CANDLE Sodium Chlorate Mounting stud Thermal insulation Chlorate candle Case Flow initiation mechanism Pin Lanyard Filter Support screen Manifold Oxygen outlet Relief valve 16-6 Oxygen Systems and Components Oxygen Storage Cylinders Gaseous Oxygen Systems Figure 16-8.  This onboard oxygen generating system uses molecular  sieve technology. Figure 16-7.  A sodium chlorate solid oxygen candle is at the core  of a chemical oxygen generator. the oxygen for breathing use. Some of the separated oxygen  is also used to purge the sieve of the nitrogen and other  gases that keep it fresh for use. Use of this type of oxygen  production in civilian aircraft is anticipated.  [Figure 16-8] Built-in and portable oxygen systems are used in civilian  aviation. They use gaseous or solid oxygen (oxygen  generators) as suits the purpose and aircraft. LOX systems  and molecular sieve oxygen systems are not discussed, as  current applications on civilian aircraft are limited.  Gaseous oxygen is stored and transported in high-pressure  cylinders. Traditionally, these have been heavy steel  tanks rated for 1800–1850 psi of pressure and capable of  maintaining pressure up to 2,400 psi. While these performed  adequately, lighter weight tanks were sought. Some newer  cylinders are comprised of a lightweight aluminum shell  wrapped by Kevlar$^{®}$. These cylinders are capable of carrying  the same amount of oxygen at the same pressure as steel  tanks but weigh much less. Also available are heavy-walled  all-aluminum cylinders. These units are common as carry-on  portable oxygen used in light aircraft. The use of gaseous oxygen in aviation is common; however,  applications vary. On a light aircraft, it may consist of a small  carry-on portable cylinder with a single mask attached via a  hose to a regulator on the bottle. Larger portable cylinders may be fitted with a regulator that divides the outlet flow for  2–4 people. Built-in oxygen systems on high performance  and light twin-engine aircraft typically have a location where  oxygen cylinders are installed to feed a distribution system  via tubing and a regulator. The passenger compartment  may have multiple breathing stations plumbed so that each  passenger can individually plug in a hose and mask if oxygen  is needed. A central regulator is normally controlled by  the flight crew who may have their own separate regulator  and oxygen cylinder. Transport category aircraft may use  an elaborate built-in gaseous oxygen system as a backup  system to cabin pressurization. In all of these cases, oxygen  is stored as a gas at atmospheric temperature in high-pressure  cylinders. It is distributed through a system with various  components that are described in this section.