Depends on the acid.
For something that is 'just an acid', even a strong acid like HCl, it will in most cases do little to no damage initially. For instance, I've often spilt ~18M HCl on my hand, and it usually takes several minutes before it starts itching (I typically wash it off before that happens). HCl is sort of like boiling water, except you have several minutes to do something before it does any damage.
However, acids with other additional chemical properties tend to be much nastier to human flesh.
Sulphuric acid, for instance, in the concentrated form is not only an acid but a very strong dehydrating agent, which is able to rip water out of organic molecules, typically leaving behind a charred charcoal-like mass. At room temperature it doesn't react with human flesh all that fast - I've got fairly concentrated H2SO4 on me on several occasions and been able to wash it off without too much damage. However, that was only ever with very small amounts. I imagine it would be a lot more dangerous if you were to get a large amount on you all at once. H2SO4 reacts very exothermically with water, so if you were to get a large amount on you, the heat generated would enough to greatly increase the reaction rate of the H2SO4, which I can't imagine would be terribly pleasant.
Acids such as nitric acid or perchloric acid are also quite nasty, because of their strong oxidising properties. In really high concentrations, they will cause organic matter to ignite.
Oh, and the one acid you really want to stay away from is hydrofluoric acid. The internet is full of horror stories of people who have died horrifically painful deaths as a result of exposure to it. It's horrific nature comes not from its acid properties at all (it is a weak acid) but from the toxicity of the fluoride ion. Because it is a weak acid, it exists mostly in the form of HF (as opposed to H3O+ and F-), which makes it much easier for the molecules to penetrate the skin. In small amounts, it will cause horrific burns which take months or years to heal, which are said to feel like being struck with a hammer. In larger amounts, the fluoride ions will penetrate into the bloodstream and precipitate out the calcium as CaF2, which leads to hypocalcaemia and cardiac arrest. Scary stuff!
18 Jan 2009, 12:58 am
