In areas that required strong resistance to heat, asbestos sponge block was a common insulating materials. Particularly likely to contain sponge blocks are places like in roofs and walls and around boilers and furnaces, since these areas needed to be fireproof and well-insulated. Both the Johns-Manville Corporation and the Philip Carey Corporation were known to produce asbestos sponge for insulation.
Even though the dangers of exposure to asbestos were known, construction and manufacturing businesses continued to use asbestos-based products until the EPA restricted their use in the late 1970s. However, the restrictions were only applicable to the production of new asbestos products, leaving the sale of existing stock still allowable. These continued to be used for almost another decade. Anyone who worked in the manufacture of construction products like sponge block made with asbestos may well have been exposed on the job. Even those living and working in the buildings that were constructed using the products may be potentially at risk. When the material degrades or is damaged, it can release deadly asbestos fibers into the air, where they are easily breathed into the lungs. Reference: