MEXICO, Maine — Five people were evaluated for exposure to dry chemicals Friday morning after a fire-suppressant system malfunctioned at the Mexico Food Trend/Circle K Shell station.

Nozzles over the pumps in the fuel-station canopy blasted out a huge cloud at 10:15 a.m. that enveloped people and vehicles with ANSUL PLUS-FIFTY C, fire and Med-Care Ambulance officials said.

It is a sodium bicarbonate-based dry chemical agent with chemical additives that can cause skin and eye irritation, said Chris Moretto, Med-Care assistant chief. But none of the people exposed had any symptoms, he said.

“There was no fire or anything that set it off,” Mexico fire Chief Gary Wentzell said. “I guess it was just a malfunction.”

The store manager declined to comment.

A Ford Ranger pickup, a Dodge Grand Caravan Sport minivan and a Dodge Neon were blanketed in white powder.

Other vehicles parked at the convenience store or nearby had powder on and inside them. The powder also covered a large area under the station canopy and the eastbound lane of U.S. Route 2 beside the station.

For people caught in the cloud, it was a frightening experience, initially touching off fears that fuel was on fire or that the suppressant powder was toxic. They described it as smoke.

Silas Sherry of Andover, who had just swiped his credit card at the pump and was about to fuel up his minivan, said he thought there was a fire.

“I thought the thing was going to blow,” Sherry said.

“I put my card in, I took my card out, I got the gas hose, and then it dumped on us, and I ran and left the gas hose down,” he said. “There was an enormous cloud of smoke that must have been 50 feet in diameter. I’ve never seen anything like that in my life.”

One woman, who didn’t want to be identified, said she stopped for fuel and to put air in her tires.

“The smoke just rained down, and then you couldn’t see anything,” she said. “The smoke came everywhere. You had to get out of it, because it was hard to breathe.”

Wentzell said it wasn’t a big deal, “but a couple of people were very upset when we first got here, which is understandable.”

One person has asthma and breathed in some powder, and he worried that the chemicals might cause an asthma attack, the chief said.

Firefighters shut down the station to incoming vehicles and cordoned it off until a cleaning crew could arrive. No gas could be pumped until the fire-suppressant system was recharged, Wentzell said.

To help allay fears of toxic-chemical exposure, Med-Care had specification sheets faxed in from ANSUL Inc. on the suppressant, and showed them to people caught in the powder dump.

Firefighters dusted off people and vehicles, then drove the vehicles to the local car wash to clean and return them. Sherry was taken to the fire station to shower.

A Mexico firefighter gave the family with children a ride to their cleaned car in a fire truck to help calm them down.