ATEX Zoning

ATEX zones classify areas where explosive atmospheres from gas, vapour, mist, or dust may be present.
DSEAR 2002 (Dangerous Substances and Explosive Atmospheres Regulations) requires employers to classify these zones.
Zone 0 means an explosive atmosphere is present continuously or for long periods — the highest risk classification.
Zone 1 means an explosive atmosphere is likely to occur occasionally during normal operations.
Zone 2 means an explosive atmosphere is unlikely during normal operations but may occur briefly.
Wastewater treatment works commonly have ATEX zones around sludge digesters, inlet works, and enclosed chambers.
Methane and hydrogen sulphide are the primary explosive gases encountered at wastewater treatment works.
Only ATEX-rated equipment, tools, and lighting may be used within classified ATEX zones on site.
Ignition sources include sparks from grinding, welding, non-ATEX electrical equipment, and static discharge.
ATEX zones are marked with the yellow EX triangle warning sign at all entry points and boundaries.

Prevent explosion	An ignition source in an explosive atmosphere causes instantaneous explosion — resulting in fatal blast injuries and structural collapse.
Legal requirement	DSEAR 2002 mandates zone classification, equipment selection, and safe systems — breaches carry significant penalties.
Common on WwTW sites	Wastewater treatment works produce methane and H2S regularly — construction workers must understand ATEX controls before entering.

Do

Don't

Check the ATEX zoning plan before starting any work on or near process plant areas.
Identify the zone classification at your work location before selecting tools or equipment.
Use only ATEX-certified tools, torches, radios, and electrical equipment within classified zones.
Carry a personal gas monitor calibrated for methane and H2S when entering ATEX areas.
Obtain a hot works permit before any welding, grinding, or flame work near ATEX zones.
Wear anti-static clothing and footwear as specified in the ATEX zone risk assessment.
Ensure continuous gas monitoring is in place before and throughout work in ATEX areas.
Know the alarm levels on your gas monitor and the evacuation procedure for your area.
Ventilate enclosed spaces thoroughly before entry to reduce gas concentration below LEL.
Report any gas alarm activation, unusual smells, or equipment faults to control immediately.

DON'T enter an ATEX zone without understanding the zone classification and its restrictions.
DON'T use standard electrical tools, phones, or cameras inside a classified ATEX zone.
DON'T smoke or carry cigarettes, lighters, or matches into any ATEX classified area.
DON'T carry out hot works within an ATEX zone without a specific permit and gas clearance.
DON'T ignore gas monitor alarms — evacuate immediately and report to the control point.
DON'T remove or reposition ATEX zone boundary signs, barriers, or warning notices.
DON'T wear synthetic clothing that generates static discharge in ATEX classified areas.
DON'T assume a zone is safe because you cannot smell gas — methane is odourless.
DON'T open or disturb process pipework, valves, or covers within ATEX zones without permits.
DON'T store flammable materials or fuel within or adjacent to ATEX classified boundaries.

See also: Methane and Biogas Hazards at WwTW | Atmospheric Monitoring and Gas Detection

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