For decades up until the 1970s, asbestos block insulation known as Duplex Blox and sold by Keasbey & Mattison was used to insulate hot water tanks and boiler pipes. These blocks were usually chalky and they were secured with either metal lath or chicken wire. Sometimes they were topped with a final seal of cloth soaked with plaster. Over time, Duplex Blox wear out and can break into small parts if moved.
These Duplex Blox were one of the many different types of insulation material that contained asbestos used in construction and insulating up until the early 1980s. In the U.S., many homes and public building still have Duplex Blox insulation in them. Attempting to take it out or handling it in anyway can send asbestos dust and fibers into the air, exposing anyone around it and putting them at risk for developing mesothelioma, a rare and aggressive form of cancer, or other asbestos-related diseases.
From the 1930s to the 1980s, anyone who worked in industries like construction, heating, and insulation received regular exposure to asbestos because of products like Duplex Blox and other insulating materials that contained asbestos. They did so without the knowledge that they were handling dangerous material even though in most cases their employers and the companies that supplied asbestos knew.