March was a turbulent month for China's explosion-proof industry, with a series of explosion and detonation accidents occurring one after another on March 21st in Yancheng, Jiangsu, March 30th in Qingzhou, Shandong, and March 31st in Kunshan, Jiangsu. In today's rapidly developing explosion-proof industry in China, bloody cases have pointed out a basic fact that there is a risk of overall loss of control in the national explosion-proof field.
So what are the reasons for losing control?
1、 Explosion proof standards lag behind
In July 1948, the International Electrotechnical Commission TC31 began to develop international explosion-proof technical standards. China started relatively late and officially started the standardization of explosion-proof technology in 1977. More than 40 years have passed, and although China's explosion-proof technology and market have undergone earth shaking changes, the country's explosion-proof standards still seriously lag behind international explosion-proof standards, especially the standard GB3836.1-2010 for general explosion-proof requirements, which only benchmarks against the IEC60079-0:2007 version. The current international explosion-proof standard is already IEC60079-0:2017, which is a total of 10 years behind by two versions.
The lag of explosion-proof standards directly leads to the backwardness of design specifications for explosion-proof products in China. Therefore, in the subsequent verification, production, and selection and application processes, we can only stick to old ways of thinking and methods.
As stated in IEC60079-14:2014 "Design, Selection, and Installation Standards for Electrical Installations", there have been significant changes in the selection and application of cable entry devices, especially for Class IIC explosion-proof cable entry devices with sealing rings. There is no longer a pursuit of limitations on the capacity of the applied equipment and requirements for on-site stripping of cable cores and filling, but rather detailed regulations for the applicable cables. Whether from the perspective of on-site operation technology or explosion-proof safety, the new standards are more mature and rigorous.
However, the latest GB/T 3836.15-2017 (compared to IEC60079-14:2007) released in 2018 still adopts the old regulations. When the IIC level explosion-proof cable entry device is applied to equipment with a capacity exceeding 2 liters, it can only be stripped and filled with stuffing boxes by construction personnel at the equipment installation site. This method is very cumbersome in terms of operation technology and requires high professional ability and professionalism of construction personnel. Improper operation in any place can bring safety hazards.
As the most basic and commonly used basic component of explosion-proof electrical equipment, cable entry devices are almost applied to every explosion-proof product. The lag in design, selection, and installation standards not only restricts the breakthrough in design and innovation in application of explosion-proof products in China from the source, but also poses real safety risks to explosion-proof products.
2、 Explosion proof technology remains stagnant
In recent decades, with the rapid development of the petrochemical industry, explosion-proof technology has also been advancing rapidly. The safety of explosion-proof products depends not only on the protection of ignition sources, but also more on considerations of environmental or human factors. In the international field of explosion-proof, according to the characteristics of various electrical equipment, application environments, and customer application needs, the composite explosion-proof mode composed of lightweight "Ex e" increased safety enclosures and "Ex d" explosion-proof or "Ex m" encapsulated components is gradually replacing the traditional single explosion-proof mode, becoming a consensus. For example, in addition to the protection of common elements such as shell strength, electrostatic protection, and hot spot combustion, the core requirement for explosion-proof in the increased safety type is to ensure the IP protection of the increased safety type shell and configure independent explosion-proof components. Each explosion-proof key element is completed by professional and skilled workers in the explosion-proof equipment factory, which is safe and easy to control, greatly facilitating on-site installation and later maintenance; The core requirement for explosion-proof type is to ensure the surface quality and explosion-proof gap of the explosion-proof shell explosion-proof surface. It is easy to make mistakes during on-site installation and later maintenance, and on-site construction or operation personnel must have corresponding professional abilities and high professional ethics. A slight negligence can bring safety risks. Moreover, in the chemical areas where explosion-proof products are applied, there are mostly corrosive environments. The explosion-proof surface made of aluminum alloy is prone to failure under on-site corrosion, and the corrosion resistance of plastic shells is much better than that of metal materials, resulting in higher overall safety. (Note: Analysis of Unqualified Projects in the National Supervision and Inspection of Explosion proof Luminaires in 2018, with a non-compliance rate of 61.5% for explosion-proof surface elements)
However, in the explosion-proof industry in China, many professional explosion-proof design institutions still adhere to tradition. The mainstream design institutes in China, which undertake user projects, have different understandings of advanced explosion-proof concepts and new technological applications. A considerable number of people still do not use non flameproof explosion-proof types. This outdated top-down explosion-proof concept hinders the development of explosion-proof technology and enterprises in China, and also poses many hidden dangers to China's explosion-proof safety.
