PLT OF AN LTT SEL FIRE DEPRESSOR ACFT TOOK OFF ON AN UNCTLED ARPT RWY WHEN A LNDG ACFT HAD NOT YET EXITED THE RWY.

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I HAD BEEN DISPATCHED TO A WILD FIRE ABOUT 5 MI W OF THE BOULDER; CO; ARPT AND ANNOUNCED ON CTAF THAT I WAS TAXIING TO RWY 26 FOR TKOF AND THAT I WAS GOING TO A FIRE. A PLANE ON DOWNWIND AT THAT TIME ANNOUNCED 'DOWNWIND WITH INTENT TO LAND BOULDER.' I REPEATED MY ANNOUNCEMENT AND THAT THERE WAS A FIRE; THINKING THAT HE MIGHT EXTEND AND ALLOW ME TO GO. HE ANNOUNCED TURNING BASE AND I HELD SHORT OF THE RWY AS I DIDN'T THINK I HAD TIME TO GO. THE PLANE ( A CUB) LANDED AND ROLLED BY 2 TURNOFFS AND PROCEEDED TO TAXI THE FULL LENGTH OF THE RWY AND EXITED THE RWY AT THE FAR END. AFTER HE WAS DOWN I ANNOUNCED 'POS AND HOLD' ON RWY 27 AND EXPECTED HIM TO TURN OFF. I PROBABLY LET THE SIGHT OF THE SMOKE FROM THE FIRE AND MY IMPATIENCE WITH THE PLANE'S CONTINUED PRESENCE ON THE RWY (WHICH I NOW THINK WAS DELIBERATE) CAUSE ME TO START MY TKOF ROLL BEFORE THE OTHER ACFT WAS CLR OF THE RWY. I ANNOUNCED 'ROLLING ON 26' AND STARTED. AS I ROLLED AND HE CONTINUED TO STAY ON THE RWY IT OCCURRED TO ME THAT HE MIGHT HAVE STALLED. I ALWAYS HAVE THE DUMP DOORS ARMED ON TKOF AND I WAS PREPARED TO DUMP THE ENTIRE 800 GALLONS OF WATER IF HE DIDN'T CLR. HE FINALLY TURNED OFF WHEN I WAS ABOUT 600 FT FROM HIM. I CONTINUED MY TKOF AND WENT TO THE FIRE. AT NO TIME DO I FEEL THERE WAS A HAZARDOUS SIT IN THAT BY DUMPING (PURE WATER) I COULD HAVE CLRED THE END OF THE RWY BY 100'S OF FT. I AM SURE THAT MY PLANE WAS A SHOCK TO HIM AS I WENT BY AND I DO REGRET THE INCIDENT. I SIMPLY WILL NOT PERMIT IT TO HAPPEN AGAIN.