AZUSA, Calif. (KABC) -- An explosion in a residential area in Azusa triggered an evacuation of nearby homes and prompted a lockdown of Longfellow and Hodge elementary schools.The incident happened at 8:37 a.m. Monday in the back yard of a house in the 1000 block of N. Sunset. The explosion seriously injured a 37-year-old man, according to Azusa police. A bomb squad and fire hazmat team responded to the scene.Police evacuated residents in the area and assisted in the evacuation of the Longfellow Elementary School. All students from Longfellow were taken to Mountain View Elementary School, according to police, who urged parents not to attempt to pick up children during the evacuation process.Hodge Elementary was locked down but not evacuated, police said. Students were released at the district's discretion.The investigation into the explosion continues. Authorities located chemicals on the property that were flammable, but it was not yet determined what role the chemicals had in the explosion.