Answer to Question #3311 Submitted to "Ask the Experts"

I have a watch (2002 model) that contains tritium gas vials in the hands of the dial. I have read that tritium can leach through plastic and, to a lesser degree, metal to finally be absorbed by the user. If this is the case, is it safe to keep the watch or should I discard it?

As a guess, I would say that the activity of the tritium in your watch might be in the 25 to 100 millicurie range (possibly less). That might sound like a lot, but the beta particles emitted by tritium are of such a low energy that the hazard is almost nonexistent.

The older versions of these gas tube light sources (GTLS), used to backlight LCD displays in digital watches, had even higher activities: up to 200 mCi.

As you indicate, the tritium will leak out of the watch and be absorbed through the skin. Since much of the tritium that is leaked goes directly into the general room air, anyone in the room will receive an exposure, not just the wearer of the watch.

Almost no dose calculations seem to have been performed for these types of watches. Instead, the dose calculations are done for watches employing tritium paint because the doses from the paint would be higher than those from GTLSs. Since the dose estimates to individuals wearing watches containing tritium paint are typically 0.04 to 0.06 mrem per year, your potential exposure would probably be less than that. Compare this to the 300 mrem per year that an average resident of the United States receives each year from natural sources of radiation. If you are still concerned, dispose of the watch. It might provide peace of mind. I wouldn't. I'd keep it.

Paul Frame, CHP, PhD