LOT/Specific/TBT-LOT-013

LOTO for Chemical Dosing Systems

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Chemical dosing systems inject measured quantities of chemicals into process streams at treatment works.
Common chemicals include sodium hypochlorite, ferric chloride, polyelectrolyte, and sulphuric acid.
LOTO for dosing systems must isolate the chemical supply, the dosing pump, and the injection point.
Residual chemical in pipework and dosing heads remains hazardous after electrical isolation.
Chemical lines must be flushed or drained as part of the isolation procedure before maintenance.
Dosing pumps are often controlled by PLCs or SCADA systems that can restart them automatically.
Isolation must prevent both electrical power to the pump and chemical flow from the bulk storage.
Manual isolation valves on chemical lines must be locked in the closed position, not just turned.
RPE, chemical goggles, and chemical-resistant gloves are required when breaking into dosed lines.
The LOTO procedure for dosing systems must be chemical-specific to address the hazards of each substance.

Chemical burns	Residual corrosive chemicals in dosing lines cause severe burns to skin and eyes when connections are opened.
Automatic restart	PLC and SCADA-controlled dosing pumps can restart without warning if electrical isolation is incomplete.
Multiple energy sources	Chemical dosing involves both electrical energy and pressurised chemical fluid — both must be isolated.

Don't

Isolate the dosing pump electrically and lock off at the motor control panel
Close and lock the chemical supply valve to prevent flow from bulk storage
Flush or drain the chemical from the dosing line before opening any connection
Disable PLC or SCADA auto-start sequences for the dosing pump during maintenance
Apply personal locks and danger tags to all isolation points
Wear chemical goggles, RPE, and chemical-resistant gloves before breaking into lines
Check the COSHH assessment for the specific chemical in the dosing system
Ensure emergency eyewash and shower stations are accessible and tested before starting
Brief the maintenance team on the chemical hazards and isolation procedure
Verify isolation by attempting to start the pump before beginning any work

DON'T assume the line is empty because the pump is off — chemical remains in pipework
DON'T open dosing line connections without flushing or draining the residual chemical first
DON'T rely on closing a valve alone — lock it in the closed position
DON'T forget to disable PLC and SCADA auto-start sequences before working on the system
DON'T break into chemical lines without RPE, goggles, and chemical-resistant gloves
DON'T skip the try-start test to confirm the dosing pump cannot be energised
DON'T remove another person's lock without following the authorised override procedure
DON'T mix incompatible chemicals during flushing — follow the COSHH assessment guidance
DON'T re-energise the dosing system before all workers are clear and locks are removed
DON'T dispose of flushed chemical down drains without checking disposal requirements

See also: LOTO Awareness | Chemical Dosing Area Safety

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