Regarding the explosion protection rating

T4 is intrinsically safe and explosion-proof, while T6 is flameproof explosion-proof; generally speaking, flameproof design offers greater versatility

The ignition temperature corresponding to T4 is between 135 degrees and 200 degrees, while the ignition temperature for T6 is between 85 degrees and 100 degrees. Therefore, the materials associated with T6 are more prone to explosion, which means that stricter requirements must be placed on the electrical equipment used with them. Taking the examples in the appendix of the \"GB50058-92 Code for Design of Electrical Installations in Explosive and Flammable Environments\" as an example, the only substance classified as t6 is ethyl nitrate (which can be used as a rocket propellant); it is clear that there are very few substances of category t6, and they are not widely used in engineering applications. Please point out any mistakes.

Temperature categories: Safe surface temperature of objects. Common explosive gases: T1 ≤ 450℃ – 46 types such as hydrogen and acrylonitrile; T2 ≤ 300℃ – 47 types such as acetylene and ethylene; T3 ≤ 200℃ – 36 types such as gasoline and butyraldehyde; T4 ≤ 135℃ – 6 types such as acetaldehyde and tetrafluoroethylene; T5 ≤ 100℃ – carbon disulfide; T6 ≤ 85℃ – ethyl nitrate and ethyl nitrite. It’s definitely better to choose T6

Of course, the requirements for T6 are higher, because the ignition temperature is lower, which means it is more prone to explosion.

1. Typical hazardous gases by gas category: According to EN 50014 by the European Committee for Standardization in electrical engineering, and NEC Article 500 in North America, CLASS 1 Table G; in China, it is specified in GB3836.1. Minimum ignition energy (microjoules): Ethyne – II CA II C20; Hydrogen – II CA II C20; Ethylene – II BC II B60; Propane – II AD II A180. Note: The GB3836 standard in China specifies that the minimum ignition energy for category II C is 19 microjoules, while for category II A it is 200 microjoules. Gas grouping and ignition temperature are related to the mixing concentration of flammable gases with air under certain ambient temperature and pressure conditions. 2. Temperature category (Group T): This refers to the maximum surface temperature of electrical equipment related to the ignition temperature of the gas (under the assumption that the ambient temperature is 40°C), with the ignition energy being independent of the ignition temperature. All flammable gases and their groups are listed in Part 1 of the standard BS5345. Maximum surface temperature (°C) Temperature categories IEC60079-8 GB3836.1: 450°C, 300°C, 200°C, 135°C, 100°C, 85°C; T1, T2, T3, T4, T5, T6. 3. Examples of markings for explosion-proof equipment 3.1 If an electrical device is of type IIB, explosion-proof, category T3, its marking will be Exe II BT3. 3.2 If the electrical equipment is of Type II increased safety type, with temperature group T2, the marking is Exe II2. 3.3 If an electrical device adopts more than one composite type, the main explosion protection type shall be indicated first, followed by the other explosion protection types. For example, if the main type is enhanced safety with internal IIC category flameproof components and the temperature group is T4, the marking will be Exed II CT4. 3.4 If the electrical equipment is of dust-proof and explosion-proof type, Group T11. The identifier is: DIPDPT11. 3.5 Below, taking the CENELEC hydrogen explosion-proof marking as an example: E E*a ⅡC T4E: According to the CENELEC marking; Ex: Explosion-proof general marking; ia: Explosion-proof type (intrinsic safety); Ⅱ: Equipment category; C: Gas category; T4: Temperature category. 4. Examples of classification, grading, and grouping of explosive gas mixtures The table below shows examples of the classification, grading, and grouping of explosive gases. Category and Grade Maximum test safety gap MESG (mm) Minimum ignition current ratio MICR Ignition temperature (°C) Group T1 T2 T3 T4 T5 T6