Bob,
I lost a roofer like that one day. We were on a barrel shaped roof and  he 
wondered over onto the side where the sun hadn't been shining. All you could  
see was where his finger nails had dug into the roof mat while trying not to go  
over the edge. He landed in some brush and was fine, but it took a while to  
scrape all the tar out of his finger nails.
 
Rummy