The pressure vessel of the boiler was usually made of steel or an alloy of steel. Because of the extreme heat produced, asbestos was used as insulation, being well-known for its fire-resistant properties.
In time, the asbestos applied to the boiler would wear down and it would need removal. As it was subjected to extreme temperatures on a constant basis, the asbestos contained in the insulation products became friable, meaning that it was easier for its fibers to become airborne when the worker would start to tear it off. You could have been exposed if:
- You were a manufacturer of boiler systems
- You installed boilers
- You assured maintenance for boiler systems
- You found yourself on a constant basis around boilers