In high-risk industries like oil extraction, chemical synthesis, and coal mining, explosive gases or dust often arise during material transportation, storage, and processing. Once these substances come into contact with electrical sparks or high temperatures, they can cause serious safety accidents. Therefore, all instruments used in these environments must possess reliable explosion-proof capabilities. This is essential for ensuring stable production operations and protecting personnel safety.
The core function of explosion-proof instruments is to maintain normal operation in flammable and explosive environments while preventing explosions from self-generated electrical sparks, high-temperature surfaces, and other risk factors, thereby providing a critical line of defense for industrial safety. To standardize safety standards for explosion-proof instruments, countries have established strict regulatory systems. In China, the current national explosion-proof standard is GB/T 3836-2021. Instruments that meet this standard after laboratory testing are issued an “Explosion-Proof Certificate” and clearly marked with the explosion-proof symbol and certificate number. These standards not only regulate the design and manufacture of explosion-proof instruments but also set clear requirements for their installation, use, and maintenance.
However, with the wide variety of explosion-proof instruments currently on the market, how can one accurately determine whether they are truly explosion-proof? Using fixed gas detectors, commonly used in industrial settings, as an example, the following describes practical identification methods based on five key dimensions.
Verifying Product Labeling and Certifications
An instrument’s labeling and certifications are fundamental to determining its explosion-proof status. Pay special attention to the following three key pieces of information:
A legitimate explosion-proof instrument will have its explosion-proof marking clearly marked on a prominent location on its housing, such as “Ex d IIB T4 Gb” or “Ex db IIB T4 Gb” according to GB/T 3836.1-2021. “Ex” is the internationally recognized explosion-proof symbol, indicating that the product possesses explosion-proof characteristics; “d” or “db” designates flameproof (a widely used explosion-proof type); “IIB” represents the gas group (used to distinguish the explosion characteristics of different flammable and explosive gases); “T4” is the temperature group (limits the maximum surface temperature of the instrument to prevent ignition of surrounding hazardous materials); and “Gb” is the equipment protection level (indicates the suitability of the instrument for use in different hazardous areas).
During identification, it is necessary to check the format and completeness of the explosion-proof marking against the GB/T 3836 series of standards. Furthermore, the actual structure of the instrument (such as the housing material and sealing method) should be considered to initially determine whether the explosion-proof marking matches the actual performance.
All compliant explosion-proof instruments must possess an “Explosion-proof Certificate.” To verify, visit the official website of the issuing authority (such as the National Explosion-Proof Electrical Product Quality Supervision and Inspection Center) and enter the certificate number marked on the instrument in the certificate query portal. Verify that the certificate information displayed on the website (such as product model, manufacturer, explosion-proof type, and applicable environment) is consistent with the actual instrument information. Additionally, confirm that the instrument’s date of manufacture is within the certificate’s validity period. If the certificate is expired, even if the markings are intact, it cannot be considered explosion-proof.
In addition to explosion-proof certificates, some explosion-proof instruments must meet other compulsory certification requirements. For example, explosion-proof products included in my country’s CCC (China Compulsory Certification) catalogue must also hold a CCC certificate and display the CCC mark on the housing. If an instrument falls into this category but lacks the CCC mark, its explosion-proof compliance should be questioned.
Inspect the Product’s Appearance and Structural Details
The appearance and structural design of an instrument directly impact its explosion-proof performance. A visual inspection can reveal many potential issues, focusing on three key areas:
The casing of an explosion-proof instrument is a crucial barrier to explosion protection. It is typically constructed of high-strength, flame-retardant, and impact-resistant materials such as die-cast aluminum alloy, 304 stainless steel, and engineering plastics (which must be certified for flame retardancy). During inspection, first inspect the casing for manufacturing defects such as cracks, pinholes, and air holes—these defects can directly compromise the integrity of the explosion-proof structure. Next, check the casing for smoothness, burrs on edges and corners, and tight fit at connections (such as between the casing and the cover, and between the terminal box and the main unit). Generally speaking, instruments with fine craftsmanship and no obvious defects have stricter production controls and more reliable explosion-proof performance. However, the final judgment should be based on the explosion-proof certification.
