A patient working at an ice plant was trapped in a room filled with sulfur dioxide. On arrival, you donned a self-contained breathing apparatus and entered the room, finding the patient unresponsive on the floor. The room remains filled with the gas. Your immediate priority in caring for this patient is to:

A) assess the airway, breathing, and circulation.
B) loosen all tight-fitting clothing.
C) start positive pressure ventilation.
D) remove him from the immediate environment.

D