A second-alarm fire at a Franklin apartment building displaced two residents and two cats.

The Riverside Housing apartment building on Lancaster Street is still structurally sound, but the main living area where the fire occurred is uninhabitable, said Franklin fire Chief Kevin LaChapelle.

He added that the resident whose apartment burned as well as another in an adjacent apartment likely won’t be able to return to their homes for a while due to the fire damage.

Those two residents were transported to Franklin Regional Hospital, one for smoke inhalation and the other for minor burns. One of the residents lived in an apartment adjacent to the one where the fire was located.

Two cats in the apartment building also survived – one was rescued by her owner while the other managed to hide during the fire and was rescued by fire crews after the blaze was extinguished, LaChapelle said.

LaChapelle said the cause of the fire is still under investigation by the Franklin Fire Department and the New Hampshire Fire Marshal’s Office.

The call initially came in as a fire alarm activation; while on their way to the scene, Franklin firefighters noticed there was black smoke coming out of the apartment doors and requested a second alarm.

Firefighters were on scene for about an hour battling the blaze, LaChapelle said.

He added his fire crews were able to respond so quickly because the building had working smoke alarms, fire code sheet rock and a heat detector that tripped the building’s alarm.

The working components of the fire code “truly saved this building last night,” LaChapelle said. “There was no delay because of the municipal fire alarm system.”

In addition to the Franklin Fire Department, Franklin, Tilton-Northfield, Belmont, Andover and New Hampton ambulance crews assisted on scene.

(Ella Nilsen can be reached at 369-3322, enilsen@cmonitor.com or on Twitter @ella_nilsen.)