Colonel: Facility should be back to normal Friday

Troops patrolled the perimeter of the Deseret Chemical Depot after an intruder was reported Thursday.

TOOELE, Utah (CNN) -- A "terrorist" alarm was sounded Thursday morning after an intruder was spotted in a fenced area at the U.S. Army's Deseret Chemical Depot, where more than 40 percent of the nation's chemical weapons are stored, officials said.

"There were four soldiers who saw the intruder in two separate patrols," said Col. Peter Cooper, commander of the depot. "When the patrols turned toward that intruder, who was dressed in black, he ran off."

Cooper said the four National Guard soldiers were patrolling in two military Humvees when they saw the unidentified man inside the fence, which was topped with barbed wire and affixed with "No Trespassing" signs.

The soldiers were armed but did not confront the person with weapons because "that is not within our rules of engagement," Cooper said.

The depot, operated by the U.S. Army Chemical and Biological Defense Command, stores and destroys chemical weapons.

Earlier this year, the facility finished destroying a large stockpile of deadly sarin gas, a chemical weapon 26 times more deadly than cyanide gas. The depot is in a remote desert area about 45 miles southwest of Salt Lake City.

A sweep of the grounds of the depot did not turn up the trespasser and "we're not sure who this individual was at this time at all," Cooper said. "At this time, we cannot confirm an intrusion."

The location where the troops saw the trespasser is about a mile from the facility where chemical weapons are stored and destroyed. Cooper said the trespasser "never got close" to the depot and no one was ever in danger.

After the trespasser was detected, operations at the facility were stopped and employees were told to report to their supervisors so that everyone on the grounds could be accounted for, Cooper said.

By Thursday night, a sweep of the compound was completed and nothing was found, Cooper said. Operations at the facility should be back to normal by Friday morning, he said.

Tooele County and state law enforcement officers helped implement security measures, said a spokeswoman for the joint task force investigating the incident.

All operations in the depot were curtailed when the alarm siren sounded at 9:24 a.m. MT (11:24 ET) and employees were put on standby, she said.

"It appears that there was never a danger to any of the citizens or the public in general," said Tooele County Commissioner Gene White.

An administration official told CNN that early reports from the depot indicated "nothing has been tampered with and nothing has been stolen."

Homeland security officials said they assumed the intruder was a trespasser who got somewhere he was not supposed to be, but until that was confirmed they would take no chances.

Wade Mathews of Tooele County Emergency Management said the Terrorist Alert Warning System was implemented at the depot after September 11 to alert employees to possible problems with intruders.

He said the use of the word "terrorist" did not necessarily indicate an attack against the facility, only that an intrusion was a possibility.