yeh the methane gas firing off over the coal fire, when you open the door, will get your attention quick, be careful. Many of the modern hand fired stoves have built in top window vents, that are fixed and nonadjustable, to constantly vent the top of the fire, and burn off the methane gas by hitting it with fresh air.
if the stove is loaded up and the ash door left wide open to get it cranking, there's a huge gas buildup inside any coal stove over the fire, and if the top door is left closed, the resulting puff and pop will be somewhat dramatic- sometimes it will puff back some smoke into the room through any open vents.
you'd want to avoid that situation
if the ash door is wide open, it's best to crack the top door, so it lights off the methane gradually- I open the top door, then close the ash door, then gradually close the top door and just before it gets fully shut, within an inch or so of the stove, the methane will slowly light off in a mild way, then I close the top door, and the methane just burns slowly- instead of closing it all up and having a puffback or small explosion inside the stove
this is the stuff you learn as you go on burning coal- and every stove is a little different