You don't know why it was turned off. Ask the owners why it was off and for their permission if your clients request that you inspect the related systems. You may want to ask the owner to turn it back on, depending on the situation. Don't remove the blower compartment door of a furnace when the unit is running. Combustion products may be drawn into the supply ducts.
Care is needed when opening the view door of an oil-fired unit.
Be aware of your necktie if you are wearing one around mechanical equipment. If a sample of suspected asbestos is to be taken from a heating pipe or duct, a spray bottle of water should be used to saturate the area first. Be alert for leaks in gas or oil lines. Electrical Top Watch for damp or wet conditions on the floor or walls when opening the main electrical panel. When you first touch the main electrical panel, do it by tapping the panel with the back of your hand.