This Radon gas will cause lung cancer (US EPA report).
Radon is a dangerous radioactive gas. It is a colorless, odorless, and tasteless gas and therefore not detectable by human senses alone.
If you don't test, you don't know!!!
Health Canada recommends 200 Bq/m3 as the 'action level'.
The World Health Organization recommends attempting to attain a level of 100 Bq/m3 or below.
And, in USA recommends 148 Bq/m3 or below.
Testing is the only way to confirm your home is safe from high radiation levels due to exposure to radon gas.