CHEMSAFE ... on the WEB

Definitions

Amount of combustible at lower explosion limit with inert gas

UNITS: mol% (molecular fraction in %) or vol% (volume fraction in %)

DEFINITION:The amount of combustible at lower explosion limit with inert gas is the amount of combustible in percent of volume or of mole at the lower explosion limit, with a given constant amount of inert gas (cf. "amount of inert gas in the mixture ") in the mixture of combustible, inert gas and oxidizer.

Amount of combustible at upper explosion limit with inert gas

UNITS:mol% (molecular fraction in %) or vol% (volume fraction in %)

DEFINITION:The amount of combustible at upper explosion limit with inert gas is the amount of combustible in percent of volume or of mole at the upper explosion limit, with a given constant amount of inert gas (cf. "amount of inert gas in the mixture") in the mixture of combustible, inert gas and oxidizer.

Amount of inert gas in the mixture

UNITS:mol% (molecular fraction in %) or vol% (volume fraction in %)

DEFINITION:The amount of inert gas in the mixture is the amount of inert gas in percent of volume or of mole in the mixture of combustible, inert gas and oxidizer.

Autoignition temperature

UNITS: °C (degrees centigrade)

DEFINITION: The autoignition temperature of flammable gases or liquids is the lowest wall-temperature measured in a glass flask by a method prescribed for its determination, at which the developing inhomogeneous gas/air or vapor/air mixture will just be stimulated to burn as a flame.

MEASURING METHOD: DIN 51794 (D) and IEC 60079-4 are applicable to gases and liquids.

SPECIAL NOTES: The autoignition temperature in oxygen may be up to 300 degrees centigrade below the one in air.
In large containers and for certain wall materials, the ignition temperature may be lower than the one determined according to the standard.
The autoignition temperature of mists can be lower than the flash point of the liquid (e.g. caused by decomposition reactions).
The autoignition temperature on convex or flat surfaces are often higher than the standard ignition temperatures.

FUNCTIONAL CORRELATIONS: The ignition temperature decreases with increasing pressure /1/.

CLASSIFICATION: The autoignition temperature allows flammable gases and vapors to be ordered in temperature classes according to their ignitibility on heated walls (cf. DIN EN 60079-14 ).

REFERENCES

  1. M. Goedde
    Zuendtemperaturen organischer Verbindungen in Abhaengigkeit von chemischer
    Struktur und Druck
    Dissertation TU Braunschweig, PTB-Bericht ThEx-8 (1998)

Brunauer-Emmett-Teller surface

Specific surface measured by Brunauer-Emmett-Teller

UNITS: m2/g

DEFINITION: Brunauer-Emmett-Teller surface The specific surface of a solid material (e.g. powder, dust) is the surface related to the mass which is freely accessible for gases.

MEASURING METHOD: The measuring method is based on the adsorption of nitrogen on a sample surface related to the mass that is freely accessible for gases (including the "inner" surface) at the temperature of liquid nitrogen. Analogue to DIN 66132.

FUNCTIONAL CORRELATIONS: BET-equation (Brunauer, Emmett, Teller)

REFERENCES:

  1. DIN 66131 Bestimmung der spezifischen Oberflaeche von Feststoffen durch Gasadsorption nach Brunauer, Emmett und Teller (BET), Grundlagen (1973), Beuth Verlag, Berlin
  2. DIN 66132 Bestimmung der spezifischen Oberflaeche von Feststoffen durch Stickstoffadsorption, Einpunkt-Differenzverfahren nach Haul und Duembgen (Juli 1975), Beuth Verlag, Berlin
  3. DIN 66126, Teil 1 Bestimmung der spezifischen Oberflaeche pulverfoermiger Stoffe mit Durchstroemverfahren, Grundlagen, laminarer Bereich. Darstellung von Korn-groessenverteilungen, Grundlagen (1974), Beuth Verlag, Berlin
  4. M. Molnarne, Th. Schendler, V. Schroeder
    Sicherheitstechnische Kenngroessen
    Band 2: Explosionsbereiche von Gasgemischen
    Wirtschaftsverlag NW - Verlag fuer neue Wissenschaft,
    ISBN 3-89701-746-6, 2003

Burning Index (Danger Class, Rating)

UNITS: -

DEFINITION: Value, which describes in which kind of reaction, if any at all, a fire spreads out in a dust layer after ignition from outside.

MEASUREMENT METHOD: VDI 2263 (D)

SPECIAL REMARKS:

RatingKind of Reaction
1No ignition
2Short ignition and fast extinction
3Local burning or smoldering with with expansion to small area
4Smoldering without emitting sparks or slow decomposition without flames
5Burning with flames or emitting sparks
6Deflagration or fast decomposition without flames

There are reference substances for the Ratings 1-6:

RatingSubstance
1Sodium chloride
2Tartaric acid
3d+Lactose
4H-acid (1-Amino-8-naphthyl-3,6-disulfonic acid), Tobacco
5Sulfur
6Black powder

REFERENCES

  1. VDI Directive 2263, Part 1
    Untersuchungsmethoden zur Ermittlung von sicherheitstechnischen Kenngroessen von Staeuben
    VDI-Handbook Reinhaltung der Luft, No. 6
    Published by: Beuth Verlag GmbH, Berlin, 1990
  2. W. Bartknecht
    Staubexplosionen, Ablauf und Schutzmassnahmen
    Published by: Springer-Verlag, Berlin Heidelberg New York
    Paris Tokyo, 1987

Characteristic values of the ternary system with air

Under this heading there is a table with the minimal inert/combustible ratio, the maximum permissible amount of combustible gas, the maximum oxygen content, then minimal inert/air ratio and the minimal required amount of inert gas in inert gas-oxidator mixture.

Characteristic values of the ternary system with oxidizing mixture

Characteristic values of the ternary system with oxidizing mixture Under this heading there is a table with the minimal inert/combustible ratio, the maximum permissible amount of combustible gas, the minimal inert/air ratio and the minimal required amount of inert gas in inert gas-oxidator mixture.

Classification according to short time MAC-value according to TRGS 900

Maximum allowable concentrations are meant as mean value over a period of 8 hours. With many substances even short deviations from this mean value to higher values need a limitation. The classification according to short time MAC-value is the factor, by which the maximum allowable concentration (MAC-value) may be exceeded shortly.

Classification according to TRGS 905

This technical rule for dangerous substances contains a list of substances that most likely are carciogenic, mutagenic or teratogenic. They are classified using assured scientific knowledge into category 1, 2, or 3 of Appendix I of the "Gefahrstoffverordnung" (German regulations on dangerous substances). The list is published after discussion in the Ausschuss fuer Gefahrstoffe (committee on dangerous substances).

Classification of carciogenic substances according to TRGS 905

According to the German regulations on dangerous substances (Gefahrstoffverordnung), Appendix I, the substances are classified as follows.

  • class 1: Substances that are known to be carciogenic for human beings
  • class 2: Substances that are considered to be carciogenic for human beings
  • class 3: Substances that may cause concern due to a possible carciogenic effect on human beings

Classification of mutagenic substances according to TRGS 905

According to the German regulations on dangerous substances (Gefahrstoffverordnung ), Appendix I, the substances are classified as follows.

  • class 1: Substances that are known to be mutagenic for human beings
  • class 2: Substances that are considered to be mutagenic for human beings
  • class 3: Substances that may cause concern due to a possible mutagenic effect on human beings

Classification of substances harming fertility according to TRGS 905

According to the German regulations on dangerous substances (Gefahrstoffverordnung), Appendix I, the substances are classified as follows.

  • class 1: Substances that are known to harm the fertility of human beings
  • class 2: Substances that are considered to harm the fertility of human beings
  • class 3: Substances that may cause concern due to possible harming of the fertility of human beings

Classification of teratogenic substances according to TRGS 905

According to the German regulations on dangerous substances (Gefahrstoffverordnung), Appendix I, the substances are classified as follows.

  • class 1: Substances that are known to be teratogenic for human beings
  • class 2: Substances that are considered to be teratogenic for human beings
  • class 3: Substances that may cause concern due to a possible carciogenic effect on human beings

Critical pressure

If you move on the vapor - liquid equilibrium line to higher temperatures, you will reach a point, at which the density of the vapor equals the density of the liquid. Therefore, there is no difference between vapor and liquid and the meniscus between vapor and liquid disappears. This point is called critical point, the corresponding temperature and pressure is called critical temperature and critical pressure.

