This animation illustrates how a standard Polychem chain and flight scraper system is assembled and installed.
The FBI stated today there are no signs of contamination near a South Carolina postal facility, where an envelope containing ricin and a threatening letter were found last week.
Federal officials say a vial found in the envelope tested positive for the deadly poison ricin. The postal facility in Greenville, S.C. has been tested.
A Homeland Security Department spokesman said that although the incident appears related to criminal threats, terrorism is not suspected.
Officials are not saying to whom the envelope was addressed or where it was postmarked. A federal law enforcement source told the Associated Press it was not addressed to a government official.
The source also said the envelope contained a letter warning that large amounts of ricin would be dumped into reservoirs if the government didn't change a rule requiring truckers to rest after ten hours on the road.
Officials claim it's unlikely the threat could be carried out. They say thousands of pounds of ricin would be needed to taint water supplies, and chemicals used to treat the water would probably render the poison harmless.