Police and firefighters are testing the city's response time in a theoretical weapons attack.
Several blocks in San Francisco's financial district were closed down for the day.
The scene was the aftermath of a chemical attack in a downtown high rise- luckily this was only a drill.
"Each time we do this the better off all of us are," said San Francisco Fire Department Chief Joanne Hayes-White.
About 500 emergency responders from San Francisco, surrounding cities, the FBI and the Army are participating in this mock release of weapons of mass destruction.
There was also drama at 1 Post Street. A mock shooter went on a rampage where another unidentified chemical had been released.
"It's truly taxing the resources here in San Francisco, but that's what it's all about," said Hayes-White.
It all started at 10 this morning and from some outsider's perspectives things were moving slowly. Students playing victims were left lying there for hours.
"We know that things start out at a low level in these exercises today," said S.F. Police Chief Heather Fong.
"Initially where you'd want to go right in, you see victims on the ground, we need to make sure that we take a step back, pause for a moment and decide what our entry is going to be like," said Hayes-White.
As the mock decontamination went on this afternoon, a local businessman said his company could help stop the situation before it got to this point.
Mike Welden of Building Protection Systems stated "We have a break-through system that's designated by the Department of Homeland Security that will detect and identify the toxin in seconds and then automatically shut down the HVAC system so the toxins are no longer circulating through the building." This product was just released earlier this year, another idea at a time when the government is being criticized about the availability of materials that could be used to make a dirty bomb.
The Government Accountability Office released a report last month saying that advances in security were moving too slowly and that customs officials don't have enough equipment to detect radiation.
In the meantime FEMA is spending a quarter of a million dollars on today's drill.
"The money is absolutely worth it because if we don't spend it now it's going to cost us so much more later on," said Tom Saragoosa of the S.F. Fire Department.