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Classification of Dusts Relative to Electrical Equipment in Class II Hazardous Locations (1982) / Chapter Skim
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Chapter 3: Dust Classification Methods
Pages 9-14

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From page 9...
... A dust that has an ignition sensitivity less than 0.2 and an explosion severity less than 0.5 poses a weak explosion hazard and does not require Class II electrical equipment. Any dust having an ignition sensitivity equal to or greater than 0.2 or an explosion severity equal to or greater than 0.5 requires electrical equipment suitable for Class II hazardous locations.
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From page 11...
... It now includes dusts with electrical resistivities both greater and less than the dividing line between conductive and nonconductive combustible dusts, and electrical equipment selected and installed according to the 1981 NEC is essentially the same for atmospheres containing Group E and electrically conductive Group F dusts. Therefore, under the proposed scheme, Group F is eliminated and equipment selection is restricted to Group E and Group G dusts.
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From page 12...
... ~2 4 ~n _ C: Q ~~~ co O ,c Q_ it\ ¢, O ~ as E _ ·— ~ X ~ 41~ 413 O ~°.Oo~c=',=~9=O L=c./\\~9 ~ o <( ~ C o ~ ~ o LO O Q ~ ~ 1 Go ,, , ~v, 1 ~C, o it j a, ~ e ~ = ~ 2 x~ ~ ~ L E ' ~ V ~ V, l ,.' i c = _ o _ ° O 0 0 to O _ X ~ ~ ~ X o ,,,, ~ o ~ X *
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From page 13...
... Subject to Overloading Equipment Not Normal Abnormal Class II Subject to Overloading Operation Operation Group °C OF °C OF °C OF E 200 392 200 392 200 392 F 200 392 150 302 200 392 G 165 329 120 248 165 329 The method employed to measure dust layer ignition temperature parallels what happens to dust that has settled on electrical equipment that generates heat. It is realized that surface temperature and ignition temperature depend on layer thickness and dust compactness; therefore, the committee recorurnends that the maximum surface temperature of the electrical equipment be lower than the specified dust layer ignition temperature by some differential value (e.g., 25°C)
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From page 14...
... The panel initially considered methods of testing for thermal and oxidative stability as well as layer ignition temperature and electrical resistivity. A review of the literature disclosed several different techniques for the determination of long-term stability, including thermogravimetric analysis, an active oxygen method, a modified ASTM oxygen bomb method, differential scanning calorimetry, and pressure differential scanning calorimetry.
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Key Terms

  • electrical equipment
  • ignition sensitivity
  • explosion severity
  • layer ignition
  • explosion hazard

  • surface temperature
  • maximum surface
  • dust layer
  • oxidative stability
  • equipment suitable

  • combustible dust
  • combustion parameters
  • scanning calorimetry
  • surface temperatures
  • determine ignition

  • classifying dusts
  • differential scanning
  • electrical resistivity
  • electrical resistivities
  • proposed international

  • includes dusts
  • requiring class
  • oxygen method
  • fundamental combustion
  • thermogravimetric analysis

  • explosions research
  • nonconductive combustible
  • require class
  • plate method
  • nec continue


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