The explosion was reported about 12:50 p.m., Monroe Assistant Fire Chief Steve Guptill said. It apparently started after a problem lighting a gas stove, he said.
Another employee was treated at the scene.
The injuries did not appear life-threatening.
The explosion occurred at the booth for a Monroe stove business, said Bronlea Mishler, a Snohomish County spokeswoman. The store owner's injuries appeared to have been caused by flying glass when the front of the stove blew out.
A woman working at the booth also was injured, Mishler said. No fair patrons were hurt.
"The aid staff who were at the fair responded almost immediately," Mishler said. "While this is something we don't want to see happen, we're very pleased with the response of everyone at the fair."
The Snohomish County Fire Marshal's Office is investigating.
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