To commemorate the 50th anniversary of the first steps taken on the moon by some phenomenal human beings, below is an excerpt from our overview. Hyperbaric chambers and space technology are, in almost every way the same technologies. Sealed environments with controllable and manageable environmental conditions common to both. In fact, as mentioned here, space craft and other vessels are indeed hyperbaric chambers in their own right. It’s how they work, right down to the carbon dioxide scrubbers that the astronauts had to modify to safely return to Earth. Many HBOT chambers, as do spacecraft, along with other similar equipment, control internal atmospheres with scrubbers such as these.
The excerpt from the chapter on oxygen toxicity reads:
…....this is incidentally the pressure that was used in the early days of space exploration with the Apollo spacecraft being pressurised to just 5 psi, about a third of atmospheric pressure.  NASA History Online. NASA routinely uses pure oxygen atmospheres, specifically in extra vehicular suits (spacesuits). Therefore, they too are pressurised to a pressure at or below the threshold of 0,5ATA under which no significant damage occurs to lungs breathing pure oxygen. [or above which level oxygen safety concerns are present] It is more common nowadays however, as the duration of missions becomes longer and longer than the early missions, with astronauts taking up residence in the ISS for months at a time, and as much as a year or more, for atmospheres to be either enriched to a lesser degree or to be comprised of air and pressurised to the standard 14,7 psi which equates to 1 ATA.  The Space-Flight Environment: The International Space Station and Beyond Thirsk Et al 2009
Hyperbaric operations, diving, and specifically saturation chamber technology and saturation diving and treatment physics and physiology, make use of the same physics as those used in space exploration. The similarity between orbital habitat modules, or the proposed Mars or Lunar habitat modules, is uncanny. They even look like saturation complexes and hyperbaric chambers with the exception of being controlled by the occupants from the inside. Space shuttles, habitat modules, rovers, and even space suits are basically hyperbaric chambers using a pure oxygen or enriched air internal atmosphere. They are kept at lower than atmospheric pressure when using pure oxygen to avoid oxygen toxicity as well as to reduce the risk of fire to some degree.
As we know, the Apollo One mission ended in the tragic deaths of Gus Grissom, Ed White and Roger B Chaffee. A fire in a pure oxygen atmosphere, started by coolant dripping onto bare and sparking wires, proved uncontrollable. Apollo One was designed to operate at a little over atmospheric pressure of 1 atmosphere, (14,7 psi), and with a pure oxygen internal atmosphere. A hazardous mix exacerbated by the presence of electrical equipment and combustible materials. The cabin was pressurised to 16.7 psi (1,15 atmospheres).
NASA learned from this and reduced the internal pressure of future lander modules, cabins and other craft to around just 5 psi, about a third of an atmosphere. and eventually, in modern times, began to use air environments at normal sea level pressure on the International Space Station.
Accordingly, in the hyperbaric market, we do not routinely compress vessels (chambers) with pure oxygen. Only those designed to be used in a pure oxygen environment are compressed with oxygen, and generally speaking, these are kept barren of any potential ignition source. Fire safety is paramount with very strict health and safety controls in place.
We compress with air and breath oxygen through a mask. The mask is called a “built in breathing system” mask, or “BIBS” mask, and receives pure oxygen via a specially designed hose and valve system and then vents outside the chamber when the occupant breathes out breath which still contains high concentrations of oxygen. Not dissimilar to test pilot and high altitude pilots masks. This maintains a normal air environment in the chamber eliminating fire risk. We also don’t allow unapproved or improperly designed electrical equipment in the chamber as well as other potential ignition sources. The lessons learned in diving and hyperbarics are echoed in the lessons learned during the Apollo One mission.
A printout version of a list of items forbidden in the chamber can be found on the download page for interests sake.
Further information on the importance of pressure and gas exchange in the lungs can be found in the overview and also the upcoming training and operations manual currently being written. This physiology of gas exchange and breathing is in essence the same physiology, and the physic is the same physics, employed in aerospace and space exploration as well as the exploration of the deep ocean.
Herewith a link of interest: