Dozens of Capitol Hill employees underwent decontamination — basically a fancy word for showering — for exposure to the deadly poison ricin (search), and so far no one has turned up ill.

That reassures health officials, who note that enough people were around the ricin-containing powder that if anyone were going to be ill, symptoms should have begun by now.

"As each minute ticks by, we are less and less concerned about the health effects," said Dr. Julie Gerberding, director of the Centers for Disease Control and Prevention (search).

Between 40 and 50 U.S. Capitol police and Senate employees underwent decontamination after ricin-containing powder was discovered in the mailroom of Senate Majority Leader Bill Frist's (search) office, according to Senate aides who spoke on condition of anonymity.

At least 12 of the Senate staffers decontaminated came from the office of Sen. Jim Jeffords, I-Vt., whose personal offices are near Frist's on the fourth floor of the Dirksen Senate Office Building (search).

"Nearly a dozen of my staff members were quarantined last night, and later decontaminated. They didn't get home until after 2 in the morning," Jeffords said. "Thankfully, everyone is feeling fine and they don't appear to have ill effects."

Ricin is a poison extracted from the bean-like seeds of the castor (search) plant, beans that are used to make castor oil, used as a laxative and industrial lubricant. Ricin made separately is a potent poison, and a small dose can be fatal if swallowed, injected or inhaled.

People exposed to ricin and certain other chemical agents can protect themselves in two ways — leaving the area to breathe fresh air and getting rid of any of the toxin that might be on the skin.

Typically, emergency workers wheel in tented showers. People take off all their clothing, which is sealed inside plastic bags to protect against spread of any toxin left on the material. Then they wash with large amounts of soap and water.

Powder was on a countertop and people had been around all day, meaning if anyone were going to be ill, signs from that contact should have appeared by now, said Michael Osterholm of the University of Minnesota, who advises the government on terrorism issues.

"It begins almost immediately," he said. "The fact that you have no clinical illnesses ... that's a good sign."

If the ricin were pure, "we would expect very early onset," CDC's Gerberding said. "The fact that we haven't seen that is reassuring."

Still, CDC recommended that anyone who could have come in contact with the poison and who experiences respiratory or intestinal problems within 12 hours of exposure go to a doctor.

In an advisory sent to Washington-area physicians shortly before 5 a.m. Tuesday, the CDC urged that they be alert to symptoms.

"In addition to the risk for inhalation, potential hand-to-mouth exposure, leading to ingestion, may have occurred," the CDC advisory says. "Clinicians are urged to review the signs and symptoms of both inhalation and ingestion of ricin and consider the diagnosis with their patients."

Watching for symptoms is important because there is no reliable test to confirm a person's exposure. Ingesting ricin causes stomach ache, diarrhea and vomiting that may become bloody. Inhaling ricin causes difficulty breathing, fever, cough and tightness in the chest.