Why Sewage Pits Need ATEX‑Rated Equipment

Kate Fuad
6 days ago
3 min read

Updated: 3 days ago

In the world of wastewater management, particularly sewage pumping stations and treatment works, flammable gases such as methane and hydrogen sulphide are ever-present byproducts. These gases can form explosive atmospheres that pose risks to equipment, infrastructure, and human life. In the UK, the legal framework for managing these hazards falls under DSEAR (the Dangerous Substances and Explosive Atmospheres Regulations 2002), which implements the ATEX directives.

What Is ATEX?

"ATEX" refers to two European directives dealing with explosive atmospheres, together, they guide how hazardous areas should be assessed, zoned, and equipped with certified equipment to reduce ignition risks:

The ATEX Workplace Directive (now implemented in UK law via DSEAR) focuses on risk management in workplaces where explosive atmospheres could arise.
The ATEX Equipment Directive sets out requirements for electrical and mechanical equipment intended for use in such areas.

The Role of DSEAR in the UK

DSEAR requires employers to:

Identify potential explosion risks from flammable gases, vapours, or dusts.
Carry out a Hazardous Area Classification (HAC).
Select equipment suitable for the zones identified.
Maintain safety systems, records, and periodic reviews.

While DSEAR applies across many sectors—from manufacturing to chemical processing—its relevance in water and wastewater infrastructure is often underappreciated. Many sewage environments are low-oxygen, low-ventilation spaces where volatile gases can accumulate rapidly.

Hazardous Area Classification (HAC): Understanding Zoning

The backbone of ATEX risk management is Hazardous Area Classification, sometimes referred to as “zoning.” This process involves identifying and categorising areas based on the frequency and duration of a potentially explosive atmosphere.

Zones are defined as follows:

Zone 0: A flammable atmosphere is present continuously or for long periods (more than 1,000 hours/year).
Zone 1: Likely presence during normal operation (10–1,000 hours/year).
Zone 2: Unlikely presence or only for short durations (less than 10 hours/year).

Most sewage pits are classified as Zone 2, though poor ventilation or high volumes of gas (e.g. from rotting sludge or aggressive agitation) may warrant a Zone 1 designation.

HAC assessments are typically performed by certified specialists (e.g. TÜV SÜD, Lloyd’s Register), who will evaluate gas sources, ventilation, release frequencies, and site geometry to develop a zoning map. This informs all downstream decisions about equipment and system design.

Equipment Selection and the ATEX Equipment Directive

Once zones are defined, equipment must be matched accordingly. ATEX equipment is certified by Category and marked with the Ex symbol:

Zone	Equipment Category
0	1G
1	2G
2	3G

Key markings on equipment include:

Ex symbol
Equipment Group (Group I for mining, Group II for industrial use)
Gas group (e.g., IIB or IIC—hydrogen environments require IIC)
Temperature class (to ensure equipment surface temperatures won’t ignite gases)

Proper selection ensures that devices such as pumps, lighting, control panels, and instrumentation won’t trigger an ignition even in the presence of flammable gases.

Verification and Ongoing Management

Initial compliance doesn't end with installation. Before equipment is brought into service, a qualified person must verify that:

Each device is certified for its specific zone.
Protective systems (e.g. earthing, ventilation, enclosures, signage) are in place and effective.

Reassessment: changes to processes, like installing a new sludge mixer, re-routing a pipe, or increasing plant throughput, can alter the gas risk profile and, therefore, the zoning and equipment requirements.

Why It Matters

Explosive atmospheres are not theoretical risks—they're real and potentially catastrophic. For those managing or supplying into the water sector—be they electrical contractors, control panel manufacturers, or civil engineers—understanding ATEX and how it applies to hazardous environments is crucial. A missed detail or incorrect classification can have serious legal and safety consequences.