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Antoine parameters
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Definition:
    The Antoine equation is a class of semi-empirical correlations describing the relation between vapour pressure and temperature for pure substances. The Antoine equation is derived from the Clausius–Clapeyron relation. The equation is: log10p = A-B/(C+T), where p is the vapour pressure, T is temperature (in °C or in K according to the value of C), and A, B and C are component-specific constants.
    The Antoine parameters are valid only within the defined temperature interval, which is given together with the constants.
Special Notes:
    The coefficients of Antoine´s equation are still today normally given in °C and torr (mmHg), even though the SI is now recommended and the use of pascals preferred. The use of these pre-SI units is based solely on tradition and stems directly from Antoine´s original publication. It is, however, easy to convert the parameters to different pressure and temperature units. For switching from °C to K it is sufficient to subtract 273.15 from the C parameter. For switching from torr to pascals it is sufficient to add the common logarithm of the factor between both units to the A parameter. The parameter B stays the same.

Autoignition temperature
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Unit:
    °C  (Degree Celsius)
Definition:
    The autoignition temperature (AIT) is the lowest temperature (of a hot surface) over the concentration range at which, under specified test conditions, an ignition of a flammable gas or vapour in mixture with air or air/inert gas occurs.
Measuring Method:
    ISO/IEC 80079-20-1 is applicable to gases and liquids. The measurement uncertainty of 3 % is subtracted from the measured value for determination of the AIT. DIN 51794 is technically identical, but the results are rounded to the nearest 5 °C.
Standards:
  • DIN 51794; Testing of mineral oil hydrocarbons - Determination of ignition temperature, measurements are technically identical to those of ISO/IEC 80079-20-1 but results are treated differently.
  • DIN EN ISO/IEC 80079-20-1:2020-09; Explosive atmospheres - Part 20-1: Material characteristics for gas and vapour classification - Test methods and data, revision of IEC 60079-20-1
Special Notes:
    The autoignition temperature in oxygen may be up to 300 °C lower than in air.
    In large containers and for certain wall materials, the self-ignition temperature may be lower than the value determined in accordance with the standard.
    The self-ignition temperature on convex or flat surfaces is often higher than the standard autoignition temperatures.
Dependencies:
    The autoignition temperature decreases with increasing pressure. [1,2]
Classification:
    The autoignition temperature can be used to assign flammable gases and vapours to temperature classes (ISO/IEC 80079-20-1).
References:
    [1] Gödde, M.; Zündtemperaturen organischer Verbindungen in Abhängigkeit von chemischer Struktur und Druck; Dissertation TU Braunschweig, 1998, PTB-Bericht Th-Ex-8, Wirtschaftsverlag NW
    [2] W. Hirsch, E. Brandes; Zündtemperaturen binärer Gemische bei erhöhten Ausgangsdrücken, 2005, Forschungsbericht PTB

Calorific values
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Definition:
    CHEMSAFE lists the terms Net calorific value (lower heating value) and Gross calorific value (higher heating value). Please refer to the specific term.
See also:
    Gross calorific value
    Net calorific value

Coefficient of nitrogen equivalency
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Unit:
    None  (no unit)
Definition:
    The coefficient of nitrogen equivalency characterizes the inerting ability of inert gases compared to nitrogen. The value for pure nitrogen is defined to be 1. It is used in ISO 10156 to classify the flammability of gases.
Standards:
  • DIN EN ISO 10156; Gas cylinders - Gases and gas mixtures - Determination of fire potential and oxidizing ability for the selection of cylinder valve outlets, German version of EN ISO 10156:2017
Classification:
    Dangerous goods: UN Model Regulations, ADR/RID
    Hazardous Materials: Guidance on the Application of the CLP Criteria, Version 5.0, July 2017
References:
    [1] M. Molnarne, T. Schendler, V. Schröder; Safety Characteristic Data, Volume 2: Explosion Regions of Gas Mixtures, 2nd Revised Edition, 2008, Wirtschaftsverlag NW, Verlag für neue Wissenschaft GmbH, Bremerhaven
    [2] V. Schröder, M. Molnarne; Flammability of gas mixtures, Part 1: Fire potential, J. Haz. Mat., 2005
    [3] M. Molnarne, P. Mizsey, V. Schröder; Flammability of gas mixtures, Part 2: Influence of inert gases, J. Haz. Mat., 2005
See also:
    Maximum permissible fraction of combustible in an inert gas/combustible mixture
    Limiting value for flammability (Tci)

Coefficient of oxygen equivalency
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Unit:
    None  (no unit)
Definition:
    The coefficient of oxygen equivalency characterizes the ability to promote burning processes compared to oxygen. The value for pure oxygen is defined to be 1.
Standards:
  • DIN EN ISO 10156; Gas cylinders - Gases and gas mixtures - Determination of fire potential and oxidizing ability for the selection of cylinder valve outlets, German version of EN ISO 10156:2017
Classification:
    Dangerous goods: UN Model Regulations, ADR/RID
    Hazardous Materials: Guidance on the Application of the CLP Criteria, Version 5.0, July 2017
References:
    [1] V. Schröder, B. Mackrodt, S. Dietlen; Determination of oxidizing ability of gases and gas mixtures, ASTM STP 1395, 2000
    [2] M. Molnarne, T. Schendler, V. Schröder; Safety Characteristic Data, Volume 2: Explosion Regions of Gas Mixtures, 2nd Revised Edition, 2008, Wirtschaftsverlag NW, Verlag für neue Wissenschaft GmbH, Bremerhaven

