It had worked during past routine tests.

But for some reason, it did not sound Wednesday during an annual drill in which a mock disaster was staged at the Umatilla Chemical Depot. About 11,000 people, mostly students in three counties, responded in some way while about 100 state and federal evaluators watched the activity.

The mock disaster involved two rockets filled with VX nerve gas exploding outside a bunker at the depot, injuring four people and sending poison gas fumes to the northwest over Irrigon and Paterson.

The evaluators will debrief government and emergency officials Friday in Pendleton on how well the region responded.

Wednesday's drill is supposed to be the last regionwide emergency response exercise before the depot begins burning 3,717 tons of nerve and mustard gas. Mid-July is the earliest incineration might begin.

At Hermiston High, the tone alert radio's job is to tell school officials that the building's approximately 1,300 students must go to the gym because nerve gas had escaped from the depot about eight miles away.

The gym is equipped so a flick of a switch will increase the gymnasium's air pressure keeping the weaker outside air form going in. It forms an island of safety if chemical gases are wafting about.

The school conducts such drills at least twice a year.

"The kids are pretty well versed to go to this area," said Brad Speedy, vice principal.

"You just get used to it," said 15-year-old freshman Jacob Hodney.

The school's staff made sure 31 key doors were closed to form another barrier between any outdoor gases and the people inside.

An electronic board in an upstairs cubbyhole showed 31 lights - red for open doors and green for closed.

Head custodian Bob Kessie watched the board, using a walkie-talkie to tell staff members which doors needed to be closed. The boys locker room door was the last to flash from red to green.

The Hermiston High drill mostly went off without a hitch, as most students have done these drills since elementary and middle school.

"People are pretty laid back about it. It's just like an earthquake drill or fire drill," said senior Kyle Warren.

Sophomore Leah Walachi remembered the first time she went through a nerve gas drill in elementary school.

"In the fifth grade, I cried. I thought I was gonna die. ... Now I feel we're gonna be safe," Walachi said. She said she now knows gases will take a while to blow in from the depot, and she has faith in the emergency procedures.

Her friend, sophomore Tara Dreher, said some students have fun by trying to beat past tallied times to reach the gym, then sit among their homeroom classmates, get counted and later released.

Wednesday's time was 14 minutes, 31 seconds before students were sent back to class.

Actually, there is no officially required time for students to reach the gym other than as fast as possible. The tallied time in each drill is more for teachers to know how much of class time was taken up with the drill so they can adjust accordingly.

Now for the school's glitch: the tone alert radio.

No one knew why it didn't sound an alert. It will be checked out and corrected.

"They found a problem, which is the purpose of the exercise. ... It's a simple thing to fix," said Jesse Seigal, a Federal Emergency Management Agency public affairs officer working with the depot's Chemical Stockpile Emergency Preparedness Program, which coordinates local emergency responses to nerve gas releases.

If the emergency had been real, a backup system of outdoor sirens would warn school officials something was wrong. The tone alert radio glitch did not affect Hermiston High's drill.

On Wednesday, school officials knew a drill would occur, but they didn't know when. The overall exercise's alarm went out at 10:36 a.m. But Hermiston High officials fretted about how a late morning drill would affect lunch periods, rippling into class times. So they got permission to start the school's drill at 10:30 a.m., not knowing the official exercise would start a few minutes later.

Similar scenes of going to over-pressurized rooms or evacuating to buses played out at all schools in western Umatilla County, northeastern Morrow County and at Paterson Elementary School in Benton County.

Emergency centers were activated in Pendleton, Hermiston, Boardman and Heppner, each with specific roles. Red Cross shelters were set up in Pendleton, The Dalles and Kennewick. Law enforcement officers, firefighters, ambulance crews and five Oregon and Washington hospitals went through their own drills.

One such drill took place outside of Hermiston's community center where Hermiston and Umatilla firefighters operated a decontamination station.

Five Umatilla High School students showed up, portraying five men with gas-related symptoms, including one who could not walk.

This was the second time for two kids volunteering to be victims, and all five had a good idea of what to expect.

Consequently, they wore swimsuits beneath their clothes.

Decontamination consists mainly of stripping down, scrubbing and showering. Four went through regular showers in a decontamination van, while the girl playing the man who couldn't walk ended up on a backboard and was sent through a scrubbing assembly line on conveyor rollers.

Besides not walking, Brianne Bieren, 14, portrayed a 20-year-old man who wheezed, had a headache and contracted pupils.

Firefighters and paramedics in full protective gear with hoods and gas mask rolled her through a tent to clean her with scrub brushes.

"It was weird," Brianne said.

After showering, the four other victims were put in white coveralls and checked by emergency medical technicians.

Two received simulated injections from a Mark 1 pack, one shot each of atropine and 2-Pam-chloride, which are antidotes for nerve gas exposure. Blue and red bands were tied around their wrists to keep track of what was done to whom before all five went on simulated ambulance rides.

"It was pretty interesting to see how (the decontamination people) worked together. If this happened for real, it'd probably be scary,' said Frank Ehrmantraut, 15.

Umatilla emergency medical technician Vicki Zachariasen said: "It's something we think about - it happening for real. That's the main reason why we go through the training and drills."