WWT/Process Areas/TBT-WWT-017

Rotating Equipment in Process Areas

Water & Wastewater Treatment › Process Areas › Rotating Equipment in Process Areas

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Rotating equipment at treatment works includes scrapers, mixers, aerators, pumps, and sludge rakes.
These items often operate automatically via PLC or timer control, starting without manual intervention.
Entanglement with rotating scrapers and chains is almost always fatal due to the slow relentless torque.
PUWER 1998 requires all dangerous parts of machinery to be guarded to prevent contact.
Guards must be fixed or interlocked so the equipment stops before the guard can be fully opened.
Maintenance of rotating equipment in process areas requires LOTO isolation before any work begins.
Walkways adjacent to rotating scrapers must have guardrails and toeboards to prevent accidental contact.
Submerged rotating equipment such as mixers and aerators cannot be seen — isolation is essential before tank entry.
Regular inspection of guards, interlocks, and emergency stop systems ensures they remain functional.
Workers must never reach over, under, or through guards to clear blockages or retrieve items.

Entanglement	Slow-moving scrapers and rakes do not stop when they catch clothing or limbs — entanglement is almost always fatal.
Automatic start	PLC-controlled equipment starts without warning — LOTO is the only protection against unexpected energisation.
Legal duty	PUWER 1998 requires guarding of dangerous parts and LOTO for maintenance of all rotating machinery.

Don't

Verify all rotating equipment has guards or interlocked barriers preventing contact
Complete LOTO isolation before any maintenance, cleaning, or adjustment work
Disable PLC and SCADA auto-start before entering any area with rotating equipment
Maintain walkway guardrails adjacent to rotating scrapers and sludge rakes
Confirm submerged mixers and aerators are isolated before entering drained tanks
Inspect guards, interlocks, and emergency stop systems regularly for correct function
Test that equipment does not start after LOTO is applied before beginning work
Brief all workers on the location and type of rotating equipment in their work area
Use the emergency stop button immediately if anyone is in danger near rotating equipment
Report missing, damaged, or defeated guards to the supervisor without delay

DON'T reach over, under, or through guards to clear blockages or retrieve items
DON'T approach rotating scrapers or chains without confirming LOTO isolation first
DON'T rely on pressing the stop button as isolation — complete full LOTO procedures
DON'T defeat or bypass interlocked guards to continue working on running equipment
DON'T enter a tank or channel with submerged rotating equipment without confirmed isolation
DON'T wear loose clothing, lanyards, or jewellery near rotating machinery
DON'T assume equipment will not start because it appears to be switched off
DON'T step over or lean against guardrails adjacent to rotating process equipment
DON'T carry out maintenance on rotating equipment without applying personal locks and tags
DON'T ignore unusual noise, vibration, or movement from guarded rotating equipment

See also: Belt and Chain Drive Safety | LOTO Awareness

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