# Research on Oxygen Components under a High-Pressure Oxygen Environment
## 2 Analysis  
### Combustion Analysis  
Fire in aircraft oxygen systems is highly dangerous. Fires are necessarily accompanied by the three elements of combustion. In order to identify which substances comprised the three elements of combustion in aircraft oxygen system fires, based on combustion principles and accident experience, a preliminary combustion analysis of the accident was conducted.  
Combustion requires three elements: a combustible material, a combustion aid, and heat. Combustion occurs when the three are mixed in the right proportions. Combustible materials can be solids, liquids, or gases. In aircraft oxygen system fires, the combustion aid is oxygen. Oxygen is not a combustible material, but most combustible materials will not burn without oxygen. Heat is a type of energy that is produced by chemical and physical changes. High heat can cause a substance to burn, and the heat generated by combustion can cause a substance to burn continuously until it is exhausted. The three elements of combustion required for ignition are called the fire triangle. According to the analysis of the accident wreckage, the combustion started at the oxygen nozzle.  
The oxygen nozzle consists of an oxygen connector, oxygen nozzle, oxygen valve, a sealing gasket, and other components. The oxygen connector is used to connect the oxygen cylinder to the oxygen nozzle, and it is usually made of copper or stainless steel. The oxygen nozzle is used to transfer oxygen from the cylinder to the equipment or appliance requiring oxygen. It is made of copper or aluminum alloy. The oxygen valve is used to control the flow and pressure of oxygen, and is made of stainless steel or copper. The sealing gasket is used to prevent the leakage of oxygen; it is usually made of rubber or ethylene. Under normal oxygen conditions, the temperature required to cause most combustible materials to burn is relatively higher; therefore, an obvious source of ignition is required to provide sufficient heat to reach the ignition point so that combustion can occur for most combustible materials. However, under high concentrations and pressures of oxygen, the ignition point of almost all combustible materials is greatly reduced. Under these conditions, substances that were originally flame-retardant no longer have flame-retardant properties, and they can be ignited at a slightly higher temperature without an obvious ignition source.  
In recent years, due to technical innovations in oxygen systems, the oxygen pressure has increased from 15.7 MPa to 20.6 MPa. It is therefore assumed that the increase in oxygen pressure caused these fires.  
According to the material parameters of the oxygen nozzle, the ignition point of Nylon 1010 is much lower than that of other materials. Nylon 1010, abbreviated as PA1010, is a common engineering plastic with high strength, wear resistance, and corrosion resistance, and therefore is usually used in the aerospace field. PA1010 is used in aircraft oxygen systems as a highly effective flame-retardant material [16; 17; 18; 19; 20]. Compared with other component materials, the ignition point of PA1010 is relatively low; thus, the possibility of its combustion is relatively high.