Will Giddings is an employee of Duncan Enterprises and seems to be architect Doug Roberts' assistant. The two of them are going through the building, looking for more evidence of Roger Simmons' cost-cutting, safety-compromising measures when they arrive on the 81st floor to discover that Doug's worst fears have been realized; a fire has broken out in a utility room.
For the moment it is contained to the room since the door is closed, but one of the security guards, seeing the smoke coming out from under the door, rather foolishly goes over and tries to open it. I guess he never saw the film Backdraft.
Will, though, knows what happens when you open a door on a fire. He charges over just as the guard opens the door, shoving him out of the way, but the door has opened enough to let oxygen in, and the flames explode the door outwards and engulf poor Will.
Despite Doug and the security guard using some drapes to smother the flames on Will's body, he suffers some pretty nasty third-degree burns. Some time later, we learn that he succumbed to these and dies at the hospital.
Although Will is a very minor character in the overall story of the film, his death scene is fairly memorable since he dies in a noble, and successful, display of self-sacrifice.
The guard he saved had better thank his lucky stars and show his gratitude by attending the wake.