On me…just got on the boat and headed to sea. Now first thing I usually have to do onboard. Is visit the head and reacquaint myself. Off going chief had closed all intakes on ventilation system to engine room and I didn’t know it. The HATCHES not just the fans. I always run them full blast when under way. I turned them on. Well after a little bit the pressure inside the tug has to equalize as engines are sucking air with no replacement air. Only opening into the tug is through the MSD system. Somebody opened the galley door into the engine room door. Tug vented through the toilet with me on it. I laugh now. I wasn’t then. Lesson learned…ALWAYS look at those intake covers