As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING BALLOON INFLATION USING AN EXTERNAL FUEL TANK AND SHERWOOD VALVE CONNECTION, THE CHECK VALVE STUCK OPEN ALLOWING PROPANE TO ESCAPE AND IGNITE RESULTING IN BURNS TO THE PILOT'S FACE AND ARMS. ALSO, DAMAGE TO THE BALLOON ENVELOPE OCCURRED.