Coefficient of nitrogen equivalency, Ki-value

REFERENCES

  1. ISO 10156(1996)
  2. M. Molnarne, Th. Schendler, V. Schroeder
    Sicherheitstechnische Kenngroessen
    Band 2: Explosionsbereiche von Gasgemischen
    Wirtschaftsverlag NW - Verlag fuer neue Wissenschaft,
    ISBN 3-89701-746-6, 2003

Coefficient of oxygen equivalency, Ci-value

The coefficient of oxygen equivalency characterizes the ability to promote burning processes, compared to oxygen. Pure oxygen has per definition the Ci value 1.

REFERENCES

  1. Schroeder, V., Mackrodt, B. and Dietlen, S.:
    Determination of oxidizing ability of gases and gas mixtures,
    ASTM STP 1395 (2000)
  2. M. Molnarne, Th. Schendler, V. Schroeder
    Sicherheitstechnische Kenngroessen
    Band 2: Explosionsbereiche von Gasgemischen
    Wirtschaftsverlag NW - Verlag fuer neue Wissenschaft,
    ISBN 3-89701-746-6, 2003

Critical temperature

The critical temperature is the temperature below which gases may be liquefied.

Diffusion coefficient

Diffusion is the mixing of different gaseous, liquid or solid substances that are in contact with each other. The diffusion coefficient D is defined by Fick's law as follows j(i) = -D grad(c(i)) with j(i) = particle flow density and c(i) = concentration of species i.

Dust Explosion Class

UNITS: -

DEFINITION:Defined ranges limited by certain KST-values

KST-Value (bar m / s)Dust Explosion Class
0 - 200ST 1
200 - 300ST 2
300ST 3

REFERENCES

  1. W. Berthold, U. Loeffler
    Lexikon sicherheitstechnischer Begriffe in der Chemie
    Published by: Verlag Chemie, Weinheim, 1981
  2. VDI 3673
    Druckentlastung von Staubexplosionen
    VDI-Handbook Reinhaltung der Luft, No. 6
    Published by: Beuth Verlag GmbH, Berlin and Koeln, 1979
  3. VDI 2263, Part 1
    Untersuchungsmethoden zur Ermittlung von sicherheitstechnischen Kenngroessen von Staeuben
    VDI-Handbook Reinhaltung der Luft, No. 6
    Published by: Beuth Verlag GmbH, Berlin, 1990
  4. H. Steen (Hrsg.)
    Handbuch des Explosionsschutzes
    Wiley-VCH, Weinheim 2000

Evaporation number

UNITS: -

DEFINITION: The evaporation number is the ratio of the evaporation time of the liquid to be tested and the evaporation time of diethyl ether as the reference substance, measured in a specified experimental apparatus.

MEASURING METHOD: Standardized measuring method according to DIN 53 170 (D).

REFERENCES

  1. K. Nabert, G. Schoen
    Sicherheitstechnische Kennzahlen brennbarer Gase und Daempfe
    2nd enlarged edition with 6th supplement, Braunschweig 1990

Explosion pressure

UNITS: bar (absolute pressure)

DEFINITION: The explosion pressure is the peak value of the time dependent pressure measured in a closed container upon deflagration of an explosive mixture of defined composition.

MEASURING METHOD: The explosion pressure of gases and vapours is determined in resting mixtures according EN 13673-1, the explosion pressure of dusts in turbulent mixtures according prEN 14034-1.

SPECIAL NOTES:The explosion pressure is almost independent of the turbulent state of the mixture and of the size and shape of the container. However, stronger influences on the explosion pressure may occur in the case of deviations from ideally spherical flame propagation.
Dusts are measured in a cloud of whirled up dust. There is no ideal spherical flame propagation.
In containers divided into compartments, considerably higher pressures may occur in individual compartments due to pre-compression.
In long containers or tubes, a deflagration can easily change into a detonation. Considerably higher pressures will then occur.
The pressures indicated here are absolute pressures for gases, vapors and dusts.

FUNCTIONAL CORRELATIONS: The explosion pressure is a function of initial pressure, temperature and concentration of the mixture.
The explosion pressure of dusts may depend on the size of the dust particles. If they are very large, e.g. > 100 um, then the explosion pressure drops considerably with increasing particle sizes /1/.

REFERENCES

  1. H. Steen (Hrsg.)
    Handbuch des Explosionsschutzes
    Wiley-VCH, Weinheim 2000

Explosion range of the system combustible/inert/air

This table represents the lower and the upper explosion limit (ACL and ACU, respectively) of the ternary system combustible/inert/oxidator in a triangular diagram. As a third concentration measure the amount of inert gas in the mixture (AIM) is given.

Explosion range of the system combustible/inert/oxidator

This table represents the lower and the upper explosion limit (ACL and ACU, respectively) of the ternary system combustible/inert/oxidator in a triangular diagram. As a third concentration measure the amount of inert gas in the mixture (AIM) is given.

Flash point

UNITS: °C (degree centigrade)

DEFINITION: The flash point is the lowest temperature of a flammable liquid at which an ignition in the gas phase initiated by a test flame will propagate. Measuring procedures and test equipments have to be well defined.

  • Determination in closed cup according to Abel-Pensky, e.g. - DIN EN ISO 13736
  • Determination in closed cup according to Abel-Pensky, e.g. - DIN 51755 (D), DIN 53213(D), DIN 53169 (D)
  • Determination in closed cup according to Pensky-Martens, e.g. - DIN EN 22719 ( comparable: ASTM D93 (USA))
  • Quick test "Seta-Flash" - DIN EN 456 ( comparable: ISO 3679, ASTM 3278 (USA))
  • Determination in open cup according to Cleveland - ISO 2592

SPECIAL NOTES:For non-halogenated, pure organic liquids, the flash point determined in a closed cup is about five degrees higher than the lower explosion point. For mixtures the difference might be even higher.
The flash point determined in an open cup are in general considerably higher (by up to 20 degrees, in individual cases even more). In Germany and some other countries these measurements must not be used for classification.
Even small impurities caused by low-boiling flammable liquids or gases will lower the flash point.
The flash point of a mixture may be lower than that of the individual components.
Halogenated organic liquids may form explosive mixtures without having a flash point /1/. For these substances the database contains the text "not easily flammable".

CLASSIFICATION:The flash point measured in a closed cup is used for the classification of flammable liquids in a great number of regulations, such as GefStoffVO, VbF, GGVSE GGVSee, ADR, RID, IMDG Code, UN Recommendations, IATA Code.

REFERENCES

  1. H. Steen, T. Redeker < br>Chem. Ing. Techn. 6, 1975, p. 262 Synopsis
  2. K. Nabert, G. Schoen
    Sicherheitstechnische Kennzahlen brennbarer Gase und Daempfe
    2nd enlarged edition with 6th supplement, Braunschweig 1990
  3. W. Berthold, U. Loeffler
    Lexikon sicherheitstechnischer Begriffe in der Chemie
    Verlag Chemie, Weinheim, 1981.

Fusion temperature

The fusion temperature is the temperature at which the liquid and the solid phase of a pure compound are in equilibrium at 1.01325 bar.

Ignition pressure limit

The explosion area (the range between the upper and the lower explosion limits) diminishes at pressure's reduction. The pressure, at which the upper and lower explosion limits are equal and fall to one value, is the ignition pressure limit. Under this pressure is no more ignition possible.

SPECIAL NOTES: The ignition pressure limit should not mixed up with the minimum decomposition pressure or stability pressure limit (SPL) of thermal instable gases.
Normally the diminishing of the explosion range starts first under appr. 300 mbars.
The Ignition Pressure Limit depends on:

  • temperature
  • shape and size of the explosion vessel
  • kind of the ignition source
Therefore the experimental conditions under which the ignition pressure limit was determined have to be specified.

REFERENCES

  1. E. Brandes, D. Pawel, J. Alpers, J. Scheffler
    Sicherheitstechnische Kenngroessen bei reduzierten Ausgangsdruecken,
    in:8. Kolloquium zu Fragen der chemischen und physikalischen Sicherheitstechnik,
    Berlin 1999, Tagungsbericht S. 85
  2. Horstmann,T.;Wischniewski,F.;Maurer,B.;Leuckel,W
    Entzuendungsverhalten von Brennstoff/Luft-Gemischen im Unterdruck
    VDI-Bericht, Nr. 1272 (1996), 149-159

Gross calorific value

The specific calorific value of a liquid or solid fuel is the quotient of the heat produced by complete combustion and the mass. The temperature of the fuel before the combustion and of the combustion products has to be 25 degrees centigrade, the water formed by the combustion has to be liquid. The nitrogen must not be oxidated. The gross calorific value is determined according to the German standard DIN 51900.

