I would be wary of the hydraulic shock (assuming the blast is near the ground), and if one is still alive, radioactive sodium will help: >Salt in seawater read

I would be wary of the hydraulic shock (assuming the blast is near the ground), and if one is still alive, radioactive sodium will help: >Salt in seawater readily absorbs neutrons into both the sodium-23 and chlorine-35 atoms, which change to radioactive isotopes. Sodium-24 has a half life of about 15 hours, while that of chlorine-36 (which has a lower absorption cross-section) is 300,000 years; the sodium is therefore the most dangerous contaminant since it has the shortsest half life. Source: https://en.wikipedia.org/wiki/Underwater_explosion https://en.wikipedia.org/wiki/Underwater_explosion