Classification standards for explosion-proof levels

Standards for classifying explosion-proof levels. This article includes the concept of explosion-proof, explosion-proof standards, division of explosion-proof areas, the meaning of explosion-proof signs, as well as some explosion-proof terminology, basic principles of explosion-proof, and the concept of explosion.
An explosion is when matter suddenly changes from one state to another state after physical or chemical changes, and releases huge amounts of energy. The energy released at a rapid speed will cause violent impact and damage to surrounding objects.

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

Why explosion-proof?
Explosive Substances: Certain flammable substances are produced in many production sites. Explosive substances exist in about two-thirds of underground coal mines; in the chemical industry, explosive substances exist in more than 80% of production workshop areas.
Oxygen: Oxygen is everywhere in the air.
Ignition source: A large number of electrical instruments are used in the production process. Various friction sparks, mechanical wear sparks, static sparks, high temperatures, etc. are inevitable, especially when instruments and electrical failures occur. Objectively speaking, many industrial sites meet explosion conditions.
When the mixed concentration of explosive substances and oxygen is within the explosion limit, an explosion will occur if an explosion source exists.
Therefore, it is necessary to take explosion protection. 

The principle of instrument explosion-proof 

Hazard classification of hazardous locations: Explosive substances Regional definition Chinese standards North American standards
Zone 0: Div.1 Gas (CLASS Ⅰ) Under normal circumstances, places where explosive gas mixtures exist continuously or for a long time 
Zone 1: Places where explosive gas mixtures may appear under normal circumstances Zone 1   
Zone 2: Div.2 Places where explosive gas mixtures are unlikely to appear under normal circumstances, but only occur occasionally or for a short period of time under abnormal circumstances

Zone 10 Div.1: Dust or fiber (CLASS Ⅱ/Ⅲ) Under normal circumstances, the mixture of explosive dust or combustible fiber and air may appear continuously, frequently in a short time or exist for a long time.
Zone 11 Div.2: A place where explosive dust or a mixture of combustible fibers and air cannot appear under normal circumstances, but only appears occasionally or for a short period of time under abnormal circumstances.

Applicability of explosion protection methods to hazardous locations:  
Serial number Explosion-proof type Code National standard Explosion-proof measures Applicable area 
1 Explosionproof type d GB3836.2 Isolate existing ignition sources Zone1, Zone2     
2 Increased safety type e GB3836.3 Try to prevent the generation of ignition sources Zone1, Zone2 
3 Intrinsically safe type ia GB3836.4 Limit the energy of ignition source Zone0-2     
     Intrinsically safe type ib GB3836.4 Limits the energy of ignition source Zone1, Zone2  
4 Positive pressure type GB3836.5 Hazardous substances are separated from ignition sources Zone1, Zone2   
5 Oil-filled type o GB3836.6 Hazardous substances are separated from ignition sources Zone1, Zone2

6 Sand-filled type q GB3836.7 Hazardous substances are separated from ignition sources Zone1, Zone2     
7 Non-sparking type n GB3836.8 Try to prevent the generation of ignition sources Zone2     
8 Pouring type m GB3836.9 Try to prevent ignition sources Zone1, Zone2   
9 Air tight type h GB3836.10 Try to prevent ignition sources Zone1, Zone2 

Applicability of explosion protection to hazardous locations: 

Classification of Explosive Hazardous Gases Based on the minimum spark energy that may detonate, my country, Europe and most countries and regions in the world classify explosive gases into four hazard levels.

 As shown in the following table: Working condition category Gas classification Representative gas Minimum detonation spark energy 

            Underground Mine Methane 0.280mJ   
            Factory outside the mine ⅡA Propane 0.180mJ                       

                                         ⅡB Ethylene 0.060mJ   
                                         ⅡC Hydrogen 0.019mJ  

The United States and Canada first divided explosive objects scattered in the air into three CLASS (categories):
CLASS Ⅰ Gases and Vapors; 
CLASS Ⅱ Dust; 
CLASS III fiber. 