REFERENCE:

  1. DIN 51900-1, Ausgabe:2000-04
    Pruefung fester und fluessiger Brennstoffe - Bestimmung des Brennwertes mit dem Bomben-Kalorimeter und Berechnung des Heizwertes -
    Teil 1: Allgemeine Angaben, Grundgeräte, Grundverfahren
  2. DIN 51900-2, Ausgabe:2003-05
    Pruefung fester und fluessiger Brennstoffe - Bestimmung des Brennwertes mit dem Bomben-Kalorimeter und Berechnung des Heizwertes
    Teil 2: Verfahren mit isoperibolem oder static-jacket Kalorimeter
  3. DIN 51900-3, Ausgabe:1977-08
    Pruefung fester und fluessiger Brennstoffe; Bestimmung des Brennwertes mit dem Bomben-Kalorimeter und Berechnung des Heizwertes, Verfahren mit adiabatischem Mantel
    Beuth Verlag GmbH, Berlin

Kg-value

UNIT: bar m/ s (bar meter/second)

DEFINITION: Characteristic value of flammable gases and vapors, calculated according to the cubic law from the pressure rise per unit time of an explosion (maximum pressure rise rate)

SPECIAL NOTES: K value for dusts: cf. Kst-value

FUNCTIONAL CORRELATIONS: Cubic law: The maximum pressure rise per unit time of an explosion (max. pressure rise rate) (dp/dt)max depends on the container volume V:
(dp/dt)max *V**(1/3) = constant = Kg-value (almost constant) The cubic law is applicable only if the other conditions are comparable, i.e. approximate spherical symmetry, identical turbulent state and identical initial temperatures and pressures. Some of the experimental results deviate considerably from this equation and furnish different Kg-values. This above all is due to the heat loss at the wall and the flow conditions during flame propagation.

REFERENCES

  1. H. Foerster, H. Steen
    PTB Report W32, Braunschweig, 1986
  2. VDI Directive 2263, Part 1
    Untersuchungsmethoden zur Ermittlung von sicherheitstechnischen
    Kenngroessen von Staeuben
    VDI-Handbook Reinhaltung der Luft, No. 6
    Published by: Beuth Verlag GmbH, Berlin, 1990
  3. W. Berthold, U. Loeffler
  4. Lexikon sicherheitstechnischer Begriffe in der Chemie
  5. Verlag Chemie, Weinheim, 1981

KST-Value

UNIT: bar m / s (bar meter / second)

DEFINITION: Specific characteristic for dust and test methods according to the Cubic Law. It is numerically equal to the value for the Maximum Rate of Pressure Rise (dp/dt)max. in a 1 m3 vessel for the conditions layed down in VDI 3673 (D).

CLASSIFICATION:The Dust Explosion Classes are related to the KST-Values.

CORRELATIONS: Cubic Law: Correlation of KST-Value with Maximum Pressure Rise per Unit Time (dp/dt)max.:
(dp/dt)max * V ** (1/3) = KST (nearly constant)
(V: Volume of the vessel)

SPECIAL REMARKS: The Cubic Law is applicable only under comparable conditions are identical, i.e. approximate spherical symmetry, identical turbulent state and identical initial temperatures and pressures. For the determination of this value it is necessary to know the (dp/dt)max.-values from tests in closed vessels of sufficient dimensions.

REFERENCES

  1. W. Berthold, U. Loeffler
    Lexikon sicherheitstechnischer Begriffe in der Chemie
    Published by: Verlag Chemie, Weinheim, 1981
  2. VDI 3673
    Druckentlastung von Staubexplosionen, VDI-Handbook Reinhaltung der Luft, No. 6
    Published by: Beuth Verlag GmbH, Berlin and Koeln, 1979
  3. VDI 2263, Part 1
    Untersuchungsmethoden zur Ermittlung von sicherheitstechnischen Kenngroessen von Staeuben, VDI-Handbook Reinhaltung der Luft, No. 6
    Published by: Beuth Verlag GmbH, Berlin, 1990
  4. W. Bartknecht
    Staubexplosionen, Ablauf und Schutzmassnahmen
    Published by: Springer-Verlag, Berlin Heidelberg New York
    Paris Tokyo, 1987
  5. M. Hattwig
    Druckentlastung von Gasexplosionen bei erhoehtem Anfangsdruck
    3. BAM/PTB-Colloquium (general remarks to the problems of the explosion hazards of chemicals in accordance with protection techniques) Report

Limiting Oxygen Concentration

UNIT: volume% (percentage of volume)

DEFINITION:Limiting Oxygen Concentration is the maximum content of oxygen in a mixture of combustible with air and inert gas, at which the mixture will just not allow an explosion. Below this limit adding any amount of combustible would not form an explosible mixture.

MEASURING METHOD: Limiting Oxygen Concentration is to be determined according VDI 2263 (D), prEN 14034-4:2000 (for dusts), respective prEN 14756 for gases and vapours.

SPECIAL REMARKS: Specific characteristic of dust and used inert gas.

REFERENCES

  1. prEN 14034-4:2000
    Determination of the explosion properties of dust clouds -
    Part 4: Determination of the limiting oxygen concentration of dust clouds
  2. VDI 2263, Part 1
    Untersuchungsmethoden zur Ermittlung von sicherheitstechnischen Kenngroessen von Staeuben
    VDI-Handbook Reinhaltung der Luft, No. 6
    Published by: Beuth Verlag GmbH, Berlin, 1990
  3. G. Leuschke, R. Osswald
    Bedeutung und Ermittlung von sicherheitstechnischen Kenngroessen brennbarer Staeube
    VDI-Berichte No. 304, S. 29-38
    Published by: VDI-Verlag, Duesseldorf, 1978
  4. K.N. Palmer
    Dust Explosions and Fires
    Chapman and Hall Ltd., London, 1973
  5. W. Bartknecht
    Staubexplosionen, Ablauf und Schutzmassnahmen
    Published by: Springer-Verlag, Berlin Heidelberg New York Paris Tokyo, 1987

Lower explosion limit

UNITS: volume% (percent by volume),; g/m3 (gramme per cubic meter at 20 °C)

DEFINITION: The lower and upper explosion limits borders the area of explosible mixtures, i.e. the range of the content of combustibles in the mixture, at which a flame can separate from the ignition source resp. can propagate. The explosion limits are not part of the explosion area. The amount indicated in vol% or the equivalent concentration indicated in g/m3 refer to the total mixture.

MEASURING METHOD:The explosion limits of Gases and vapors are determined according EN 1839.The explosion limits generally refer to an initial pressure of the mixture of 1013.25 mbar (atmospheric pressure).
In the case of liquids, the initial temperature of the mixture is selected to lie at a point far enough above the condensation point (generally 20 degrees centigrade). Then the value given is calculated from the measured value using the reference temperature of 20 degrees centigrade.

SPECIAL NOTES: The conversion of vol% into g/m3 and vice versa can lead to incorrect results, as all data have been rounded to the safe side.

FUNCTIONAL CORRELATIONS: The lower explosion limit depends on pressure, temperature and ignition energy. The temperature pertaining to the lower explosion limit - the lower explosion point - can be calculated from the vapor pressure curve. For experimental reasons, the flash point may be up to five degrees below the flash point.

REFERENCES

  1. VDI Richtlinie 2263, Blatt 1
    VDI Handbuch "Reinhaltung der Luft", volume 6
    published by Beuth Verlag, Berlin 1990
  2. H. Steen (Hrsg.)
    Handbuch des Explosionsschutzes
    Wiley-VCH, Weinheim 2000

Lower explosion point

UNIT: °C (degrees centigrade)

DEFINITION: The lower explosion point of a flammable liquid is the temperature related to 1013.25 mbar, at which the concentration of a saturated vapor/air-mixture equals the lower explosion limit.

SPECIAL REMARKS: With pure substances this definition is sufficient. But it is possible to measure different explosion points of mixtures depending on the volume ratio of gaseous and liquid phase (h-ratio). Therefore the lower explosion point of mixtures must not be given without the h-ratio.

