Aircraft Pressurization Systems Pressure of the Atmosphere Oxygen System Inspection and Maintenance Prevention of Oxygen Fires or Explosions connections. Be sure to begin wrapping the Teflon$^{®}$ tape at  least two threads from the end of the fitting. This prevents  any tape from coming loose and entering the oxygen system.  Precautions must be observed when working with or around  pure oxygen. It readily combines with other substances,  some in a violent and explosive manner. As mentioned,  it is extremely important to keep distance between pure  oxygen and petroleum products. When allowed to combine,  an explosion can result. Additionally, there are a variety of  inspection and maintenance practices that should be followed  to ensure safety when working with oxygen and oxygen  systems. Care should be used and, as much as possible,  maintenance should be done outside.  dedicated for work on oxygen systems. There should be  absolutely no smoking or open flames within a minimum of  50 feet of the work area. Always use protective caps and plugs  when working with oxygen cylinders, system components,  or plumbing. Do not use any kind of adhesive tape. Oxygen  cylinders should be stored in a designated, cool, ventilated area  in the hangar away from petroleum products or heat sources.  Oxygen system maintenance should not be accomplished  until the valve on the oxygen supply cylinder is closed and  pressure is released from the system. Fittings should be  unscrewed slowly to allow any residual pressure to dissipate.  All oxygen lines should be marked and should have at least  2 inches of clearance from moving parts, electrical wiring,  and all fluid lines. Adequate clearance must also be provided  from hot ducts and other sources that might heat the oxygen.  A pressure and leak check must be performed each time the  system is opened for maintenance. Do not use any lubri cants,  sealers, cleaners, etc., unless specifically approve for oxygen  system use. When working on an oxygen system, it is essential that the  warnings and precautions given in the aircraft maintenance  manual be carefully observed. Before any work is attempted,  an adequate fire extinguisher should be on hand. Cordon off  the area and post “NO SMOKING” placards. Ensure that all  tools and servicing equipment are clean and avoid power on  checks and use of the aircraft electrical system. When working around oxygen and oxygen systems,  cleanliness enhances safety. Clean, grease-free hands, clothes,  and tools are essential. A good practice is to use only tools  The gases of the atmosphere (air), although invisible, have  weight. A one square inch column of air stretching from sea  level into space weighs 14.7 pounds. Therefore, it can be  stated that the pressure of the atmosphere, or atmospheric  pressure, at sea level is 14.7 psi.  [Figure 16-34] 16-21 Figure 16-34.  The weight exerted by a 1 square inch column of air stretching from sea level to the top of the atmosphere is what is  measured when it is said that atmospheric pressure is equal to 14.7 pounds per square inch.  Height of Earth’s atmosphere (about 50 miles) Entire air column weight 14.7lb Sea level inch 1 inch Thermosphere  Tropopause Stratosphere Ozone layer Troposphere Earth Mesosphere 18 km 14 km 350 km 90 km 50 km