oo water supplies are contaminated, and the fission products from underground nuclear detonations largely become fixed at and near the site of the explosion. Whereas, theoretical calculations suggest that concentrations of tritium in the water may be above acceptable limits for some underground nuclear detonations,'" this refers only to the water immediately around ground zero. Some dilution is to be expected if it moves off- site and, more importantly, the criterion of ‘“‘acceptable limits” is based on the assumption that all of the water drunk throughout a lifetime will contain the same concentration of tritium as set by the limits. The quantity of water initially contaminated to these limits by an underground nuclear explosion is relatively small and would not constitute the sole supply for a lifetime. years. Further, tritium decays with a half-life of about 12 Much less radioactive fallout debris enters the body by inhalation than by ingestion. While the debris is in the air out- side the body the radiation exposure is much less than after the material has been deposited on the groundwith the possible exception of certain situations noted above. 20