“These are navigation devices intended to help mariners,” he said. It’s a matter of safety, said Cosulich-Schwartz. People who keep watch on the weather conditions from the bridge sergeant’s office at the south end of the span determine when it’s foggy enough to switch on the foghorns as required by federal maritime law. The foghorns are stationed in two locations: three mid-span and two on the south tower pier. “It can be sunny in Noe Valley and you can only see a foot in front of you in the channel beneath the bridge,” he said. Reached in the afternoon, he said the bridge deck - and more importantly, the shipping channel beneath - was shrouded in thick fog, which requires the district to sound its five foghorns. The Golden Gate Bridge was likely at fault, admitted Golden Gate Bridge spokesman Paolo Cosulich-Schwartz. “Fog horns at/near the Golden Gate Bridge have been going off since the overnight hours,” tweeted Elaine Leung on Wednesday morning.