Knob and tube wiring is an older type of electrical wiring that's no longer used and generally not considered safe. However, some homes still have it, or may have a knob and tube wiring system that was incorrectly modified or rigged to work with a modern electrical system. Knob and tube wiring may contain asbestos insulation, but the only way to know is to have the material professionally tested.

If you own a stereo microscope, you should be able to see the fibers. The stereo microscope often can perform magnification up to 50x. But unless you have experience viewing asbestos fibers, you may not know exactly what you are seeing. Some fibers are curly, while others are long and straight. Blue, brown, white, and gray colored fibers are all possible.

There are products that still contain asbestos, but they were typically installed decades ago. Common places where you may still find asbestos-containing materials are in siding, wrapped around ductwork, in older appliances (i.e., stove and gravity furnaces), and in floors. Asbestos was primarily used as an insulator, so anywhere in an older home where you lose heat is where you will most likely find asbestos.

Typical methods for asbestos removal include encapsulation, enclosure, and complete removal.