FUNCTIONAL CORRELATIONS:The lower explosion point of a pure compound can be calculated from its vapor pressure curve and the lower explosion limit. The lower explosion point is comparable to the flashpoint, but caused by experimental reasons the lower explosion point of pure substances is up to about five degrees lower than the flash point. Lower explosion points of mixtures deviates even more.

REFERENCE

  1. K. Nabert, G. Schoen
    Sicherheitstechnische Kennzahlen brennbarer Gase und Daempfe
    2nd, extended edition with 6th extension, Braunschweig 1990

Maximal Stability Ratio

UNIT: -

DEFINITION: The maximum stability ratio is the mixture ratio set up from the portion of a chemical instable gas and that portion of any other admixture at which under specified test conditions a decomposition of the instable gas may not yet be initiated.

SPECIAL REMARKS: The maximal stability ratio depends on:

  • temperature and pressure.
  • size and dimensions of the reaction vessel
  • type of the ignition source
Therefore it is necessary to denote the test conditions, at which the value for the maximal stability ratio was determined.

REFERENCES

  1. T.Schendler, H.-P. Schulze
    Stabilitaetsgrenzdruecke von Acetylen/Gas-Gemischen

Maximum allowable concentration according to TRGS 900 (MAC-value)

This value is the maximum allowable concentration of a substance as a gas, a liquid or a dust suspended in the air at a working place that does not harm the health of the workers or molest them inadequately according to the present knowledge, if they are exposed to the substance repeatedly over an extended range of time, but normally not more than 8 hours a day. TRGS means "Technische Regeln fuer Gefahrstoffe" in German

Maximum Burning Velocity

UNITS: m/s (meter/second)

DEFINITION: The maximum burning velocity of flammable gases and vapors is the maximum value of the velocity - measured by varying the composition of the mixture - at which the fresh gas flows into the stationary flame vertical to its surface when a flame reaction takes place.

MEASURING METHOD: Bunsen burner method and others /1/.

FUNCTIONAL CORRELATIONS: An increase of the fresh gas temperature generally leads to an increase, whilst an increase of the pressure generally results in a decrease of then maximum burning velocity.

REFERENCES

  1. E. Brandes et al. in: H. Steen (ED.)
    Handbuch des Explosionsschutzes
    Wiley-VCH, Weinheim 2000, S. 357 ff.

Maximum experimental safe gap (MESG)

UNIT: mm (millimeter)

DEFINITION: The maximum experimental safe gap of flammable gases and vapors is the lowest value of the safe gap measured according to IEC 60079-1-1 (2002) by varying the composition of the mixture ("flame propagation in the most incendive mixture"). The safe gap is the gap width at which in the case of a given mixture composition, a flashback just fails to occur.

MEASURING METHOD: International standard for gases and vapors IEC 60079-1-1 (2002)

SPECIAL NOTES:Caution: The maximum experimental safe gap (determined with a gap length of 25 mm) must not be confused with the "flameproof gap" of an apparatus. This flameproof gap strongly depends on the shape and dimensions of the gap to be evaluated in practice and is in many cases considerably lower than the maximum experimental safe gap. The measuring method IEC 60079-1-1 (2002) is also applicable to mixtures with a volume fraction of oxygen of up to 25%.

FUNCTIONAL CORRELATIONS: In addition to the minimum ignition energy the maximum experimental safe gap which in turn is correlated with the maximum burning velocity can be used as a measure of the ignitibility at nearly punctual ignition sources.
It has been proved for a greater variety of substances that minimum ignition energy, minimum ignition current and maximum experimental safe gap are correlated with one another so that the classification of substances is preserved when classification is made according to each of these three quantities.

CLASSIFICATION: The maximum experimental safe gap serves to classify flammable gases and vapors according to their flame transmission capability and so helps ordering protection measures of electrical apparatus.

REFERENCES

  1. T. Redeker
    PTB Report W18, Braunschweig, 1981

Maximum explosion pressure

UNITS: bar (absolute pressure)

DEFINITION: The explosion pressure is the peak value of the time dependent pressure measured in a closed container upon deflagration of an explosive mixture of defined composition. The maximum explosion pressure is the maximum value of the explosion pressure determined by varying the composition of the mixture.

MEASURING METHOD: The explosion pressure of gases and vapours is determined in resting mixtures according EN 13673-1, the explosion pressure of dusts in turbulent mixtures according prEN 14034-1.

SPECIAL NOTES: The maximum explosion pressure of gases and vapors is almost independent of the turbulent state of the mixture and of the size and shape of the container (cf. maximum rate of pressure rise, Kg-value, KST-value). In the case of deviations from the ideally spherical flame propagation, stronger influences may, however, be exerted on the maximum explosion pressure.
Dusts are measured in a cloud of whirled up dust. There is no ideal spherical flame propagation.
In containers divided into compartments, considerably higher pressures may occur in the individual compartments due to pre-compression.
In long containers or tubes, a deflagration can easily change into a detonation. Considerably higher pressures will then occur.
The indicated pressures are absolute pressures for gases, vapors and dusts.

FUNCTIONAL CORRELATIONS: The maximum explosion pressure is a function of pressure, temperature, and concentration of the initial mixture.
The explosion pressure of dusts may depend on the size of the dust particles. If they are very large, e.g. > 100 um, then the explosion pressure drops considerably with increasing particle sizes /3/.

REFERENCES

  1. H. Steen (Hrsg.)
    Handbuch des Explosionsschutzes
    Wiley-VCH, Weinheim 2000

Maximum oxygen concentration (for gases)(MOC)

UNITS: mol% (molecular fraction in %) or vol% (volume fraction in %)

DEFINITION:The maximum oxidizer content, at which no explosive mixtures can be created by adding more combustible. If the oxidator is air and the maximum oxidizer content is related to the oxygen content of the air, the maximum oxidizer content is equivalent to the limiting oxygen concentration.

MEASURING METHOD:The maximum oxidizer content is measured according prEN 14756 (for gases and vapours) or VDI 2263 (D) and prEN 14034-4:2000 (for dusts).

REFERENCES

  1. M. Molnarne, Th. Schendler, V. Schroeder
    Sicherheitstechnische Kenngroessen
    Band 2: Explosionsbereiche von Gasgemischen
    Wirtschaftsverlag NW - Verlag fuer neue Wissenschaft,
    ISBN 3-89701-746-6, 2003

Maximum permissible amount of combustible gas

UNITS: mol% (molecular fraction in %) or vol% (volume fraction in %)

DEFINITION:The maximum amount of combustible in percent of volume or of mole in a mixture of combustible and inert gas, which is not explosive or flammable by adding any amount of oxidizer to the mixture. If the inert gas is nitrogen and the oxidizer is air, the maximum permissible amount of combustible gas is identical with the Tci-value. The Tci-value is defined at room temperature and atmospheric pressure (cf. ISO Standard 10156).

REFERENCES

  1. M. Molnarne, Th. Schendler, V. Schroeder
    Sicherheitstechnische Kenngroessen
    Band 2: Explosionsbereiche von Gasgemischen
    Wirtschaftsverlag NW - Verlag fuer neue Wissenschaft,
    ISBN 3-89701-746-6, 2003

Maximum Rate of Pressure Rise

UNIT: bar/s

DEFINITION: The maximum rate of pressure rise (dp/dt)max is the highest (maximum) value of the rate of pressure rise during the explosion of a gas, vapor or dust obtained by varying the amount of combustible in its mixture with air (and sometimes inert gas). The rate of pressure rise (dp/dt)ex is the steepest gradient of the pressure-time curve of an explosion of a defined mixture of combustible and air (and sometimes inert gas) in a closed vessel under defined measuring conditions.

MEASUREMENT: Dust: VDI 2263 (D); VDI 3673 (D)

SPECIAL REMARKS: The maximum rate of pressure rise depends on the volume and the shape of the vessel and the state of turbulence of the mixture. Data of the maximum rate of pressure rise without denotation of test conditions are not reliable for determination of explosion protection measures.

