A cloud of ammonia leaked from a broken pipe at the Columbus Salame plant on Forbes Avenue in South San Francisco.
Twenty-four people were exposed to the ammonia leak and were transported to the nearby Genentech parking lot to be treated and decontaminated. Eight of them ended up in the hospital.
Edward Borja is a UPS driver. He was loading his truck when he started feeling sick.
"You can't breathe, you can' breathe, and my throat started to itch," said Borja.
"We started to get a sore throat, getting dizzy, some of us threw up," said UPS employee Sandra Garcia.
"The ammonia affects your respiratory system, they were having some difficulty breathing and we were doing decontamination, they were washing them down and decontaminating them," said fire marshall Luis DaSilva.
The source of that leak was the cooling system on the roof of the Columbus Meat Processing Plant in South San Francisco. It's used to chill the meats. The CEO of the company said a valve suddenly ruptured.
"It was actually changed a few days ago and tested and verified and worked and for some reason ruptured today," said Columbus Foods CEO Ralph Denisco.
The accident happened at 5:30 a.m. as workers were starting the first shift. Hundreds of employees at other companies nearby were also affected.
Cars and trucks traveling on Forbes Boulevard were diverted, causing backups on Highway 101.
Just last month the company had a major fire at its packaging and slicing facility just a few blocks from Cabot Road. Fire investigators still don't know how that fire started.
After that fire, most of the workers at that facility were transferred to another plant and about 30 were laid off.
Friday's accident shut down production for about six hours. The plant reopened once hazardous materials teams said it was safe to come back to work.