Critical density
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Definition:
    The critical density is the density of a substance at the thermodynamic critical point.
See also:
    Critical point

Critical point
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Unit:
    None  (no unit)
Definition:
    The point on the vapour/liquid equilibrium line in the phase diagram at which the density of the vapour equals the density of the liquid. The corresponding temperature and pressure are called the critical temperature (° C) and critical pressure (bar).
See also:
    Critical density

Diffusion coefficient
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Unit:
    cm2/s  (Square centimetre per second)
Definition:
    Diffusion is the mixing of different gaseous, liquid or solid substances that are in contact with each other. The diffusion coefficient (D) is used in the application of the Fick laws for calculating the thermal mass transport.

Evaporation number
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Unit:
    None  (no unit)
Definition:
    The evaporation number is the ratio of the evaporation time of a liquid and the evaporation time of diethyl ether as the reference substance, measured in a specified experimental apparatus.
Standards:
  • DIN 53170; Solvents for paints and varnishes - Determination of the evaporation rate, 2009-08

Explosion limits
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Definition:
    The lower and upper explosion limits are the boundaries that define a flammable substance´s explosive concentration range. This is the range of concentration of a substance in mixture with an oxidizing gas at which a flame can separate from the ignition source and propagate through the unburnt mixture. In CHEMSAFE the oxidizing gas is generally air unless otherwise specified in the data set.
    CHEMSAFE lists the terms Lower explosion limit and Upper explosion limit. Please refer to the specific term.
See also:
    Lower explosion limit
    Upper explosion limit

Explosion point
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Definition:
    CHEMSAFE lists the terms Lower explosion point and Upper explosion point. Please refer to the specific term.
See also:
    Lower explosion point
    Upper explosion point

Explosion pressure ratio
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Unit:
    None  (no unit)
Definition:
    The explosion pressure ratio is the ratio between the explosion pressure and the initial pressure before ignition for a certain mixture concentration.
Special Notes:
    The explosion pressure is normalized to 1 bar (absolute) by division with the initial pressure. This property can be used to easily demonstrate the dependence of the explosion pressure on the initial pressure. Other mixture compositions can result in higher pressure ratios.
    The explosion pressure ratio is not necessarily indicated for the concentration at which the maximum explosion pressure occurs.
References:
    [1] SafeKinex-EU-Projekt: TU Delft, BAM, BASF, INERIS, Warsaw University of Technology; Report on the experimentally determined explosion limits, explosion pressures and rates of explosion pressure rise - Part 1: methane, hydrogen and propylene, 2006

Flash point
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Unit:
    °C  (Degree Celsius)
Definition:
    The flash point is the lowest temperature of a flammable liquid at which the application of an ignition source causes the vapour of the test portion (mixed with the surrounding air) to ignite and the flame to propagate across the surface of the liquid. At this temperature, the liquid gives off vapours in such quantity as to enable the formation of an ignitable vapour/air mixture above the lower explosion limit. To account for variations in atmospheric pressure, the flash point is the measurement value corrected to 1013 mbar and rounded in accordance with the standards. There are two basic types of flash point measurement: open cup and closed cup. The flash point determined in an open cup is in general considerably higher than in a closed cup (by 20 °C, in some cases even more). In Germany and some other countries, open cup measurements are not recommended for use in classification.
Measuring Method:
    The measurement methods are standardized as the result depends on the temperature range and the type of sample used.
Standards:
  • DIN EN ISO 13736; Determination of flash point - Abel closed-cup method, German version of EN ISO 13736:2021 + A1:2022
  • DIN 51755; Testing of Mineral Oils and Other Combustible Liquids; Determination of Flash Point by the Closed Tester according to Abel-Pensky
  • DIN EN ISO 2719; Determination of flash point - Pensky-Martens closed cup method, German version of EN ISO 2719:2016 + A1:2021
  • DIN EN ISO 3679; Determination of flash point - Method for flash no-flash and flash point by small scale closed cup tester, German version of EN ISO 3679:2022
  • DIN EN ISO 2592; Petroleum and related products - Determination of flash and fire points - Cleveland open cup method, German version of EN ISO 2592:2017
  • DIN EN ISO 1516; Determination of flash/no flash - Closed cup equilibrium method, German version of EN ISO 1516:2002
  • DIN EN ISO 1523; Determination of flash point - Closed cup equilibrium method, German version of EN ISO 1523:2002
Special Notes:
    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.
    There are two types of closed cup testers: non-equilibrium, such as Pensky-Martens, where the vapours above the liquid are not in temperature equilibrium with the liquid; and equilibrium, such as Small Scale (commonly known as Setaflash), where the vapours are deemed to be in temperature equilibrium with the liquid.
    The flash point is closely related to the lower explosion point. For pure, non-halogenated organic liquids, the flash point determined in a closed cup is about 5 °C higher than the lower explosion point. For mixtures the difference may be even higher.
    Halogenated organic liquids may form explosive mixtures without having a flash point [1]. For these substances the database contains the comment "not easily flammable".
    EN ISO 3679 is comparable to ASTM 3278.
Classification:
    The flash point measured in a closed cup is used for the classification of flammable liquids in a great number of regulations: CLP regulation, BetrSichV, GefStoffV, GGVSE, GGVSee, ADR, RID, IMDG Code, UN Recommendations, IATA Code.
References:
    [1] H. Steen, T. Redeker; Explosionsgefahren beim Umgang mit Chlorkohlenwasserstoffen und deren Gemischen mit brennbaren Flüssigkeiten, Chem.-Ing.-Tech., 1975
See also:
    Lower explosion point
    Lower explosion limit

