A fire that began around 10 p.m. Monday in the 100 block of Broadway damaged businesses across roughly half a block in Somerville, sending two firefighters to the hospital and leaving three storefronts slated for demolition. The firefighters were treated for electrical shock and released, Fire Chief Charles Breen said. No other injuries were reported. Fire crews from Somerville and neighboring communities battled the blaze overnight and remained at the scene Tuesday morning. The fire caused major damage to Damata Barbershop, Brazilian restaurant Rei da Picanha and a Santander Bank branch. Part of the roof and first floor collapsed. The building’s condition and the intensity of the fire made it too dangerous for crews to fight the flames from inside, Breen said, so firefighters attacked from outside. Breen said officials believe the fire may have started in the basement, but the cause has not been determined. He described the building as old, with multiple renovations and concealed spaces that complicated firefighting. Burning roofing materials also produced especially harsh smoke, he said. Luis Morales Jr., a co-owner of the commercial strip, said many of the businesses were likely total losses. He said about 95% of the businesses in the building were minority-owned. The fire also affected a nearby meat market toward Wisconsin Avenue, where water flooded the basement and ruined an estimated $50,000 in merchandise. The full extent of cleanup and how long surviving businesses may be unable to operate were not yet clear. Broadway westbound remained closed between Illinois Avenue and Wisconsin Avenue for demolition work. Eversource shut off power at the scene. The fire chief called the overnight response a difficult fight and said crews were fortunate the blaze did not destroy the entire business block. A Somerville resident said there was widespread alarm, but expressed relief that nearby homes were not involved.