RICHMOND, Calif. -- A huge white cloud of sulfuric acid spewed out of a ruptured railroad car yesterday, engulfing thousands of homes and sending more than 2,900 people to hospitals with such symptoms as burning eyes and breathing problems.
The stinging, smelly chemical poured out of the rail car for more than three hours -- sending up a cloud 1,000 feet high and up to 8 miles wide -- before rail yard workers were able to cap the leak.
The thick chemical fog rolled east and north, growing larger as it spread through densely populated neighborhoods and industrial sections of Richmond, San Pablo, El Sobrante and Pinole, Calif., before dissipating over San Pablo Bay.
"The cloud was so thick you could hardly see," said Orlean Pitri, who lives near the General Chemical Corp. rail yard in Richmond, where the leak occurred. "By the time I closed the windows, the whole house smelled like rotten eggs. It smelled terrible."
The spill temporarily shut down busy Interstate 80, commuter trains, bus service and mail delivery in the Richmond area, across the bay from San Francisco.
Paramedics set up one impromptu first aid station at a fire house, hosed down victims in the parking lot and gave them hospital gowns to wear before busing them to hospitals for further treatment.
Hospitals were inundated with people who came by ambulance or on their own with complaints of breathing difficulties, nausea, irritated skin and burning eyes, mouths and throats.
At least six people were hospitalized with complications of existing lung conditions. But most victims were treated and released.
As much as 70 tons of oleum -- a highly concentrated form of sulfuric acid used in manufacturing soap, among other products -- escaped from the General Chemical tank car when the disk in a safety valve ruptured.
The safety valve was designed to pop open if pressure should reach the dangerous level of 100 pounds per square inch. But instead, it ruptured when the pressure was only 55 pounds per square inch, General Chemical spokesman Eric Miller said.
"We're still . . . uncertain about the cause," Mr. Miller said.
The chemical, which was manufactured at the General Chemical facility, was being transferred from one part of the plant to another when the accident occurred.
About 30 tons of the oleum had already been unloaded from the car when the valve broke at 7:15 a.m. Workers were able to stop the leak at about 11 a.m.
Authorities evacuated a small area around the scene of the accident but directed residents in the path of the cloud to stay indoors, shut their windows and turn off their air conditioners.
But children playing outside, joggers and motorists on their way to work were caught by the toxic cloud as it passed through the area. By a little after noon, the directive to stay inside was lifted.