NASA Photo ID: STS046-33-028       File Name: 10064840.jpg
  Film Type: 35mm                    Date Taken: 08/08/92
  Title: STS-46 MS Hoffman & MS Chang-Diaz wear masks during pre-breathe on OV-104
  Description:
  STS-46 Mission Specialist (MS) and Payload Commander (PLC) Jeffrey A.
  Hoffman  and MS Franklin R. Chang-Diaz, wearing breathing apparatus masks,
  pose on the  forward flight deck of Atlantis, Orbiter Vehicle (OV) 104,
  during pre-breathe  session.  With the possibility of an extravehicular
  activity (EVA) being  added to the STS-46 agenda, the astronauts reported
  to this station and began  the "pre-breathe" process when problems
  developed during the extension of the  Tethered Satellite System 1 (TSS-1). 
  When the human body is exposed to a  sudden decrease in atmospheric
  pressure (for instance, from the 10.2 ppsi in  the crew cabin to the 4.5
  ppsi of the extravehicular mobility unit (EMU)),  nitrogen traces in the
  bloodstream will expand.  This expansion can create  tiny bubbles and
  potential for the "bends".  In order to lessen the effect,  an astronaut
  must "pre-breathe" pure oxygen (the same pure oxygen he will  breathe in
  the suit) to help "purge" nitrogen from his bloodstream before  exerting
  himself in the low-pressure environment of the suit.  The  "pre-breathe"
  exercise and the EVA were cancelled as the TSS-1 procedures  were resumed
  by remote operations.      
  Subject terms:
  ASTRONAUTS                              
  ATLANTIS (ORBITER)                      
  BREATHING APPARATUS                     
  CREW PROCEDURES (INFLIGHT)              
  CREWS                                   
  FLIGHT DECK                             
  MASKS                                   
  ONBOARD ACTIVITIES                      
  STS-46                                  
  

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