Burns because of sweaty shirt

Hey everyone, volunteer youth firefighter here.

We have a special training exercise planned in my Departement where we visit a special facility where they teach fire fighters how to handle actual house fires as we aren’t able to simulate something like that in a normal practice. As far as I understood there’s a concrete house with some metal doors that is set ablaze and then our mission is it to go inside and experience what it’s actually like in a real fire with the heat and all and then try and put out the fire.

Now I’m the Mail I’ve got they told us to also take spare shirts with us as it could be dangerous when we go inside a burning building while sweaty as it could cause burns.

My question is: does this really has a good possibility of happening? Or is it more like something thar happens very rarely. I mean what would you do in an actual fire where you can’t just leave and get another shirt every 20 minutes because it’s hot?