A three-hour power outage on Wednesday — the hottest day of the year — forced businesses to close, raised concerns among Islanders and threw Vashon’s two grocery stores into a frantic rush to keep food items from spoiling.

At Vashon Thriftway, where the generator was able to power the lights and cash registers but not the store’s huge refrigeration system, workers quickly loaded up shopping carts with frozen meats, ice cream and other vulnerable items to put into the store’s walk-in freezers.

“The coolers hold their temperature a lot longer,” said Melinda Tibeau, a Thriftway employee.

Meanwhile, with the temperature reaching 102, others bought bags of ice, grabbing them off of a large pallet that the store had sitting out next to its cash registers.

“Everyone’s desperate. I’m surprised they have any ice at all,” said Mike Calder, the just-retired jewelry teacher at Vashon High School. “It’s miserable at home.”

IGA, meanwhile, closed its doors, unable to operate at all, workers said.

“If necessary, we’ll be throwing a lot of food into the Dumpster tonight ,” one employee said.

The power outage, which started around 3 p.m. and was over by 6:15, affected 700 customers on Vashon, most of them near town and on the Island’s east side, Andy Wappler, a spokesman for Puget Sound Energy, said.

It was caused by an equipment failure at the substation off of Cemetery Road, he said. The breakdown likely occurred because of the heat, as well as a surge in power use by Islanders running fans and air conditioning units in an attempt to stay cool, he said.

“Certainly, this kind of heat puts a lot of stress on the system,” he said.

Meanwhile, Vashon Island Fire & Rescue was on heightened alert, said Chief Hank Lipe. With the temperature high and the humidity low, fires are of great concern, as are heat strokes and other medical emergencies, he said.

By 5 p.m. Wednesday, however, the department had received no heat-related emergency calls.

The fire department visited the Island’s adult day homes to make sure their elderly residents were hydrated and cared for, said firefighter Jason Everett. The fire department also held an afternoon hose-down at Ober Park, spraying kids with water from one of its firetrucks. Dozens of kids and parents turned out for the event.

But even with the activity at Ober Park, the town Wednesday afternoon was almost eerily quiet. Several businesses, from Café Luna to Vashon Island Music, had signs posted on their doors that they had closed due to the heat and lack of electricity.

Some were frustrated by the closures.

A woman walked up to the door of the Vashon Library, only to read a sign that said it was closed due to the heat.

“I can’t believe these people,” she said. “They close for everything.”

But Marianne McHugh, who showed up at the library to use the computer only to find it closed, was a bit more philosophical about the turn of events.

“It’s disappointing. But that’s the way it goes,” said McHugh, who had no power at her own home. “Hopefully, tomorrow it’ll be better.”