Chemical smoke is an important part of radon diagnostic procedures. Smoke is used to determine air pressure field extension and flow rate of a mitigation fan.
Smoke can also check for leaks in the floor and walls after a mitigation system is operating. And never to be over looked is using smoke to test for back drafting of combustion appliances. Back drafting is often a contributing factor of high carbon monoxide levels in homes.
These smoke pens are adjustable and reusable. Refills also available here.