Fraction of combustible at lower explosion limit with inert gas
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Unit:
    Vol%  (Volume fraction in %)
    Mol%  (Amount-of-substance fraction in %)
Definition:
    This value is given together with a related "fraction of inert gas in the mixture". The mixture itself consists of combustible, inert gas, and oxidizer. The fraction of oxidizer depends on the size of the other two fractions.
References:
    [1] M. Molnarne, T. Schendler, V. Schröder; Safety Characteristic Data, Volume 2: Explosion Regions of Gas Mixtures, 2nd Revised Edition, 2008, Wirtschaftsverlag NW, Verlag für neue Wissenschaft GmbH, Bremerhaven
    [2] V. Schröder, M. Molnarne; Flammability of gas mixtures, Part 1: Fire potential, J. Haz. Mat., 2005
    [3] M. Molnarne, P. Mizsey, V. Schröder; Flammability of gas mixtures, Part 2: Influence of inert gases, J. Haz. Mat., 2005
See also:
    Fraction of inert gas in the mixture
    Fraction of combustible at upper explosion limit with inert gas

Fraction of combustible at upper explosion limit with inert gas
More
Unit:
    Vol%  (Volume fraction in %)
    Mol%  (Amount-of-substance fraction in %)
Definition:
    This value is given together with a related "fraction of inert gas in the mixture". The mixture itself consists of combustible, inert gas, and oxidizer. The fraction of oxidizer depends on the size of the two other fractions.
References:
    [1] M. Molnarne, T. Schendler, V. Schröder; Safety Characteristic Data, Volume 2: Explosion Regions of Gas Mixtures, 2nd Revised Edition, 2008, Wirtschaftsverlag NW, Verlag für neue Wissenschaft GmbH, Bremerhaven
    [2] V. Schröder, M. Molnarne; Flammability of gas mixtures, Part 1: Fire potential, J. Haz. Mat., 2005
    [3] M. Molnarne, P. Mizsey, V. Schröder; Flammability of gas mixtures, Part 2: Influence of inert gases, J. Haz. Mat., 2005
See also:
    Fraction of inert gas in the mixture
    Fraction of combustible at lower explosion limit with inert gas

Fraction of inert gas in the mixture
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Unit:
    Vol%  (Volume fraction in %)
    Mol%  (Amount-of-substance fraction in %)
Definition:
    The fraction of inert gas in the mixture is given in a data set together with the fraction of combustible. The fraction of oxidizer depends on the size of the two other fractions.
References:
    [1] M. Molnarne, T. Schendler, V. Schröder; Safety Characteristic Data, Volume 2: Explosion Regions of Gas Mixtures, 2nd Revised Edition, 2008, Wirtschaftsverlag NW, Verlag für neue Wissenschaft GmbH, Bremerhaven
See also:
    Fraction of combustible at lower explosion limit with inert gas
    Fraction of combustible at upper explosion limit with inert gas

Gross calorific value
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Unit:
    kJ/kg  (Kilojoule per kilogram)
    kWh/m3  (Kilowatt hour per cubic metre)
Definition:
    The gross calorific value (higher heating value) of a liquid or solid fuel is the ratio of the heat produced by complete combustion and the mass. The gross calorific value of a gas is the quotient of the heat produced by complete combustion and the volume. A reference temperature of 25 °C is used for the initial pre-combustion fuel temperature and for the temperature of the combustion products. The water formed by combustion is in the liquid state. The nitrogen is not oxidized.
Measuring Method:
    The gross calorific value of solid and liquid fuels is determined according to the German standard DIN 51900 (Parts 1 to 3). For gaseous fuels see ISO 6976.
Standards:
  • DIN 51900-1:2000-04; Testing of solid and liquid fuels - Determination of gross calorific value by the bomb calorimeter and calculation of net calorific value - Part 1: Principles, apparatus, methods, revision of DIN 51900-1:1989-11
  • DIN 51900-2:2003-05; Testing of solid and liquid fuels - Determination of the gross calorific value by the bomb calorimeter and calculation of the net calorific value - Part 2: Method using isoperibol or static, jacket calorimeter, revision of DIN 51900-2:1977-08
  • DIN 51900-3:2005-01; Testing of solid and liquid fuels - Determination of gross calorific value by the bomb calorimeter and calculation of net calorific value - Part 3: Method using adiabatic jacket, revision of DIN 51900-3:1977-08
  • DIN EN ISO 6976:2016-12; Natural gas - Calculation of calorific values, density, relative density and Wobbe indices from composition, German version EN ISO 6976:2016, revision of DIN EN ISO 6976:2005-09
See also:
    Wobbe index

