Pure oxygen is a strong oxidant, especially compressed pure oxygen is more strongly oxidizing. According to the national standard GB6944-86 "Dangerous Goods Classification and Product Name No.", dangerous goods are divided into 9 categories, and compressed pure oxygen belongs to Category 2 dangerous goods (combustible gas). The oil will slowly oxidize and deteriorate in the air, and when it is in contact with pure oxygen, a severe oxidation reaction will occur, and the accumulated heat will heat up and spontaneous combustion of the oil will occur. Therefore, the safety regulations stipulate that the oxygen bottle is strictly prohibited from contacting the grease.
Low carbon steel is heated to 1500 ° C (melting point) in air, but is melted into liquid iron, but heated to 1350 ° C (fire point), in the pure oxygen will be intense combustion, the formation of iron oxide powder, and the burning speed is extremely fast. If there is a fire accident in the oxygen pipeline system, even if a fire extinguisher is used, it is often too late to extinguish the fire, which will not help. According to the information provided by the International Welding Society, the ignition point of the metal decreases with the increase of pure oxygen pressure (see Table 1).
Form 1 Metal ignition temperature (°C)
Metal name | Oxygen pressure (MPa) |
0.1 | 1 | 3.5 | 7 | 12.6 |
copper | 1085 | 1050 | 905 | 835 | 760 |
Low-alloy steel | 950 | 920 | 825 | 740 | 630 |
Low-carbon steel | | 1277 | 1104 | 1018 | 944 |
The above data also shows the strong oxidizing properties of pure oxygen, and the more oxidizing it is with the increase of oxygen pressure.
Pure oxygen can be mixed with almost all combustible gases and combustible vapors to form an explosive mixture. This mixture has a wide range of explosion limits. For example, the explosion limit of hydrogen and air is 4% to 75%, and the explosion limit mixed with pure oxygen. It is 4% to 94%. Porous organic matter (charcoal, carbon black, peat, wool fiber, etc.) is saturated with liquid oxygen (so-called liquid bomb), which produces a severe explosion under a certain impact. Once the liquid oxygen storage tank is leaking and escaping, it may catch fire or explode if it encounters grease.
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