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Hazardous Area Protection Guide

Date:2010-7-9 14:57


 

Explosion Protection

There are many ways of protecting Plants from risk of explosion due to hazardous Gasses and Dusts.

 

The Explosion Triangle shows we need three component parts to create an explosion:

1 Oxidiser (Oxygen / Air)

2 Fuel (Gas / Dust)

3 Energy (Ignition Source)

Remove any one and the area is safer.

Air
This is naturally occuring all around us and would be very difficult to remove.

Gas / Dust
This has to be the right mixture before an explosion will occur. Too much air or too much gas / Dust and the mixture will not ignite.
If the explosive atmosphere is caused by gases, vapours and mists the hazardous area is coded G. If the explosive atmosphere is caused by dusts the hazardous area is coded D.

Ignition Source
This can be in the form of a Naked Flame, A Hot Surface, Mechanically Generated Sparks, Electrically Generated Sparks, or Electrostatic Discharge etc..

ATEX

What is ATEX?  

     

ATEX is the term used for the European Unions directive 94/9/EC that concerns equipment and protective systems intended for the use in potentially explosive atmospheres. The purpose of the directive is to facilitate trade within the EU buy aligning the laws of the member states regarding the safety requirements for hazardous area products.

 The Directive does not cover:

1 Medical devices intended for use in a medical environment

2 Equipment and protective systems where the explosion hazard results exclusively from the presence of explosive substances or unstable chemical substances

3 Equipment intended for use in domestic and non-commercial environments where potentially explosive atmospheres may only rarely be created, solely as a result of the accidental leakage of fuel gas.

4 Personal protective equipment covered by Directive 89/686/EEC

5 Seagoing vessels and mobile offshore units together with equipment on board such vessels or units Means of transport, i.e. vehicles and their trailers intended solely for transporting passengers by air, road, rail or water networks, as well as means of transport in so far as such means are designed for transporting goods by air, by public road or rail networks or by water.

6 Vehicles intended for use in a potentially explosive atmosphere shall not be excluded.

Symbols
 Under the Old Directive, the "Epsilion x" (shown) symbol indicated conformity with CENELEC requirements. This symb
 Under the New Directive, the "Epsilion x" symbol will move into the marking string and be used to indicate explosion
 

Explosion Groups

Explosion protected electrical equipment is classified in terms of the ignition temperature, the ignition capability and flame transmission capacity of the explosive atmosphere in which it is designed to operate.

In the first instance equipment is divided into two groups depending on its location above or below ground.

Group I Electrical equipment for use below ground in areas susceptible to firedamp.
Group II Electrical equipment for all other areas.
Group II equipment is further divided into three sub groups depending on the ignition and flame transmission characteristics of the explosive hazard.

These sub-groups are designated IIA, IIB and IIC.

Zones the probability of an explosive atmosphere occurring

Zone 0 defines an area in which an explosive atmosphere caused by a mixture of air and gases, vapours and mists is present continuously for long periods or very frequently (Category 1G under Atex)

Zone 1 defines areas in which an explosive atmosphere caused by a mixture air and gases, vapours and mists is expected to occur occasionally. (Category 2G under Atex)

Zone 2 defines areas in which an explosive atmosphere caused by a mixture of air and gases, vapours and mists is unlikely and if it should occur it will be for a short time and then only rarely. (Category 3G under Atex)

Zone 20 defines an area in which an explosive atmosphere caused by a cloud of combustible dust and air is present continuously for long periods or very frequently. (Category 1D under Atex)

Zone 21 defines areas in which an explosive atmosphere caused by a cloud of combustible dust and air is expected to occur occasionally. (Category 2D under Atex)

Zone 22defines areas in which an explosive atmosphere caused by a cloud of combustible dust and air is unlikely and if it should occur it will be for a short time and then only rarely. (Category 3D under Atex)

The main differences within ATEX are that Zones 0, 1 & 2 have now been replaced with Categories 1, 2 & 3, the inclusion of D

Zone

Category

Presence of explosibles atmospheres

Group II equipment

zone 0

category 1 G

Continuous, frequent
or for long periods

zone 20

category 1 D

zone 1

category 2 G

Intermittent
in normal operation (likely)

zone 21

category 2 D

zone 2

category 3 G

Occasionalor for short periods
(never in normal operation)

zone 22

category 3 D

Group I equipment

 

category M 1

Presence(methane, dust)

 

category M 2

Risk of presence(methane, dust)

 

Types of Electrical Equipment Suitable for use in Potentially Explosive Atmospheres
Different techniques are used to prevent electrical equipment from igniting explosive atmospheres. There are restrictions on where these different types of equipment can be used as follows:

 

European - Area of use Designation Standard
 

IEC - Area of use Designation Standard
 

USA - Area of use Designation Standard

Flameproof Enclosure – An enclosure used to house electrical equipment, which when subjected to an internal explosion will not ignite a surrounding explosive atmosphere.
 

Zones 1 & 2
EExd
EN50018
 

Zones 1 & 2
Exd
IEC60079-1
 

Class 1 Divisions 1 & 2
UL1203

Intrinsic Safety – A technique whereby electrical energy is limited such that any sparks or heat generated by electrical equipment is sufficiently low as to not ignite an explosive atmosphere.
 

Zones 0, 1 & 2
EExi
EN50020
 

Zones 1 & 2
Exi
IEC60079-11
 

Class 1
Divisions 1 & 2
UL913

Increased Safety – This equipment is so designed as to eliminate sparks and hot surfaces capable of igniting an explosive atmosphere.
 

Zones 1 & 2
EExe
EN50019
 

Zones 1 & 2
Exe
IEC60079-7
 

Purged and Pressurised – Electrical equipment is housed in an enclosure which is initially purged to remove any explosive mixture, then pressurised to prevent ingress of the surrounding atmosphere prior to energisation.
 

