What Is the Difference Between Intrinsically Safe Explosion-proof (Exi) and Explosion-proof (Exd)

Industrial instrumentation, if their own performance deficiencies, or the use of the process in the environment, or the existence of irrationality in the operating process, etc., may lead to the risk of explosion, resulting in economic losses, and even jeopardize personal safety. The explosion-proof instrumentation does not exist in their own safety hazards, in order to play a truly protective role.

Explosion conditions, generally explosive substances, oxygen, ignition source. Objectively speaking, many industrial sites to meet the conditions of this explosion, when the explosive substances and oxygen mixed concentration reaches a certain value, and it happens that the value is within the explosive limit, if there is an ignition source, then the explosion is imminent. Therefore, explosion-proof is important.

What Is the Difference Between Intrinsically Safe Explosion-proof (Exi) and Explosion-proof (Exd)

 

The Difference Between Intrinsically Safe Explosion-Proof and Explosion-Proof

Intrinsically safe explosion-proof (EXi), explosion-proof (EXd) is often seen in industrial instrumentation. So what is intrinsically safe explosion-proof? What is explosion-proof?

Intrinsically safe explosion-proof, that is, intrinsically safe, is the instrument whether in a normal state or fault state, the circuit, the system generates a point spark and the temperature reached will not ignite the explosive mixture. Intrinsically safe instrumentation explosion-proof performance, is the circuit itself to achieve, and is not the use of external measures to achieve, and therefore is intrinsically safe, suitable for all hazardous locations and explosive gases, vapors, mixtures, and can be directly applied in the most hazardous area 0 places.

Explosion-proof, that is, pressure-resistant explosion-proof, the ability to ignite explosive mixtures of instrumentation components enclosed in a shell, the shell is very strong, can withstand the explosion of the internal explosive mixture of explosive pressure, to prevent explosive mixtures to the outside of the shell to prevent the transmission of the explosion. Explosion-proof type is likely to explode, but only in the shell. This instrument has to have strict explosion-proof requirements for the combination surface of the components, the number of threaded turns, component gaps, wire ports and so on. Explosion-proof to note is that when opening the cover of the shell, be sure to turn off the power supply first, in order to prevent the occurrence of danger.

The Installation Site Is In Different Hazardous Areas Should Be How to Choose

Zone 0: flammable gas always or for a long time; continuous existence of the danger is greater than 1000 hours / year of the region, can choose ia type, S type (refers to the S type designed specifically for the 0 zone).

Zone 1: flammable gas is likely to occur or exist in the normal operation of the instrument; intermittent presence of the danger of 10~1000 hours/year area, may be in addition to the n-type (intrinsically safe) other than the type;

Zone 2: Areas where flammable gases are not normally present and are present for a short time even if they occur occasionally; areas where the hazard exists in an accidental condition for 0.1-10 hours/year, all explosion-proof types are optional.

How to Reasonably Select the Explosion-Proof Instrument

According to the instrument installation, the use of hazardous areas to choose the explosion-proof type of instrumentation.

Zone 0: can only choose ia type, S-type (refers to the S-type designed specifically for Zone 0);

Zone 1: may be in addition to the n type (intrinsically safe) other types;

Zone 2: all explosion-proof types are optional;

Table 1 Hazardous area classification

Explosive substances Definition of regions Chinese standard North American Standard
 

 

 

Gas(CLASS I)

Places where explosive gas mixtures are present continuously or for a prolonged period of time under normal conditions. Zone 0 Div.1
Places where explosive gas mixtures are likely to occur under normal conditions Zone 1
Under normal circumstances explosive gas mixtures are unlikely to occur, only in abnormal circumstances, occasional or short-term occurrence of the place Zone 2 Div.2
 

 

 

 

 

 

Dust or fibers(CLASSII/III)

Under normal circumstances, explosive dust or combustible fibers and air mixtures may be continuous, short-time frequent or long-time presence of the place Zone 10 Div.1
Under normal circumstances, explosive dust or combustible fibers and air mixtures can not be present, only in abnormal circumstances, occasional or short-term occurrence of the site Zone 11 Div.2

According to the possible flammable gases, vapors, explosion levels and ignition temperature group, select the explosion-proof level of the instrument and the maximum allowable surface temperature group.

