Division into Temperature Classes

The temperature class indication can be guaranteed only if the ambient temperature specified for the operating device is respected (seeTechnical Data or Rating Plate). Strict compliance is a mandatory requirement.

Once the maximum surface temperature of any apparatus reaches the ignition temperature of the surrounding hazardous atmosphere an explosion can occur.

Because of this, all equipment classified to Group II is divided into temperature classes. To allow for the possibility of potential hazardous atmospheres, the lowest ignition temperature must always be higher than the maximum surface temperature.

Below Explosive Level	Explosive Area	Above Explosive Level
Mixture to thin		Mixture too rich
No combustion		Partial combustion
No explosion		No explosion
100% <<<<<<<<<<<< Concentration of air<<<<<<<<<<<<<< 0%
0% >>>>>>>>>> Concentration of substance>>>>>>>>>> 100%

Explosions are dependent on many parameters.

Only for atmospherical conditions and pure substances sufficient comparative values and data are shown. An explosion can only occur where a flammable substance in the form of gases, vapours, smoke and dust exists along with sufficient oxygen to support -combustion and there is a source of ignition.

E.g.:

Hydrogen: 4,0 to 77,0 % in air
Propane: 1,7 to 10,6 % in air
Ammonia: 15,4 to 33,6 % in air
Methane: 4,4 to 16,5 % in air

Fundamental principles:

The manufacturer of operating devices for areas rendered potentially explosive through dust must indicate the maximum surface temperature of all devices that dust can penetrate (usually expressed in °C - indication of the temperature class should be avoided here).This temperature is part of the dust Ex-designation.

Designation examples:

II 2 D T90°C IP64

(If the ignition protection type is based on the housing, the housing protection rating should also be stated as an IP Cede). or il 2 D Ex iaD 21 T96°C

Dust explosion protection - temperature:

Combustion and explosion parameters for dusts depend on the their condition. Parameters that affect combustion and explosion behaviour include particle size, particle shape, water content, purity and where applicable the content of the flammable solvents. The particle size distribution and the mean value (value for average particle size) should also be known.

In accordance with 1999/921/G Directive (ATEX 137, replacing:ATEX 118a), the system operator employer is obliged to make a hazard assessment and must therefore be aware of the minimum glow temperature of the dust.

There are simple calculations to determine the two " temperatures " and they are carried out thus:

These two limit temperatures must now be examined to confirm which guarantees the greater safety..

Example 1:
Minimum ignition temperature = +330°C, minimum glow temperature = +300°C:

Greater safety: Limit temperature (1) = +220°C Here a device with a max. surface temperature in the event of failure <= +220°C must be used. As stated, the device designation includes a corresponding value.

Example 2:

Minimum ignition temperature = +186°C, minimum glow temperature = +180°C:

Greater safety: Limit temperature (2) = +105°C.
Here a device with a max. surface temperature in the event of failure <= +105°C must be used.

The value for the glow temperature applies with a dust layer thickness of 5mm.The temperature safety distance must be increased for larger layer thicknesses.

Special case - Category 3 devices:

In contrast to Category 1 and 2 devices, potential hazards in the event of failure (e.g. short circuiting, connection break etc.) do not have to be considered for Category 3 devices (for use only in Zones 2 respectively 22).The device is evaluated only in respect of hazards during normal operation, it is relatively unlikely that the device should fail at the same time as a shortterm explosive atmosphere is present No EC Type Approval Test Certificate is therefore required for Category 3 operating devices. The manufacturer may confirm that the operating device complies with the relevant standard. Nonetheless, Category 3 devices are still tested by a certified centre and. EGAMASTER, S.A is then awarded a declaration of conformity. (- Of course, Category 2 operating devices also offer significantly greater safety in Zones 2 respectively 22.)

Dust explosions - albeit of a predominantly minor nature - occur relatively frequently.

A leaflet issued by the Government Safety Organisation of the Federal Republic of Germany states:

"According to documentation published by property insurers, it can be assurned that an average of one dust explosion per day occurs in the Federal Republic of Germany; around one in four of these explosions are caused by foodstuff or animal feed dusts."

Dust explosions are a world-wide problem. Between 1980 and 1990 in the USA, for example, some 200 serious foodstuff or animal feed related dust explosions were recorded, causing 54 deaths, 256 injuries and property damage amounting to 165 million US dollars.

Electrical operating devices represent only a small proportion of the ignition sources found to cause dust explosions -not least due to the safety stipulations in the regulations for erecting electrical plants in potentially-explosive areas.

The introduction of the (Regulation on electrical plants in potentially-explosive areas) - ElexV" [1.4] in 1980 specified a type examination certificate for electrical operating devices used in Zone 10 (from 01.07.2003 in Zones 20 and 21).

"Dust explosion-protected" operating devices, the surface temperatures of which lies below the acceptable limit for standardised dust thickness of 5mm, can, despite the existence of an official test certificate, become a danger source if, contrary to the conditions, they become covered or completely encased with a thick layer of dust.

Ignition protection type "n":

Ignition protection type n is applicable only for Category 3 operating devices used in areas rendered potentially explosive by gases. Because only normal operation and no equipment failures are considered here, small differences occur in the designation for ignition protection type:

nA: non-sparking electrical equipment (revolving machines, fuses, lamps, gauges and equipment with low energy).

nC: Sparking equipment or equipment with hot surface under operating conditions (dosed indexing mechanism and non-ignitable components, air-tight equipment, leak-proof sealed equipment.

nR: vapour-proof casing.

nL: equipment and circuit with limited energy.

nP: simplified overpressure casing.

Safety is our first st priority

At all places where inflammable substances are produced, processed, transported or stored, safety is extremely important - especially in the chemical and petrochemical industry, in oil and natural gas production and in mining.

In order to provide the highest level of safety possible, most state’s legislations have developed corresponding conditions in the form of laws, regulations and standards. In the course of globalisation, enormous progress could be made in uniform guidelines for explosion protection, It is the European Union that is leading the way. The 94/9/EG guideline lays the foundation for a complete unification. As of 01 july 2003, all new devices must be approved in accordance with this guideline.

Meaning of the zone classification:

Zone 0/20: Danger is always present, for a long time or frequently

Zone 1/21: Danger is occasionally present

Zone 2/22: Danger is seldom present or present for a short time