A "turtle shell," or chest cuirass, is used by people who have difficulty breathing on their own, especially polio survivors. The shell is strapped to a person's chest, and a hose that fits on the opening attaches to a small ventilator that sucks air from the shell. This causes the chest to rise, and air enters the nose. The shell allows the individual to sit up and do many things not possible when lying in an iron lung. It is much smaller than an iron lung and frees the person's arms and head to allow more activity. Drinker and Collins, designers of the first commercial iron lung, designed the turtle shell in 1939.