# 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 ... –  WetSavannaAnimal aka Rod Vance Apr 25 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. –  WetSavannaAnimal aka Rod Vance Apr 25 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. –  Blackbody Blacklight Apr 26 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 ... –  WetSavannaAnimal aka Rod Vance Apr 26 at 3:58
a minute or so you're answer is likely right. –  WetSavannaAnimal aka Rod Vance Apr 26 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.

-

If you're in the pool the pressure wave could crush you depending on strength of blast. Water can't compress. 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.

-

It depends on the yield of Nuclear Weapon. If it's original Atom Bomb used in Japan, 10Km is in safe zone. But, you should avoid open sky as there's heavy chance of deadly Black Rain.

If the weapon is powerful and 10Km isn't in the safe zone, hiding in pool is bad idea. If you're inside fireball, all water would be vaporized and splitted up giving you third degree burn to kill you instantly (if your body wasn't vaporized by luck). Even if you're outside fireball, there's heavy chance that all water would be vaporized due to high amount of infrared radiations or it'd be super hot. If some water survived with low temperature by luck, it can't protect you from everything. There are other energetic radiations like Gamma Ray which can ionize your atoms.

If you want to survive, jump to underground heavy-concrete bunker having lead lining. If you don't have one, now is a good time to start building it.

Update:
If you have nothing else but a water body, go ahead to jump in. It can slightly increase your survival chance than you being in open. However, if there's a home nearby, you should consider that first. Assuming it's emergency, it's safe to assume that you don't have oxygen cylinder to stay inside water body for long.

-
+1 for building a nuclear bunker –  Dylan Cleaver Apr 25 at 0:35
For the record, if you weren't in the safe zone of an imminent nuclear blast and all you had around you was a body of water, you would definitely be safer jumping into it than standing out in the open. Water is an excellent radiation shield, it shields against ballistic projectiles, it douses fire, and the process of it evaporating would absorb heat that would otherwise be pumped into you. Plus it means you would be below ground-level, which is always a good idea when avoiding an explosion –  Jim Apr 25 at 3:13
@Jim Suppose you survived hot water, for how long can you hold your breath? Anyways, I have updated the answer. –  Sachin Shekhar Apr 25 at 7:37
Acid rain? Do you mean radioactive fallout? Why would fallout be acidic? –  Blackbody Blacklight Apr 25 at 7:40
@BlackbodyBlacklight Yes, I meant Nuclear Fallout. I have listened that Black Rain contains Sulphur Dioxide. –  Sachin Shekhar Apr 25 at 8:00