For asbestos they are microscopic glass toothpicks that penetrate to the smallest reaches of the lung and get stuck. They are not cleared and will form a unique type of lung cancer. Theoretical cancer models, one hit hypothesis, is what your hearing about. Its theory. The suggestions to encapsulate are good ones. The approach to not disturb/sand etc. is also the best way to reduce an exposure risk. Wear PPE and you’ll be fine. Note the asbestosis lawyer commercials, they were occupational exposures without PPE.

If the fibers were left after an asbestos removal project, they may not be asbestos. The asbestos removal folks who worked on my house removed a bathroom floor because the tile had asbestos in it. The bathroom was not even on the list of items to check. They found the stair treads to the basement had asbestos and several other obscure tile patches under the water heater and a washer. They really tested everything!

The most impressive part of the cleanup was the clean room approach, they used zip walls to create plastic rooms around all exposure point and sealed second chambers to get in and out. All air circulation was completely filtered with special filters. The room had to be washed down and the air filtered until a air quality meter showed a safe level of particulates for an extended period of time.

Best $1500 (1993) I spent for my family and my mental health of not having to worry any more.