of dusts

DEKRA EXAM determines values relevant for measures of explosion protection

The determination of flame and explosion characteristics of inflammable dusts has immediate impact on handling those materials. Such characteristics are relevant for choosing and assessing appropriate measures of explosion protection within the scope of hazard assessment according to the Regulations of Occupational Safety (explosion protection document). In our accordingly certified laboratories DEKRA EXAM determines accurately the flame and explosion characteristics required.

Inflammable dusts

The definition of inflammable dusts refers to solid substances of fine particles that may oxidise exothermally. These may include organic substances (e.g. coal, wood, fibres, foodstuffs, luxury foodstuffs, animal feed, plastics, resins, rubber and pharmaceutics) as well as inorganic substances (metals and alloys, soot or sulphur).

Factors impacting characteristics and representative selection of dust sample

There are several parameters which influence the response of dust to an explosion. The two major factors are the grain size, which is defined by its median, and the humidity. The more grain size and humidity are decreasing, the more the dust will be inclined towards explosion as finer dusts are more easily flammable and show a fiercer response than those of a coarser grain. Therefore it is important to select a dust sample which covers even the most critical incident with regard to explosion technology. Generally, all inspections of dust settlements should use grain sizes of less than <250 µm, and those of stirred dust should use grain sizes of less than 63 µm. Nevertheless, we often inspect dusts supplied in a combination of grain sizes which is representative in relation to the procedure to be assessed.

Thus the first step is always to determine the grain size and the humidity of each dust sample. Additionally, DEKRA EXAM may carry out an immediate analysis or determine the specific volume resistance if required. The sample volume depends on the characteristics to be determined.

Relevance of characteristics

The type and volume of the tests are always adapted to each specific case (e.g. plant, procedure, process conditions and organisational measures) and thus should be defined together with DEKRA EXAM. Otherwise, the assessment of hazards or explosion protection measures may be misinterpreted.

Do not hesitate to contact DEKRA EXAM if you have further questions on this issue.

The following table gives an overview of the key characteristics and their testing methods. Principally, all tests are done at ambient conditions.

(Chart for download: characteristics.gif )

The characteristics stated in this table only list the reaction between dust and oxygen in air. For dust-like products which may show exothermal reactions without coming into contact with atmospheric oxygen, additional examinations are needed which exceed the procedures described here.

Do not hesitate to contact DEKRA EXAM if you have further questions regarding this field.