I. Concepts of Explosion and Explosive Environments

An explosion is the sudden transformation of a substance from one state to another through physical or chemical changes, releasing a huge amount of energy. The rapid release of energy will cause violent impact and damage to surrounding objects. Three conditions must be met for an explosion (commonly known as the "explosion triangle", see Figure 1):

1) Explosive substances: substances that can react with oxygen (air), including gases, liquids, and solids (gases: hydrogen, acetylene, methane, etc.; liquids: alcohol, gasoline; solids: dust, fiber dust, etc.).
2) Oxidizer: oxygen (air).
3) Ignition source: including open flames, electrical sparks, mechanical sparks, static sparks, high temperatures, chemical reactions, light energy, etc.

Definition of explosive environment: An explosive environment usually refers to a mixture of hazardous substances in the form of gas, vapor, mist or dust with air under atmospheric conditions. When ignited, the combustion will spread throughout the unburned mixture. Many production sites generate certain flammable substances. About two-thirds of the underground coal mine sites have explosive substances; in the chemical industry, more than 80% of the production workshop areas have explosive substances. Moreover, oxygen in the air is ubiquitous. During the production process, a large number of electrical instruments are used, and various sparks from friction, mechanical wear, static electricity, high temperatures, etc. are inevitable, especially when instruments and electrical equipment malfunction.

II. Explosion-proof Directives and Explosion-proof Certification

1. Application and Use of Explosion-proof Directives

Chinese explosion-proof standards GB are basically equivalent or equivalent to IEC standards. Since IEC (International Electrotechnical Commission, abbreviated as IEC) standards and EN standards (European standards, the standard-setting institutions are CENELEC and CEN, abbreviated as EN) are basically consistent, Chinese standards GB are also equivalent or equivalent to EN standards. Important difference: IEC and EN standards allow manufacturers to self-certify (self-declaration) for Zone 2 equipment. However, in China, all explosion-proof products used in Zone 0, Zone 1, and Zone 2 sites must be certified by a national authorized explosion-proof inspection institution before they can be put into use.

