Difference between explosion protection marks Ex d and Ex db

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There is a difference between the explosion protection markings Ex d and Ex db; the marking Ex d refers to the requirements for devices protected by an explosion-proof enclosure of type “d” as specified in the old standard GB3836.2-2010； The explosion-proof marking Ex db should comply with the new version of the standard GB/T3836.2-2021; it is also applicable to explosive environments. There are similarities between them, as well as some differences. The following is a detailed comparison of the two. I. Ex d mark 1. Meaning: In the old standard 2-2010, Ex d denotes the specific requirements for the design and testing of electrical equipment intended for use in explosive gas environments, and which is protected by an explosion-proof enclosure of type “d”; it indicates that the equipment is suitable for use in such environments where explosions can be caused by sparks and arcs. Devices with such markings usually feature an explosion-proof enclosure design. Devices protected by Ex d have a device protection level “EPL” of Gb or Mb. 2. Working principle: The flameproof enclosure design involves enclosing components that may generate sparks or arcs within a robust casing, to prevent explosive gases from entering and causing an explosion. When an explosion occurs inside the device, the casing can withstand the explosive pressure and prevent the spread of explosive gases, thereby protecting the safety of the surrounding environment. 3. Application scenarios: Devices with the Ex d marking are typically suitable for explosive gas environments in industries such as pharmaceuticals and petrochemicals. II. Ex db marking 1. Meaning: In the new standard GB/T3836.2-2021, Ex db is used to denote electrical equipment designed for use in explosive gas environments and protected by an explosion-proof enclosure of type “d”. Such an enclosure is capable of withstanding internal explosions of explosive mixtures that enter it through any joints or gaps in the enclosure without being damaged, and it also prevents ignition of the explosive gas environment outside due to one or more gases or vapors. In the new standard, devices protected by Ex db form a device protection level “EPL” of Gb or Mb. In the relevant sections of the new standard GB/T3836.2-2021, electrical equipment protected by an explosion-proof enclosure of type “d” is classified into the following protection levels – the “da” protection level (EPL “Ma” or “Ga”) ； ——“db” protection level (EPL “Mb” or “Gb”) ； ——“dc” protection rating (EPL“Gc”) ； Among them, the “da” protection rating is only applicable to the catalytic sensors of portable combustible gas detectors. The requirements for the “dc” protection rating apply to electrical equipment with electrical switching contacts and Ex components. Regarding the requirements for the \"db\" protection level, in addition to the specific requirements for the \"da\" and \"dc\" protection levels, all other requirements of the new standard GB/T3836.2-2021 apply to the \"db\" protection level. 2. Working principle: Components that may be exposed to an explosive gas environment inside must be able to withstand the pressure generated by an explosion of the explosive mixture inside, and prevent the explosion from spreading to the explosive gas environment surrounding the enclosure. 3. Application scenarios: Devices marked with Ex db are suitable for areas with explosive gas environments. III. Common points: Explosion-proof design of the flameproof type involves placing the live components of electrical equipment within a special enclosure. This enclosure serves to isolate the sparks and arcs generated by the electrical components inside from any explosive mixtures outside the enclosure, and it is capable of withstanding the explosive pressures resulting from such mixtures being ignited by the sparks and arcs from the electrical equipment inside, without the enclosure being damaged ； At the same time, it prevents the explosion products inside the shell from propagating to the explosive mixture outside the shell, thus avoiding combustion and explosion of that external explosive mixture. Based on the explosion-proof principle of flameproof instrument equipment, it can be seen that the flameproof enclosure should possess explosion resistance and flameproofing properties. Explosion resistance refers to the ability of the casing to withstand the explosive pressure generated by an explosion of an explosive mixture inside it, without suffering damage or dangerous deformation itself ； The explosion-proof performance refers to the ability of the enclosure to prevent the flames emitted from an explosion of an explosive mixture inside it from causing an explosion in any flammable mixtures outside the enclosure. Therefore, the flameproof enclosure must meet two basic conditions: ① The enclosure must have sufficient mechanical strength to withstand the internal explosion pressure without being damaged or suffering from permanent deformation that could affect its flameproof properties. ； ② All seams and openings on the shell wall that are in contact with the outside environment are smaller than the corresponding maximum allowable safety gap; therefore, the explosion-proof shell must possess both blast resistance and explosion isolation properties. 1. Complies with standards: Equipment marked Ex d meets the specific requirements of the old standard 2-2010 regarding the construction and testing of electrical equipment for use in explosive gas environments, protected by an explosion-proof enclosure of type “d” ； Devices marked with Ex db meet the requirements of the new standard GB/T3836.2-2021 for equipment used in explosive gas environments protected by an explosion-proof enclosure of type “d”. 2. Explosion-proof markings for explosive gas environments: The new version of the standard may introduce more detailed requirements regarding explosion-proof markings in explosive gas environments, such as temperature groups and equipment categories. 3. Other technical requirements and specifications: In addition to the explosion-proof marking, the new version of the standard may also include other technical requirements and specifications that differ from those in the old version, all of which need to be taken into account during design and use.