Ron,

It may not have been just DE powder. Many PC companies have dusted under homes with FICAM, Boric acid powders, Tempo dust and others.

I seriously doubt that a one time exposure is going to cause any problem but maybe some irritations to the nose and throat for a day or so.

If anyone opens a crawlspace entry and see's any dust thats a sure reason on why you should have a respirator on.

rick