An 18-year-old Petaluma man was injured when a pipe bomb exploded in a portable toilet located near a baseball field in the city on the Fourth of July, according to police. At about 10:35 p.m., Officer Matthew Capitelli was flagged down at Lucchesi Park to assist with someone who had been injured. The victim had a severe injury to his back and was losing a large amount of blood, police said. Medical personnel arrived while Capitelli was assisting him and transported him to the hospital. The man said he was walking by the portable bathroom located near the park when he heard a loud bang and felt the injury to his back. The portable bathroom had evidence that a pipe bomb had been detonated inside, according to police. The shrapnel from the pipe bomb had blown through all the walls and the roof of the portable bathroom. A piece of shrapnel from the pipe bomb hit and injured the victim. The man is in stable condition and an investigation is ongoing, according to the police department.