Ignition energy at decomposition of gases
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Unit:
    J  (Joule)
Definition:
    This ignition energy is an experimental parameter used for the determination of the stability pressure limit of chemically unstable gases.
Special Notes:
    It should not be confused with the minimum ignition energy.
Dependencies:
    The stability pressure limit depends on the applied ignition energy.
References:
    [1] Lietze,D.; Pinkofsky,H.; Schendler,T.; Schulze,H.P.; Stability Pressure Limit of Acetylene, Chem. Ing. Tech., 1989, Chem. Ing. Tech.
    [2] M. Molnarne, T. Schendler, V. Schröder; Safety Characteristic Data, Volume 2: Explosion Regions of Gas Mixtures, 2nd Revised Edition, 2008, Wirtschaftsverlag NW, Verlag für neue Wissenschaft GmbH, Bremerhaven
See also:
    Stability pressure limit

Ignition pressure limit
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Unit:
    bar  (Bar)
Definition:
    In a graphical plot the explosion region is the area between the lower and the upper explosion limits. It diminishes when the pressure is reduced. The pressure at which the upper and lower explosion limits converge is called the ignition pressure limit. Below this pressure no ignition is possible.
Special Notes:
    The ignition pressure limit should not be confused with the stability pressure limit of thermally unstable gases.
    In most cases, the ignition pressure limit lies below 300 mbar.
    The ignition pressure limit depends on:
    - temperature
    - shape and size of the explosion vessel
    - type and energy of the ignition source
    It is therefore necessary to specify the experimental conditions under which the ignition pressure limit is determined.
References:
    [1] E. Brandes, D.Pawel, J. Alpers, J. Scheffler; Sicherheitstechnische Kenngrößen bei reduzierten Ausgangsdrücken, 8. Kolloquium zu Fragen der chemischen und physikalischen Sicherheitstechnik, 1999
    [2] Horstmann,T.; Wischniewski,F.; Maurer,B.; Leuckel,W.; Flammability characteristics of combustible substances with air in vacuum, 1996, VDI-Bericht
See also:
    Stability pressure limit

Ignition temperature of a defined gas mixture (not autoignition temperature)
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Unit:
    °C  (Degree Celsius)
Definition:
    Lowest temperature of a hot surface at which, under specified conditions, a specific mixture concentration ignites.
Special Notes:
    The ignition temperature of a defined gas mixture is measured in a homogeneous mixture with a fixed mixture concentration. Any deviation in the mixture composition could result in a lower ignition temperature. By contrast the autoignition temperature is determined by varying the concentration of the combustible component. The ignition temperature of a certain gas mixture with a defined concentration should not be confused with the autoignition temperature. The classification of substances in temperature classes is only done using the autoignition temperature.
References:
    [1] SafeKinex-EU-Projekt: BAM and TU Delft; Report on the experimentally determined self-ignition temperature and the ignition delay time, 2003
See also:
    Autoignition temperature

KG value
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Unit:
    bar m/s  (Bar times metre per second)
Definition:
    Characteristic value of flammable gases and vapours calculated according to the cubic law from the maximum rate of pressure rise over the concentration range.
Dependencies:
    Cubic law: The maximum rise in pressure of an explosion per unit time (maximum rate of pressure rise) (dp/dt)max depends on the container volume (V). This dependence is normalized using the following equation: KG value = (dp/dt)max V(1/3) = almost constant.
    The cubic law is applicable only if the other conditions are comparable in 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 is primarily due to the heat loss at the wall and the flow conditions during flame propagation.
References:
    [1] H. Förster, H. Steen; PTB-Report W32, 1986
    [2] M. Hattwig; Druckentlastung von Gasexplosionen bei hohen Anfangsdrücken, Amts- und Mitteilungsblatt der Bundesanstalt für Materialforschung und -prüfung (BAM), 1987
    [3] W. Berthold, U. Löffler; Lexikon sicherheitstechnischer Begriffe in der Chemie, 1981, Verlag Chemie
See also:
    Maximum rate of pressure rise (dp/dt)max
    KGex value at a defined concentration

