This Article provides a comprehensive overview of the design and utilization of equipment intended for use in areas that may potentially contain explosive atmospheres caused by gases, vapors, and combustible dusts or fibers. These areas are commonly known as hazardous area zones. A “hazardous area” is characterized as a location where the atmosphere contains, or has the potential to contain, flammable or explosive gases, dusts, or vapors in quantities that are significant.
To safeguard installations against potential explosions, it is necessary to employ a methodology for analyzing and classifying areas that could be hazardous. The primary objective of this process is to guarantee the appropriate choice and proper installation of equipment, ultimately aiming to prevent explosions and ensure the safety of individuals.
Explosion-proof electrical equipment is classified and applicable to explosive areas based on their construction, as shown in the table below
|
Name & Code |
Definition and Characteristics |
Diagram |
Suitable Areas |
|
pressure-resistant explosion-proof （d） |
(1) The enclosure is equipped with electrical components such as NFB, MS, etc., which may generate sparks during normal operation. (2) If hazardous gases escape and potentially cause an explosion, the enclosure must be able to withstand the explosion pressure and prevent flame leakage from the junction, igniting explosions of external hazardous gases. |
|
ZONE 1 ZONE 2 |
|
safety-enhanced explosion- proof （e） |
(1) The enclosure is designed solely for airtightness and lacks pressure resistance capability. (2) The interior can only accommodate components that do not generate sparks or excessive heat during normal operation, such as Eexe terminals and Eexd-modules (pressure-resistant explosion- proof modules). The pressure-resistant explosion-proof electrical components produced through Eex-d molding are new products that are absolutely free from sparks and excessive heat, making them suitable for use in various control boxes. |
|
ZONE 1 ZONE 2 If there are electrical components that may generate sparks or excessive heat, they can only be used in ZONE 2. |
|
internal pressure explosion- proof （p） |
The enclosure is a typical distribution box but made in a fully sealed manner. The internal pressurization generates a slightly higher pressure than atmospheric pressure to prevent the ingress of hazardous gases from the outside. The convection of the inflation pipeline helps to dissipate internal heat. It is commonly used in large equipment or entire control rooms |
|
ZONE 1 ZONE 2 |
|
inherently safe explosion-proof （i） |
(1) Designed for electronic circuits or low-energy electricals to prevent the occurrence of gas explosions around instruments and circuits, regardless of normal or abnormal operations. (2) The circuit outputs or inputs of the intrinsic explosion-proof electrical components are designed to be controlled below the energy level that is capable of causing hydrogen gas ignition and explosion. |
|
ZONE 0（ia） ZONE 1（ia，ib） ZONE 2（ia，ib） |
|
oil-immersed explosion- proof （o） |
(1) The electrical components inside the enclosure are transformers, and high flashpoint insulating oil is used for isolation to achieve explosion-proof effect. (2) This type of equipment has poor reliability and is rarely used nowadays. |
|
ZONE 1 ZONE 2 |
|
filled explosion-proof （q） |
(1) Electronic circuits such as capacitors, resistors, and small transformers are installed inside the enclosure and isolated with fine sand filling to achieve explosion-proof effect. (2) This type of structure is not used separately, but rather installed inside an EExe enclosure for usage. |
|
ZONE 1 ZONE 2 |
|
injection molded pressure -resistant explosion-proof （m） |
(1) This is a method of explosion protection where components that may generate sparks or excessive heat are encapsulated with an overall polyester molding, ensuring that the surface of the entire molded enclosure will not produce sparks or temperature rise that could cause ignition of hazardous gases. (2) Control components of general switches below 630A are processed by molding using polyester material according to the requirements of pressure resistance explosion-proof specifications and approved by EEx-d. |
|
ZONE 1 ZONE 2 |
|
special explosion-proof (s) |
The special explosion-proof structure refers to special electrical combinations or control methods, which are processed according to the aforementioned structures. They must be individually designed for the specific electrical equipment suitable for use in the required hazardous locations and approved by explosion-proof certification authority. |
ZONE 0 ZONE1 ZONE 2 |
An common mistake that many people make is to use the terms
“pressure-resistant explosion-proof zone”or “safety-increased explosion-proof zone”,
which is incorrect. The correct terminology should be used to describe the
classification of explosion-proof areas as ‘0 level’, ‘1 level’, or ‘2 level’
premises. The terms “pressure-resistant” and “safety-increased” should be used to
describe the construction of explosion-proof electrical devices, rather than
referring to specific zones. It is important for everyone to distinguish between
these concepts.
