On: Cherenkov Radiation

[delecti]

Or unless it's in water, in which case you're actually probably fine.

[rbanffy → delecti]

If you swim too close to it, you might as well not bother to surface.

[delecti → rbanffy]

Yes, "too" close by definition would be a problem. But even a meter of water between you and the source absorbs 99.994% of the radiation (down to 6 thousandths of a percent vs in air, or by a factor of about 1/16000).

[rbanffy → delecti]

If the source is 16000x the exposure needed to kill you, then 1m will be too close.