Answer to Question #12957 Submitted to "Ask the Experts"

I have installed ultraviolet short wave (UV-C) lights in my heating, ventilation, and air conditioning (HVAC) unit, the coil box to be exact. Is there any danger of the UV-C lights on aluminum, stainless steel, copper, or galvanized metal that constitute the inside of the box? When the furnace starts it smells metallic, and I'm concerned about the fumes being toxic.

In short, the use of these lights is not hazardous inside the system and any metallic odors you smell may be the result of the production of ozone gas by the UV-C lights.

When UV-C light shines on metals, the light has sufficient energy to eject electrons from many metals, especially aluminum. The electron that is ejected from the metal is not hazardous and is rapidly absorbed by the air or recombined with metals possibly producing a very small electric current. This is the process by which electric eyes work on doors or other equipment. There is no hazard from the UV-C light shining on the metal, especially within an enclosed space.

You describe a "metallic" odor when your furnace starts. People describe the smell of ozone like an electrical spark or metal so I believe what you are smelling is ozone gas. UV-C lights can also produce ozone that will accumulate in enclosed environments. Since the ozone is also germicidal it will have a beneficial use inside your air conditioning system. As the lights continue to shine, the UV-C will produce ozone that will be distributed throughout your house when the furnace starts. Most people will smell ozone at concentrations around 0.01 parts of ozone to a million parts of air; that is 0.01 ppm. When you no longer smell the ozone, its concentration should be below 0.01 ppm. Medical devices that produce ozone are not to produce more than 0.050 ppm as regulated by the Food and Drug Administration.

In summary, the UV-C light shining on the metal portions of your furnace are not harmful to you or your furnace. When your furnace starts, we believe what you are smelling is ozone and once you no longer smell the gas, the concentration is very safe and below levels regulated by the FDA. There should be no long-term health effects from this exposure.

Dr. Paul Charp