LOT/General/TBT-LOT-014

LOTO for HVAC Systems

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HVAC systems contain electrical, mechanical, refrigerant, and water energy sources that must all be isolated.
Fan motors, compressors, pumps, and actuators can start automatically from thermostats, timers, or BMS signals.
Fan blades and belt drives inside air handling units create severe entanglement and cutting hazards.
Refrigerant systems under pressure must be depressurised before opening any connections.
Hot water and steam coils within HVAC units can cause severe scalding burns during maintenance.
Electrical supplies may feed the unit from multiple sources including mains, control, and emergency power.
LOTO must isolate every energy source — electrical power, refrigerant pressure, hot water, and damper actuators.
BMS and control system auto-restart functions must be disabled before maintenance begins.
Ductwork connections may need blanking to prevent airflow through the isolated unit from other fans.
A try-start test after LOTO is applied confirms the system cannot energise during maintenance.

Automatic restart	HVAC systems controlled by BMS and thermostats can start without manual intervention, catching workers by surprise.
Multiple energy sources	Electrical, mechanical, refrigerant, water, and pneumatic energy must all be isolated to make the system safe.
Entanglement	Fan blades and belt drives inside AHUs rotate at high speed, causing fatal entanglement and cutting injuries.

Don't

Identify all energy sources for the HVAC unit including electrical, water, and refrigerant
Isolate at every energy source — motor, control panel, BMS signal, and fluid supplies
Disable BMS auto-start functions and timer-controlled sequences before starting work
Apply personal locks and danger tags at each isolation point
Carry out a try-start test to confirm the system cannot energise
Allow hot water or steam coils to cool before opening access panels on the unit
Depressurise refrigerant circuits before disconnecting any refrigerant connections
Blank or isolate ductwork connections to prevent airflow from other running systems
Brief the maintenance team on all energy sources and the LOTO sequence
Confirm all workers are clear and locks removed before re-energising the HVAC system

DON'T open AHU access panels without completing the full LOTO procedure first
DON'T rely on switching off the unit at the thermostat — it is not LOTO isolation
DON'T forget BMS and timer auto-restart — these must be disabled at the controller
DON'T enter the air handling unit while fan blades are still spinning down
DON'T touch hot water or steam coils until they have cooled to a safe temperature
DON'T open refrigerant connections without first depressurising the circuit safely
DON'T remove another person's lock without the authorised override procedure
DON'T re-energise the system until all access panels and guards are refitted
DON'T assume isolating the electrical supply alone makes the HVAC system safe
DON'T skip the try-start test — it is the final verification before work begins

See also: LOTO Awareness | HVAC System Installation Safety

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