I have read that granite tiles emit radioactive radon gas, which is a health hazard.
Is this true?
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The EPA article, Radiation Protection - Granite Countertops and Radiation confirms that granite tiles do in fact emit radon gas:
Any type of rock could contain naturally occurring radioactive elements like radium, uranium and thorium. Some pieces of granite contain more of these elements than others, depending on the composition of the molten rock from which they formed. If present, these radioactive elements will decay into radon, a colorless, odorless, radioactive gas which may be released from the granite over time.
However, the amount of radon emitted by granite tiles (for example in countertops) is highly unlikely to be a health risk
However, since granite is generally not very porous, less radon is likely to escape from it than from a more porous stone such as sandstone. It’s important to know that radon originating in the soil beneath homes is a more common problem and a far larger public health risk than radon from granite building materials. Also, any radon from granite countertops in kitchens or bathrooms is likely to be diluted in the typical home since those rooms are usually well ventilated.
In addition to radon, the other natural radioactive material in the granite can emit radiation. However, it is extremely unlikely that granite countertops in homes could increase the radiation dose above that the normal, natural background dose that comes from soil and rocks.