Why explosion proof?
Explosive Substances: Some flammable substances are produced at various production sites. Approximately two-thirds of underground coal mines contain explosive substances.
In the chemical industry, more than 80% of production facilities contain explosive substances.
Oxygen is present throughout the air. There are numerous electrical instruments used in the production process, which can serve as an ignition source. Electrical sparks caused by friction, mechanical wear, electrostatic discharge, high temperature, etc. are common and especially likely to occur when electrical instruments and equipment malfunction.
Many industrial facilities objectively meet the conditions for an explosion. When the mixture of explosive substances and oxygen is within the explosive limit, an explosion will occur if there is an ignition source. Therefore, it is crucial to implement explosion-proof measures.
Hazard classification of hazardous locations:
|
Explosive materials |
Area definition |
Chinese pattern |
North American Standard |
|
Gas （CLASSI） |
Places where explosive gas mixtures exist continuously or for a long period under normal conditions. |
Zone 0 |
Division 1 |
|
Places where explosive gas mixtures may occur under normal conditions. |
Zone 1 |
||
|
Locations where explosive gas mixtures are unlikely to occur under normal conditions, only occasionally or for a short period of time under abnormal conditions. |
Zone 2 |
Division 2 |
|
|
Dust or fiber（CLASSII/III） |
Under normal conditions, explosive dust or the mixture of combustible fiber and air may occur continuously, often for a short period of time, or exist for a long period of time. |
Zone 10 |
Division 1 |
|
Under normal conditions, explosive dust or combustible fiber and air mixture cannot appear, but only under abnormal conditions, occasionally or for a short period of time. |
Zone 11 |
Division 2 |
Applicability of explosion protection in hazardous locations:
|
NO. |
Explosion-proof type |
code |
national standard |
Explosion-proof measures |
applicable scope |
|
1 |
Flameproof type |
d |
GB3836.2 |
Isolate existing ignition sources |
Zonal.Zona2 |
|
two |
greater security |
It is |
GB3836.3 |
Try to avoid the ignition source |
Zone1.Zone2 |
|
3 |
Intrinsically safe |
I a |
GB3836.4 |
Limit ignition source energy |
Zone0-2 |
|
Intrinsically safe |
I |
GB3836.4 |
Limit ignition source energy |
Zone1,Zone2 |
|
|
4 |
Barotropic type |
P |
GB3836.5 |
Hazardous substances must be separated from the source of ignition |
Zonel,Zone2 |
|
5 |
Oil-filled type |
O |
GB3836.6 |
Hazardous substances must be separated from the source of ignition |
Zone1.Zone2 |
|
6 |
Sand filled mold |
q |
GB3836.7 |
Hazardous substances must be separated from the source of ignition |
Zone1.Zone2 |
|
7 |
Sparkless type |
n |
GB3836.8 |
Try to avoid the ignition source |
Zone2 |
|
8 |
ex |
I |
GB3836.9 |
Try to avoid the ignition source |
Zonel,Zone2 |
|
9 |
Airtight type |
H |
GB3836.10 |
Try to avoid the ignition source |
Zone1, Zone2 |
Classification of dangerous explosive gases
According to the minimum energy required to ignite an explosive gas, China, Europe and most countries around the world classify explosive gases into four danger levels based on the following table:
|
Working Condition Category |
Gas classification |
Representative gas |
Minimum ignition spark energy |
|
Factory under the mine |
I |
If it's damp |
0.280mJ |
|
Factory outside the mine |
AI |
propane |
0.180mJ |
|
IIB |
ethylene |
0.060mJ |
|
|
CII |
hydrogen |
0.019mJ |
The United States and Canada initially categorized airborne explosive objects into three categories:
Class I: Gases and vapors;
Class II: Dust;
Class III: Fibers.
Then, the gases and dust were divided into groups.
| Group | Representative gas or dust |
| A | etino |
| B | hydrogen |
| W | ethylene |
| D | propane |
| AND | metallic dirt |
| F | coal dust |
| G | grain powder |
Gas temperature group division:
| Temperature groups | Safe object surface temperature | Common explosive gas |
| T1 | ≤450℃ | Hydrogen, acrylonitrile and 46 other types |
| T2 | ≤300℃ | Acetylene, ethylene and 47 other types |
| T3 | ≤200℃ | Gasoline, butenal and 36 other types. |
| T4 | ≤135℃ | Acetaldehyde, tetrafluoroethylene and other 6 types |
| T5 | ≤100℃ | carbon disulfide |
| T6 | ≤85℃ | Ethyl nitrate and ethyl nitrite |
Explosion-proof instrument signs
Meaning of Ex(ia) Ⅱ C T6:
| Signal content: | Symbol | Meaning |
| Explosion-proof declaration | Ex | Comply with certain explosion-proof standards, such as China's national standards |
| Explosion-proof mode | I a | Class I intrinsically safe explosion-proof method is adopted, which can be installed in Zone 0 |
| Gas category: | CII | It is permitted to involve class IIC explosive gas |
| Temperature groups | T6 | The surface temperature of the instrument should not exceed 85 ℃ |
Meaning of Ex(ia)ⅡC:
| Signal content: | Symbol | Meaning |
| Explosion-proof declaration | Ex | Comply with European explosion-proof standards |
| Explosion-proof mode | I a | Class I intrinsically safe explosion-proof method is adopted, which can be installed in Zone 0. |
| Gas category: | CII | It is permitted to involve class IIC explosive gas. |
Note: This symbol does not include a temperature group, indicating that the instrument is not in direct contact with the explosive gas.
Explosion-proof terminology:
Safety barrier parameter definitions:
Maximum Allowable Safety Barrier Voltage: One This parameter ensures the intrinsic safety performance of the intrinsically safe end of the safety barrier and represents the maximum voltage that can be input to the non-intrinsically safe end.
Safety barrier maximum open circuit voltage: Uoc This parameter represents the maximum voltage when the intrinsically safe terminal is open within the maximum allowable voltage range.
Safety Barrier Maximum Short-Circuit Current: Isc This parameter represents the maximum current value when the intrinsically safe terminal is short-circuited within the maximum allowable voltage range.
Allowable distributed capacitance of the safety barrier: Ca This parameter represents the maximum allowable external capacitance of the intrinsically safe terminal, while ensuring intrinsic safety performance.
Allowable distributed inductance of the safety barrier: La This parameter represents the maximum allowable external inductance of the intrinsically safe terminal, while ensuring intrinsic safety performance.
Explosion-proof signal format description:
The explosive hazardous substances in the factory or mining area must be scientifically categorized and classified based on their ignition energy, minimum ignition temperature and duration of the presence of explosive hazardous gas in the location. This information is used to determine explosion-proof signs and explosion-proof equipment required on site.
Explosion-proof sign format:
Ex(ia)ⅡC T4
This format consists of explosion-proof mark, explosion-proof grade, gas group and temperature group.
Explosion-proof grade description:
Grade IA:
Electrical equipment that cannot ignite explosive gas mixtures during normal operation, even with one or two failures.
During normal operation, the safety factor is 2.0; in the event of a failure, the safety factor is 1.5; and in the case of two faults, the safety factor is 1.0.
Note: Any sparking contact must be equipped with an explosion-proof enclosure, airtight enclosure or double factor of safety.
Grade IB:
Electrical equipment incapable of igniting explosive gas mixtures, even in the event of a failure during normal operation.
The safety factor during normal operation is 2.0, and in the event of a failure, the safety factor is 1.5.
During normal operation, contact with sparks must be protected by a flameproof or airtight enclosure, and measures for self-diagnosis of faults must be implemented.
The safety factor in the event of a failure is 1.0.
