ATEX and Hazardous Area Classification

• Fuel storage, tanker loading gantries, filling stations and petrol handling workshops
• Paint spraying, coating, printing and any process using solvent based materials
• Flour mills, bakeries, sugar handling, animal feed and any plant moving combustible powder
• Woodworking and joinery where fine dust is extracted or collected
• Anaerobic digestion, landfill gas, biogas upgrading and hydrogen generation or storage
• Sewage treatment works with digesters, gas holders and sludge handling
• Chemical and pharmaceutical plant using solvents in reactors, dryers, centrifuges or charging points
• Battery charging rooms where hydrogen can accumulate
• Any site whose zone drawings are undated, unsigned or predate a plant change

Practitioners often quote annual durations against those definitions, typically more than 1,000 hours a year for Zone 0, between 10 and 1,000 hours for Zone 1 and fewer than 10 hours for Zone 2. HSE itself describes those figures as non official. Treat them as a sense check rather than a legal test.

The equipment

• Group I covers underground mines and the parts of surface installations liable to be endangered by firedamp or combustible dust. Category M1 stays functional when energised in an explosive atmosphere. Category M2 is intended to be de energised if one occurs.
• Group II covers everywhere else, in categories 1, 2 and 3, each split into G for gas, vapour and mist and D for dust.
• Category 1G and 1D goes in Zone 0 and Zone 20, 2G and 2D in Zone 1 and Zone 21, 3G and 3D in Zone 2 and Zone 22. Higher category equipment may always be used in a lower risk zone. The reverse is never acceptable.
• Category is read together with the gas group, IIA, IIB or IIC, the dust group, IIIA, IIIB or IIIC, plus the temperature class from T1 at 450 degrees C down to T6 at 85 degrees C. The T class must sit below the ignition temperature of the substance present.

The work

• Source of release identification and grading as continuous, primary or secondary, which drives the zone before ventilation is considered
• Ventilation grade and availability assessment, which sets the extent of each zone
• Zone extent calculation and drawings to BS EN IEC 60079-10-1:2021 for gases and vapours and to BS EN IEC 60079-10-2 for dusts
• A hazardous area schedule tying every zone back to its release source and its basis
• Plate by plate equipment verification of group, category, gas or dust group, temperature class and equipment protection level against the zone
• Protection concept review, from intrinsic safety and encapsulation in Zone 0 through flameproof and increased safety in Zone 1 to type n and restricted breathing in Zone 2
• Non electrical equipment assessment to BS EN ISO 80079-36 and BS EN ISO 80079-37, which replaced the withdrawn EN 13463 series
• EX signage review at zone entry points, plus identification of container and pipe contents

Inspection under BS EN IEC 60079-17

Three grades of inspection sit behind any Ex maintenance regime. A visual inspection identifies defects apparent to the eye without access equipment or tools. A close inspection adds defects apparent only by using access equipment such as steps and by using tools, without normally opening the enclosure or de energising the equipment. A detailed inspection adds defects apparent only by opening the enclosure or by using tools and test equipment.

There are three types. Initial inspection covers everything before it enters service and is normally detailed. Periodic inspection covers the whole installation at set intervals. Sample inspection covers a proportion of it under continuous supervision by skilled personnel, which the standard offers as an alternative to periodic inspection rather than as an addition.

On intervals, be careful what you are told. DSEAR sets no inspection interval and neither does any other UK regulation. The widely applied rule taken from the standard is that the period between periodic inspections should not exceed three years without consulting a person with expert knowledge. Treat that as a strong convention rather than a statutory deadline. The legal test is DSEAR regulation 6 with regulation 5 of the Provision and Use of Work Equipment Regulations 1998, which require the installation to be maintained in an efficient state, in efficient working order and in good repair. Grade and interval then follow zone, protection level, environment, modification history and the last set of results. The standard requires skilled personnel. CompEx is the UK benchmark qualification suite. It is a certification scheme rather than a legal requirement.

The explosion protection document, said accurately

The term comes from Article 8 of Directive 1999/92/EC. It does not appear anywhere in DSEAR 2002. In UK law the requirement is met by the recorded risk assessment under regulation 5(4), which must show that explosion risks have been assessed, that adequate measures will be taken, which places have been zoned and that the workplace and work equipment are designed, operated and maintained with due regard to safety. Producing a document with that title is still worth doing, since auditors and insurers ask for it by name. What we will not do is call it a statutory document under UK law. It is your recorded risk assessment, presented well.

• Hazardous area classification drawings showing Zones 0, 1 and 2 and Zones 20, 21 and 22 with extents
• A hazardous area schedule listing every source of release, its grade, the ventilation basis and the resulting zone
• An equipment register recording group, category, gas or dust group, temperature class, equipment protection level and certificate reference
• A non compliance list separating equipment that must be replaced from equipment that can stay under a defined control
• An inspection regime specifying grade, scope, interval and competence for initial, periodic and sample inspection
• An explosion protection document pack with a prioritised action plan, owners and target dates