In many areas of industry, it is a basic requirement to handle gases, vapours, mists or dust; in other fields these flammable substances are generated during processing.
If these substances are mixed with air and come into contact with an ignition source, there is a risk of an explosion.
In order to prevent an explosion and all subsequent damages to personnel, material and environment, explosion protection measures have been developed.
The explosion protected devices presented in this catalogue, mainly accord to protection type "intrinsic safety", i.e. the energy within the circuit is limited to such an extent that sparks or arcs are incapable of igniting an explosive atmosphere.
Compared to other protection methods, "intrinsic safety" has the advantage that it possible to service and wire live circuits.
Following please find some general guidelines on explosion protection.
We will be pleased to send you more detailed information.
In 1994, explosion protection regulations within the European Union were harmonised by the framework directive 94/9/EC, the so-called ATEX directive.
From 1 July 2003 on, all devices to be placed on the market must meet the requirements of ATEX and be certified accordingly.
Continuance of existing installations is protected.
The likelihood of the occurrence of a dangerous explosive atmosphere (EN 60079-10, EN 1127) is the basis for zone classification.
Classifications range from zones 0 to 2 (flammable gases, mists and vapours) to zones 20 to 22 (explosive atmospheres due to flammable dusts):
Zone 0: Dangerous atmospheres due to gases that are present continuously, frequently or for long periods
Zone 1: Dangerous atmospheres that are present occasionally
Zone 2: Occurrence of dangerous atmospheres is unlikely and for a short period only
Zone 20: Dangerous atmospheres due to dust clouds that are present continuously, frequently or for long periods - simple dust deposits do not constitute a zone 20 determination.
Zone 21: A dust cloud may occur occasionally during normal operation
Zone 22: It is unlikely that a dust cloud will occur during normal operation and if so, only for a short period.
Zone classifications for gases had previously been regulated within the European Union, whereas the ATEX classifications for combustible dusts are new.
Therefore it is particularly important for installers in those states where, to date, zone divisions for combustible dusts did not yet apply, to pay special attention to these new zone definitions.
Every device for explosion protected areas must be clearly marked.
In this context, one distinguishes between intrinsically safe equipment which may be installed directly in the explosion hazardous area and
associated apparatus which can be regarded as the interface to the explosion hazardous area.
According to ATEX, the new type of marking gives information about the equipment's constructional level of safety and the group definition.
From these two indications the zone can be derived:
I mining and related installations above ground
II all other areas (e.g. chemical industry)
1 very high safety level - zones 0 / 20
2 high safety level - zones 1 / 21
3 normal safety level - zones 2 / 22
M1 explosive atmosphere continuously present (firedamp, combustible dusts) - mining
M2 explosive atmosphere present occasionally - mining
G explosion protection against gas
D explosion protection against dust
"II 1 G" is, for example, the appropriate marking for intrinsically safe equipment to be used in gaseous atmospheres in the chemical industry, zone 0;
"II (1) G" is, for example, the marking of associated equipment.
Further information on the type of protection is provided by marking to CENELEC according to EN 60079-0ff.
Ex stands for compliance with regulations.
Intrinsically safe equipment according to EN 60079-11 features two independent means of protection
ia or one independent means of protection ib.
According to ATEX, devices for underground mining are marked with I and for all other locations in which a potentially explosive atmosphere exists with
II.
Based on the fact that not all materials require the same ignition energy, these are divided into three groups:
A - a "high" level of energy,
B - a "medium" level of energy, and
C - a "low" level of energy.
For detailed information on the different ignition energy of flammable materials please refer to related standards and literature.
The surface temperature of an apparatus can be an additional ignition source.
Intrinsically safe equipment is divided into six temperature classes: e.g.
T1 accords to a surface temperature of 450 °C and T6 to a temperature of 85 °C.
Associated equipment is not subject to temperature classification because it may not be installed in explosion hazardous areas.
Brackets are an additional means of identification.
For example:
the marking of intrinsically safe equipment is Ex ia IIC T6 and
associated apparatus [Ex ia] IIC. Alongside this marking, the relevant electrical data such as current, voltage, power, capacitance and inductance are provided.
