# Would being underwater help survive a nuclear bomb?

If I jump in my pool, on the river near my house knowing that a nuclear bomb, or atomic or H-Bomb exploded around 10 km from my house, would I survive?

The way I see it is that water will protect me from the heat, so then I will be able to surface up after the explosion and escape.

• This depends on a great many factors - how big the bomb is. Water shields, but shields by absorbing radiation, i.e. it may well heat up with fatal outcomes. The way I see it, someone needs to do a calculation to answer this question properly. I'm not up on the morbid subject, but I seem to recall that the "fireball" is where the air absorbs most of the immediately harmful gammas and soft Xrays and heats up producing the enormous shock wave. So if you're outside the fireball, the main threat is radiant heat and blast. People died here in Victoria, Australia in 2008 bushfires ... Apr 25 '14 at 23:27
• ... with much less radiant heat than you're talking about when they jumped into smallish swimming pools and the latter heated and cooked them (but with that much radiant heat, there would be precious little you could do to live). So I'd be doubtful without calculations. The Tsar Bomba fireball was 8km diameter, so you're almost certainly outside the fireball. Apr 25 '14 at 23:29
• @WetSavannaAnimalakaRodVance As I note in my answer, the surface of the water will boil off without heating the entire body. Nuclear bombs release energy instantaneously, and the fireball only has any meaningful duration because the energy flux through air is limited by ionization. A layer of residually heated water at the top of the pool won't burn you because water's boiling point is fairly low relative to tolerable temperatures, and the layer is limited to centimeters by absorption. Apr 26 '14 at 3:45
• @BlackbodyBlacklight Don't you think we need some kind of rough calculation to verify this? the fireball is hot and nearby: let's say $6000K$ (I've really no idea about details - that's a wild guess) and $2km$ in diameter: Stephan Boltzmann then implies flux of $74MW\,m^{-2}$ at the fireball's surface, so at $10km$ way we're getting $0.74MWm^{-2}$: depending on the fireball's height there is a $\cos\theta$ intensity factor, so let's assume $0.2MW\,m^{-2}$. That's enough to heat the first metre of water at a rate of $0.05K,s^{-1}$. So if your pool's deep enough and you hold your breath for ... Apr 26 '14 at 3:58
• a minute or so you're answer is likely right. Apr 26 '14 at 3:58

Water provides excellent shielding against ionizing radiation. While the radiation from the initial detonation is setting everything nearby on fire, the surface of the water will harmlessly evaporate. Since the boiling point of water isn't very high and the flash doesn't last very long, the whole body of water will stay cool, even if it's only a swimming pool.

I'm not as sure about the physics, but water should also give good protection against the shock waves generated by the explosion. Because water is much more dense than air, with high surface tension, acoustic waves tend to bounce off rather than go in (this is why you mainly hear only underwater things while swimming), and intense wind tends to generate foam on the surface rather than stir up turbulence underwater.

Falling debris will be falling slower, if at all, after it breaks the surface. The safety of diving in such conditions is doubtful, but I can't really quantize that.

All considered, if you are under nuclear attack, yes that is a good time for a swim. You might as well continue swimming until things stop falling and the air becomes relatively clear. Use a makeshift dust mask while going up for air. Since water stops neutrons so well, the radioactive isotope concentration would have to be pretty high for underwater fallout to be as dangerous as that in the air, but take care not to swallow too much.

• Water will protect you from the heat yes, but what about the blast wave? If something explodes underwater, the blast wave will kill all the nearby fish, for example. But if a bomb explodes in the air, I'm not sure whether or not the blast wave loses strength transitioning to water such as a swimming pool. Aug 26 '21 at 10:21

If you're in the pool the pressure wave could crush you depending on strength of blast. Water can't compress, but if you're in the water you'll be crushed. So there's a two fold issue to entertain your idea, heat and pressure. Radiation will be your next concern if you survive the initial blast.

• You say water can't compress but also say the pressure wave would crush you... May 31 '16 at 16:39
• @ClassicStyle Go watch YouTube videos on surviving a grenade by jumping in a pool. Very fascinating stuff! The water will not compress, so when pressure is applied to the water, it will compress the body instead (because air exists inside the body). When the water fails to compress, the large majority of that pressure is compounded and applied to the body. Think of pushing a metal rod attached to a spring... The spring will compress but the rod will not, because the pressure is being transferred through the rod to the spring (because the rod cannot compress). Aug 11 '17 at 5:00
• How well would the blast wave in the air transition to water? This is a bit different from the underwater blast Swivel mentions above. Here you have an established wave in the air, moving in a direction perpendicular to the surface of the water. The critical question is to what degree the blast wave would transition to the water under those conditions. I'd love to know the answer to that. It might also matter if the pool is indoors or out. Aug 26 '21 at 11:26

I think if you had one of those above ground, or deck pools, you'd find that the structure would burn or melt away during the blast, which would allow the water to quickly empty out. You would have to have an outdoor pool, that is underground to have a chance. If it were indoor, the house would probably catch fire or disintegrate, leaving you with other problems, like falling and burning debris. Even if you had a deep, outdoor pool, you would still have to worry about debris flying into the pool. I've watched those nuclear test videos and stuff is flying around everywhere. You have the initial blast wave, and then you have a secondary wave caused by air rushing in to fill the vacuum. Who knows what kind of crap would be flying into your pool.

• This seems to be more of a practical answer, rather than one that addresses the physics of what happens (the latter, of course, being more of what we expect on a physics site). Dec 24 '15 at 13:19