KGex value at a defined concentration
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Unit:
    bar m/s  (Bar times metre per second)
Definition:
    The KGex value is the normalized rate of explosion pressure rise (dp/dt)ex of flammable gases and vapours for a volume of 1 m³ calculated according to the cubic law.
Special Notes:
    It should not be confused with the KG value, which is calculated from the maximum rate of pressure rise over the concentration range.
Dependencies:
    Cubic law: The explosion pressure rise per unit time (rate of explosion pressure rise) (dp/dt)ex depends on the container volume (V). This dependence is normalized by using the following equation: KGex value = (dp/dt)ex V(1/3) = almost constant.
    The cubic law is applicable only if the other conditions are comparable in 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 KGex values. This is primarily due to the heat loss at the wall and the flow conditions during flame propagation.
References:
    [1] SafeKinex-EU-Projekt: TU Delft, BAM, BASF, INERIS, Warsaw University of Technology; Report on the experimentally determined explosion limits, explosion pressures and rates of explosion pressure rise - Part 1: methane, hydrogen and propylene, 2006
See also:
    Rate of explosion pressure rise (dp/dt)ex
    Maximum rate of pressure rise (dp/dt)max
    KG value

Kinematic viscosity
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Unit:
    m2/s  (Square metre per second)
    cSt  (Centistokes)
Definition:
    Viscosity is the property of a liquid or a gas to resist the mutual laminar translation of two neighbouring layers. The dynamic viscosity is defined as the ratio of the shear stress and the velocity gradient perpendicular to the direction of flow. The kinematic viscosity is the ratio of the dynamic viscosity to the density of a fluid.

Limiting oxygen concentration
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Unit:
    Vol%  (Volume fraction in %)
    Mol%  (Amount-of-substance  fraction in %)
Definition:
    The limiting oxygen concentration (LOC) is the maximum content of oxygen in a mixture of a combustible with air and inert gas at which no explosion of the mixture can occur. Up to this limit, no flammable mixture can be formed regardless of how much combustible is added.
Measuring Method:
    Usually, experiments are done to first determine the limiting concentration for air. The limiting oxygen concentration is then calculated from this value by multiplying it by the factor 0.209 .
Standards:
  • DIN EN 1839:2017-04; Determination of the explosion limits and the limiting oxygen concentration (LOC) for flammable gases and vapours, German version of EN 1839:2017, revision of DIN EN 14756:2007-02, DIN EN 1839:2012-12
Special Notes:
    The limiting oxygen concentration is a characteristic that depends on the combustible, the inert gas, the initial condition, and the test method.
Dependencies:
    The LOC characteristic is the most frequently seen special case of the maximum oxidizer content (MOC).
See also:
    Maximum oxidizer content

Limiting value for flammability (Tci)
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Unit:
    Vol%  (Volume fraction in %)
    Mol%  (Amount-of-substance  fraction in %)
Definition:
    This characteristic can be used to calculate the maximum amount of combustible gas in mixture with nitrogen at which this mixture will remain non-flammable in any mixture with air. It is measured under defined conditions. The maximum permissible amount of combustible gas in an inert gas/combustible mixture at room temperature and atmospheric pressure and with nitrogen used as the inert gas is identical to the limiting value for flammability (Tci value).
Standards:
  • DIN EN ISO 10156; Gas cylinders - Gases and gas mixtures - Determination of fire potential and oxidizing ability for the selection of cylinder valve outlets, German version of EN ISO 10156:2017
Classification:
    Dangerous goods: UN Model Regulations, ADR/RID
    Hazardous Materials: Guidance on the Application of the CLP Criteria, Version 5.0, July 2017
References:
    [1] M. Molnarne, T. Schendler, V. Schröder; Safety Characteristic Data, Volume 2: Explosion Regions of Gas Mixtures, 2nd Revised Edition, 2008, Wirtschaftsverlag NW, Verlag für neue Wissenschaft GmbH, Bremerhaven
    [2] V. Schröder, M. Molnarne; Flammability of gas mixtures, Part 1: Fire potential, J. Haz. Mat., 2005
    [3] M. Molnarne, P. Mizsey, V. Schröder; Flammability of gas mixtures, Part 2: Influence of inert gases, J. Haz. Mat., 2005
See also:
    Maximum permissible fraction of combustible in an inert gas/combustible mixture

Lower explosion limit
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Unit:
    Vol%  (Volume fraction in %)
    Mol%  (Amount-of-substance fraction in %)
    g/m3  (Gram per cubic metre)
Definition:
    The lower explosion limit is the lower concentration limit of the explosion range of a flammable gas or vapour. It is not part of the explosion range. It is the concentration at which an explosion just barely fails to occur during tests (see EN 1839:2017). The term lower flammable limit is used in ISO/IEC 80079-20-1:2019. For the purposes of Ex equipment, it was previously referred to as the lower explosive limit.
Measuring Method:
    The explosion limits generally refer to an initial pressure of the mixture of 1013 mbar (atmospheric pressure). The initial temperature of the mixture is usually 20 °C (ambient temperature).
    In the case of liquids, the initial temperature of the vapour mixture with air is selected to be well above the flash point (generally 20 °C).
Standards:
  • DIN EN 1839:2017-04; Determination of the explosion limits and the limiting oxygen concentration (LOC) for flammable gases and vapours, German version of EN 1839:2017, revision of DIN EN 14756:2007-02, DIN EN 1839:2012-12
Special Notes:
    The values given in g/m³ are related to a reference temperature of 20 °C and a pressure of 1013 mbar. The molar volume is then 24 l.
Dependencies:
    The lower explosion limit depends on pressure, temperature, and ignition energy. The temperature pertaining to the lower explosion limit of vapours is the lower explosion point of a liquid. It is where the vapour pressure curve intersects the temperature-dependent lower explosion limit curve.
See also:
    Lower explosion point
    Upper explosion limit

