Groton — Wal-Mart was evacuated and was temporarily closed Wednesday evening following reports of the smell of gas inundating the store and surrounding area, fire officials said.

The Poquonnock Bridge and Groton City fire departments responded to the store at 150 Gold Star Highway at 7:12 p.m. After using a ladder truck to access the propane heating units on the roof of the building and check for gas leaks, firefighters determined the store had run out of propane.

Heating units start misfiring when they run out of propane and emit the classic rotten egg smell of the chemical additive mercaptan, officials said. The chemical is added to propane, which is odorless, to make it easier to detect.

Fire officials said tests taken in the store detected no propane. Firefighters remained at the scene at 8 p.m. and said propane had been shut off and there would be no heat to the building until the propane was refilled.

A Wal-Mart representative said the store was back open as of 8:30 p.m.