A thick fog muffled the warning siren, but it was loud enough. By the time Carnation Elementary Principal Doug Poage was done announcing that the Tolt Dam breach evacuation drill was in progress Wednesday morning, students and teachers were filing down the sidewalk toward the class checkpoint.

“New students, over here!” one teacher announced. A few children, mostly Kindergartners, clustered around her looking excited, while most, veterans of the drill, were cleared after a quick headcount by their teachers to do their part of the evacuation.

“This is actually a partial drill this year,” explained Poage.

Every other year, both Carnation Elementary School and Tolt Middle School complete a full evacuation of the school buildings, in preparation for a possible breach of the South Fork Tolt Dam above and east of Carnation. Teachers and staff march with students more than a mile, along the Snoqualmie Valley Trail then up Entwistle to the Tolt Highlands Road and the emergency evacuation site for the city of Carnation. In alternate years, only students new to the school such as Kindergartners at Carnation Elementary, and sixth graders at Tolt, complete the full evacuation.

The rest, like Christie Isler’s class, make a circuit of a couple of city blocks then, celebrating their survival for another year, head back to class within about 20 minutes.

They treat it like fun, but PE teacher Allison Hoover, the checkpoint commander for the drill, said students do take it seriously. “They know what it’s about,” she added.

If the dam were to fail and the 18 billion-gallon Tolt Reservoir overflowed, safety consultants estimate it would take about 48 minutes for the first of the water to reach the city of Carnation, and another 30 minutes, 78 total, to peak at more than 12 feet deep within the city. Flooding from a dam breach is projected to reach as far west as Everett, and as far east as Snoqualmie Falls. Seattle Public Utilities, which owns and operates the reservoir, maintains an elaborate early-warning system at the reservoir, and tests it every Wednesday in Carnation with a siren and pre-recorded announcement. The system should give residents about an hour’s notice to evacuate.

The last students to leave the school, a group of 29 Kindergartners and first-graders, made use of their hour by playing games, picking flowers, and observing everything.

“Raise your hand if you see leaves on the ground!” said one teacher.

“This looks just like my neighborhood,” a little boy announced.

“Look! A spider web for Halloween!” said another.

One thing 6 year-old Joshua Ward didn’t see on his walk was his Mom, Christie Dick, but she was there at the end of the trail, waiting to congratulate her first-grader for completing his first drill after three weeks at his new school.

“I looked everywhere for you!” she said. Joshua didn’t get a chance to say much because he arrived just in time to catch the bus back to school, but Dick expected she’d hear all about it when he got home from school.

“He was really excited about it this morning,” she said.

Her family just moved to the area from Idaho, and although she was used to warning sirens in her hometown, she said the first couple of times she heard the Tolt Dam siren, she was ready to jump in the car with the kids and drive to safety.

“I’m kind of glad that do this,” she said. “I think it’s a great idea that they do.”