Lower explosion point
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Unit:
    °C  (Degree Celsius)
Definition:
    The lower explosion point of a flammable liquid is the temperature, corrected to 1013.25 mbar, at which the concentration of a saturated vapour/air-mixture equals the lower explosion limit.
Standards:
  • DIN EN 15794:2010-02; Determination of explosion points of flammable liquids, German version of EN 15794:2009
Special Notes:
    For pure substances this definition is sufficient. But it is possible to measure different explosion points of mixtures depending on the volume ratio of the gaseous and liquid phases (h ratio). The lower explosion point of mixtures must therefore not be given without the h ratio.
Dependencies:
    The lower explosion point of a pure compound can be calculated from its vapour pressure curve and the lower explosion limit [1]. The lower explosion point is related to the flash point, but due to better equilibrium conditions the lower explosion point of pure substances can be as much as 5 °C below the flash point. Lower explosion points of mixtures deviate even more widely.
References:
    [1] E. Brandes, W. Möller; Safety Characteristic Data, 2008, Wirtschaftsverlag NW-Verlag für neue Wissenschaften
See also:
    Lower explosion limit
    Flash point
    Upper explosion point

Maximum experimental safe gap
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Unit:
    mm  (Millimetre)
Definition:
    The maximum experimental safe gap (MESG) of flammable gases or vapours is the highest value of a safe gap at which flame transmission just barely fails to occur. It is measured under standardized conditions under variation of the mixture composition.
Measuring Method:
    This method is also applicable to mixtures with a volume fraction of oxygen of up to 25 %.
Standards:
  • DIN EN ISO/IEC 80079-20-1:2020-09; Explosive atmospheres - Part 20-1: Material characteristics for gas and vapour classification - Test methods and data, revision of IEC 60079-20-1
Special Notes:
    Caution: The maximum experimental safe gap (determined with a gap length of 25 mm) should not be confused with a real "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.
Dependencies:
    The maximum experimental safe gap correlates with the maximum burning velocity. There is no profound correlation with the minimum ignition energy.
Classification:
    The maximum experimental safe gap serves to classify flammable gases and vapours into explosion groups according to their flame transmission capability. It aids in selecting equipment groups used in explosion protection measures for electrical and non-electrical apparatus.
References:
    [1] T. Redeker; Classification of flammable gases and vapours by the flameproof safe gap and the incendivity of electrical sparks, PTB-Bericht W18
See also:
    Minimum ignition energy

Maximum explosion pressure
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Unit:
    bar  (Bar)
Definition:
    The maximum explosion pressure is the maximum value of the explosion pressure determined by varying the composition of the mixture. 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 a homogeneous, quiescent mixture.
Standards:
  • DIN EN 15967:2011-10; Determination of maximum explosion pressure and the maximum rate of pressure rise of gases and vapours, German version EN 15967:2011, revision of DIN EN 13673-1:2003-09, DIN EN 13673-2 Amendment 1:2007-08, DIN EN 13673-2:2005-12, replaced by DIN EN 15967:2022-03
Special Notes:
    The maximum explosion pressure of gases and vapours is almost independent of the turbulent state of the mixture and the size and shape of the container. This in contrast to the simultaneously determined maximum rate of pressure rise (dp/dt)max.
    If there are deviations from the ideally spherical flame propagation, stronger influences may, however, be exerted on the maximum explosion pressure.
    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 transform into a detonation. Considerably higher pressures will then occur.
    For gases and vapours the maximum explosion pressures given in CHEMSAFE are absolute pressures.
Dependencies:
    The maximum explosion pressure is a function of pressure, temperature, and concentration of the initial mixture.
See also:
    Maximum rate of pressure rise (dp/dt)max
    KG value

Maximum oxidizer content
More
Unit:
    Mol%  (Amount-of-substance fraction in %)
    Vol%  (Volume fraction in %)
Definition:
    The maximum oxidizer content in mixture with inert gas and combustible is the concentration of oxidizer at which no explosive mixture can be created by adding more combustible. It is measured under standardized conditions. If the oxidizer is air, the maximum oxidizer content correlates with the limiting oxygen concentration.
Standards:
  • DIN EN 1839:2017-04; Determination of the explosion limits and the limiting oxygen concentration (LOC) for flammable gases and vapours, German version of EN 1839:2017, revision of DIN EN 14756:2007-02, DIN EN 1839:2012-12
Special Notes:
    The maximum oxidizer content depends on the combustible and on the inert gas.
Dependencies:
    This safety characteristic is an extended definition of the special case of the limiting oxygen concentration.
References:
    [1] M. Molnarne, T. Schendler, V. Schröder; Safety Characteristic Data, Volume 2: Explosion Regions of Gas Mixtures, 2nd Revised Edition, 2008, Wirtschaftsverlag NW, Verlag für neue Wissenschaft GmbH, Bremerhaven
See also:
    Limiting oxygen concentration