REFERENCES

  1. W. Berthold, U. Loeffler
    Lexikon sicherheitstechnischer Begriffe in der Chemie
    Published by: Verlag Chemie, Weinheim, 1981
  2. VDI 3673
    Druckentlastung von Staubexplosionen
    VDI-Handbook Reinhaltung der Luft, No. 6
    Published by: Beuth Verlag GmbH, Berlin and Koeln, 1979
  3. VDI 2263, Part 1
    Untersuchungsmethoden zur Ermittlung von sicherheitstechnischen
    Kenngroessen von Staeuben
    VDI-Handbook Reinhaltung der Luft, No. 6
    Published by: Beuth Verlag GmbH, Berlin, 1990
  4. W. Bartknecht
    Staubexplosionen, Ablauf und Schutzmassnahmen
    Springer-Verlag, Berlin Heidelberg New York Paris Tokyo, 1987
  5. M. Hattwig
    Druckentlastung von Gasexplosionen bei erhoehtem Anfangsdruck
    3. BAM/PTB-Colloquium (general remarks to the problems of the explosion hazards of chemicals in accordance with protection technics)
  6. Berufsgenossenschaft der chemischen Industrie
    Explosionsschutzrichtlinien (EX-RL)
    Heidelberg 1986
  7. G. Leuschke, R. Osswald
    Bedeutung und Ermittlung von sicherheitstechnischen Kenngroessen brennbarer Staeube
    VDI-Berichte No. 304, S. 29-38
    VDI-Verlag, Duesseldorf, 1978
  8. K.N. Palmer
    Dust Explosions and Fires
    Chapman and Hall Ltd., London, 1973

Median value

UNIT: micrometer

DEFINITION: The median value of a dust is used to represent a characteristic particle size of the grain size distribution of a dust sample. It should be noted that the only meaningful characteristic of a dust sample is the complete particle size distribution. The median value is defined as that particle size in a distribution above and below of which 50 weight-% of a sample are found by a sieving analysis.

FUNCTIONAL CORRELATIONS: particle size, particle size distribution

REFERENCES

  1. VDI 2263 Staubbraende und Staubexplosionen, Gefahren, Beurteilung, Schutzmass-nahmen (1992)
  2. DIN 53734 Pruefsiebung von pulverfoermigen Kunststoffen mit dem Luftstrahl-Siebgeraet (1973), Beuth Verlag, Berlin

Minimal inert/air ratio

UNITS: -

DEFINITIONThe minimum ratio of inert gas and oxidizer, at which the mixture combustible, inert gas and oxidizer is no longer explosive or flammable, even if more combustible is added.

REFERENCES

  1. M. Molnarne, Th. Schendler, V. Schroeder
    Sicherheitstechnische Kenngroessen
    Band 2: Explosionsbereiche von Gasgemischen
    Wirtschaftsverlag NW - Verlag fuer neue Wissenschaft,
    ISBN 3-89701-746-6, 2003

Minimal inert/combustible ratio

UNITS: -

DEFINITIONThe minimal inert/combustible ratio is the minimum ration of inert gas and combustible, at which the mixture of combustible, inert gas and oxidizer is no longer flammable with any amount of oxidizer added.

REFERENCES

  1. M. Molnarne, Th. Schendler, V. Schroeder
    Sicherheitstechnische Kenngroessen
    Band 2: Explosionsbereiche von Gasgemischen
    Wirtschaftsverlag NW - Verlag fuer neue Wissenschaft,
    ISBN 3-89701-746-6, 2003

Minimum ignition energy

UNITS: mJ (milliJoule)

DEFINITION: The minimum ignition energy of flammable gases and vapors is the minimum value of the electric energy, capacitively stored in the discharge circuit with as small a loss in the leads as possible, which - upon discharge across a spark gap - just ignites the mixture at rest in the most ignitable composition. For a given composition the parameters of the discharge circuit such as capacitance, inductivity and charging voltage as well as shape and dimensions of the electrodes and the interelectrode distance must be varied to get the optimum conditions. Then the most ignitable mixture is determined by variation of the mixture composition.

MEASURING METHOD: Standardized method: ASTM E582-76 (USA)

SPECIAL NOTES: The minimum ignition energy is a measure of the ignitability of flammable gases and vapors by electric sparks. According to the concept of equivalent energy it serves also to evaluate the incendivity of electrostatic discharge processes (high voltages) and the ignition power of other quasi-point-ignition sources (e.g. friction sparks). Not the minimum ignition energy but other characteristic data (e.g. minimum ignition current) serve to evaluate low-voltage circuits (intrinsic safety "i").

FUNCTIONAL CORRELATIONS: In addition to the minimum ignition energy, the maximum experimental safe gap which in turn is correlated with the maximum normal burning velocity can also serve as a measure of ignitability at nearly point-ignition sources. It has been proved for a great variety of substances that minimum ignition energy, minimum ignition current and maximum experimental safe gap are correlated with one another so that the classification of substances is preserved when classification is made according to each of these three quantities.

CLASSIFICATION: The minimum ignition energy is used to classify flammable gases and vapors with respect to their ignitability by electric discharges (not with respect to their ignitability on hot surfaces, cf. ignition temperature). By this the substances are classified for necessary protection means at electrical equipment.

REFERENCES

  1. T. Redeker
    PTB Report W18, Braunschweig, 1981
  2. H. Kraemer in:
    DECHEMA-Monographie vol. 107, 349-361
    VCH-Verlagsgesellschaft, 1987

Minimum Ignition Temperature of a Dust Cloud

UNIT: °C (degrees centigrade)

DEFINITION: Lowest temperature of a heated surface, at which in accordance with the test conditions a dust-air mixture of optimal composition just can be ignited.

MEASUREMENT: VDI 2263 (D); DIN EN 50281-2-1; modified BAM-oven

REFERENCES

  1. W. Berthold, U. Loeffler
    Lexikon sicherheitstechnischer Begriffe in der Chemie
    Published by: Verlag Chemie, Weinheim, 1981
  2. VDI 2263, Part 1
    Untersuchungsmethoden zur Ermittlung von sicherheitstechnischen Kenngroessen von Staeuben
    VDI-Handbook Reinhaltung der Luft, No. 6
    Published by: Beuth Verlag GmbH, Berlin, 1990
  3. Berufsgenossenschaft der chemischen Industrie
    Explosionsschutzrichtlinien (EX-RL)
    Heidelberg 1986
  4. G. Leuschke, R. Osswald
    Bedeutung und Ermittlung von sicherheitstechnischen Kenngroessen brennbarer Staeube
    VDI-Berichte No. 304, S. 29-38
    Published by: VDI-Verlag, Duesseldorf, 1978
  5. K.N. Palmer
    Dust Explosions and Fires
    Chapman and Hall Ltd., London, 1973
  6. W. Bartknecht
    Staubexplosionen, Ablauf und Schutzmassnahmen
    Published by: Springer-Verlag, Berlin Heidelberg New York Paris Tokyo, 1987
  7. W. Hensel
    Methoden zur Bestimmung der Zuendtemperatur von Staub/Luft-Gemischen an heis-sen Oberflaechen, eine vergleichende Untersuchung
    BAM-Jahresbericht (annual report of BAM) 1984, page 86-88
  8. W. Hensel, W. John
    Die Schichtdickenabhaengigkeit der Glimmtemperaturen
    Fortschritts-Berichte VDI, Reihe 3, Nr. 244
    Published by: VDI-Verlag, Duesseldorf, 1991

Minimum Ignition Temperature of a Dust Layer, Glow Temperature

UNIT: °C (degree centigrade)

DEFINITION: Lowest temperature of a heated, insulated surface, at which under specified test conditions a dust layer of defined thickness, which is placed on the surface, just can be ignited.

MEASUREMENT:VDI 2263 (D) (5 mm thickness of the dust layer); DIN EN 50281-2-1 (5 mm thickness of the dust layer); US-Standard (USA) (13 mm thickness of the dust layer)

SPECIAL REMARKS: The ignition temperature of a dust layer depends strongly on the thickness of the dust layer. Therefore data of this temperature from tests with dust layers of different thicknesses are not comparable. The German standard methods VDI 2263 and DIN and the European method IEC define this ignition temperature from tests with dust layers of 5 mm thickness. Therefore this thickness is a default value in CHEMSAFE.
Otherwise CHEMSAFE presents the ignition temperature of a dust layer with the according thickness of the dust layer.

