Photo by NASHUA FIRE RESCUE Crews work at the scene of the apartment fire that displaced about 50 residents of the Laton House in Railroad Square late Wednesday night. The fire was contained by the sprinkler system, but the water flowed to the first floor, forcing the evacuations. (Photo by NASHUA FIRE RESCUE)

NASHUA – Several firefighters were tended to for heat-related conditions but no other firefighter or civilian injuries were reported in Wednesday afternoon’s 3-alarm blaze that left a Concord Street apartment building uninhabitable, officials said.

The cause of the fire, which was initially reported shortly before 3 p.m. at 53 Concord St., remains under investigation, but officials believe it was accidental and is not considered suspicious.

Meanwhile, an estimated 50 residents of the Laton House, 28 Railroad Square, had to be transported to temporary quarters at local motels after a fire in a fourth-floor apartment activated the building’s sprinkler system and forced authorities to shut down the water and electrical service.

Nashua Fire Rescue deputy chief Glen MacDonald said that the building’s smoke detectors and sprinkler system were triggered by the fire, which alerted residents and set off the sprinkler head in the apartment.

Although the sprinkler succeeded in confining the fire to the room where it started, it also caused water to flow from the fourth floor down to the first floor, which MacDonald said resulted in “significant damage” to the building.

Telegraph photo by DEAN SHALHOUP A police officer stands with a woman and three children who are believed to be residents of 53 Concord St. as they watch firefighters battle the 3-alarm blaze that heavily damaged the multi unit building. (Telegraph photo by DEAN SHALHOUP)

Representatives of the city Emergency Management department coordinated the evacuations, MacDonald said, using a Nashua Transit bus to transport the evacuees to their temporary quarters.

When the residents may be able to return isn’t yet known.

As for the Concord Street fire, initial indications were that one or more people were still in the building when firefighters arrived, their subsequent search of the structure confirmed everyone who was home at the time had evacuated safely.

It also appears the occupants who have pets were able to rescue them as well. As firefighters worked, some of the occupants stood in the shade of a large tree in front of the house next door.

Officials said representatives of the local American Red Cross chapter responded to the scene to assist eight people who were displaced by the fire.

Telegraph photo by DEAN SHALHOUP As flames roll out of a top floor window, smoke becomes visible at the other end of the large apartment building heavily damaged by a 3-alarm fire this afternoon.No injuries were reported but several people were forced to seek temporary housing. (Telegraph photo by DEAN SHALHOUP)

MacDonald said the crew of Engine 1, led by Lt. Andy Martineau, was first on the scene and reported heavy fire in the attic of the two-and-a-half-story building and heavy smoke conditions.

Due to the age and size of the building, which was built around 1900 and currently has three apartments, as well as the hot weather conditions, MacDonald said scene commanders struck a second alarm, followed by a third alarm a short time later.

That brought all on duty Nashua firefighters to the scene, along with crews from Merrimack and Hollis. Crews from several area towns, including Hudson, Manchester, Londonderry, and Tyngsborough and Chelmsford Massachusetts, covered four of Nashua’s six stations during the fire.

Along with the cause of the fire, the point of origin also remains under investigation, MacDonald said. He said the building is equipped with working smoke detectors.

Also in response were crews from AMR ambulance, who assisted firefighters by evaluating their conditions as they rotated in and out of the building.

Telegraph photo by DEAN SHALHOUP Heavy smoke envelopes the area around 53 Concord St. this afternoon as firefighters, barely visible in the background, set ladders on the roof to get at the flames. The blaze, which broke out just before 3 p.m., heavily damaged the two and a half story apartment building. (Telegraph photo by DEAN SHALHOUP)

A representative of the city Building Department was sent to the scene to evaluate the condition of the building for the safety of the investigators who worked inside once the blaze was extinguished.

A tent shelter was set up to provide shade and serve as a watering station for crews.

The house is on the east side of Concord Street between Rogers and Courtland streets.

City property tax records show that it is owned by a couple from Park City, Utah.

Dean Shalhoup may be reached at 594-1256 or dshalhoup@nashuatelegraph.com.

Photo by JEFFREY HASTINGS An AMR paramedic cools down a firefighter using cold packs and a large fan at the scene of Wednesday's 3-alarm fire on Concord Street. (Photo by JEFFREY HASTINGS)

Photo by JEFFREY HASTINGS AMR personnel assist a firefighter as he recovers from the extreme heat crews faced in battling Wednesday's 3-alarm fire on Concord Street. (Photo by JEFFREY HASTINGS)

Telegraph photo by DEAN SHALHOUP Nashua firefighter Ron Koser makes his way up a ladder to prepare to fight the heavy fire blowing through the roof of the Concord Street apartment house that went up in flames this afternoon. (Telegraph photo by DEAN SHALHOUP)