Looks medium rare to me.
A few thoughts here.
It is a concrete basement, so like as not, the fire wouldn’t have gotten to Steve on the stairs directly, particularly if the floor is sloped to a drain (which does not show). Heat, fumes, and lack of oxygen would be the real killers. Actual burns would have come from the backdraft that knocked Ace back. Steve being a cotton shirt and black denim guy at least didn’t get his clothes cooked into his skin. Ace is similarly lucky, but those rubber flip flops are an issue.
The floor above is wooden. Even if Steve didn’t manage to splash fuel up that high, flames could have reached it in the first few minutes. If not, then the backdraft would easily have caught it.
What Ace is doing is really dangerous. Rocky’s not 100% right about there being no air, but he is in an oxygen deprived environment. He can function for a few minutes, but passing out is a possibility.
Steve is dead. If he’s not beyond resuscitation, he’s in for a world of suffering.