A small explosion in a state environmental lab Tuesday forced the temporary evacuation of a building that houses the Department of Public Health and Human Services, and has prompted the agency to review its procedures. Officials said the explosion in an "oven type" device at about 9:45 a.m. prompted an evacuation for about an hour. One worker was taken to the hospital and treated for minor injuries after the event, which took place on the second floor of the Cogswell Building. The worker was tossed against a wall by the explosion, officials said. The Helena Fire Department was investigating the incident, trying to determine a cause. Officials said no chemicals were ever released from the lab, and the explosion did not threaten any other workers. DPHHS said its laboratory testing procedures will be reviewed. "At this point, our number one concern is for the safety of our employees," DPHHS director Anna Whiting Sorrell said. "We're going to work very hard to ensure something like this doesn't happen again." The explosion occurred when an employee was undertaking a routine water quality test using samples mixed with methanol. Glass containers with the samples were placed in the drying oven that then exploded. The employee was following prescribed methods, which will now be reviewed. Damage was estimated at about $2,000.