Maximum permissible fraction of combustible in an inert gas/combustible mixture
More
Unit:
    Vol%  (Volume fraction in %)
    Mol%  (Amount-of-substance  fraction in %)
Definition:
    This value characterizes the maximum fraction of combustible in an inert gas/combustible mixture at which the mixture will remain non-flammable regardless of the amount of oxidizer added.
    If the inert gas is nitrogen and the oxidizer is air, the maximum permissible fraction of combustible gas in an inert gas/combustible mixture at room temperature and atmospheric pressure is identical with the limiting value for flammability (Tci value).
References:
    [1] M. Molnarne, T. Schendler, V. Schröder; Safety Characteristic Data, Volume 2: Explosion Regions of Gas Mixtures, 2nd Revised Edition, 2008, Wirtschaftsverlag NW, Verlag für neue Wissenschaft GmbH, Bremerhaven
    [2] V. Schröder, M. Molnarne; Flammability of gas mixtures, Part 1: Fire potential, J. Haz. Mat., 2005
    [3] M. Molnarne, P. Mizsey, V. Schröder; Flammability of gas mixtures, Part 2: Influence of inert gases, J. Haz. Mat., 2005
See also:
    Minimum inert gas/combustible ratio
    Limiting value for flammability (Tci)

Maximum rate of pressure rise (dp/dt)max
More
Unit:
    bar/s  (Bar per second)
Definition:
    The maximum rate of pressure rise (dp/dt)max is the highest rate of explosion pressure rise (dp/dt)ex obtained by varying the amount of combustible in mixture with air (and inert gas). It is measured in a closed vessel under standardized measurement conditions.
Measuring Method:
    For gases and vapours, it is determined in quiescent, homogeneous mixtures.
Standards:
  • DIN EN 15967:2022-03; Determination of maximum explosion pressure and the maximum rate of pressure rise of gases and vapours, German version EN 15967:2022, revision of DIN EN 15967:2011-10
  • DIN EN 1127-1:2019-10; Explosive atmospheres - Explosion prevention and protection - Part 1: Basic concepts and methodology, German version EN 1127-1:2019, revision of DIN EN 1127-1:2011-10
Special Notes:
    The maximum rate of pressure rise depends on the volume and shape of the vessel and the state of turbulence in the mixture. For explosion protection purposes, data on the maximum rate of pressure rise can only be considered reliable if the applied test conditions are specified.
References:
    [1] M. Hattwig; Druckentlastung von Gasexplosionen bei hohen Anfangsdrücken, Amts- und Mitteilungsblatt der Bundesanstalt für Materialforschung und -prüfung (BAM), 1987
See also:
    KG value

Maximum stability ratio
More
Unit:
    None  (no unit)
Definition:
    The maximum stability ratio is the mixture ratio of the portion of a chemically unstable gas and that portion of any other admixture at which, under specified test conditions, a decomposition of the unstable gas just barely fails to initiate.
Special Notes:
    The maximum stability ratio depends on
    - temperature and pressure
    - size and dimensions of the reaction vessel
    - type and energy of the ignition source
    It is therefore necessary to denote the test conditions under which the value for the maximum stability ratio is determined.
References:
    [1] Schendler,T.; Schulze,H.P.; Stability Pressure Limits of Acetylene-Gas Mixtures, Chem. Ing. Tech., 1990, Chem. Ing. Tech.
See also:
    Stability pressure limit

Melting point
More
Definition:
    At the melting point, the liquid and the solid phase of a pure compound co-exist in equilibrium. The melting point consists of a melting temperature (°C) and a melting pressure (bar).

Minimum ignition energy
More
Unit:
    mJ  (Millijoule)
Definition:
    The minimum ignition energy of flammable gases and vapours is the minimum electric energy needed to ignite the most ignitable composition of the flammable mixture when in a quiescent state. The energy is capacitively stored in the discharge circuit with as little loss in the leads as possible and discharges across a spark gap.
Measuring Method:
    For a given composition, the parameters of the discharge circuit (such as the capacitance, inductivity and charging voltage as well as the shape and dimensions of the electrodes and the interelectrode distance) must be varied to achieve the optimum conditions. The most ignitable mixture is then determined by varying the mixture composition.
Standards:
  • ASTM E 582:2021; Standard Test Method for Minimum Ignition Energy and Quenching Distance in Gaseous Mixtures
Special Notes:
    The minimum ignition energy is a measure of the ignitability of flammable gases and vapours by electric sparks.
    According to the concept of equivalent energy, it also serves to evaluate the incendivity of electrostatic discharge processes (high voltages) and the ignition power of other quasi point-ignition sources (e.g., friction sparks).
    Unlike the minimum ignition current, the minimum ignition energy is not used to evaluate low-voltage circuits (intrinsic safety).
Dependencies:
    There is no profound correlation between the minimum ignition energy and the maximum experimental safe gap.
Classification:
    The minimum ignition energy is used to classify flammable gases and vapours with respect to their ignitability by electric discharges (not with respect to their ignitability on hot surfaces, for which the autoignition temperature is used).
References:
    [1] T. Redeker; Classification of flammable gases and vapours by the flameproof safe gap and the incendivity of electrical sparks, PTB-Bericht W18
See also:
    Maximum experimental safe gap
    Autoignition temperature

