IEC Hazardous Fundamentals

Last updated: Sept. 24th 2001

By: Robert Johnson - EPM Technical Sales Manager

Hazardous Area

A hazardous area can be defined as "An area in which flammable substance in the form of gas, vapor or dust when mixed with the air, is present in such proportions that it can explode when in contact with an ignition source.  This mixture of gas and air in proper proportions is important in the equation.  The mixture must be between the lower flammable limit and the upper flammable limit in order for an explosion to occur. Most traditional flammable gases and vapors have limits between 2% - 10% fuel to oxygen ratios.  In order for ignition to occur, a certain amount of energy is needed.  The minimum ignition energy is the smallest possible amount of energy which is converted during the discharge of a capacitor and is just enough to ignite the most ignitable mixture.  The minimum ignition energy is around 10-5J for Hydrogen.

Area Classification

Hazardous areas are classified with respect to the potential danger of an explosion and the areas are divided into zones:

Zone 0: An area in which an explosive atmosphere is continually present or present for long periods, typically over 100 hours per year

Zone 1: An area in which an explosive atmosphere is likely to occur in normal operation, typically between 10 and 100 hours per year

Zone 2: An area in which an explosive atmosphere is not likely to occur in normal operations and, if it does occur, will exist for only a short time, typically less than 10 hours per year

Primary Explosion protection

The term primary explosion protection refers to all precautions which prevent a dangerous, explosive atmosphere from being created.  This can be achieved by avoiding the flammable substances, deactivation, limitation of the concentration, or natural or artificial ventilation.  The various protection techniques listed below employ some of these protection concepts.

• Explosion Protection Techniques

  Ex 'o' "Oil Immersion" Protection - EN 50015 This is an old technique primarily used for switchgear. The spark is formed under oil and venting is controlled. (The use of hydrocarbon oil has obvious disadvantages and the method of protection is confined to the remotely hazardous area.) Zone 2 Suitable

  Ex 'p' "Pressurized Apparatus" Protection - EN 50016 These are system methods. One maintains a positive static pressure inside the apparatus and the other a continuous flow of air or inert gas to neutralize or carry away any flammable mixture entering or being formed within the enclosure. Essential to these methods are monitoring systems and purging schedules to ensure their reliability. Zone 2 Suitable

  Ex 'q' "Powder Filling" Protection - EN 50017 This involves the mounting of potentially incentive components in an enclosure filled with sand or similar inert powder and having a vent. It is primarily of use where the incendive action is the abnormal release of electrical energy by the rupture of fuses or failure of components such as capacitors. Usually it is used for components inside Ex 'e' or Ex 'N' apparatus and for heavy duty traction batteries. Zone 2 Suitable

  Ex 'd' "Flameproof Enclosure" Protection - EN 50018 The potentially incentive components are contained within an enclosure into which the flammable atmosphere can enter but which will contain any resultant explosion and prevent it's transmission outside the enclosure. Typically used for switch devices, small breakers, and control enclosures. Zone 1,2 Suitable

  Ex 'e' "Increased Safety" Protection - EN 50019 Normally sparking components are excluded. Other components are designed to reduce substantially the likelihood of the occurrence of fault conditions which could cause ignition. This is done by reducing and controlling working temperatures, ensuring the electrical connections are reliable, increasing insulation effectiveness, and reducing the probability of contamination by dirt and moisture ingress. Zone 1,2 Suitable

  Typical Brass Gland being installed in a Fiberglass Reinforced Polyester Terminal Box rated Ex 'e' Notice the earthing plate to maintain grounding continuity

  Ex 'i' "Intrinsic Safety" Protection - EN 50020 The circuit parameters are reliably controlled to reduce potential spark energy to below that which will ignite the specific gas mixture. This includes the occurrence of one (b) or two (a) components faults in the apparatus. It should be noted that this method does not protect entirely against the local over-heating of damaged connections or conductors and these should be kept sound and suitably enclosed against damage. Zone 0,1,2 Suitable (Ex ia) or Zone 1,2 Suitable (Ex ib)

  Ex 'm' "Encapsulation" Protection - EN 50028 Potentially incendive components are encapsulated by a method which excludes the flammable atmosphere and controls the surface temperature under normal and fault conditions. Zone 1,2 Suitable

  Ex 's' "Special" Protection - BASEEFA SFA 3009 - This method, being special has no definite rules. In effect it is any method which can be shown to be safe in use. Much of the apparatus having 's' protection was designed with encapsulation and this has been superseded by EN50028. In addition, the 's' coding is used when apparatus has been assessed to one of the individual parts of the CENELEC series but does not exactly comply with it. Because 's' by definition, have a set of rules it will not become part of the harmonized series of standards. Special protection is likely to emerge is some apparatus which will be certified in accordance with the ATEX Directive. Zone 0,1,2 Suitable

  Ex 'N' "Non-Sparking" Protection - EN 50021 Precautions are taken with connections and wiring to increase reliability, though not to as high a degree as for Ex 'e'. Where internal surfaces are hotter than the desired T rating they can be tightly enclosed to prevent the ready access of a flammable atmosphere into the internal parts. This is the "restricted breathing enclosure" technique. Its employment also means that high ingress protection ratings of IP65 and above are built into the design. The Ex 'N' methods are developed around the use of 'N' equipment in the remotely hazardous area commonly referred to as Zone 2. Zone 2 Suitable

