growing up in Czechoslovakia in the 60s we put burning candles and sparklers on our Christmas trees.
(the sparklers only lasted a while, but we’d leave the candles on for hours).
There were probably a few fires here and there but I don’t recall that it was a major problem.
Though I don’t think they use candles now.
The total power peaks at around 6 megawatts, and the radiant flux inside the test compartment reaches 150-180 kW per square meter; enough for a tactical laser target ballpark, but over way larger total area.