Please help me ... locked door in the canteen

[RayMarden]

Working on setting the barrel aflame.

Spoiler below!

A flare won't work, but you could drag it over to that broken, sparking fusebox and try pulling its power switch.

And the doors will open in an emergency/alarm.

Spoiler below!

That room has some fairly distinct fire sprinklers/detectors. You could easily set them off by dragging a now-burning barrel under them....