Each of the aforementioned explosion-proof constructions has specific manufacturing
regulations. In the case of pressure-resistant explosion-proof devices, special
requirements must be met due to the presence of electrical components that may
generate sparks or excessive heat during normal operation. Typically, the shell of
these devices needs to have a greater thickness (strength) and must withstand a
pressure of at least 10 Kg/Cm² from explosive gas mixtures such as H2 without
experiencing any damage after repeated testing (commonly known as explosion tests).
Additionally, the tolerances and depths of the joints between the shell components
are strictly regulated. Typically, the testing procedure involves filling the
external environment of the shell with an inflammable gas mixture, and if the
internal flame of the shell does not ignite the external gas for ten consecutive
tests, it can be considered as passing the test. Alternatively, compliance with
safety regulations can also be confirmed by adhering to international testing
standards. The following table provides an example based on the JIS (Japanese
Industrial Standards) criteria, with slight variations to the values used in Europe
and the United States (which are generally similar).
|
Explosion Level |
Clearance m/m |
volume of the box |
depth of the clearance |
|
1 |
Above 0.6 |
(A) 2000CM³ |
≧25m/m |
|
2 |
0.4 above 0.6 below |
(B) 2000～100CM³ |
≧15m/m |
|
(C) 100～2CM³ |
≧10m/m |
||
|
3 |
0.4 below |
(D) 2CM³Below |
≧5m/m |
|
Jap |
EU |
USA |
|
1 |
IIA |
D |
|
2 |
IIB |
C |
|
3 3a 3b 3c 3n |
IIC |
B |
|
A |
According to the table above, it is noted that the representation is consistent between Japan and Europe, while the United States follows a different approach. However, it represents two different situations. Firstly, if the explosion level is represented by the Japanese style of 1, 2, 3, or the European style of IIA, IIB, IIC, or the American style of A, B, C, D, then the pressure-resistant explosion-proof shell must be manufactured according to the data in the table. Secondly, besides representing the conditions, it also relatively represents the hazardous gas (liquid) environments applicable to a specific group. In fact, European A, B, C and American A, B, C, D represent the sensitivity of hazardous gases (liquids) to spark explosions and the required level of pressure-resistant explosion-proof construction. Common hazardous gases (liquids) are classified separately by Europe and the United States (as shown in Table six). This classification is based on the hazardous nature of sparks (i.e., flashpoint) and the ignition point of various hazardous gases (liquids), indicating the temperature at which they will ignite even without sparks. Therefore, it is necessary to specify the ignition temperature of hazardous gases (liquids) relative to the surface temperature of explosion-proof electrical devices (as shown in Table seven) in order to achieve complete safety protection.
|
Lgnition Temperature to /l/in℃ |
EN OR IEC |
JIS |
NEC |
Lgnition Temperat ure to /2/in℃ |
|||
|
Group |
Flash Point ℃ |
Typical gases or Vapours |
IGNI- TION CLASS |
Group |
Typicsl Gases or vapours |
||
|
540 515 425 460 630 630 555 365 340 505 370 530 215 240 220 595 455 475 210 285 360 220-300 470 405 455 550 490 535 385 415 140 605 425 535 495 180 440 415 |
II A |
-19 GAS 11.1 GAS -11.1 28.9 -4 -21.7 GAS 11 12 32.7 -42.8 GAS 11.7 -32.7 32 17.2 -37.8 GAS |
Aceton Athan Athanol Athylacetat Athylnitrit Ammoniak Anilin Benzol Butan Butanol Butanon Butylaacetat Dichlorathy Heptan Hexan Heizol Methan Methanol Methylacetat Octan Pentan Pentanol Petroleum-Naphta Petrolum(einschl.Fahtbenzin ) Propan Propanol Propylen Pyridin Styrol Toluol Viny lacetat Viny lCHLORID Xylole Acetaldehyd Kohlenmonoxid |
1 |
D |
aceton athane ethanol(ethyl alcohol) ethyl acetate ammonia benzene butane 1-butanol 2-butanol methyl ethyl ketone n-butyl acetate ethylene dichloride heptanes hexanes methane(natural gas) methanol(methyl alcohol) octanes pentanes 1-pentanol petroleum naphtha gasoline propane 1-propanol 2-propanol propylene pyridine styerne toluene vinyl acetate Vinyl chloride Xylenes |