REFERENCES

  1. VDI 2263; Part 1
    Untersuchungsmethoden zur Ermittlung von sicherheitstechnischen Kenngroessen von Staeuben
    VDI-Handbook Reinhaltung der Luft, No. 6
    Published by: Beuth Verlag GmbH, Berlin, 1990
  2. G. Leuschke, R. Osswald
    Bedeutung und Ermittlung von sicherheitstechnischen Kenngroessen brennbarer Staeube
    VDI-Berichte No. 304, S. 29-38
    Published by: VDI-Verlag, Duesseldorf, 1978
  3. K.N. Palmer
    Dust Explosions and Fires
    Chapman and Hall Ltd., London, 1973
  4. H. Steen (Hrsg.)
    Handbuch des Explosionsschutzes
    Wiley-VCH, Weinheim 2000
  5. W. Berthold, U. Loeffler
    Lexikon sicherheitstechnischer Begriffe in der Chemie
    Published by: Verlag Chemie, Weinheim, 1981
  6. Berufsgenossenschaft der chemischen Industrie
    Explosionsschutz-Regeln (EX-RL) Band I, Regeln fuer das Vermeiden der
    Gefahren durch explosionsfaehige Atmosphaere mit Beispielsammlung
    Werbe-Druck Winter, Postfach 1320, 69201 Sandhausen,2000
  7. W. Bartknecht
    Staubexplosionen, Ablauf und Schutzmassnahmen
    Published by: Springer-Verlag, Berlin Heidelberg New York Paris Tokyo, 1987

Minimum required amount of inert gas in inert gas-oxidator mixture

UNIT: -

The minimum required amount of inert gas in percent of volume or of mole in an inert gas/oxidizer mixture, which is not exposible by adding any amount of combustible.

REFERENCE

  1. M. Molnarne, Th. Schendler, V. Schroeder
    Sicherheitstechnische Kenngroessen
    Band 2: Explosionsbereiche von Gasgemischen
    Wirtschaftsverlag NW - Verlag fuer neue Wissenschaft,
    ISBN 3-89701-746-6, 2003

Moisture content

Moisture is the water content of substances. Ordinate intercept of the regression line lg(V/A) vs. 1/T

UNIT: -

DEFINITION: The ordinate intercept corresponds to the section of the regression line with the y-axis in the diagram lg(V/A) vs. 1/T of hot storage tests of dust accumulations. V is the volume of the cylindrical dust container (height equal to diameter) in cubic meters, and A is the sur-face area of the same container in square meters. Unit of V/A is meter. The abscissa is the reciprocal self-ignition temperature of the dust accumulation. The unit of abscissa is 1/Kelvin. Intercept (b) and slope (m) are necessary values to construct the regression line in the diagram lg(V/A) vs. 1/T in order to calculate the dependence between the vol-ume/surface ratio and the self-ignition temperatures of dust accumulations.

SPECIAL REMARKS: see special remarks at self-ignition temperature of the dust accumulation.

FUNCTIONAL CORRELATIONS: log(V/A) = b + m/T, where T - self-ignition temperature of a dust accumulation

REFERENCES

  1. VDI Richtlinie 2263, Blatt 1
    Untersuchungsmethoden zur Ermittlung von sicherheitstechnischen Kenngroessen von Staeuben
    VDI Handbuch "Reinhaltung der Luft", Bd. 6 Beuth Verlag GmbH, Berlin 1990
  2. Berufsgenossenschaft der chemischen Industrie
    Explosionsschutzrichtlinien (EX-RL)
    Heidelberg 1998
  3. G. Leuschke, R. Osswald
    Bedeutung und Ermittlung von sicherheitstechnischen Kenngroessenbrennbarer Staeube
    VDI-Berichte Nr. 304, S. 29-38
    VDI-Verlag, Duesseldorf, 1978
  4. W. Bartknecht
    Staubexplosionen, Ablauf und Schutzmassnahmen
    Springer-Verlag, Berlin Heidelberg New York Paris Tokyo, 1987
  5. W. Hensel
    Entzuendung abgelagerter Staeube
    VDI-Berichte Nr. 701, S. 143-146
    VDI-Verlag, Duesseldorf, 1989
  6. W. Hensel, W. John
    Die Schichtdickenabhaengigkeit der Glimmtemperatur - Theorie und Praxis der Selbstentzuendungsvorgaenge von Staeuben.
    Fortschrittbericht VDI Reihe 3 Nr. 244,
    VDI-Verlag, Duesseldorf, 1991
  7. U. Krause
    Zuendgefahren lagernder Staubschuettungen und -schichten - Berechnungsmethoden und Diagramme für die Praxis.
    Fortschrittbericht VDI Reihe 3 Nr. 422,
    VDI-Verlag, Duesseldorf, 1996

Net calorific value (lower calorific value)

The specific net calorific value of a liquid or solid fuel is the quotient of the heat produced by complete combustion and the mass. The temperature of the fuel before the combustion and of the combustion products has to be 25 ° centigrade, the water either formed by the combustion or already present in the fuel has to be gaseous. The nitrogen must not be oxidated.

Ordinate intercept of the regression line

UNIT: -

DEFINITION:The ordinate intercept corresponds to the section of the regression line with the y-axis in the diagram lg(V/A) vs. 1/T of hot storage tests of dust accumulations. V is the volume of the cylindrical dust container (height equal to diameter) in cubic meters, and A is the surface area of the same container in square meters. Unit of V/A is meter. The abscissa is the reciprocal self-ignition temperature of the dust accumulation (ITB). The unit of abscissa is 1/Kelvin. Intercept (INT) and slope (SLO) are necessary values to construct the regression line in the diagram lg(V/A) vs. 1/T in order to calculate the dependence between the volume/surface ratio and the self-ignition temperatures of dust accumulations.

SPECIAL REMARKS: see special remarks at self-ignition temperature (ITB).

FUNCTIONAL CORRELATIONS:log(V/A) = INT + SLO / T
where T - self-ignition temperature of the dust accumulation (ITB)

REFERENCES:

  1. VDI Richtlinie 2263, Blatt 1
    Untersuchungsmethoden zur Ermittlung von sicherheitstechnischen
    Kenngroessen von Staeuben
    VDI Handbuch "Reinhaltung der Luft", Bd. 6
    Beuth Verlag GmbH, Berlin 1990
  2. Berufsgenossenschaft der chemischen Industrie
    Explosionsschutz-Regeln (EX-RL) Band I, Regeln fuer das Vermeiden der
    Gefahren durch explosionsfaehige Atmosphaere mit Beispielsammlung
    Werbe-Druck Winter, Postfach 1320, 69201 Sandhausen,2000
  3. G. Leuschke, R. Osswald
    Bedeutung und Ermittlung von sicherheitstechnischen Kenngroessen brennbarer Staeube
    VDI-Berichte Nr. 304, S. 29-38
    VDI-Verlag, Duesseldorf, 1978
  4. W. Bartknecht
    Staubexplosionen, Ablauf und Schutzmassnahmen
    Springer-Verlag, Berlin Heidelberg New York Paris Tokyo, 1987
  5. W. Hensel
    Entzuendung abgelagerter Staeube
    VDI-Berichte Nr. 701, S. 143-146
    VDI-Verlag, Duesseldorf, 1989
  6. W. Hensel, W. John
    Die Schichtdickenabhaengigkeit der Glimmtemperatur - Theorie und
    Praxis der Selbstentzuendungsvorgaenge von Staeuben.
    Fortschrittbericht VDI Reihe 3 Nr. 244,
    VDI-Verlag, Duesseldorf, 1991
  7. U. Krause
    Zuendgefahren lagernder Staubschuettungen und -schichten -
    Berechnungsmethoden und Diagramme fuer die Praxis.
    Fortschrittbericht VDI Reihe 3 Nr. 422,
    VDI-Verlag, Duesseldorf, 1996
  8. H. Steen (Hrsg.)
    Handbuch des Explosionsschutzes
    Wiley-VCH, Weinheim 2000

Oxidizing power

UNIT: -

DEFINITION: The oxidizing power of gases characterizes the ability to promote burning processes, compared to air. Reference combustible is the gas ethane. Oxidizing power can be calculated according to the following equation:

OP = Sum (xi * Ci)i

xi = molecular fraction of the oxidizing component in mol%
Ci = coefficient of oxygen equivalency

REFERENCES

  1. ISO 10156(1996)
  2. M. Molnarne, Th. Schendler, V. Schroeder
    Sicherheitstechnische Kenngroessen
    Band 2: Explosionsbereiche von Gasgemischen
    Wirtschaftsverlag NW - Verlag fuer neue Wissenschaft,
    ISBN 3-89701-746-6, 2003

Packing density

Density of a dust heap.

