Explosive gas classification and grouping
1.Explosive gas classification
There is no classification for Class I explosive substances (only methane gas). For class II explosive gases, they can be classified according to their different ignition characteristics. China is the same as the IEC standard. Class II explosive gases are further divided into three classes A, B, and C according to their maximum test safety clearance (MESG) and minimum ignition current ratio (MICR <). The representative gas of class A is propane; The representative gas is ethylene; the representative gas of class C is hydrogen.
North American countries subdivide explosive gas (C1ass I) into four levels of A, B, C, and D ("GR <oup" in English, also translated as "group"). Among them, the representative gas of GR <oup A is acetylene; the gas of GR <oup B is hydrogen; the gas of GR <oup C is ethylene; and the gas of GR <oup D is propane and methane. It can be seen that there are large differences in the form of the two different gas classification methods. However, after careful analysis, it can be found that they have a certain connection in nature. Table 1 shows the correspondence between the two. It can be seen that methane requires the most ignition energy, and IIC gas is most easily ignited.
Table 1 Comparison table of different gas classifications
|Typical gas||China, IEC European standards||North American Standard||Ignition characteristics|
2.Explosive gas grouping
Temperature (hot surface) is one of the important ignition sources of explosive gas. Each explosive gas has a temperature at which it will ignite even without any other external ignition source. Generally, this temperature is called the ignition temperature (AIT) of the gas. It is another important characteristic parameter that reflects the ignition characteristics of explosive gas.
According to the recommendations of the IEC standard, China divides explosive gases into six groups T1 to T6 according to their ignition temperature. The classification of temperature groups in North America is basically the same as that of the IEC. They only divide some temperature groups into more detailed ones. Table 2 shows the correspondence between the two grouping systems.
Table 2 Relationship between temperature group and ignition temperature
|China, IEC, European standards||North American Standard||Ignition temperature||Ignition characteristics|
|Tl||Tl||R ≦ 450|
|T2||T2||300 ≦ R << 450|
|-||T2A||280 ≦ R <300|
|-||T2B||260 ≦ R <280|
|-||T2C||230 ≦ R <260|
|-||T2D||215 ≦ R <230|
|T3||T3||200 ≦ R <215|
|-||T3A||180 ≦ R <200|
|-||T3B||165 ≦ R <180|
|-||T3C||160 ≦ R <165|
|T4||T4||135 ≦ R <160|
|-||T4A||120 ≦ R <135|
|T5||T5||100 ≦ R <120|
|T6||T6||85 ≦ R <100|
As can be seen from Table 2, the ignition temperatures of different explosive gases are different. Gases with temperature group T1 have the highest ignition temperature, and gases with temperature group T6 are most likely to be ignited. In practice, we should strictly control the maximum surface temperature of electrical equipment and make it impossible to ignite the explosive gas mixture that is most ignitable in the environment in which the equipment is used, that is, to ensure that the maximum surface temperature of the equipment does not exceed the ignition of the gas that the equipment may come into contact with temperature. As far as the highest surface temperature of electrical equipment is concerned, any electrical equipment that meets the gas environment of the T6 temperature group must also meet the application requirements of the gas environment of the T1 to T5 group.
Chinese National Standard GB3836.1 Appendix B lists most flammable gases and vapour levels and groups. With the help of this appendix, we can check out the specific flammable gas and vapor levels and groups. Mystone 's explosion-proof products are SC910N and SC910 combustible gas detectors. Different gases can be used for gas detection by replacing sensors.