Portable prebreathing system was developed which recirculates and reconditions respiratorily exhaled oxygen. Apparatus reduces fire hazards, simplifies prebreathing procedures, and does not require extensive enclosure venting system usage

Jaax, J. R.

Mills, G. P.

English

NASA Technical Reports Server

December 1972 B72-10690 
NASA TECH BRIEF 
Manned Spacecraft Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
An Efficient Prebreathing Apparatus for Humans During Decompression 
.
The problem: 
Humans subjected to decompression require pre-
breathing of oxygen. Oxygen, in this case, reduces 
dissolved inert gases in the human body to a level that 
exists under normal atmospheric pressure and thus elimi-
nates the risk of decompression sickness (dysbarism). In 
enclosed environments, the existing systems used for such 
prebreathing release all of the oxygen that is not metabo-
lically consumed into the enclosure and thus increase fire 
hazards. Also, they increase the total atmospheric pressure 
within the enclosure which requires undesirable cycling of 
enclosure pressure relief valves to the outside.
The solution: 
A portable prebreathing system was developed which 
recirculates and reconditions the respiratorily exhaled 
oxygen. It reduces fire hazards, simplifies prebreathing 
procedures, and does not require any extensive usage of 
enclosure venting systems. 
How it's done: 
In application of the prebreathing apparatus, shown in 
the figure, the user connects the two hoses of the 
mask/hose assembly to the prebreathing assembly and 
dons the face mask. The prebreathing assembly is acti-
vated by opening the adjustable bleed valve in conjunction 
Suit
Oxygen Flow 
	
_quit	
Sensor	
1 
	
Disconnect	
Ventilator -	 - -	 - - -
	
j 
I	 Ii 
Face Mask 
Disconnects
Relief Valve 
Adjustable 
Bleed Valve IF 
Heat Rejector 
•'•4 
Control Assembly
Oxygen 
Bottle 
Secondary I 
Power Supply I 
so
ill-- ILrD
J 
pp 
Electrical 
Control
Adjustable 
Bleed Orifice 
Secondary Oxygen 
Supply Disconnect 
Pressure Transducer 
Fill Connector 
Power Supply 
Receptacle 
Pressure 
Regulator 
Check 
Valves 
.
• 
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19720000689 2020-03-17T03:43:40+00:00Z
with the adjustable bleed orifice and opening the primary 
oxygen supply shutoff valve. Initially, the assembly is set 
at the high purge rate, approximately 2.73 kg/hr (6.0 
lb/hr), for a predetermined time (approximately two 
minutes) then the adjustable valves are reset to the 
nominal oxygen bleed rate of 0.045 5 to 0.091 kg/hr (0.1 
to 0.2 lb/hr). The makeup oxygen being supplied from the 
high pressure storage bottle is mixed with the recon-
ditioned respiratory gas prior to going to the mask. 
The gas expired by the user re-enters the prebreathing 
assembly where carbon dioxide, water vapor, odors, and 
trace contaminants are removed by a replaceable chemical 
bed containing lithium hydroxide, silica gel, and charcoal, 
respectively. The reconditioned oxygen is then recir-
culated back to the user. The bleed/purge capability is 
provided to reduce the nitrogen content of the recircu-
lated gas. In addition to the nitrogen, a small amount of 
the oxygen, water vapor, carbon dioxide, and trace 
contaminants are vented to the surrounding environment. 
The heat of reaction from the chemical bed is rejected to 
the surrounding environment by either radiation or forced 
convection. A pressure regulator in the prebreathing 
apparatus maintains the oxygen face mask at a pressure 
slightly above ambient pressure. A pressure relief valve is 
provided in case pressure exceeds expected values.
Notes: 
1. In addition to the described function, the system can 
ventilate space suits. Approximately 17 m 3 /hr (10 
cfm) are provided by the fan. 
2. This system can be used as a compact oxygen 
respirator, which provides extended capability. 
3. Requests for further information may be directed to: 
Technology Utilization Officer 
Manned Spacecraft Center 
Code JM7 
Houston, Texas 77058 
Reference: TSP72.10690 
Patent status: 
NASA has decided not to apply for a patent. 
Source: J. R. Jaax 
Manned Spacecraft Center and 
G. P. Mills of 
United Aircraft Corp. 
under contract to 
Manned Spacecraft Center 
(MSC-14151)
I 
B72-10690	 Category 05


An efficient prebreathing apparatus for humans during decompression

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