[JT]

Avoiding grain dust is likely overblown for the home brewer.  Chronic exposure would probably be more of a concern.  You can see where exposure is a concern though here: http://www.cdc.gov/niosh/pel88/graindst.html
My favorite line is "Grain dust is a complex mixture of husk particles, cellulose hairs and spikes, starch granules, spores of fungi, insect debris, pollens, rat hair, and approximately 5 percent mineral particles."
Mmm... rat hair...
At any rate the "spores of fungi" is likely the biggest concern with inhalation, other than general irritation. 

[wedwards]

If I don't wear a mask while crushing my grain I get really bad asthma for an hour afterwards. That's enough reason for me to avoid it.

[flbrewer]

(places order for milled grain)

[Slowbrew]

If I don't wear a mask while crushing my grain I get really bad asthma for an hour afterwards. That's enough reason for me to avoid it.

That's a reason I can understand. Thanks!

Shovel out 35 year old soybean beans out of bins for a week sometime and you'll understand my "meh" response to grain dust.  I took that job one summer.  25 - 3000 bushel bins of old sealed government contract grain (old grain storage program).  Six days of pushing black soybeans into an auger for $9.50/hour.  The respirators plugged up in 15 minutes.     I looked like a coal miner at the end of each day and cough up "stuff" for two weeks after.  Sooo, a little cloud of barley dust seems easy to deal with but I don't have asthma.

You don't want to hear any stories about hog confinement buildings.   

Paul

[troybinso]

If I don't wear a mask while crushing my grain I get really bad asthma for an hour afterwards. That's enough reason for me to avoid it.

Me too!

It also causes a rash on my face if I don't have it covered. I usually use a bandanna.

[flbrewer]

Ran a couple of pounds of 2-row through the Barley Crusher today w/ the hand crank and bucket underneath. Really no dust at all. Perhaps when I pour the grained mill into the MT, I'll wear a dusk mask for that portion.