 Radon decays to form solid radioisotopes that form coatings on the inside of pipework.High concentrations of radon in homes were discovered by chance in 1985 after the stringent radiation testing conducted at a new nuclear power plant revealed that Stanley Watras, a construction engineer at the plant, was contaminated by radioactive substances even though the reactor had never been fueled.Typical domestic exposures are of approximately 100 Bq/m3 (2.7 pCi/L) indoors.