Particle size

UNIT: micrometer

DEFINITION: The size of dust particles in general will be measured by sieving. The particle size is defined as a characteristic length of a particle just passing a sieve of known aperture. This aperture is used to represent the particle size. The fineness of a dust can only be described comprehensively by the particle size distribution. Often only the median value is given as a reference.

MEASURING METHOD: Sieving analysis according to DIN 53734. Important hint: This DEFINITION is not valid for optical measuring methods.

FUNCTIONAL CORRELATIONS: median value

REFERENCES

  1. DIN 566141 Darstellung von Korngroessenverteilungen; Grundlagen (1974), Beuth Verlag, Berlin
  2. DIN 53734 Pruefsiebung von pulverfoermigen Kunststoffen mit dem Luftstrahl-Siebgeraet (1973), Beuth Verlag, Berlin

Particle size distribution

The particle size distribution specifies, of which parts with a distinct particle size a dust consists. It is determined by a sieve analysis from the residues resisting on the sieves and on the bottom.In this data base the particle size distribution is given in tabular form. Thereby the amounts of masses (in %) lying between upper and lower size limits are given (particle size distribution density)

MEASURING METHOD: Sieving analysis according to DIN 53734. Important hint: This DEFINITION is not valid for optical measuring methods.

FUNCTIONAL CORRELATIONS: median value.

REFERENCES

  1. DIN 566141 Darstellung von Korngroessenverteilungen; Grundlagen (1974),
    Beuth Verlag, Berlin
  2. DIN 53734 Pruefsiebung von pulverfoermigen Kunststoffen mit dem Luftstrahlsiebgeraet (1973),
    Beuth Verlag, Berlin

Relative density

The relative density of a solid or liquid substance is the ratio of the mass of a defined volume of that substance and the mass of the same volume of water at 4 °C.
The relative density of a gas is the ratio or the densities of a substance and air at the same temperature and pressure.

Self Ignition Temperature of a Dust Accumulation

UNIT: °C (degrees centigrade)

DEFINITION:Lowest temperature, at which under specified test conditions a dust accumulation under the influence of high temperature in the surroundings will just be ignited by self heating.

MEASUREMENT: VDI 2263 (D)

SPECIAL REMARKS: The self-ignition temperature of a dust accumulation depends on the volume and the shape of the dust sample. Data without denotation of these conditions are insufficient. The Bundesanstalt fuer Materialpruefung (German Federal Institute for Materials Research and Testing) defines the self ignition temperature of a dust accumulation as the average value, which is calculated from the lowest experimental value, at which the dust just can be ignited and the highest value, at which the dust can not yet be ignited.
Data of self-ignition temperatures of dust accumulations of industrial scale will be obtained by linear extrapolation of experimental values taht are plotted in a lg(V/A) vs. 1/T -diagram. (V = volume of cylindrical sample in m3, A = geometrical overall surface area of cylindrical sample in m2, T = lowest absolute environment temperature of the dust accululation in case of ignition)

REFERENCES

  1. VDI 2263, Part 1
    Untersuchungsmethoden zur Ermittlung von sicherheitstechnischen Kenngroessen von Staeuben
    VDI-Handbook Reinhaltung der Luft, No. 6
    Published by: Beuth Verlag GmbH, Berlin, 1990
  2. Berufsgenossenschaft der chemischen Industrie
    Explosionsschutzrichtlinien (EX-RL)
    Heidelberg 1986
  3. G. Leuschke, R. Osswald
    Bedeutung und Ermittlung von sicherheitstechnischen Kenngroessen brennbarer Staeube
    VDI-Berichte No. 304, S. 29-38
    Published by: VDI-Verlag, Duesseldorf, 1978
  4. W. Hensel
    Entzuendung abgelagerter Staeube
    VDI-Berichte Nr. 701, page 143-146
    published by VDI-Verlag Duesseldorf 1989
  5. W. Bartknecht
    Staubexplosionen, Ablauf und Schutzmassnahmen
    Published by: Springer-Verlag, Berlin Heidelberg New York Paris Tokyo, 1987
  6. H. Steen (Hrsg.)
    Handbuch des Explosionsschutzes
    Wiley-VCH, Weinheim 2000

Slope of the regression line lg(V/A) vs. 1/T

UNIT: -

DEFINITION: The slope of the regression line will be taken from the diagram lg(V/A) vs. 1/T of hot storage tests of dust accumulations. V is the volume of the cylindrical dust container (height equal to diameter) in cubic meters, and A is the surface area of the same container in square meters. Unit of V/A is meters. The abscissa is the reciprocal self-ignition tempera-ture of the dust accumulation. The unit of abscissa is 1/Kelvin. Intercept (INT) and slope (SLO) are necessary values to construct the regression line in the diagram lg(V/A) vs. 1/T to calculate the dependence between the volume/surface ratio and the self-ignition temperature of a dust accumulations.

SPECIAL REMARKS: see special remarks at self-ignition temperature of the dust accumulation.

FUNCTIONAL CORRELATIONS: lg(V/A) = INT + SLO*1/T
where T - self-ignition temperature of a dust accumulation)

REFERENCES:

  1. VDI Richtlinie 2263, Blatt 1
    Untersuchungsmethoden zur Ermittlung von sicherheitstechnischen Kenngroessen von Staeuben
    VDI Handbuch "Reinhaltung der Luft", Bd. 6 Beuth Verlag GmbH, Berlin 1990
  2. Berufsgenossenschaft der chemischen Industrie
    Explosionsschutz-Regeln (EX-RL) Band I, Regeln fuer das Vermeiden der
    Gefahren durch explosionsfaehige Atmosphaere mit Beispielsammlung
    Werbe-Druck Winter, Postfach 1320, 69201 Sandhausen,2000
  3. G. Leuschke, R. Osswald
    Bedeutung und Ermittlung von sicherheitstechnischen Kenngroessen brennbarer Staeube
    VDI-Berichte Nr. 304, S. 29-38
    VDI-Verlag, Duesseldorf, 1978
  4. W. Bartknecht
    Staubexplosionen, Ablauf und Schutzmassnahmen
    Springer-Verlag, Berlin Heidelberg New York Paris Tokyo, 1987
  5. W. Hensel
    Entzuendung abgelagerter Staeube
    VDI-Berichte Nr. 701, S. 143-146
    VDI-Verlag, Duesseldorf, 1989
  6. W. Hensel, W. John
    Die Schichtdickenabhaengigkeit der Glimmtemperatur - Theorie und Praxis der
    Selbstentzuendungsvorgaenge von Staeuben.
    Fortschrittbericht VDI Reihe 3 Nr. 244,
    VDI-Verlag, Duesseldorf, 1991
  7. U. Krause
    Zuendgefahren lagernder Staubschuettungen und -schichten - Berechnungsmethoden und Diagramme für die Praxis.
    Fortschrittbericht VDI Reihe 3 Nr. 422,
    VDI-Verlag, Duesseldorf, 1996

Smolder temperature, Smoldering point

UNIT: °C (degrees centigrade)

DEFINITION: Lowest temperature, at which under specified test conditions a dust produces flammable vaporous or gaseous products in such a quantity that these products can be ignited in the gaseous phase above the dust.

MEASUREMENT: VDI 2263 (D)

REFERENCES

  1. W. Berthold, U. Loeffler
    Lexikon sicherheitstechnischer Begriffe in der Chemie
    Verlag Chemie, Weinheim, 1981
  2. VDI Richtlinie 2263, Blatt 1
    Untersuchungsmethoden zur Ermittlung von sicherheitstechnischen Kenngroessen von Staeuben
    VDI Handbuch "Reinhaltung der Luft", Bd. 6
    Beuth Verlag GmbH, Berlin 1990
  3. Berufsgenossenschaft der chemischen Industrie
    Explosionsschutzrichtlinien (EX-RL)
    Heidelberg 1986
  4. G. Leuschke, R. Osswald
    Bedeutung und Ermittlung von sicherheitstechnischen Kenngroessen brennbarer Staeube
    VDI-Berichte Nr. 304, S. 29-38
    VDI-Verlag, Duesseldorf, 1978

Stability Pressure Limit (minimum decomposition pressure)

UNIT: bar

DEFINITION: Pressure limit, at which the decomposition of a thermal instable gas (in the absence of air or oxygen) may not yet be initiated.

SPECIAL REMARKS: The Stability Pressure Limit depends on:

  • temperature
  • shape and size of the explosion vessel
  • kind of the ignition source

Therefore the experimental conditions under which the stability pressure limit was determined have to be specified.