3、 There are loopholes in the explosion-proof system
1) The international explosion-proof system adopts a combination of "sample certification" and "factory audit". On the one hand, strict verification of samples is carried out according to the requirements of explosion-proof standards. On the other hand, through regular reviews of the qualifications, management responsibilities, production inspection facilities and equipment calibration, product design and development, procurement, production process control, monitoring and measurement, as well as the control of non-conforming products of explosion-proof production enterprises, all factors that affect the quality of explosion-proof products are comprehensively controlled as a whole. This method has been fully tested by the market and is recognized and adopted by most countries and regions in the world. However, the domestic explosion-proof system adopts the management method of "explosion-proof qualification certificate" and "production license". The production license is only audited every 5 years when it is renewed, without any monitoring of the entire production process of the enterprise. There is no effective supervision of the quality control of various production links that are crucial to the quality of explosion-proof products. Especially for explosion-proof lighting fixtures, the lack of a "production license" has left endless hidden dangers for the quality and safety of explosion-proof products. The results of the 2018 national supervision and spot check on the quality of explosion-proof lighting products showed that out of 26 batches of explosion-proof lighting products from 26 enterprises, 13 batches were found to be unqualified. This sampling was only conducted for enterprises above a certain scale. If the evaluation of products in the mobile market is conducted, the pass rate is expected to be even lower. For explosion-proof products that are related to the safety of people's lives and property, the failure rate has reached an astonishing 50%. This actually indicates that there are significant loopholes in the system supervision of explosion-proof products.
2) The majority of explosion-proof certification issued by explosion-proof organizations do not clearly specify the manufacturing conditions of products according to standard requirements and product characteristics, especially the execution of factory routine tests such as power frequency withstand voltage and overvoltage tests, which are crucial for determining the quality of explosion-proof products. Combined with the fact that the production license for explosion-proof products is only responsible for sampling samples, there are no requirements for the production control process that affects the quality of explosion-proof products. There are obvious loopholes in the regulatory system, which not only violate the original intention of strict control over safety products, but also leave room for some explosion-proof equipment manufacturers to not or less comply with the standard provisions, which will inevitably lead to significant safety hazards in the explosion-proof products put on the market.
3) There is no specific recall measure for products that fail the international sampling inspection. Knowing that the unqualified products are still used in potentially explosive places makes it impossible to talk about explosion-proof safety protection. In addition, counterfeiting and imitation of well-known brand enterprises' explosion-proof products have been rampant in the market, relying solely on the rights protection of the counterfeit enterprises themselves, and the lack of national quality supervision is serious;
4、 Lack of self-discipline in production enterprises
The self-discipline of enterprises is the cornerstone of ensuring product quality, and the self-discipline of manufacturers of explosion-proof products is closely related to the safety of thousands of households. However, some explosion-proof enterprises, due to inadequate supervision, market competition and other reasons, neglect their responsibilities and bring safety risks to users.
1) Not implementing standards;
According to the explosion-proof standard regulations (GB3836.2-2010 Article 15.2), unless the volume is less than 10 cubic centimeters or has passed a 4-fold overvoltage test in the type test, every explosion-proof product must undergo an overvoltage test before leaving the factory, and the shell of the welded structure should undergo an overvoltage test under any circumstances. However, many explosion-proof enterprises are aware of the requirements of standard specifications, but refuse to comply due to cost savings or lack of confidence in product performance.
Most explosion-proof products are made of aluminum alloy material through die-casting. Due to the characteristics of aluminum alloy die-casting process, a certain amount of process defects are inevitable. Especially for explosion-proof lamps with transparent glass, the glass piece is bonded to the explosion-proof shell through a casting process to form a whole. The casting process is very sensitive to curing parameters and process environment, and has high requirements for the surface of the aluminum alloy shell that is bonded to the glass. It cannot guarantee that every sealed product is qualified. At this time, as the last control point for explosion-proof safety, overvoltage testing is very important. According to relevant data analysis results, 1 to 2 out of every 100 explosion-proof products cannot pass the overvoltage test. Unlike civilian products, if these one or two unqualified products are used in potentially explosive locations, it undoubtedly poses a great safety risk to the site.
2) The claimed information does not match the actual situation
The national explosion-proof standard (GB3836.2-2010, Article 5.2.7) clearly stipulates that the volume of IIC level (typical gas acetylene) square explosion-proof boxes with flat joint surfaces shall not exceed 500 milliliters.
Opening the samples or promotional materials of various explosion-proof enterprises, there are many explosion-proof box products with a capacity exceeding 500 milliliters, or even 50 liters. Some companies have expanded or falsely advertised the explosion-proof performance and consistency requirements of their products during the sales process of such explosion-proof boxes. Due to the lack of professional identification ability from customers, this poses a great risk to their explosion-proof safety.
3) Production without control
The quality control of the production process of explosion-proof products is closely related to the final performance of explosion-proof products. The international explosion-proof quality system standard IEC 80079 specifies in detail the consistency control procedures for the production and certification of explosion-proof products. Clear regulations have been established for raw material procurement, inspection and testing, equipment calibration, process control, routine inspection, non-conforming management, and certificate validity control. Regular reviews of the above control measures and records are required to identify and improve problems, continuously improve the quality control and management level of the enterprise, and fully ensure the consistency between the verified samples and the produced products, thereby ensuring the explosion-proof performance of the produced products.
This quality management system has very high requirements for explosion-proof enterprises in both product and management aspects. From feeding to shipping, every link is interrelated, and any failure to meet the requirements will result in subsequent processes being unable to proceed. Enterprises must strictly control the process in order to meet the management requirements of the quality system. However, many domestic enterprises do not have many conditions for systematic control. Some products have defects from the source of product design, which cannot meet the quality control requirements of the quality system in the subsequent production process, resulting in the quality and performance of the produced explosion-proof products not matching the verified samples, leaving infinite hidden dangers to explosion-proof safety.
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