We hear a loud pop and a puff or white “smoke” rises out of the back corner of the boat.   We were at the time under a shade tree 30 ft away.    Seems the daytime high of 99F degrees with a bright sun was just too much for the boat air horn.  You know the kind used as an annoyance at stadiums.  It blew sinkers all over the boat but other than the container which contained the propellant nothing else was damaged.  Upon further inspection the can says maximum temp is 120F, opps!