Answer:
A non-rebreather mask aka a trauma mask that delivers a maximum inspired FiO2 of 85%. It is essentially a normal Hudson mask with a reservoir bag attached to which oxygen is piped in at a rate of over 10L/min. The mask is essential as even at rest, peak inspiratory flow rate may reach 15L/min, which is the maximum rate at which most wall oxygen systems and certainly cylinders deliver at.
The point of a rebreather mask is to prevent rebreathing of expired gases via one way ports on the walls of the mask and to provide a reservoir of oxygen to prevent entrainment of air if inspiratory flow rates rise.