Explosion Proof

Design and Installation of Electrical Systems for Hazardous Areas.

The design and selection of electrical apparatus for hazardous areas applications should be in accordance with the following :-

• Classification of the hazardous area
• Temperature class or ignition temperature of the gas, liquid, vapour, mist, dust or fibre.
• Where applicable, the gas, vapour or dust classification in relation to the group or sub-group of the electrical apparatus.
• External influences and ambient temperature.

  Apparatus Selection for Zone 0

• Intrinsic Safety 'ia'

   Apparatus Selection for Zone 1

• Electrical apparatus permitted for use in Zone 0, or
• Flameproof enclosure 'd'
• Pressurised apparatus 'p'
• Powder filling 'q'
• Oil immersion 'o'
• Increased safety 'e'
• Intrinsic safety 'ib'
• Encapsulation 'm'

  Apparatus Selection for Zone 2

• Electrical apparatus permitted for use in Zone 0 and Zone 1, or
• Electrical apparatus designed specifically for Zone 2 (e.g. type of protection 'n') or
• Electrical apparatus complying with the requirements of a recognised standard for industrial electrical apparatus, which does not, in normal operation, have ignition capable hot surface and does not in normal operation produce arcs or sparks. This equipment must be in an enclosure with a degree of protection and mechanical strength suitable for the environment and be assessed by a person who is familiar with the requirement of any relevant standards and codes of practice.

Apparatus Selection for Zone 20, 21 and 22

• IEC/EN 61241-0 - Electrical apparatus for use in the presence of combustible dust. General requirements. and
• IEC/EN 61241-1 - Electrical apparatus for use in the presence of combustible dust. Protection by enclosure 'tD'.

Type of Protection

• Exd - Flameproof (motor, lighting, junction boxes) - Equipment is robust can stand an explosion from within, without transmitting the flame to the outside. Equipment has flameproof gaps (max 0.006" propane​/ethylene, 0.004" acetylene/hydrogen)​/
•  Exe - Increased Safety (motor, lighting, junction boxes) - Equipment is very robust and components are made to a high quality
•  Exo - Oil Immersion (transformer) - Equipment components are completely covered with a layer of oil
• Exq - Powder Filled (capacitors, electronics)  - Equipment components are completely covered with a layer of Sand, powder or quartz
• Exm - Encapsulation (electronics-no heat) - Equipment components of the equipment are usually encased in a resin type material
• Exp - Pressurised Enclosure / Rooms (power apparatus) - Equipment is pressurised with a positive pressure; gas cannot get in for air coming out or equipment is purged with a diluting gas such as air. If air is used, it is ducted in from outside the hazardous area.
• Exi - Intrinsic Safety (instrumentation, control, measurement) - Any arcs or sparks in this equipment has insufficient energy (heat) to ignite a vapour. Equipment can be installed in ANY housing provided to IP54. A 'Zener Barrier' or 'opto isol' or 'galvanic' unit may be used to assist with certification.
• Exn - Non Sparking (motor, lighting, junction boxes, electronics) - Equipment is non-incendive or non-sparking.
• Exv - Ventilation -
• Exs - Special Protection - This method, being by definition special, has no specific rules. In effect it is any method which can be shown to have the required degree of safety in use. Much early equipment having Ex s protection was designed with encapsulation and this has now been incorporated into IEC 60079-18 [Ex m]. Ex s is a coding referenced in IEC 60079-0. The use of EPL and ATEX Category directly is an alternative for “s” marking.

Click to enlarge

References :

• IEC/EN 60079-0  - General Requirements
• IEC/EN 60079-1  - Flameproof Enclosure 'd'
• IEC/EN 60079-2  - Pressurisation 'p'
• IEC/EN 60079-5  - Powder Filling 'q'
• IEC/EN 60079-6  - Oil Immersion 'o'
• IEC/EN 60079-7  - Increased Safety 'e'
• IEC/EN 60079-11 -Intrinsic Safety 'i'
• IEC/EN 60079-15 -Electrical Apparatus type 'n'
• IEC/EN 60079-18 -Encapsulation 'm'
• IEC/EN 61241-1   -Dust protection by enclosure

explosion proof | explosion proof motor | explosion proof enclosure | explosion proof light | intrinsically safe | explosion proof fans | explosion proof lamp

HAZARDOUS AREA CLASSIFICATION

Hazardous Area

A hazardous area is defined as an area in which an explosive atmosphere is present, or may be expected to be present, in quantities such as to require special precautions for the construction, installation and use potential ignition sources.