  

  It is very common to note that many International standard products have multiple means of protection within one product.  For example, light fixtures may be increased safety (Housing and terminals), flameproof (Disconnect switch), and encapsulated (ballast).  This enables the manufacturer to combine protection techniques that are best suited for the application.  One point to note is that the order of techniques listed on the label of the product will very often tell the user the construction of the product.  For example, a product listed Eex 'de' would most likely be flameproof with increased safety components inside.  Another product listed Eex 'ed' would most likely be non-flameproof (Stainless Steel or Glass Reinforced Polyester as examples) with flameproof switches or components installed inside.  Both products would be suitable for Zone 1, but they use different means of protection to get there.  Users can make informed decisions as to how best to utilize protection techniques that provide a balance between cost, performance and safety. 

  Apparatus Grouping

  Gases are grouped together based on the amount of energy required to ignite the most explosive mixture of gases with air. Equipment is classified into groups according to the gases and vapours for which it is suitable and must be selected with a grouping which covers the gases and vapours which will be present where it is to be installed:

  Group I - Methane - Ignition energy of 320 Micro joules

  Group IIA - Propane - Ignition energy of 300 Micro joules (Similar to NEC Group D)

  Group IIB - Ethylene - Ignition energy of 160 Micro joules (Similar to NEC Group C)

  Group IIC - Hydrogen - Ignition energy of 40 Micro joules (Similar to NEC Group A&B)

  Temperature Classification

  To ensure that there is no risk of ignition due to hot surfaces, the equipment is classified with regard to the maximum surface temperature of any part of the equipment while in operation based on the ambient temperature of 40 C, this is also known as the 'T' rating. Equipment must be selected with a suitable temperature classification for the gases and vapours present where the equipment is to be installed.

  Temperature Classification	T1	T2	T3	T4	T5	T6
  Maximum Surface Temperature	450 C	300 C	200 C	135 C	100 C	85 C

  What is CENELEC?

  CENELEC is the European Committee for Electrotechnical Standardization. It was set up in 1973 as a non-profit making organization under Belgian Law.

  It has been officially recognized as the European Standards Organization in its field by the European Commission in Directive 83/189 EEC.

  Its members have been working together in the interests of European harmonization since the late fifties, developing alongside the European Economic Community. CENELEC works with 40,000 technical experts from the 19 European Community countries including Austria, Belgium, Denmark, Finland, France, Germany, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom.

  

  What is the International Electrotechnical Commission (IEC)?

  The IEC was founded in 1906 in St. Louis and is presently comprised of 40 countries including the U.S. Its stated purpose is to establish standards for a wide variety of electrical products with the intent of encouraging international trade.  IEC publications which deal with explosion protection for electrical apparatus and installations are developed by the Technical Committee TC31,  IEC publications have the status of recommendations which are used for national and regional standards.  The IEC has introduced a procedure the so called IEC-Ex scheme intended to become a globally recognized test and certification procedure in the field of explosion protected electrical apparatus.

  What is Euronorm?

  Standards developed by CENELEC applying to apparatus intended for use in hazardous locations. EN50018 is the EURONORM standard for flameproof equipment.

  What is BASEEFA?

  (British Approvals Service for Electrical Equipment in Flammable Atmospheres).  BASEEFA is the British national testing and certification authority for use in flammable atmospheres other than Mining.   BASEEFA is the British equivalent to UL.

  What is the ATEX Directive?

  The ATEX Directive 94/9/EC is a directive adopted by the European Union (EU) to facilitate free trade in the aligning the technical and legal requirements in the member states for products intended for use in potentially explosive atmospheres.  It becomes mandatory for all member countries to comply with the directive on July 1st 2003.

  What are the specific ATEX marking requirements and how do they differ from the Cenelec marking information?

  Listed below are the traditional marking requirements in force today.  The new marking requirements made mandatory in 2003 are to include:

•     Certification authority/test house (Example PTB from Germany code will be 0102)
•     Category group (Category 1 = Zone 0, Category 2 = Zone 1 & Category 3 = Zone 2)
•     Indication of Atmosphere (D = Dust or G = Gas)

  For example the additional marking may look like this:  EX 0102  II (2) G

   

• Ingress Protection (IP) Codes

	First Number Protection against solid bodies	Second Number Protection against liquid
0	No protection	No protection
1	Objects greater than 50mm	Vertically dripping water
2	Objects greater than 12mm	Angled dripping water
3	Objects greater than 2.5mm	Sprayed water
4	Objects greater than 1mm	Splashed water
5	Dust-protected	Water jets
6	Dust-tight	Heavy seas
7		Effects of immersion (1 meter)
8		Indefinite immersion

IP Codes can and sometimes include additional letters to specify suitability for applications beyond the simple two letter designations.  The following is a list of the letters that may be used:

Back of the Hand

letter A

Finger Proof

letter B

Tool Proof

letter C

Wire Proof

letter O

High Voltage equipment

letter H

Water-proofing during operation

letter M

Water-proofing during standstill

letter S

Weather conditions

letter W

The letter W is the most common extra letter that is usually added and could be extra protection for humidity, frost, or some other condition not covered the the two digit nomenclature.

