Since a thoroughly dependable parachute oxygen apparatus is not yet generally available, experimental tests were made to determine from what altitudes a rescue with open parachute without oxygen is possible. Therefore, sinking experiments were carried out in which the mask was taken off after ascent with O2 (for speed of ascent of the chamber see fig. 1), and, after a waiting period of 10 seconds the sinking was begun.
In the experiment no altitude sickness occurred at 9 km. [29,500 ft.] as was expected.
In the sinking experiments, from 10 km. [32,800 ft.] altitude, typical altitude sickness occurred after about 2 minutes, i. e., at an altitude of about 8.6 km. [28,200 ft.], which was indicated by a very pronounced scrawling in the writing test. However, no loss of consciousness occurred. (Kloos’ writing test.)
[page 7 of original]
The experiments from 12 to 15 km. altitude were made partly during suspension in a parachute harness, partly in a sitting position, and partly in a prone position. These experiments show that the body attitude has a very essential influence on the tolerance for a high degree of lack of oxygen. Since, besides this, every bodily exertion is of great importance, in one portion of the experiments six knee bends were made by the subject during the waiting period before beginning the descent. These six knee bends consisted of three knee bends while breathing oxygen followed by deep inhaling and holding of the breath, and then three more knee bends without oxygen breathing. This procedure was chosen in order not to neglect the bodily work involved in an actual parachute jump. The descending experiments from 12 km. [39,400 ft.] altitude yielded the following average times:
Table 1
| Descending experiment | Unconsciousness | Recovery of consciousness |
| from 12 km. [39,400 ft.] | after— | after— |
| Sitting without knee bends | 1′39″ = 10.85 km. | 6′38″ = 7.45 km. |
| [35,600 ft.]. | [24,440 ft.]. | |
| Sitting after 6 knee bends | 55″ = 11.4 km. | 6′55″ = 7.25 km. |
| [37,400 ft.]. | [23,786 ft.]. | |
| Suspended in parachute harness | 37″ = 11.65 km. | 7′40″ = 6.77 km. |
| [38,220 ft.]. | [22,212 ft.]. | |
It is to be noted in connection with the stated time and altitude values that the beginning of unconsciousness, or of the recovery, was calculated from the withdrawal of oxygen, while in most experiments the sinking or free fall was begun at the expiration of the 10-second waiting period. Since in addition to this the stages of altitude were read off at the moment of unconsciousness, small variations from the times given in figs. 2 and 3 [not reproduced] are possible
[page 8 of original]
since, especially in the falling experiments, variations occurred because of the somewhat crude valve control. These variations, however, are small and may be overlooked since in any case the fall and sinking time under practical conditions are dependent on the flying attitude at the moment of the leap from the catapult seat. In addition to this, the calculated fall and sinking time are influenced to a high degree under actual conditions by weight and air resistance.