REFERENCES

  1. Lietze, D.; Pinkofsky, H.; Schendler, Th.; Schulze, H.-P.
    Stabilitaetsgrenzdruck von Acetylen
    Chem.-Ing.-Tech., 61, No. 9, page 736-738 (1989)
  2. Schendler, Th.; Schulze, H.-P.
    Stabilitaetsgrenzdruecke von Acetylen/Gas-Gemischen
    Chem.-Ing.-Tech., 62, No. 1, page 41-43 (1990)

Stoichiometric fraction of combustible in mixture with air

UNIT: Mol %

DEFINITION: The molar stoichiometric fraction of combustible in mixture with air is the molar fraction of combustible which is needed for a stoichiometric combustion in air.

SPECIAL REMARKS: The stoichiometric fraction depends on the stoichiometry of the equation of the overall reaction. In most cases the reaction leads to completely oxidized products(e.g. water and carbon dioxide).

Stoichiometric fraction of combustible in mixture with oxygen

UNIT: Mol %

DEFINITION: The molar stoichiometric fraction of combustible in mixture with oxygen is the molar fraction of combustible which is needed for a stoichiometric combustion in oxygen.

SPECIAL REMARKS: The stoichiometric fraction depends on the stoichiometry of the equation of the overall reaction. In most cases the reaction leads to completely oxidized products (e.g. water and carbon dioxide)

Technical concentration limit

The technical concentration limit is defined as the concentration of a substance as a gas, a liquid or a dust suspended in the air that may be achieved according to the technical progress and may be used as a criterion for protection measures and technical controlling by measurement at the working place.

Triple point temperature

The triple point is the point in the phase diagram of a pure compound at which three phases (e.g. vapor, liquid, solid) are in a non-variant equilibrium with each other.

Tci-value, limiting value for flammability

UNIT: mol%

DEFINITION: This characteristic is the maximum permissible amount of combustible gas in nitrogen, at which this combustible/nitrogen mixture is not flammable in any mixture with air, measured under defined conditions.

REFERENCE

  1. ISO 10156(1996)
  2. M. Molnarne, Th. Schendler, V. Schroeder
    Sicherheitstechnische Kenngroessen
    Band 2: Explosionsbereiche von Gasgemischen
    Wirtschaftsverlag NW - Verlag fuer neue Wissenschaft,
    ISBN 3-89701-746-6, 2003

Upper explosion limit

UNITS: vol% (volume fraction in %); g/cm3 (gram per cubic meter at 20 ° centigrade and 1013.25 mbar)

DEFINITION: The lower and upper explosion limits borders the area of explosible mixtures, i.e. the range of the content of combustibles in the mixture, at which a flame can separate from the ignition source resp. can propagate. The explosion limits are not part of the explosion area. The amount indicated in vol% or the equivalent concentration indicated in g/m3 refer to the total mixture.

MEASURING METHOD:The explosion limits of Gases and vapors are determined according EN 1839. (The upper explosion limit of dusts is only of limited interest. There is no standardized measuring method for it.)
The explosion limits generally refer to an initial pressure of the mixture of 1013.25 mbar (atmospheric pressure). The initial temperature of the mixture usually amounts to 20° Celsius (ambient temperature). In the case of liquids, the initial temperature of the mixture is selected to lie at a point far enough above the condensation point (generally 20 degrees centigrade). Then the value given is calculated from the measured value using the reference temperature of 20 °C

SPECIAL NOTES:The conversion of vol% into g/m3 and vice versa can lead to incorrect results, as all data have been rounded to the safe side. For dusts the upper explosion limit is of little interest. Because of that there is no standardized method for determing this property.

FUNCTIONAL CORRELATIONS: The upper explosion limit depends on pressure, temperature and ignition energy. The temperature pertaining to the upper explosion limit - the upper explosion point - can be calculated from the vapor pressure curve.

REFERENCES

  1. K. Nabert, G. Schoen

    Sicherheitstechnische Kennzahlen brennbarer Gase und Daempfe

    2nd enlarged edition with 6th supplement, Braunschweig 1990
  2. W. Berthold, U. Loeffler

    Lexikon sicherheitstechnischer Begriffe in der Chemie

    Verlag Chemie, Weinheim, 1981

Upper explosion point

UNIT: °C (degrees centigrade)

DEFINITION: The upper explosion point of a flammable liquid is the temperature related to 1013.25 mbar, at which the concentration of a saturated vapor/air-mixture equals the upper explosion limit.

SPECIAL REMARKS: For pure substances this definition is sufficient. But it is possible to measure different explosion points of mixtures depending on the volume ratio of gaseous and liquid phase (h-ratio). Therefore the upper explosion point of mixtures must not be given without the h-ratio.

FUNCTIONAL CORRELATIONS:The upper explosion point of a pure compound can be calculated from its vapor pressure curve and the upper explosion limit.

REFERENCE

  1. K. Nabert, G. Schoen
    Sicherheitstechnische Kennzahlen brennbarer Gase und Daempfe
    2nd extended edition with 6th extension, Braunschweig 1990

Viscosity

Viscosity is the property of a liquid or a gas, to resist the mutual laminar translation of two neighboring layers. The dynamic viscosity is defined as the quotient of the shear-tension and the velocity gradient perpendicular to the direction of flow.

Volume surface ratio

UNIT: -

DEFINITIONThe volume surface ratio of a dust heap is calculated from the geometry of the adiabaticly stored dust heap.

SPECIAL REMARKS:The ignition temperature of a dust heap depends strongly of the volume and the shape of the sample. The Bundesanstalt fuer Materialforschung und -pruefung (Federal Institute for Material Research and Testing) uses for the ignition temperature the mean value of thelowst measured temperature that did cause an ignition and of the highest temperature that did not cause an ignition.

REFERENCE

  1. VDI Richtlinie 2263, Blatt 1
    Untersuchungsmethoden zur Ermittlung von sicherheitstechnischen
    Kenngroessen von Staeuben
    VDI Handbuch "Reinhaltung der Luft", Bd. 6
    Beuth Verlag GmbH, Berlin 1990
  2. Berufsgenossenschaft der chemischen Industrie
    Explosionsschutz-Regeln (EX-RL) Band I, Regeln fuer das Vermeiden der
    Gefahren durch explosionsfaehige Atmosphaere mit Beispielsammlung
    Werbe-Druck Winter, Postfach 1320, 69201 Sandhausen,2000
  3. G. Leuschke, R. Osswald
    Bedeutung und Ermittlung von sicherheitstechnischen Kenngroessen brennbarer Staeube
    VDI-Berichte Nr. 304, S. 29-38
    VDI-Verlag, Duesseldorf, 1978
  4. W. Bartknecht
    Staubexplosionen, Ablauf und Schutzmassnahmen
    Springer-Verlag, Berlin Heidelberg New York Paris Tokyo, 1987
  5. W. Hensel
    Entzuendung abgelagerter Staeube
    VDI-Berichte Nr. 701, S. 143-146
    VDI-Verlag, Duesseldorf, 1989
  6. W. Hensel, W. John
    Die Schichtdickenabhaengigkeit der Glimmtemperatur - Theorie und Praxis der Selbstentzuendungsvorgaenge von Staeuben.
    Fortschrittbericht VDI Reihe 3 Nr. 244,
    VDI-Verlag, Duesseldorf, 1991
  7. U. Krause
    Zuendgefahren lagernder Staubschuettungen und -schichten - Berechnungsmethoden und Diagramme fuer die Praxis.
    Fortschrittbericht VDI Reihe 3 Nr. 422,
    VDI-Verlag, Duesseldorf, 1996
© DECHEMA e.V. Terms of Use Privacy Contact Imprint

Aim of this website?

This website allows you to search online within DECHEMA's numerical databases:

  • DETHERM: thermophysical properties of pure substances and mixtures
  • CHEMSAFE: recommended safety data of gases, liquids and dusts

Even without registration you can search and preview the databases.

With registration you can also download the data in various formats:

  • Direct display
  • PDF
  • XLS
  • IKC
 OK 

EU-Citizens only:

Please choose your country for proper VAT calculation

For electronic delivery to countries outside the European Union (EU):

  • VAT is not charged, if you supply a Tax Payer Certificate of your country.
  • German VAT is charged, if you do not supply a Tax Payer Certificate.
 OK