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Flame and explosion characteristics of dusts

DEKRA determines values relevant for measures of explosion protection

Knowing the flame and explosion characteristics of inflammable is necessary for handling those materials safely. Such characteristics are relevant for

  • Operators of systems and plants who have to choose and assess appropriate measures of explosion protection within the scope of hazard assessment according to the Regulations of Occupational Safety (explosion protection document).
  • Manufacturers and planners of systems and plants who have to define a concept of explosion protection as part of their engineering.
  • Manufacturers of dust-type products (bulk goods) which have to state details of dust explosion hazards in the safety data sheets of their products in the paragraph "Physical and chemical properties".

The type and volume of the tests are always adapted to each specific case (e.g. plant, procedure, process conditions and organisational measures). In particular, processes of segregation or enrichment of fine dust have to be considered. Otherwise, the assessment of hazards or explosion protection measures may be misinterpreted.

Do not hesitate to contact us if you have any questions regarding this point.

Parameter packages

Our work is based on the following principle: "We only determine what you really need – and are there to support you with our expertise."

Therefore, we offer suitable packages of parameter determination as a kind of starter kind for hazard assessment. In addition, we will be able to carry out all types of parameter determination and specific further examinations.

Issue Pckg. Refenrences & Advantages
Data of explosion protection needed for safety data sheet

Flame and explosion characteristics not known at all

Design of a comprehensive concept for explosion protection including measures of protection by prevention and by construction

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Package “Complete determination”

  • Includes common flame and explosion characteristics;
  • The better these characteristics are known, the better the explosion measures deducted from them;
  • Provides information on safety range of the plant operation analysed;
  • No cost risk when ordering as only the reasonably delivered modules will be charged.
Dust not likely to be explosive (coarse, low proportion of fine dust or high proportion of inert material)

Are measures of explosion protection to be carried out at all?

At which proportion of inert material is a dust mixture not explosive?

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Package “Explosiveness”

  • Only safe method to come to the conclusion not explosive;
  • Key precondition for all subsequent measures of explosion protection;
  • Also includes determining the lower explosion limit if the product turns out to be explosive;
  • Developing recipes of non-explosive mixtures.
The dust is explosive.

Are preventive measures of explosion protection sufficient?

What must the design of electrical and non-electrical equipment look like with regard to their maximum surface temperature?

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Package “Prevention of ignition sources”

  • Only if ignition sensitivity of settle or stirred dust is known, measures can be taken to exclude operational sources of ignition; The amount of the minimum ignition energy (MIE)
  • provides hints if prevention of ignition sources is sufficient as a sole measure; Even at plants protected by constructional measures a concept of how to prevent ignition
  • sources is reasonable to utilise the plant most.
The dust is explosive.

 

The result of the hazard assessment shows that an explosion inside the system or plant cannot be safely excluded (e.g. smouldering nests may enter the system). Thus measures of construction are necessary to ensure safe plant operation.

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Package “Explosion protection by construction”

  • Determining the pmax and KSt values values in order to dimension explosion-proof construction and to design measures for the relief, suppression and decoupling of explosion pressure.

Specific examinations

For all packages you can choose additional examinations that may be relevant for particular issues. Those examinations include the following:

1-m³ vessel Beside the standard testing device of the 20-l sphere we also offer a determination of characteristics using a 1-m³ vessel. This larger testing device is often the only opportunity to examine dusts and fibres which are coarse and difficult to stir up.
Limit concentration of oxygen
The limit concentration of oxygen is measured to determine the parameters for inerting plants and procedures.
Increased temperature
The heatable explosion containers allow for a determination of characteristics at temperatures of up to 200 °C
Spontaneous ignition
Storage tests at hot temperatures and with sample containers of up to 12.8 l are to assess large volumes of > 1m³.

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 moisture. The more grain size and moisture 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 protection. 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 relevant operating procedures. Thus the first step is always to determine the grain size and the humidity of each dust sample. Additionally, DEKRA Testing and Certification may carry out an immediate analysis or determine the specific contact resistivity if required. The sample volume required for the examination depends on the characteristics to be determined. The details stated below give some orientation how much dust is needed for which examination. The size of the dust sample needed in your specific case we will discuss with you before you send off the sample.

Individual examinations

All packages can be completed by individual examinations based on the individual hazard assessment. The determination of all characteristics always include the spread of the grain size and the moisture.
The following table gives an overview of the key characteristics and their testing methods plus the sample size needed for the examination.

Parameter Standard for testing Amount needed

Explosivness

Median value (sieving analysis)

VDI 2031

100 g

Moisture

Hygroscopic moisture

100 g

Explosivness

DIN EN 14034-3

3 kg (20-l sphere)

Lower explosion limit LEL

DIN EN 14034-3

3 kg (20-l sphere)

Prevention of potentially explosive atmosphere

Limit concentration of oxygen (LOC)

DIN EN 14034-4

5 kg (20-l sphere)

Prevention of iginition sources

Burning behaviour (class number)

VDI 2263-1

200 ml

Smouldering temperature LIT
(Minimum ignition temperature of a dust layer)

DIN EN 50281-2-1

500 ml

Ignition temperature MIT
(Minimum ignition temperature of a dust cloud)

DIN EN 50281-2-1

400 g

Minimum ignition temperature MIE (with/without inductivity)

DIN EN 13821

1 kg

Auto-ignition temperature
(400 cm³)

DIN EN 15188

3 l

Conductivity, specific resistance of a dust fill

DIN EN 61241-2-2 or
DIN IEC 60093

500 ml

Grewer temperature (spontaneous ignition)

VDI 2263-1

200 ml

Assessment factor (impact sensitivity according to Lütolf)

VDI 2263-1

100 g

Explosion protection by construction

Maximum explosion pressure pmax

DIN EN 14034-1

5 kg (20-l sphere)

Maximum pressure rise time,
KSt value

DIN EN 14034-2

25 kg or 100 l

Dust explosion class St 1, St 2, St 3

DIN EN 14034-2

25 kg (1-m³ vessel)

Analysis of hazardous goods

ADR class 4.1,
Packaging group

Combustion speede
(UN test N. 1)

500 ml

ADR class 4.2,
Packaging group

Auto-heating capacity
(UN test N.4)

2.5 l

ADR class 4.3,
Packaging group

Substances which in contact with water emit flammable gases (UN test N.5)

200 g

 

Services

Questions?

Thomas Burkhardt
Mobil: 0151.62941022
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Contact

DEKRA Testing and Certification GmbH
Laboratory for product testing
Fon +49.711.7861-3454
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