HERMISTON -- Chalk it up as one of the biggest fire drills anybody in these parts has ever seen.

About 10,000 schoolchildren practiced evacuating or "sheltering in place" -- a sort of "duck-and-cover" air raid drill for the 21st century -- as part of an emergency test Wednesday in Eastern Oregon and southeastern Washington. It was all part of a simulated nerve gas accident at the U.S. Army's Umatilla Chemical Depot.

The Army is scheduled to begin incinerating 7.4 million pounds of obsolete liquid nerve and mustard agents on July 17 at the depot and continue for about six years. That prospect has sparked an intensive set of drills to prepare for a potential leak.

"If it goes as scheduled, this will be the last exercise" before incineration gets under way, said Jesse Seigal, spokesman for the Federal Emergency Management Agency.

The five-hour drill tested the skills of hospitals, police, firefighters and volunteers at 31 schools in Oregon's Umatilla and Morrow counties and Benton County, Wash., said organizers with the federal Chemical Stockpile Emergency Preparedness Program. The Red Cross set up simulated evacuation shelters in Pendleton and The Dalles, along with a unified headquarters in Kennewick, Wash.

The focus of Wednesday's emergency drill centered inside a zone extending roughly10 miles from the depot, an area with a population of about 42,000 people, organizers said.

Construction of the $2.4 billion natural gas-fired incinerators, known as the Umatilla Chemical Agent Disposal Facility, was completed in 2001. The four incinerators have been undergoing tests, and the final decision on their readiness of will be made in mid-July by the Oregon Environmental Quality Commission, said Mary Binder, depot spokeswoman. Incineration is supposed to destroy 99.9 percent of the chemicals, with the residue sent to hazardous waste landfills.

Chemical weapons have been warehoused since 1962 at the 19,727-acre depot in 90 half-buried concrete bunkers known as "igloos." The chemical weapons inventory includes 3,717 tons of nerve gases. The toxics include roughly 4 million pounds of liquid mustard agent stored aboveground in one-ton tanks, plus liquid nerve agents in 220,000 separate munitions, including rockets, mines, artillery shells and bombs.

The liquid agents include VX and Sarin, or GB, both organic phosphate nerve agents designed to kill by absorption through the skin after being transformed into a mist when the weapons explode, and blister agents such as mustard gas. VX and Sarin were developed by the Nazis. Mustard gas was created by German scientists before World War I.

The opening act

In Wednesday's drill, participants assumed two M55 rockets armed with GB Sarin nerve agent exploded outside at 10:26 a.m. at the depot while being transported to the incinerators. Under the drill scenario, four workers were injured, 11 other rockets armed with chemicals were damaged and leaking, and a plume of lethal nerve gas drifted off the depot and over the town of Irrigon.

Adding to the pressure, the script included a group of high school students being injured in a simulated traffic accident and being rushed to a hospital, another simulated motor vehicle accident, and students in 31 schools being evacuated or sheltered in place.

"It's tense, it's not joking -- we treat it as the real thing," said Rick Kelley of Hermiston.

He represented Washington Group International, one of the companies that built the incinerators.

After the emergency drill was announced, about 1,400 Hermiston High School students hurried to the school's gym where an "overpressure system" theoretically would keep them alive by keeping the deadly chemicals out.

"It would be scary" if the scenario were real, said Gabriella Esparza, 16, a high school junior taking part in the drill. "Every time we do this, we pretend it's real."

If a real disaster strikes

In an actual emergency, numerous roads would be closed, and residents of Irrigon would be told to stayin their homes and seal windows and doors with plastic until the plume passed over the town, said Capt. Pat Hart of the Hermiston Fire Department. The government distributed about 16,000 "home shelter kits" that included plastic, scissors and duct tape.

As added protection, 852 recirculating air filters valued at about $300 each were given to residents and businesses.

"What we are dealing with is airborne, and where there is no liquid, it will pass over," Hart said.

The counties tested outdoor sirens; highway reader boards; tone-alert radios in roughly 16,000 homes, schools and businesses; test messages to local radio and television stations; and the readiness of highway advisory radio systems. Benton County, Wash., officials simulated disaster response activities in Washington state's Plymouth and Paterson areas.

Although the Army thinks long-term storage is more dangerous than incineration, opponents disagree. Karyn Jones, a Hermiston activist representing a group called GASP, is more nervous about the potential for an accident during incineration than about long-term storage. Her group has urged the government to consider adopting alternative technologies in place of incineration.

Because of the war on terrorism, some outcomes of Wednesday's exercise may not be reported to the public, said Don Jacks, one of the organizers of the drill.

"There are things that go on in the exercises that we don't want the bad guys to know about -- places where we had weaknesses," he said.

Richard Cockle: 541-963-8890; rcockle@ucinet.com