In older apparatus made up to the early 1970s, boards made of compressed asbestos may be found; while this is an adequate insulator at power frequencies, handling or repairs to asbestos material will release dangerous fibers into the air and must be carried out with caution.

Even if the workers are protected, such maintenance operation may release fibers into the air, which may be inhaled by others.

Measurements are typically made at a time when there is no activity in a building, and when asbestos would not be disturbed and therefore would not release fibers, he said.

Asbestos was commonly used in insulation until the 1970's, when it was discovered to release fibers that can lodge in the lungs and cause cancer.

In either case, you are not scraping the asbestos while it is dry, so there is much less chance of releasing hazardous fibers into the air.

"And exposed insulation around a pipe in a basement is very different from ceiling tiles releasing fibers."

The chief concern is friable asbestos, typically molded to go around heating pipes, which crumbles with age and releases fibers into the air.