Identify the item of equipment depicted below.
Outline the principles of operation of this item.
Reservoir oxygen mask / non-rebreather or partial rebreather oxygen mask
That image comes from www.acesurgical.com; no permission whatsoever has been granted for its use, and it remains in place only until somebody complains.
Anyway. The basics:
Garcia, Juan A., et al. "The oxygen concentrations delivered by different oxygen therapy systems." CHEST Journal 128.4_MeetingAbstracts (2005): 389S-b.
Abe, Yukiko, et al. "The efficacy of an oxygen mask with reservoir bag in patients with respiratory failure." The Tokai journal of experimental and clinical medicine 35.4 (2010): 144-147.