Your're giving it too much air. Sometimes I struggle to get hedge to burn just because I don't give it enough air. Just a little too much, and I get thermal runaway where the hotter it burns, the stronger the draft, and the dense coals radiate a lot of heat.
With the air leaks my stove has, I adjust how I setup the fire, and keep a bottle of water handy (an old alcohol or peroxide bottle to squirt it from) to cool the coals if it gets too hot. It's near impossible to put a "fire" out completely even with a half gallon or so of water, though that will knock it down to hardly a smolder for 5min.