Bird nests next to chimney stacks of a coffee roaster at 327 Main Avenue in Norwalk appear to have caused a fire that took more than 40 firefighters from Norwalk and Wilton nearly four hours to bring under control.  Most of the firefighters working at this fire experienced symptoms of heat exhaustion, while three required IVs and hospital evaluation.  Firefighters made an aggressive attack, opening walls and the roof in order to minimize structural damage and fire extension.  They made a good stop despite adverse conditions.