Asbestos was used for decades in building materials because it's strong and fire-resistant. In older buildings it can turn up in roofing felts and coatings, floor tiles and adhesives, siding, pipe and boiler insulation, and ceiling texture.
Undisturbed and in good condition, many of these materials pose little risk. The danger comes when they're cut, broken, or torn out during renovation or demolition, which releases fibers into the air.
That's why testing comes first. Before a renovation or demolition, suspect materials should be sampled and tested by a qualified lab. The results decide what has to be removed and how.
When removal is needed, the work area is contained, the material is kept wet to limit dust, and it's packaged and disposed of following state and federal rules. Cutting corners here can expose workers and occupants and put the project on hold.
If you're planning work on an older building, bring up asbestos at the estimate. Planning for it up front keeps the schedule and the budget honest.