An explosion of an apparent drug lab injured three people and damaged a San Diego motel Wednesday, police said. Investigators suspected guests at the Heritage Inn in the city's Midway district were cooking a batch of methamphetamine or some other illicit drug in a second-floor room when the blast occurred late Wednesday morning, police said. The explosion blew out a wall, sent window glass flying and sparked a fire that spread to the third story and the roof of the motel, firefighters told KNSD-TV, San Diego. Witnesses said one victim was burned from head to foot. All three of the injured were transported by ambulance to hospitals. The motel is located approximately 1 mile from Sea World.