Definition of Intrinsic Safety Equipment Mark

Ex — Explosion-proof marking

ia — Explosion-proof rating

Ga — Equipment Protection Level

II C — Gas group a Ga] II C.

 

 

The explosion-proof rating of our company’s products is: [Ex ia Ga] II C.

 

 

Explosion-proof rating

ia : Under normal operating conditions, as well as under single-count-fault and double-count-fault conditions, it must be incapable of igniting explosive gas mixtures. The intrinsically safe side of the safety barrier in this category may be connected to intrinsically safe equipment installed in hazardous locations of Zone 0, Zone 1, or Zone 2. For “ia”-class electrical equipment, components that are susceptible to interference must be designed with a “triple-redundancy” architecture.

 

ib : Under both normal operating conditions and in the event of a single fault, it must be incapable of igniting an explosive gas mixture. The intrinsically safe side of safety barriers in this category may be connected to intrinsically safe equipment installed in Zone 1 or Zone 2 hazardous locations. For “ib”-class electrical equipment, components that are susceptible to interference must be designed with redundancy.

ic : Under normal operating conditions, it shall not ignite explosive gas mixtures. The intrinsically safe side of the safety barrier in this category may be connected to intrinsically safe equipment located in Zone 2 hazardous areas.

 

Gas Group

Group I electrical equipment: intended for use in coal mine environments susceptible to methane.

Class II electrical equipment: Suitable for use in hazardous explosive environments other than coal mines.

Electrical equipment in Group II can be further subdivided according to the ignition energy required by the flammable substances present. The subgroups are designated by uppercase English letters, as shown in the following table: Group IIC requires the lowest ignition energy; consequently, equipment in Group IIC is universally applicable to both Group IIA and Group IIB.

Temperature Class

The equipment temperature class specifies the maximum permissible surface temperature of the equipment. The equipment temperature class must be lower than the ignition temperature of the flammable substances present in the hazardous location where the equipment is used; otherwise, combustion and explosion may occur.

As shown in the table above, the vast majority of common explosive gases belong to temperature classes T4 and higher.

 

Zoning of Explosive Hazardous Areas

In the design of safety and explosion-proof systems and in the selection of explosion-proof products, in addition to classifying and grouping the gases present in explosive atmospheres, it is also necessary to delineate hazardous areas for explosive gases based on the frequency of their occurrence and the duration of their presence:

 

Our company’s Class IIA, Group II C gas-category products are suitable for Zone 0 and also for Zones 1 and 2.

 

Intrinsic Safety Performance Certification Parameters for Safety Barriers

Maximum Voltage (Um)

　　The maximum voltage (AC RMS value or DC voltage) that may be applied to the non-intrinsic safety connection device of the associated equipment without compromising its explosion-proof type.

Maximum Input Voltage (Ui)

　　The maximum voltage (AC peak or DC) that may be applied to an intrinsically safe circuit connection device without compromising its intrinsic safety performance.

Maximum Output Voltage (Uo)

　　Under open-circuit conditions, when the voltage applied to the equipment connection device reaches the maximum voltage (including Um and Ui), the resulting maximum output voltage of the intrinsically safe circuit—whether AC peak or DC—may occur.

Maximum Input Current (Ii)

　　The maximum current (AC peak or DC) that may be applied to an intrinsically safe circuit connection device without compromising its intrinsic safety performance.

Maximum Output Current (Io)

　　The maximum current (AC peak or DC) of the intrinsically safe circuit originating from the electrical equipment connection device.

Maximum Input Power (Pi)

　　The maximum input power to an intrinsically safe circuit that may be consumed within the electrical equipment, provided that such connection to an external power source does not compromise the intrinsically safe performance of the equipment.

Maximum Output Power (Po)

　　The maximum output power of an intrinsically safe circuit that can be derived from electrical equipment.

 

Maximum Internal Capacitance (Ci)

　　The total equivalent internal capacitance of electrical equipment arising from the connection device of electrical equipment.

Maximum External Capacitance (Co)

　　The maximum capacitance of an intrinsically safe circuit that can be connected to an electrical equipment connection device without compromising its intrinsic safety performance.

Maximum Internal Inductance (Li)

　　The total equivalent internal inductance of electrical equipment arising from the electrical equipment connection device.

Maximum External Inductance (Lo)

　　The maximum inductance of an intrinsically safe circuit that can be connected to an electrical equipment connection device without compromising its intrinsic safety performance.

Maximum Permissible Distributed Capacitance of the Cable

　　The difference between the maximum allowable external capacitance (Co) of the associated equipment and the intrinsically safe equipment’s maximum internal capacitance (Ci).

Maximum Permissible Distributed Inductance of the Cable (Lc)

　　The difference between the maximum external inductance (Lo) allowed for the associated equipment and the maximum internal inductance (Li) of the intrinsically safe equipment.

Maximum external inductance-to-resistance ratio (Lo/Ro)

The ratio of inductance to resistance in an external circuit that can be connected to an electrical equipment connection device without compromising intrinsic safety performance.

 

 

Most industrially advanced countries worldwide adopt a “parameter-based certification” approach, under which a set of safety parameters is specified separately for associated equipment and field equipment. Users are then free to combine electrical equipment from different manufacturers; from a safety perspective, it is sufficient to ensure that the following relationship is satisfied:

Principles for Selecting Safety Barriers

a) Determine the required explosion-proof rating of the safety barrier based on the type of hazardous location and the on-site explosion-proof requirements. The explosion-proof rating of the safety barrier must be no lower than the explosion-proof marking rating of the intrinsically safe field equipment.

 

b) Install safety barriers of the appropriate type based on the equipment type at the site;

 

c) Determine the maximum voltage rating of the safety barrier based on the highest voltage that may be present or generated by the control room instrumentation;

 

d) Determine the polarity of the safety barrier based on the polarity of the signals and power supplies relative to ground at the field equipment; the safety barrier must be compatible with the intrinsically safe field instruments in terms of safety polarity and signal transmission method.

 

e) Consider the impact of the voltage drop across the safety barrier’s termination resistor to determine the maximum short-circuit current of the safety barrier and whether the system can operate normally;

 

f) Whether the permissible distributed parameters of the safety barrier meet the requirements.