A good seal prevents flammable and explosive substances from entering the instrument, preventing contact with electrical components and potentially causing risks. Key areas of the instrument, such as the cable inlet, junction box cover, and observation window, require special inspection: Check whether the cable inlet is equipped with an explosion-proof gland (for securing and sealing the cables) or an oil-resistant, high-temperature-resistant seal. Ensure that an elastic gasket is installed between the junction box cover and the instrument body, and that the gasket is free of aging, deformation, or damage. Ensure that the observation window glass and the casing are fitted with sealant or a sealing ring, and that the glass is free of cracks. Loose seals or seal failure will significantly reduce the instrument’s explosion-proof performance.
Explosion-proof instruments with metal casings must be equipped with a comprehensive grounding system to prevent static electricity accumulation or leakage that could cause sparks. When inspecting, first check the casing for a clear grounding mark (usually the grounding symbol “⊕”) and a dedicated grounding bolt (mostly made of copper or galvanized steel and free of rust). Then, confirm that the grounding bolt is securely fastened and not loose or stripped. Finally, check that the grounding wire meets the specified specifications (for example, the copper wire’s cross-sectional area must meet the required current requirements) and that the connection between the grounding wire and the grounding bolt is secure and free of loose connections. If the instrument lacks a grounding device or is poorly grounded, even if other explosion-proof structures meet the requirements, safety risks remain.
Verifying Explosion-Proof Capability Through Technical Principles
The core technology of explosion-proof instruments lies in the design and manufacture of their casings. Flameproof instruments are a common type of explosion-proof instrument. Their casings must be able to withstand the explosive pressure of the explosive gas mixture within and prevent the internal explosion from propagating to the surrounding explosive mixture. Therefore, when inspecting an instrument, you can use the basic definition of explosion-proofing to determine whether the instrument meets explosion-proof requirements based on the casing’s dimensions and structure.
According to the requirements of the explosion-proof standard for industrial instruments, the basic definition of explosion-proof type is: (1) Gap explosion-proof technology, which relies on gaps and meshing lengths to achieve cooling and flameout effects. (2) Allowing dangerous gases to enter the explosion-proof enclosure, which may cause explosions inside the enclosure. However, the enclosure must have sufficient strength; and each enclosure joint must have a sufficiently long meshing length and a sufficiently small gap to ensure that the internal explosion does not pass through the explosion-proof joint surface and cause an explosion in the external environment. (3) An electrical equipment enclosure that can withstand the explosion pressure of the internal explosive gas mixture and prevent the internal explosion from spreading to the explosive mixture around the enclosure. IV. Tracing the source of the product and the manufacturer’s qualifications The production source of the instrument and the reputation of the manufacturer are indirect but important bases for ensuring explosion-proof performance. They can be verified from two dimensions: 1. Confirm the compliance of the purchasing channel Prioritize regular and qualified purchasing channels, such as the official website of the instrument manufacturer, authorized dealers (who must provide authorization certificates issued by the manufacturer) or platforms with explosion-proof product sales qualifications. The products of these channels have been reviewed by the manufacturer and can effectively reduce the risk of buying counterfeit and inferior products. Avoid purchasing from unqualified intermediaries, secondhand markets, or online stores with unknown sources—products from these channels may be non-explosion-proof products with counterfeit explosion-proof markings and fail standard testing.
Verify the manufacturer’s qualifications and reputation
Before purchasing, thoroughly understand the manufacturer’s qualifications:
Check whether the manufacturer possesses an “Explosion-Proof Instrument Production License” or a “Special Equipment Manufacturing License” (if the instrument falls under the special equipment category);
Use industry associations, market regulatory authorities’ official websites, or third-party review platforms to verify the manufacturer’s record (e.g., penalties for product quality issues, numerous customer complaints, etc.);
Study the manufacturer’s reputation within the industry, such as whether it has participated in the development of explosion-proof standards or whether it provides supporting products for well-known companies.
Generally, manufacturers with long-term production experience, comprehensive qualifications, and a good reputation are more likely to provide products with guaranteed explosion-proof performance.
Conduct actual testing when conditions permit
Gas environment testing: Subject to safety regulations, the instrument is placed in an environment containing a certain concentration of explosive gas for actual testing to determine its explosion-proof performance. However, this method is dangerous and destructive, requiring professional personnel in a specialized environment.
Electrical performance testing: Using specialized instruments, the instrument’s electrical parameters, such as insulation resistance and ground resistance, are tested to determine if they meet the corresponding explosion-proof standards. Failure to meet these standards may affect explosion-proof performance.
Generally speaking, the above methods can easily determine whether industrial instruments meet explosion-proof requirements.