Table 2 combustible gases, vapors, ignition and explosion levels

Working Condition Category Gas Classification Representative gases Minimum spark energy
Underground mine I Methane 0.280m
 

Plant outside the mine

IIA Propane 0.180m
IIB Ethylene 0.060m
IIC Hydrogen 0.019m

Table 3 Ignition temperature groups of flammable gases and vapors

Temperature grouping Surface temperature of Safe object Common explosive gases
T1 ≤450℃ Hydrogen, acrylonitrile and 46 others
T2 ≤300℃ Acetylene, ethylene, etc. 47 kinds
T3 ≤200℃ Gasoline, butenal, etc. 36 kinds
T4 ≤135℃ Acetaldehyde, tetrafluoroethylene, etc. 6 kinds
T5 ≤100℃ Carbon disulfide
T6 ≤85℃ Ethyl nitrate and ethyl nitrite
  1. combustible gases, vapors, explosion level is also the explosion-proof level of electrical equipment, the two are the same.
  2. combustible gases, vapors, ignition temperature group and the highest surface temperature of electrical equipment group corresponds to each other.

Explosion-Proof Type of Applicability in Hazardous Locations

Table 4 explosion-proof type of applicability in hazardous locations

Serial Number Nicknames Chinese national standard Explosion-proof measures Area of application
1. Flameproof GB3836.2 Isolation of ignition sources present Zone1,Zone2
2. Increased safety GB3836.3 Attempts to prevent the creation of ignition sources Zone1,Zone2
3. Intrinsically Safe GB3836.4 Limiting the energy of the ignition source Zone1-2
4. Intrinsically Safe GB3836.4 Limiting the energy of the ignition source Zone1,Zone2
5. Positive Pressure GB3836.5 Isolation of hazardous substances from ignition sources Zone1,Zone2
6. Oil-filled GB3836.6 Separate hazardous substances from ignition sources Zone1,Zone2
7. Sand-filled GB3836.7 Separation of hazardous substances from ignition sourcesZone1,Zone2 Zone1,Zone2
8. Non-sparking type GB3836.8 Attempts to prevent the creation of ignition sources Zone2
9. Sealable GB3836.9 Trying to Prevent Ignition Sources Zone1,Zone2
10. Airtight GB3836.10 Trying to prevent ignition sources Zone1,Zone2

What Is the Meaning of the Explosion-Proof Marking of the Instrument

Meaning of Ex(ia) IIC T6:

Logo content Notation Meaning
Explosion-proof declaration Ex Conforms to a certain explosion-proof standard, such as our national standard
Explosion protection method ia Intrinsically safe explosion-proof method of class ia, can be installed in zone 0
Gas category IIC Allowed to involve the IIC class explosive gas
Temperature group T6 Instrument surface temperature does not exceed 85 ℃

Meaning of Ex(ia)ⅡC :

Logo content Notation Meaning
Explosion-proof declaration Ex Conforms to European explosion-proof standards
Explosion protection method ia Intrinsically safe explosion-proof method of class ia, can be installed in zone 0
Gas category IIC Allowed to involve the IIC class explosive gas

Installation of Instrumentation in Explosion Hazardous Locations Requirements

  1. Explosion-endangered places to use the instrumentation, electrical equipment and installation materials such as junction boxes, distribution boxes, terminal boxes, etc., must have been issued by the national authorized agencies explosion-proof certificate of conformity should be checked before installation of its specifications, models are in line with the design requirements, and its external should be free of damage, cracks.
  2. In explosion-hazardous areas can also be set up positive pressure explosion-proof instrumentation box, non-explosion-proof instrumentation and other electrical equipment, instrumentation box ventilation pipe must be kept free, before the power supply, should be passed into the box volume of more than 5 times the gas for replacement.
  3. Explosion-hazardous areas within the instrument wiring, must ensure that in the unlikely event of grounding, short-circuiting, disconnection and other accidents, but also does not lead to the formation of ignition sources. Thus, cables, wires must be laid through the pipe, the use of pressure-resistant explosion-proof metal pipe, threaded between the protection pipe and protection pipe and junction boxes, junction boxes, cable boxes, cable boxes, should be used between the cylindrical pipe threaded connections, threads should be effectively engaged part of the more than 5 ~ 6 buckles. Explosion-proof flexible connection pipe should be used when flexible connection is required. Instrumentation wiring in Zone 2, generally should also be threaded, but only to protect the insulation of cables and wires from trauma.
  4. Wire sinks, cable trenches, protective tubes across the demarcation line between different levels of explosion hazardous places, sealing measures should be taken to prevent explosive gases from being strung from one hazardous place into another hazardous place.

Conclusion

In general, intrinsically safe instruments are suitable for non-explosive hazardous areas in general industrial places, while explosion-proof instruments are suitable for hazardous areas in explosive gas or dust environments with higher protection levels. It is very important to choose the right type of instrumentation according to the actual working environment and hazardous requirements.

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