Leo's HVAC Tip: Lock Out/Tag Out/Block Out

March 31, 2005
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Whenever you work on fans or other machinery, be positive that the machinery can't start when you are not ready. Save your fingers.

  • Be positive the power is off.

  • Be sure it can't start until you start it.

    Locking Out On Large Jobs

  • Turn off the main disconnect switch and put a padlock on it. Add a tag with your name and the date. Even if the switch is already locked out, put your own lock on it.

  • Check to see if there is another switch within reach of the fan. If there is, turn it off and on to be sure the fan is de-energized. (Sometimes a switch is wired wrong and can still be energized even if the switch seems to be off.) If there is no switch, test the circuit with an ammeter or circuit tester to be sure the power is off.

    Locking Out On Residential Jobs

  • Throw the correct circuit breaker and put a piece of tape over it.

  • Make sure that all do-it-yourselfers in the house know that the breaker is not to be touched.

  • Test the circuit with an ammeter or circuit tester to be sure the power is off. You could have the wrong breaker. Also, strange things can happen to residential wiring.

    Blocking Out

    Large fans should be blocked with a piece of wood even if the power is off. Air moving through the system can cause a fan to move.

    Adapted from Safety for the Indoor Environment Technician by Leo Meyer, from the Indoor Environment Technician's Library series; www.lamabooks.com.

    Publication date: 04/04/2005

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