ATEX is an acronym for "ATmosphere EXplosible". ATEX is also an EU directive
2014/34/EC(also known as ATEX 95), the Directive on the placing on the market of explosion-proof electrical and mechanical equipment, components and protective systems
Provisions were made.
Scope of application: Equipment and protection systems for use in potentially explosive environments; Used outside of potentially explosive environments, but required
Safety equipment, control equipment and regulating equipment for the protection system that is responsible for the safety functions of the equipment and for the risk of explosion.
Basic requirements: Equipment, protection systems and installations covered by this Directive must be satisfied, taking into account the purpose for which they are used
The corresponding health and safety requirements laid down in Annex II of Directive 94/9/EC.
In the European explosion-proof Directive 2014/34/EU for the first time put forward a series of requirements for intrinsic safety and relative health, on the one hand, applicable
Non-electrical equipment used in explosive environments, facilities that cause explosions due to dust and protective systems in potential explosive areas, and,
It is also applicable to equipment or protective systems associated with explosion risk that are not used in potentially explosive environments but must or require safe operation
One. This means that the scope is further extended compared to current national legislation.
In addition to ATEX 2014/34/EC (ATEX 95), the Commission has adopted a supplementary Directive 1999/92/EC(ATEX 95)
137), aimed at improving the protection of the health and safety of persons who may be threatened by explosive environments.
The ATEX 137 directive includes: sets out the minimum requirements for improving the protection of the health and safety of persons; For a field with a potentially explosive environment
Have been divided; Warning signs for areas where explosive environments may occur.
According to the application and use requirements of the explosion-proof directive, all equipment installed in the hazardous area, including the weight sensor in the weighing system,
Weighing instruments, junction boxes, etc., must be certified for explosion protection, and all installed equipment that does not comply with the current directive must be updated.
At present, the main electrical explosion-proof technologies accepted in China are: 1) flameproof type (Ex d) 2) intrinsic safety type (Ex ia/ib) 3) increased safety type (Ex e) 4)
Positive pressure type (Ex px, py, pz) 5) Oil immersed type (Ex o) 6) Sand filled type (Ex q) 7)n type (Ex nA, nC, nL, nR, nZ) 8) pouring and sealing
Type (Ex ma, mb,mc) 9) Dust explosion-proof (tD, DIP A/B) 10) Other (such as mine hat lamp, mixed hot cable, etc.) the main solution
The ignition source is an electrical spark and thermal effect caused by electrical factors.
2. Explosion proof certification
Explosion-proof certification bodies by region (not fully listed, only listed part) :
NEPSI: China national instrument explosion-proof safety supervision and inspection station
CQST: China National Explosion-proof Electrical Product Quality Supervision and Inspection Center
PCEC: China National Explosion-Proof Products Quality Supervision and Inspection Center (Tianjin)
CEE: International Electrical Equipment Accreditation Code Committee
IEC: International Electrotechnical Commission
CENELEC: European Electrotechnical Committee
BASEEFA: British explosion-proof inspection authority
FM: Federation of American Factories
UL: Underwriters Laboratories
NEC: National Electrical Code
NEMA: National Electrical Manufacturers Association
CSA: Canadian explosion-proof inspection agency
PTB: German explosion-proof inspection agency
So what are the differences between different certifications? Take ATEX and IEC Ex certification for example.
ATEX certification is mandatory throughout Europe and covers all stages from manufacturing to installation and use of the equipment. And the CE mark is strong
Products that comply with all the provisions of the ATEX Directive must bear the CE marking. Therefore, explosion-proof products are affixed with the CE mark
Special proof of compliance with the basic requirements of the ATEX Directive and the implementation of conformity assessment procedures specified in the Directive.
IEC Ex certification is the abbreviation of the International Electrotechnical Commission explosion-proof electrical product certification system, which is specially used in petroleum, chemical, coal, textile,
Electrical equipment for explosive hazardous places such as explosive gases, vapors, dust or fibers that may accumulate in food processing and military industries
Prepared for authentication. While ATEX is a mandatory application limited to Europe, IEC Ex is one that is accepted in several countries
International certification, designed to help build confidence in the safety of Ex equipment. It also promotes equipment and services for use in explosive environments
International trade.
IEC Ex certification provides assurance and ensures compliance with everything from equipment and installation to the manufacture, operation and maintenance of certified products
IEC International standards and fit for purpose.
While there are some subtle differences between each certification, ATEX and IEC Ex are very similar. The main difference is recognition and acceptance
The geographic location of the certification. ATEX certification is the European version of the explosion-proof directive, while IEC Ex is an internationally accepted explosion-proof directive in many countries.
Third, the definition and division of explosion environment area
In China and IEC, explosive substances are divided into three categories: Class I: mine methane; Class II: Explosive gas mixture (including vapor, mist);
Class III: Explosive dust and fibers.
China and IEC area definition: According to the frequency and duration of explosive environment, hazardous sites are divided into different zones.
The gas site is divided into three zones: Zone 0, Zone 1 and zone 2; Dust sites are divided into three zones: Zone 20, Zone 21 and Zone 22.
1) Zones 0, 1 and 2, gas, steam and mist environments
Zone 0: An explosive environment in which flammable substances in the form of gas, steam or mist mix with air continuously or chronically or frequently.
Zone 1: Flammable substances may appear or occasionally form when mixed with air in the form of gas, steam or mist during normal operation
The explosive environment.
Zone 2: It is unlikely that flammable substances will appear or form when mixed with air in the form of gas, steam or mist during normal operation
An explosive environment, or one that exists only for a short time if present.
2) Zones 20, 21, 22: Dust environment
Zone 20: explosive environment with continuous or long-term or frequent presence of combustible dust in the air;
Zone 21: An explosive environment in which combustible dust may or may occasionally form in the air during normal operation;
Zone 22: An explosive environment in which flammable dust is unlikely to occur or form in the air during normal operation, or only when it does
It's an explosive environment that exists for a short time.
3) In North America (United States and Canada) explosive substances are divided into three categories (called Class) Class I: explosive gases; Class II: Explosion
Explosive dust; Class III: Fiber.