Byline: Chad Saleska

Oct. 9--When Durham's Paul Bloom, a veteran of five Chicago Marathons, saw people walking the course just five miles into the race, he knew it was too hot to run a marathon.

"I dropped out because the conditions were miserable," Bloom said, who passed the halfway mark in 1:55:51. "I saw people walking very early on -- as early as five miles -- and that was a clear signal that there was trouble ahead. I got to about the 12- or 13-mile marker and I knew my hotel was only about five blocks away, so I decided it was time to quit."

Bloom, 60, wasn't the only one.

According to race officials, about 10,000 of the 45,000 registered runners didn't ...