Zones 1 & 2
EExp
EN50016
 

Zones 1 & 2
Exp
IEC60079-2
 

Class 1
Divisions 1 & 2
NFPA496

Encapsulation – A method of exclusion of the explosive atmosphere by fully encapsulating the electrical components in an approved material.
 

Zones 1 & 2
EExm
EN50028
 

Zones 1 & 2
Exm
IEC60079-18
 

Oil Immersion – The electrical components are immersed in oil, thus excluding the explosive atmosphere from any sparks or hot surfaces.
 

Zones 1 & 2
EExo
EN50015
 

Zones 1 & 2
Exo
IEC60079-6
 

Class 1
Division 2
UL698

Powder Filling – Equipment is surrounded with a fine powder, such as quartz, which does not allow the surrounding atmosphere to come into contact with any sparks or hot surfaces.
 

Zones 1 & 2
EExq
EN50017
 

Zones 1 & 2
Exq
IEC60079-5
 

Non-sparking – Sparking contacts are sealed against ingress of the surrounding atmosphere, hot surfaces are eliminated.
 

Zone 2
EExn
EN50021
 

Zone 2
Exn
IEC60079-15
 

Special Protection – Equipment is certified for use in a Potentially Explosive Atmosphere but does not conform to a type of protection listed above.
 

Zones 0, 1 & 2
*Exs
 

Zones 0, 1 & 2
Exs
 

Ignition temperature - temperature class  

Many factors such as size, shape, type and surface quality have an influence on the ignition temperature. IEC, CENELEC and other standardisation committees have agreed on a method for gases and vapours defined in IEC 60079-4 „Method of test ignition temperature“. This method is defined in such a way, that a value very close to the lowest practically possible, is determined.

By means of this method, gases and vapours are divided into temperature classes. According to these temperature classes, the surface temperatures in explosion-protected equipment and other technological objects is designed in such a way that ignition by the surface is not possible. In th

Group I

Temperatures < 150°C or < 450°C
according to coal dust accumulation on equipment

Group II

Temperature
classes

Ignition temperature
range of the mixture

Permissible surface temperature
of the electrical equipment

T1

> 450 °C

450 °C

T2

> 300 ... ≥450 °C

300 °C

T3

> 200 ... ≥300 °C

200 °C

T4

> 135 ... ≥200 °C

135 °C

T5

> 100 ... ≥135 °C

100 °C

T6

> 85 ... ≥100 °C

85 °C

Self Ignition Temperature and Temparature Classes

Self Ignition Temperature °C

Temperature Class of the Equipment

T6

T5

T4

T3

T2

T1

(85°)

(100°)

(135°)

(200°)

(300°)

(450°)

85° ≤ T ≤ 100 °c

 

 

 

 

 

 

100° ≤ T ≤ 135 °c

 

 

 

 

 

 

135° ≤ T ≤ 200 °c

 

 

 

 

 

 

200° ≤ T ≤ 3 00 °c

 

 

 

 

 

 

300° ≤ T≤ 450 °c

 

 

 

 

 

 

450° ≤

 

 

 

 

 

 

 

 

 

=   EXPLOSION

Gases groups

Groups

Gas

Ignition
temperatures

Temperatures classes

T1

T2

T3

T4

T5

T6

I

methane (firedamp)

 

 

 

 

 

 

 

II

A

acetone
acetic acide
ammonia
ethane
methylene chloride
methane (CH4)
carbon monoxyde
propane

540 °C
485 °C
630 °C
515 °C
556 °C
595 °C
605 °C
470 °C

 

 

 

 

 

 

n-butane
n-butyl

365 °C
370 °C

 

 

 

 

 

 

n-hexane

240 °C

 

 

 

 

 

 

acetaldehyde
ethyl ether

140 °C
170 °C

 

 

 

 

 

 

ethyl nitrite

90 °C

 

 

 

 

 

 

B

ethylene
ethyl oxyde

425 °C
429 °C - 440 °C

 

 

 

 

 

 

hydrogen sulfide

270 °C

 

 

 

 

 

 

C

acetylene (C2H2)

305 °C

 

 

 

 

 

 

carbon disulphide (CS2)

102 °C

 

 

 

 

 

 

hydrogen (H2)

560 °C

 

 

 

 

 

Ignition temperature for dusts

The dust ignition temperature depends on its consistency and nature.
The ignition temperatures for various types of dust are available from reference tables: See examples

Dusts

Ignition temperature

Clouds

5 mm layer

Aluminium

560°C

=450°C

Charcoal

520°C

320°C

Coal dust (lignite)

380°C

225°C

Cocoa

590°C

250°C

Coffee (ground)

580°C

290°C

Corn

530°C

460°C

Methyl cellulose

420°C

320°C

Paper fiber

570°C

335°C

Phenolic resin

530°C

>450°C

Polyethylene

440°C

melts

PVC

700°C

>450°C

Sugar

490°C

460°C

Soot

810°C

570°C

Toner

520°C

melts

Wheat

510°C

300°C

Nota: temperature information is given as an example and cannot be used as a reference table.

Products lables

The ATEX standards call for the manufacturers of hazardous area electrical equipment to label their products with the following information.
 

1. Name of manufacturer

2. Product type code

4. Year of manufacture

3. Address of manufacturer

5. Marking in accordance with directive 94/9/EC II 3 GD – group II location, category 3 equipment, for gas and dust hazards

6. Marking in accordance with European standards EEx nR II T – built and tested to European standards, type of protection, explosion group, temperature class

7. CE marking together with notified body registration number

8. Notified testing body and reference number

9. Serial number

10. Technical data

11. Ingress protection

Marks of explosion protection for Europe 

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