A test number shows that the equipment has been subjected to EC type examination.
This number consists of the identification number of the authorized body, the year of issue, the term ATEX to signify accordance with directive 94/9/EC and an internal certificate number (e.g. PTB 97 ATEX 2128).
Approvals and Electrical Data of TURCK devices find you in the corresponding data sheets
Intrinsically safe equipment may only be installed by trained and qualified personnel familiar with the applicable standards (such as EN 60079-14 and EN50020).
Following some important guidelines:
It is required to observe the specified clearances, i.e. a thread measure of 50 mm must be observed between intrinsically safe and non-safe connections.
When interconnecting intrinsically safe apparatus, it is required to provide a "Proof of Intrinsic Safety".
Equipment may not be opened or modified.
Installations must be inspected regularly with regard to explosion protection.
Construction, insulation and installation of cables are subject to special requirements.
Cables must be specially marked.
If color-coded, their color must be light blue.
Electro-magnetic capability must be observed.
Intrinsically-safe and non-safe circuits may not be conducted in the same cable.
Switzerland has accepted the ATEX directive by the VGSEB and translated it into national regulations.
All devices with ATEX approval may be directly installed.
Those countries wanting to become members of European Union apply the ATEX standards and directives but a separate national approval is required.
Explosion protection in the United States and Canada differs significantly from the regulations in the European Union.
In the United States, there are two different systems for classification of explosion hazardous areas.
The method of Intrinsic Safety is accepted by both systems.
The primary and still most prevalent system is described in the Article 500 of the ANSI/ NFPA 70 NEC (US National Electrical Code).
This system has been in use in North America for many years and is still the most prevalent method.
Classes, Divisions and Groups are used to define the type of hazard as well as the probability of the hazard being present in an ignitable concentration.
Class defines the basic hazardous material:
- Class I: Gases and vapors
- Class II: Dusts
- Class III: Fibers
Division defines the probability of the hazardous material being present in an explosive concentration:
- Division 1: Present under normal conditions
- Division 2: Present under fault conditions
Group defines specific groups of hazardous materials with similar ignition properties, typified by the following gases/dusts:
- Group A: Acetylene
- Group B: Hydrogen
- Group C: Ethylene
- Group D: Propane
- Group E: Metal dust
- Group F: Coal dust
- Group G: Grain dust
T Codes, or maximum surface temperature codes, are also defined and have identical meaning to those of the EU and IEC classification systems.
However, in the Article 500 system, there are additional codes that divide codes
T2, T3, and T4 into smaller subdivisions.
The additional codes include
T2A (= 280 °C),
T2B (= 260 °C),
T2C (= 230 °C),
T2D (= 215 °C),
T3A (= 180 °C),
T3B (= 165 °C),
T3C (= 160 °C),
T4A (= 120 °C).
The second system first appeared as Article 505 of the 1996 edition of the NEC.
It was intended to promote harmonization with the rest of the world, and it is nearly identical to the "Zone" system described in IEC 60079.
It is officially accepted as an alternative to the Article 500 system and is becoming gradually more prevalent.
However, the two systems cannot be mixed together, making it difficult to implement the new system in existing facilities.
Devices must be certified to US national standards.
Device marking is similar to the IEC 60079 system, except that "Class" (with the same meaning as in the Article 500 system) and "Zone" are added as shown in the following examples:
Class I, Zone 0, AEx ia IIC T6
Class I, Zone 0, AEx [ia] IIC
The "A" to indicate that the device is certified to the appropriate American national standard.
At this time, only Class I atmospheres are covered by Article 505.
The situation of having two parallel systems is similar in Canada, although the systems are defined in CSA 22.1, the Canadian Electrical Code (CEC).
Canada has gone a step further and mandated the IEC-style system for use in new installations.
Installation guidelines for Intrinsically Safe Systems in the US can be found in ANSI/ISA RP12.6.
Installation guidelines for Canadian systems can be found in Appendix F of the CEC.
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