Andrew Gabriel wrote:

I didn't mean to imply air in blood vessels -- I don't know what
the damage mechanism is when such air passes through the skin*.
I can tell you what it looks like - a really bad bruise, except it
took much longer to go than a normal bruise.

Ah, righto, yes that isn't an embolus that's simply high pressure
injection damage. It's actually quite difficult to do, and from the
usual 8bar compressed air source it requires the air gun to be "dead
ended" on the skin. It is extremely serious and can lead to amputation
as a consequence of the immediate tissue damage or as a consequence of
gangrene.

It's odd, I see various anaecdotes about air guns causing embolus, but
never a paper in a peer-reviewed journal. There are many papers on high
pressure injection damage and that leads me to suspect that the embolus
claim is urban myth.

Although this isn't a scholarly article, it's a relatively sane and
sober discussion of the issues.

http://everything2.com/title/High+pr...jection+injury

And in this medical discussion of the consequences of HPI injuries it is
stated that injection of clean air or water usually has no other
consequence than immediate mechanical damage but injection of paint, oil
and grease can lead to amputation.

http://www.tripdatabase.com/spider.html?itemid=816462

Again, no mention of embolism as a consequence of air injection. And one
would have to ask why no soldier has died of air embolus after receiving
an air injection delivery of vaccine.