465 515 356 427 651 560 405 365/405 516 425 413 280 225 539 385 220 260 300 288 280-456 450 440/399 460 482 490 480 427 472 530 |
|
C |
Acetaldehyde Carbon monoxide Ethylene hydrogen cyanide cyclopropane diethyl ether |
175 610 490 500 160 |
|||||
|
II B |
GAS GAS GAS |
Athylen Cyanwasserstoff Cylclopropan Diathylather Tetrafluorathylen Acrylaldehyd (Acroleiin) Athylenoxid Butadien-1,3 |
2 |
||||
|
B |
Acrolein Ethylene oxide Butadiene |
220 429 420 |
|||||
|
Lgnition Temperature to /l/in℃ |
EN OR IEC |
JIS |
NEC |
Lgnition Temperat ure to /2/in℃ |
|||
|
Group |
Flash Point ℃ |
Typical gases or Vapours |
IGNI- TION CLASS |
Group |
Typicsl Gases or vapours |
||
|
560 430 560 305 95 |
IIB |
GAS -37.2 |
Koksofengas Propy lenoxid |
2 |
B |
manufactured gases (containing more than 30% hydrogen (by volume) propy lene oxide Hydrogen |
449 400 |
|
II C |
GAS GAS -30 |
Wasserstoff Acetylen Athylnitrat Schwefelkoh -Lenstoff |
3a 3 3c 3b |
||||
|
A |
Acetylene |
305 |
|||||
|
Special Safeguards |
Carbon disulfide |
100 |
|||||
|
Remark |
In the above table, within the Japanese JIS explosion level 3, due to its higher level, there are fewer hazardous gases (liquids) classified under this level. Specifically, gases (liquids) designated as 3a| 3b and 3c directly represent this level, while the rest that are unspecified are represented as 3N. |
||||||
|
Level |
Temp Range |
Code Jap |
Code EU |
Code USA |
|||
|
1 |
450℃ above |
G1 |
T1 or G1 |
T1 450℃ |
|||
|
2 |
300～450℃ |
G2 |
T2 or G2 |
T2 |
300℃ |
T2C |
230℃ |
|
T2A |
280℃ |
T2D |
215℃ |
||||
|
T2B |
260℃ |
||||||
|
3 |
200～300℃ |
G3 |
T3 or G3 |
T3 |
200℃ |
T3B |
165℃ |
|
T3A |
180℃ |
T3C |
160℃ |
||||
|
4 |
135～200℃ |
G4 |
T4 or G4 |
T4 |
135℃ |
T4A |
120℃ |
|
5 |
100～135℃ |
G5 |
T5 or G5 |
T5 100℃ |
|||
|
6 |
85～100℃ |
G6 |
T6 or G6 |
T6 85℃ |
|||
There is an important concept regarding the temperature
values in the temperature class, which is commonly misunderstood by the general
public. In Table 7, if it refers to the regulations for explosion-proof electrical
equipment, it means that the surface temperature of the electrical enclosure must
not exceed that value. It does not imply the temperature resistance of the
electrical components. Typically, when selecting electrical equipment, the surface
temperature will be lower than the ignition point of the hazardous gas (liquid) in
that particular location, aiming to enhance safety.
Considering the information above, it appears that the presence of sparks or
temperatures above the ignition point of the hazardous gas (liquid) is not the only
concern. In reality, there are three factors that can lead to combustion: 1.
Presence of flammable or combustible vapors. 2. Ignition source (such as sparks or
surface temperature reaching the ignition point of the hazardous gas). 3.
Availability of oxidizing agents (such as air or pure oxygen). Hence, even if there
are potential ignition sources in areas where hazardous materials are present,
explosions may not occur if the concentration of the hazardous substance is too high
or if there is insufficient oxidizing air. Similarly, if the concentration of the
hazardous substance is too low, it generally does not pose a significant risk. Each
hazardous material has different concentration levels, and concentrations within the
specified range are considered extremely dangerous. This means that the three
elements of combustion can only occur within this range, providing a better
understanding of certain characteristics of explosion-proof environments.
In the future, it is also important to understand the expression of explosion-proof
symbols used in Europe, America, and Japan in order to make appropriate product
choices. (Such as Table 8).
|
|
System Code |
First No. Construction Code |
Second No. Explosion Level Code |
Third No. Flash point temperature Level |
Remark |
|
EU |
IEC （EEx） |
d 、e 、i 、q 、s |
IIA 、IIB 、IIC |
T1～T6 G1～G6 |
Example: EExde IIc T6 |
|
USA |
NEC （NEMA） |
CLASS 1 DIV 1 CLASS 1 DIV 2 |
A 、B 、C 、D |
T1～T6 |
Example: CLASS 1 DIV 1 GROUP C@ D |
|
Jap SK CHN |
NEC （JIS） （CKS） （CNS） |
d 、e 、I 、q 、s |
1 、2 、3 3a 3b 3c 3n |
G1～G6 |
Example d3nG6 d2G4 eG3 |
