hear ya go

http://www.strangehorizons.com/2002/.../manhole.shtml

the article wanders at bit....but it gets back to the "facts" your interested
in near the end of the longish article...

I used to have a link dirrectly to an article written by the scientist in
charge of the project...it was nice little article with facts from the guy that
WAS there....but alas I cant find it...maybe you can with the info the
article...

take care

Bll