Electric boards were usually made of a material known as Bakelite that had asbestos fibers included in its manufacturing process. This was done in order to strengthen it so the final product could be able to sustain damage from heat. As in most electrical appliances, crocidolite (blue asbestos) was used for these types of products.
When the electric board sustained damage, usually from external sources, the asbestos lining would become friable, putting its microscopic particles in a state that made them more likely to be released into the atmosphere. You could have been exposed if: