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EEHA | Electrical Equipment Hazardous AReas

This is a short summary of a complex process, if in doubt email the writer as below or refer to someone with appropriate competancies to the Australian/New Zealand standard AS/NZS4761.

Identifying the Hazard and Preventing Ignition

There are two (2) distinctly separate issues involved; one is the definition of the hazard and the other is the selection of a suitable protection mechanism to protect against igniting the hazards.   The first step is to identify and define the actual hazard.

Area hazards are identified based on an assessment of explosivity.  Specific methods for assessment are defined in standards.  Assessment is done by hazardous area assessors/inspectors and apparatus to be used in hazardous areas are tested and certified to various levels by laboratories approved under the standards regime.

The site assessments and classifications and the equipment compliance testing are two (2) distinctly different entities. 

Hazard Identification

The hazards (gas and/or dust) are identified and grouped relative to their explosivity and ignition temperature. 

Hazards Classification is as follows:

Degree of Risk (Zones)

The likelihood or probability of the hazard occurring are defined as Zones (in the US system they are referred to as Divisions). This identifies the likelihood of the hazard occurring, as below.

Zone 0 is an area in which an explosive gas atmosphere is present continuously or for long periods or frequently

Zone 1 is an area in which an explosive gas atmosphere is likely to occur in normal operation occasionally

Zone 2 is an area in which an explosive gas atmosphere is not likely to occur in normal operation but, if it does occur, it will exist for a short period only

Zone 20 is an area in which an explosive dust atmosphere, in the form of a cloud of dust in air, is present continuously, or for long periods or frequently.

Zone 21 is an area in which an explosive dust atmosphere, in the form of a cloud of dust in air, is likely to occur in normal operation occasionally.

Zone 22 is an area in which an explosive dust atmosphere, in the form of a cloud of dust in air, is not likely to occur in normal operation but, if it does occur, will persist for a short period only.

Groups

The hazard is then divided into groups with similar attributes as below:

Mining:    Group I             Underground mines, typically IA as A is the subcategory for Methane (firedamp).

Gas:          Group II            Above ground Gas which is further subdivided in A, B or C based on explosivity of the hazardous gas.

Dust:        Group III           Dust which is then also divided into sub-categories A, B or C based on the conductivity of the dust.

The hazardous materials are then further divided into sub-groups.

Gas and Dust Groups

Group IIA                             Propane

Group IIB                             Ethylene

Group IIC                             Hydrogen

Group IIIA                           Combustible flyings

Group IIIB                            Non-conductive dust

Group IIIC                            Conductive dust

Temperature Class

The hazard is then allocated a Temperature Classes.

This temperature group is based on the maximum temperature of equipment before ignition is possible (with a safety margin).

The Temperature classes are as follows:

Temperature class required by the area classification

Ignition temperature of gas or vapour in °C

 

T1

>450°C

T2

>300°C

T3

>200°C

T4

>135°C

T5

>100°C

T6

>85°C


Note:  Dusts are typically described with an actual Temperature, e.g. 135°C instead of a “T” Class.

The resultant hazardous area assessment and classification drawings give us the basis for selecting appropriately safe equipment. (NOTE: We have ignored undergound mining in this partof th eproces to avoid ocnfusion, our products are not nornmally used undergound.)

E.g. a Zone 1 risk with above ground gas hazard of Ethylene Group IIB Gas hazard at ignition temperature of say T2 (actual ignition temperature 440°C meets T2 requirements).

Selection of Suitable Product

Select a technique that is suitable for the hazard from the table below. Some techniques are suitable for some hazards and some are not.

Protection Techniques include Intrinsic Safety (I.S.)

There are a number of techniques used to protect electrical equipment in hazardous areas (EEHA) of which Intrinsic Safety (Ex i) or sometimes referred to as “I.S.” equipment is only one.  Intrinsic safety is common in portable low powered equipment.

Other Techniques that may be used

Gas

 

 

Zone

Technique

Group

Zone 0

Zone 1

Zone 2

Intrinsically Safe Ex ia

II

Intrinsically Safe Ex ib

II

 

Intrinsically Safe Ex ic

II

 

 

Encapsulation Ex ma

II

Encapsulation Ex mb

II

 

Flameproof Ex d

II

 

Increased Safety Ex e

II

 

Non Incendive Ex n

II

 

 

Powder Filling Ex q

II

 

Oil Immersion Ex o

II

 

Pressurised Ex p

II

 

Special Protection Ex s

Subject to conditions of Certification – READ the Certificate

Or for Dust:

 

 

Zone

Technique

Group

Zone 20

Zone 21

Zone 22

Intrinsically Safe Ex iaD

III

Intrinsically Safe Ex ibD

III

 

Intrinsically Safe Ex ic

III

 

 

Encapsulation Ex ma (or Ex mD)

III

Encapsulation Ex mb

III

 

Protection by Enclosure Ex tD A20 sometimes shown as “Ex ta”

III

Protection by Enclosure Ex tD A21 sometimes shown as “Ex tb”

III

 

Protection by Enclosure Ex tD B21 sometimes shown as “Ex tb”

III

 

Protection by Enclosure Ex tD B22 sometimes shown as “Ex tc”

III

 

 

Protection by Enclosure DIP A20

III

Protection by Enclosure DIP A21

III

 

Protection by Enclosure DIP B21

III

 

Pressurised Ex pD

III

 


Then:

Select product which meets or exceeds ALL of the parameters for the defined hazard, i.e.

NOTE: Equipment with higher levels of protection can be used in areas needing lesser protection BUT all parameters must meet or exceed those of the hazard.

Example

If Propane is used in an above ground storage and processing facility it will typically (subject to reading or the hazardous area classification document) have some Zone 1 areas and some Zone 2 areas.

The gas is identified as follows:

Propane (CH3CH2CH3) is defined as being Group IIA with an ignition temperature class for ignition is “T2” ignition temp 450°C refer the following standard:

AS/NZS 60079.20.1:2012 IEC 60079-20-1, Ed. 1.0 (2010) Australian/New Zealand Standard Explosive atmospheres Part 20.1: Material characteristics for gas and vapour classification—Test methods and data.

If your product is intrinsically safe Ex i, then minimum product specification will be Ex ib IIC T2 Gb.

Where:

Ex = (Explosion protected) and

ia = Intrinsically Safe (suitable for Zone 0, 1, 2) or ib = Intrinsically safe (suitable for Zone 1 or Zone 2)

IIA for Propane above ground.

“T2” Ignition temperature 450°C.  (NOTE: T1 >450°C not equal to so we must take the higher level of protection.

For more information or to answer any questions oplease email the writer at DCA Extech at support@dcaexpro.com

  

Telephone: (+61) 407 254 975 email: sales@dca-extech.com.au Address: 46B Gould Avenue West Albury NSW 2640 Australia

Post: PO Box 605 Albury NSW 2640 Australia

How do I select appropriate equipment? | What is "Intrinsic Safety"? | What other methods of protection exist?

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