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Explosion Parameters
Examples of the assignment of gases and vapours to the respective temperature classes and explosion sub-groups:
| Designation of the solid material | Ignition temperature EN-ISO/IEC 80079-20-2 T5 mm layer (°C) | Ignition temperature EN-ISO/IEC 80079-20-2 TCloud (°C) | Permissible surface temperature of the equipment lowest value of the calculation (T5 mm layer - 75 K) and 2/3*TCloud | |||||||||
| > 300 ...450 | > 280 ...300 | > 260 ...280 | > 230 ...260 | > 215 ...230 | >200 ...215 | > 180 ...200 | > 165 ...180 | > 160 ...165 | > 135 ...160 | |||
| Dust from natural materials (examples) | ||||||||||||
| Cotton | 350 | 560 | 275 | |||||||||
| Brown coal | 225 | 380 | 150 | |||||||||
| Cellulose | 370 | 500 | 295 | |||||||||
| Cereals | 290 | 420 | 215 | |||||||||
| Sawdust (wood) | 300 | 400 | 225 | |||||||||
| Cocoa | 460 | 580 | 385 | |||||||||
| Cork | 300 | 470 | 225 | |||||||||
| Fooder concentrate | 295 | 525 | 220 | |||||||||
| Milk powder | 340 | 440 | 265 | |||||||||
| Paper | 300 | 540 | 225 | |||||||||
| Soya | 245 | 500 | 170 | |||||||||
| Starch | 290 | 440 | 215 | |||||||||
| Hard coal | 245 | 590 | 170 | |||||||||
| Tobacco | 300 | 450 | 225 | |||||||||
| Tea | 300 | 510 | 225 | |||||||||
| Wheat floor | 450 | 480 | 320 | |||||||||
| Dust of chemical technical products (examples) | ||||||||||||
| Cellulose ether | 275 | 330 | 200 | |||||||||
| Isosorbide dinitrate | 240 | 220 | 146 | |||||||||
| Unvulcanised rubber | 220 | 460 | 145 | |||||||||
| Petroleum coke | 280 | 690 | 205 | |||||||||
| Polyvinyl acetate | 340 | 500 | 265 | |||||||||
| Polyninyl chloride | 380 | 530 | 305 | |||||||||
| Soot | 385 | 620 | 310 | |||||||||
| Laminated plastic | 330 | 510 | 255 | |||||||||
| Sulphur | 280 | 280 | 186 | |||||||||
| Metal dust (examples) | ||||||||||||
| Aluminium | 280 | 530 | 205 | |||||||||
| Bronze | 260 | 390 | 185 | |||||||||
| Iron | 300 | 310 | 206 | |||||||||
| Magnesium | 410 | 610 | 335 | |||||||||
| Manganese | 285 | 330 | 210 | |||||||||
Ignitition temperature from dusts (layer and cloud)
For different types of dust, the method for determining the ignition temperature has been unified and coded in document EN-ISO/IEC 80079-20-2. Please note that dust in its deposited form (layer) has a different ignition (read: smouldering) temperature than in its stirred form (cloud).
The permissible surface temperature for those parts of systems and equipment is determined by subtracting 75 K (Tmax = T5 mm - 75 K) from the smouldering temperature value determined for the 5 mm dust layer and by taking 2/3 (Tmax, = 2/3TCloud) of the ignition temperature value determined for the dust cloud.
The permissible surface temperature of the equipment shall always be smaller than the lowest outcome of the Tmax. values determined by using above mentioned formulas. Temperature classes are not defined for dust, so a concrete type of dust must always be considered. The parameters are made available in comprehensive tables, laboratories determine the values on request, and a small, non-official overview is contained in the downloadable brochure ‘basic concepts’ (edition 14).
Equipment sub-groups for combustible Dusts
From the point of view of electrical engineering, it is not possible to classify dust as precisely as the chemically defined gases and vapours. For that reason, it is considered sufficient to divide the dust according to type and conductivity. EN-ISO/IEC 80079-20-2 contains the test method to determine the specific electrical resistance of dust. Dust is divided into 3 sub-groups:
- IIIA - combustible flyings
- IIIB - non-conductive combustible dust, specific electrical resistance > 10³ Ω
- IIIC - conductive combustible dust, specific electrical resistance < 10³ Ω