 

Selection of Electrical Equipment for Hazardous Areas Equipment Certification Marking:

 



Fixture listed above would be rated EEx edm IIC T4 IP67 (Additional ATEX marking would have Test House, Catagory & Hazardous Group included)

E - European Certification	Ex - Hazardous Area Equipment	d - Protection Method
IIC - Apparatus Grouping	T6 - Temperature Classification	IP66 - Ingress Protection

What are some of the common European wiring practices in the various industries?

It is very common in the North Sea Offshore market to note the use of braided cables for typical wiring practices, with a brass EX 'e' or 'd' gland. 95% of the hazardous equipment used is Ex 'e' increased safety while usually less than 5% of the equipment is 'd' flameproof.  This is due to weight, corrosion resistance and ease of maintenance.  In the onshore market, SWA armoured cable is most frequently used.  Again, a vast majority of equipment is also rated Ex 'e' as opposed to 'd' for the same reasons listed above.

Why are the use of brass connectors so popular with the Europeans in the use of connectors for hazardous location?

First, Brass is very easy to machine and work with to produce products with very fine tolerances.  Secondly, brass when produced in large amounts, can be just as cost effective as copper-free aluminum here in the U.S.  If you made a comparison of the various brass MC cable terminators available and compared the price to North American aluminum connectors, you would find no difference in price.  In fact, in some cases, brass with a nickel plating can be less expensive than the comparable aluminum gland.  Finally, aluminum has been shown to not hold up as well as nickel plated brass glands in the North Sea and other various offshore markets for many years now.  Below, you will find a comparison of two series of connectors exposed to a salt spray test simulating 500 hrs. of service.  Notice how the threads on the aluminum connector become white with galvanic corrosion, while the nickel plated product has shown little effect from the elements.

Copper Free Aluminum After 500 hr. Salt Spray Test

Nickel-Plated Brass After 500 hr. Salt Spray Test

 

 

 

 

 

 

 

 

         The CE Mark.. What does it mean to users and manufacturers?

The CE mark is the official marking required by the European Community for all Electric and Electronic equipment that will be sold or put into service for the first time, anywhere in the European Community. It proves to the buyer or user that his product fulfills all essential safety and environmental requirements as they are defined in the so-called European Directives. The CE markings directive (93/68/EEC) was adopted on July 7th 1993. It amends 12 other directives also part of the EEC.

In return for fulfilling the CE marking requirements, the manufacturer or its agent gets the opportunity to cover the entire European market using only one approval procedure for the topics covered in the miscellaneous directives. The member states of the EC cannot refuse any electronic or electrical product that has been CE marked (unless fraud suspected).

The manufacturer needs however:

• be European
• or have an official department in the EC
• or have an official agent or representative that is willing to take the liability for the CE-marking.

Although one CE mark is sufficient for all EC members, their are some restrictions left over for language variations in user documentation. Be prepared to translate some part of the safety instructions in the language you are exporting to. The major directive that exists for hazardous location equipment is Electrical Safety (Low Voltage Directive)(73/23/EEC) mandatory since January 1st 1997.  The CE marking need not appear on the product if the mark is made on the packaging and/or installation guide for the product.

AWG vs. MM2 Cable comparison chart

AWG	Metric (mm2)	AWG	Metric (mm2)
16	1.31	1	42.41
-	1.5	-	50
15	1.65	1/O	53.49
14	2.08	2/O	67.43
-	2.5	-	70
13	2.63	3/O	85.01
12	3.31	-	95
-	4	4/O	107.2
11	4.17	-	120
10	5.261	250	127
-	6	-	150
9	6.631	300	152
8	8.367	350	177
-	10	-	185
7	10.55	400	203
6	13.3	450	228
-	16	-	240
5	16.77	500	253
4	21.15	550	279
-	25	-	300
3	26.67	600	304
2	33.62	650	329
-	35	700	355
1	42.41	750	380

What are the differences between the AEx marking for North America and the EEx marking requirements for Europe?

With the introduction of Article 505 in the NEC a few years back, many of the protection techniques used in International community can be safely used in facilities in the United States.  However, some test standards that are based upon the IEC standards have been modified in some respects to allow deviations to address North American concerns.   The new marking requirements that will be showing up on many products in the U.S. to comply with NEC 505 are very similar to the Cenelec marking requirements.  An example of a typical product meeting U.S. specifications might have a marking as followed:

Class 1, Zone 1, AEx e IIC T5

Notice that the big difference is the statement that tells the user which Zone this product is suitable for which has been missing from the traditional Cenelec marking requirements.  With the advent of the ATEX directive, marking requirements in Europe will also reflect Zone or Category suitability.  The two systems are close, but not identical. 

The preceding information is reprinted by kind permission of Electrical Products Marketing Inc.
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