Asbestos was often used to insulate boiler pipes in commercial and residential properties. These asbestos insulated pipes can be very friable (prone to fiber release) and present significant hazard when they become damaged.

Boiler pipe insulation that contains asbestos
Unsealed joint ends on asbestos insulation
Exposed asbestos on boiler pipes
Insulation covering peeled back
Asbestos fibers exposed
Significantly damaged asbestos pipe insulation
Closeup of asbestos fibers