WESTMINSTER, Colo. (AP) -- A 16-year-old boy set himself on fire at a suburban Denver high school on Monday in an apparent suicide attempt that left him critically injured, authorities said. The boy didn't make any threats before starting the fire in the cafeteria at Standley Lake High School at about 7:15 a.m., Westminster Police Department spokeswoman Cheri Spottke said. A custodian was able to use a fire extinguisher to put out the blaze before it could spread, Spottke said. Several other students were in the cafeteria at the time, but none were injured. Investigators went through the school with bomb detection dogs as a precaution, and no devices were discovered, Spottke said. Investigators are also talking to students, faculty members and family members to find out what happened, she said. "We don't have any indication that there's any threat against the high school. We do believe that this is a suicide attempt," she said. Spottke didn't know how the student set the fire, which caused extensive smoke in the building. The school was closed for the day and students were sent home, Jefferson County Public Schools spokeswoman Lynn Setzer said. Students without cars were taken by buses to a local middle school, where they were picked up by their parents. No classes will be held at the school on Tuesday either but the district will provide counseling to students there in the morning. Monday's incident was the latest to affect a Denver-area school in recent weeks. On Thursday, Columbine High School, where two gunmen killed 13 people in 1999, went on high security alert after receiving a series of threatening phone calls. The alert applied to a half-dozen other schools in the area, in the same school district as Standley Lake, but was lifted the same day. On Dec. 13, student gunman Karl Pierson, 17, fatally shot Claire Davis, a 17-year-old classmate at Arapahoe High School in Centennial before killing himself in the school's library. Pierson reportedly had threatened a teacher and librarian who had disciplined him last year and allegedly was seeking that teacher when he entered the school, investigators have said. Colorado state lawmakers are considering a bill to spend about $250,000 to continue a hotline students and teachers can use to report threats and bullying anonymously. State officials say the hotline has prevented more than two dozen school attacks since its creation in 2004. Westminster was home to 10-year-old Jessica Ridgeway, who was abducted on her way to school and killed in 2012. Austin Sigg, who was 17 at the time of the crime, was sentenced to a life sentence plus 86 years. Jessica's disappearance put Westminster and neighboring Denver suburbs on edge as police, aided by an army of volunteers, searched for her and then her killer.