The combination of a building fire and scorching weather sent a firefighter to a Bethesda hospital early this morning, county fire officials said.

A passing motorist called at 3:50 a.m. to report smoke coming from the BECO office building at 11140 Rockville Pike, said Montgomery County Fire and Rescue Service spokesman Capt. Oscar Garcia. Firefighters arrived to find a fire on the first floor of the four-story building, he said.

Due to the early hour, no employees were in the building, Garcia said.

One firefighter was hospitalized due to the high temperature and work required to combat the flames, he said.

“It was a labor intensive fire; they had to do a lot to get to the fire and extinguish it,” Garcia said. “At that time in the morning it was still 80 degrees outside.”

Officials expect the firefighter to be released from the hospital today, after being treated for minor heat-related injuries, Garcia said.

Additional units were called in just before 4 a.m. to allow firefighters to rotate out and rehydrate in an air-conditioned bus, Garcia said. Rehabilitation centers are set up at fire scenes in hot weather or when a fire could take longer than normal to extinguish.

“Firefighters have to report to a rehab center where medical personnel take their pulse, ensure their blood pressure is within normal limits, and they also hydrate in some cases,” Garcia said. “If it’s a long incident, they have food for them so they can be rotated and go back to work when their vital signs return to normal.”

Supervisors give firefighters email and verbal reminders about the importance of hydrating before and during work hours in hot weather, Garcia said.

The National Weather Service expects temperatures exceeding 100 degrees over the next three days and the fire service is taking such conditions into account, he said.

“We always err on the side of caution. Coming to work and starting to hydrate is too late.”

Firefighters extinguished most of the blaze within 15 to 20 minutes, largely limiting damage to the first floor but shutting down power to much of the rest of the building, Garcia said. Officials believe the fire was accidental. Damage is estimated at about $500,000.

Rockville Pike was shut down between Security Lane and Edson Lane during the fire, but was reopened by 7 a.m., Garcia said.