What type of fire extinguisher poses a suffocation threat if used in a confined area?

A dry chemical fire extinguisher might be the best choice for confined spaces. The powder isn't particularly pleasant to breathe, but could be fairly well filtered through a hankie or bandanna across the nose. The carbon dioxide (CO2) extinguisher might displace the air (and the oxygen) in the space and render the would-be firefighter unconscious. The results may be fatal. In any case, attempting to suppress a fire in a confined space is something that should be approached with great care by anyone who is not trained or equipped (clothed, including breathing apparatus) to do the job safely.