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.

Asbestos is commonly found in certain older homes, depending on the time period in which they were built. Asbestos use in home construction began in the 1920s and peaked after World War II before being limited by legislation in the ’70s, so a house constructed in 1880 is unlikely to contain asbestos, while one built in 1950 is much more likely to. Research a home’s history to determine the time period when it was built and any renovations made since.

It is strongly advised not to touch or disturb asbestos-containing materials unless necessary. Asbestos fibers can be released into the air when the material is damaged or disturbed, posing serious health risks if inhaled. It is best to leave any handling of asbestos to trained professionals who can remove the asbestos safely.

Asbestos was most commonly produced and integrated into building products from the 1920s to the late 1980s. In reality, asbestos use should have ceased much sooner because asbestos was linked to cancer in studies produced as early as the 1950s. You can even extend that number past the 1980s due to stockpiled materials and because some countries treat asbestos use differently. It may also be found more in commercial applications than residential.