Then divide the gas and dust into Group:  

Group name Representative gas or dust  

A Acetylene 
B Hydrogen
C Ethylene  
D Propane  
E Metal dust 

F Coal dust

G Grain dust

Gas temperature group division:  

   Temperature Group Safe Object Surface Temperature Common Explosive Gases 

      T1 ≤ 450°C 46 types including hydrogen, acrylonitrile, etc.  
      T2 ≤ 300°C 47 kinds of acetylene, ethylene, etc. 
      T3 ≤ 200°C 36 kinds of gasoline, crotonaldehyde, etc.  
      T4 ≤ 135°C 6 types including acetaldehyde, tetrafluoroethylene, etc. 
      T5 ≤ 100°C Carbon disulfide 
      T6 ≤ 85°C Ethyl nitrate and ethyl nitrite

Example: The meaning of the explosion-proof mark of the instrument  

The meaning of Ex(ia)ⅡC T6:  

Logo content Symbol Meaning 
Explosion-proof statement Ex conforms to certain explosion-proof standards, such as my country's national standards
Explosion protection: ia - uses ia-grade intrinsic safety, suitable for installation in Zone 0 
Gas category ⅡC Category ⅡC is allowed to involve explosive gases of category ⅡC 
Temperature group T6 The surface temperature of the instrument does not exceed 85°C 

The meaning of Ex(ia)ⅡC 
Logo content Symbol Meaning 
Explosion-proof statement Ex Complies with European explosion-proof standards

Explosion-proof method through restle from from using the 
Gas Category ⅡC ⅡC Class ⅡC explosive gases are allowed to be involved 
Note: There is no temperature group item in this mark, indicating that the instrument is not in direct contact with explosive gases.

Explosion-proof terminology: Related explosion-proof terminology and standards 

Safety barrier safety parameter definition:    
*8226; The maximum allowable voltage of the safety barrier: Um ensures the intrinsically safe performance of the intrinsically safe end of the safety barrier and allows the highest possible input voltage at the non-intrinsically safe end. 
*8226; The maximum open circuit voltage of the safety barrier: Uoc The maximum voltage when the intrinsically safe end is open within the maximum allowable voltage range 

*8226; Maximum short-circuit current of the safety barrier: Isc The maximum current value when the intrinsically safe terminal is short-circuited within the maximum allowable voltage range 
*8226; Allowable distributed capacitance of the safety barrier: Ca Maximum allowable external capacitance at the intrinsically safe end while ensuring intrinsic safety performance  
*8226; Allowable distributed inductance of the safety barrier: La Maximum allowable external inductance at the intrinsically safe end while ensuring intrinsic safety performance

Explosion-proof mark format description: 

Scientifically classify and classify the explosive hazardous media in factories or mining areas according to their ignition energy, minimum ignition temperature, and the time period during which explosive hazardous gases exist on site to determine the explosion-proof signs and explosion-proof forms of on-site explosion-proof equipment. 

Explosion-proof mark format:                 

      Ex       (ia)        ⅡC              T4 
(Explosion-proof mark, explosion-proof level, gas group, temperature group)

Explosion-proof grade description:

 Ia level:  
Electrical equipment that cannot ignite explosive gas mixtures during normal operation, one fault or two faults.
During normal operation, the safety factor is 2.0; 
When a fault occurs, the safety factor is 1.5; 
When there are two faults, the safety factor is 1.0.    
Note: Contacts with sparks must be equipped with flameproof enclosures, airtight enclosures or double the safety factor.  

 Ib level: 
Electrical equipment that cannot ignite explosive gas mixtures during normal operation and when a fault occurs.  
During normal operation, the safety factor is 2.0; 
When a fault occurs, the safety factor is 1.5. 
During normal operation, the sparking contacts must be protected by a flameproof shell or an airtight shell, and there are measures for self-display of faults. The safety factor when a fault occurs is 1.0.