An explosion will occur when three basic conditions are present and remove any of these basic conditions and an explosion will not occur :

• Explosive material (Gas,Liquid,Dust)
• Oxygen / Air
• Source of Ignition (Temperature Rise, Spark)

Classification of Hazardous Areas

The purpose of area classification is to provide a basis for the correct selection, installation and location of electrical and non-electrical equipment in those areas. Areas must be classified depending on the properties of the flammable vapours, liquids, gases, mists, combustible dusts or fibres that may be present and the likelihood that a flammable or combustible concentration or quantity is present.

The aim of area classification is to avoid ignition of flammable release that may be occur in the operation of facilities. The intent is to reduce to an acceptable minimum level that probability of a flammable atmosphere and an ignition source occurring at the same time.

The classification of ZONE is a complex problem but the main factors to consider are :

• The probability of the presence of gas.
• The quantity and duration of hazardous vapour.
• The amount of ventilation.
• The nature of gas : either lighter or heavier than air.

Hazardous areas may be sub-divided into three zones, as shown below


(FOR FLAMMABLE GASES AND VAPOURS):

• Zone 0 - An area in which an explosive atmosphere is constantly present, or present for long periods.
• Zone 1 - An area in which an explosive atmosphere is likely to occur in normal operation.(Rough Guide : 10 hours or more per year but less than 1000 hours per year)
• Zone 2 - An area in which an explosive atmosphere is not likely to occur in normal operation and if it occur it will exist only for a short time. (Rough Guide : Less than 10 hours per year)

 (FOR COMBUSTIBLE DUSTS):

• Zone 20 - An area in which combustible dust, as a cloud, is present continuously or frequently during normal operation in sufficient quantity to be capable of producing an explosive concentration of combustible dust in a mixture with air.
• Zone 21 - An area in which combustible dust, as a cloud, is occasionally present during normal operation in sufficient quantity to be capable of producing an explosive concentration of combustible dust in a mixture with air.
• Zone 22 -  An area in which combustible dust, as a cloud, may occur infrequently and persist for only a short period, or in which accumulations of layers of combustible dust may give rise to an explosive concentration of combustible dust in a mixture with air.

Click to enlarge

Group Classification

The grouping of gases and vapours are classified into Group I and Group II categories. Group I is for Mining Applications and Group II is for General Industry. Group I equipment has a representative gas of Methane and all equipment used in underground mining applications fall into this categories. Any other equipment will be Group II classified.

• I     - Methane
• IIA - Propane
• IIB - Ethylene
• IIC - Hydrogen, Acetylene

Equipment and apparatus certified with Group IIC can be used either in IIA, IIB and IIC areas. But items certified with IIA only can be used in IIA areas and so on.

Temperature Classification

The temperature classification on the electrical equipment label will be one of the following (Maximum Surface Temperature in degree Celsius) :

• T1 - 450
• T2 - 300
• T3 - 200
• T4 - 135
• T5 - 100
• T6 - 85

Temperature classes T1 to T6 are used for all protection techniques, and correspond to the electrical devices maximum operational temperature.The better the equipment, the lower the rated surface temperature.

Therefore, those items certified as being T6, can be used in T1, T2, T3, T4, T5 and T6 gases. Whereas a T2 certification only allows a piece of equipment to be used in T1 and T2 gases.

References:

1. IEC/EN 60079-0    - General Requirements
2. IEC/EN 60079-10  - Electrical apparatus for explosive gas atmospheres. Classification of hazardous areas.
3. IEC/EN 60079-14 - Explosive atmospheres. Electrical installations design, selection and erection.
4. IEC/EN 61892-7   - Mobile and fixed offshore units. Electrical installations. Hazardous areas.  

hazardous area | hazardous area classification | explosion proof | hazardous areas | hazardous classification