parameters, and earth loop impedance testing. Requires competent CompEx-qualified personnel with appropriate test equipment.
Inspection intervals — initial inspection interval (IEI) is typically one to three years for Zone 1 and Zone 21 equipment, and three years for Zone 2 and Zone 22. The interval can be extended based on the results of initial inspections. All inspection findings must be formally recorded and defects formally managed through a corrective action process.

07 · Specialist Sector

CompEx Qualification for Petrochemical Electricians

CompEx is the UK industry-recognised qualification framework for personnel who install, inspect, and maintain electrical equipment in explosive atmospheres. It is a requirement for petrochemical electrical work and is specified by most major UK petrochemical operators and principal contractors as a condition of employment.

CompEx Foundation (ExI01–ExI04) — covers the fundamentals of explosive atmospheres, zone classification, Ex d flameproof, Ex e increased safety, and Ex i intrinsic safety installation. This is the minimum requirement for most petrochemical installation roles. Typically delivered as a five-day course with practical and written assessments.
CompEx Maintenance (ExM01–ExM04) — covers inspection and maintenance of Ex installations to BS EN 60079-17. Essential for maintenance electricians on petrochemical sites. Covers inspection grades, inspection records, and corrective action management.
CompEx Dust (ExD units) — covers dust zone classification and equipment selection for Zones 20, 21, and 22. Relevant for petrochemical sites with solid catalyst handling, powder processing, or other combustible dust risks.
Reassessment every five years — CompEx certification must be renewed by reassessment every five years. The reassessment demonstrates that the candidate has maintained their competence and is aware of any changes to the standards and regulations since their previous assessment.

CompEx-certified electricians working in petrochemical facilities typically command significant pay premiums. Experienced CompEx-qualified petrochemical electricians in permanent or long-term contract roles typically earn £45,000 to £70,000 per year. Self-employed contractors earn £40 to £65 per hour, with higher rates during shutdown and turnaround periods when demand peaks.

08 · Specialist Sector

Permit to Work Systems in Petrochemical Facilities

All electrical work on petrochemical sites is managed through a formal permit to work (PTW) system. The PTW is the safety management mechanism that ensures all hazards are identified, appropriate precautions are in place, and work is properly authorised before it commences.

Electrical isolation — all electrical work on live or potentially live circuits requires a formal isolation and lock-off procedure. The PTW specifies the isolation points, the lock-off procedure, and the verification testing required to confirm the system is dead before work commences. Isolation is typically achieved by a person authorised by the duty holder.
Hot work permits — any work that creates a source of ignition — angle grinding, welding, use of non-Ex tools — in or near hazardous areas requires a hot work permit in addition to the standard electrical PTW. Hot work permits require gas testing before commencement and a fire watch during and after the work.
Confined space permits — working inside process vessels, tanks, or enclosed spaces (even without an active explosive atmosphere risk) requires a confined space entry permit. Many petrochemical electrical tasks involve cable pulling or equipment installation in confined spaces.

09 · Specialist Sector

For Electricians: Breaking Into Petrochemical Electrical Work

Petrochemical electrical work is financially rewarding, technically interesting, and in sustained demand from UK refineries, chemical plants, and the energy transition sector. CompEx certification is the essential first step.

Start with CompEx Foundation

Book CompEx ExI01–ExI04 (Foundation) as your first step. Without it, no petrochemical operator or principal contractor will engage you for hazardous area electrical work. Add ExM01–ExM04 if you are targeting maintenance roles. Register with petrochemical electrical specialist agencies — most major UK refineries use a small number of specialist contractors for shutdown work.

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CompEx requires five-yearly reassessment. 18th Edition must be renewed. Use Elec-Mate to track all your certifications and renewal dates, and to produce professional test records and inspection reports that meet the documentation standards expected on petrochemical sites.

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Frequently Asked Questions About Petrochemical Electrical Installation

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Petrochemical Electrical Installation UK: Refinery & Chemical Plant Guide

Key Takeaways

Petrochemical Electrical Installation in the UK

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DSEAR & ATEX Zone Classification

Ex Protection Concepts: Ex d, e, i, m, n

Area Classification Drawings

Ex Equipment Selection & Marking

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Ex Equipment Inspection & Maintenance: BS EN 60079-17

CompEx Qualification for Petrochemical Electricians

Permit to Work Systems in Petrochemical Facilities

For Electricians: Breaking Into Petrochemical Electrical Work

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Keep Your Certifications Current

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Frequently Asked Questions About Petrochemical Electrical Installation

What is DSEAR and who does it apply to?

What is the difference between ATEX and IECEx certification?

What is CompEx and what units are required?

What does BS EN 60079-17 require for Ex equipment inspection?

What are the main Ex protection concepts and where is each used?

How do I read Ex equipment marking?

What is an Explosion Protection Document and who must produce it?

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