Minimum inert gas/combustible ratio
More
Unit:
    None  (no unit)
Definition:
    The minimum ratio of inert gas and combustible at which a mixture of combustible, inert gas, and oxidizer is no longer flammable even if more oxidizer is added.
References:
    [1] M. Molnarne, T. Schendler, V. Schröder; Safety Characteristic Data, Volume 2: Explosion Regions of Gas Mixtures, 2nd Revised Edition, 2008, Wirtschaftsverlag NW, Verlag für neue Wissenschaft GmbH, Bremerhaven
    [2] V. Schröder, M. Molnarne; Flammability of gas mixtures, Part 1: Fire potential, J. Haz. Mat., 2005
    [3] M. Molnarne, P. Mizsey, V. Schröder; Flammability of gas mixtures, Part 2: Influence of inert gases, J. Haz. Mat., 2005
See also:
    Maximum permissible fraction of combustible in an inert gas/combustible mixture

Minimum inert gas/oxidizer ratio
More
Unit:
    None  (no unit)
Definition:
    The minimum ratio of inert gas and oxidizer at which a mixture of combustible, inert gas, and oxidizer is no longer flammable even if more combustible is added [1]. This value is specific to the combustible substance.
References:
    [1] M. Molnarne, T. Schendler, V. Schröder; Safety Characteristic Data, Volume 2: Explosion Regions of Gas Mixtures, 2nd Revised Edition, 2008, Wirtschaftsverlag NW, Verlag für neue Wissenschaft GmbH, Bremerhaven
See also:
    Minimum required fraction of inert gas in an inert gas/oxidizer mixture

Minimum required fraction of inert gas in an inert gas/oxidizer mixture
More
Unit:
    Mol%  (Amount-of-substance  fraction in %)
    Vol%  (Volume fraction in %)
Definition:
    This value characterizes the minimum fraction of inert gas in an inert gas/oxidizer mixture required to keep the mixture non-flammable if any amount of combustible is added. It is specific to the combustible substance.
References:
    [1] M. Molnarne, T. Schendler, V. Schröder; Safety Characteristic Data, Volume 2: Explosion Regions of Gas Mixtures, 2nd Revised Edition, 2008, Wirtschaftsverlag NW, Verlag für neue Wissenschaft GmbH, Bremerhaven
See also:
    Minimum inert gas/oxidizer ratio

Net calorific value
More
Unit:
    kJ/kg  (Kilojoule per kilogram)
Definition:
    The net calorific value (lower heating value) of a liquid or solid fuel is the ratio of the heat produced by complete combustion and the mass. The reference temperature of 25 °C is used for the initial pre-combustion fuel temperature and for the temperature of the combustion products. The water formed by combustion or already present in the fuel is gaseous. The nitrogen is not oxidized.
Standards:
  • DIN 51900-1:2000-04; Testing of solid and liquid fuels - Determination of gross calorific value by the bomb calorimeter and calculation of net calorific value - Part 1: Principles, apparatus, methods, revision of DIN 51900-1:1989-11
  • DIN 51900-2:2003-05; Testing of solid and liquid fuels - Determination of the gross calorific value by the bomb calorimeter and calculation of the net calorific value - Part 2: Method using isoperibol or static, jacket calorimeter, revision of DIN 51900-2:1977-08
  • DIN 51900-3:2005-01; Testing of solid and liquid fuels - Determination of gross calorific value by the bomb calorimeter and calculation of net calorific value - Part 3: Method using adiabatic jacket, revision of DIN 51900-3:1977-08
  • DIN EN ISO 6976:2016-12; Natural gas - Calculation of calorific values, density, relative density and Wobbe indices from composition, German version EN ISO 6976:2016, revision of DIN EN ISO 6976:2005-09
See also:
    Gross calorific value
    Wobbe index

Rate of explosion pressure rise (dp/dt)ex
More
Unit:
    bar/s  (Bar per second)
Definition:
    The rate of explosion pressure rise is the maximum slope value from the pressure-time curve of an explosion. It is determined under specified test conditions in a closed vessel and is specific to the flammable gas at a specified concentration in air or in inert gas and air. Other mixture compositions can result in higher rates of explosion pressure rise. The highest rate of explosion pressure rise over the whole concentration range is called the maximum rate of pressure rise.
Standards:
  • DIN EN 15967:2022-03; Determination of maximum explosion pressure and the maximum rate of pressure rise of gases and vapours, German version EN 15967:2022, revision of DIN EN 15967:2011-10
Special Notes:
    The value is used to calculate the KGex value according to the cubic law.
References:
    [1] SafeKinex-EU-Projekt: TU Delft, BAM, BASF, INERIS, Warsaw University of Technology; Report on the experimentally determined explosion limits, explosion pressures and rates of explosion pressure rise - Part 1: methane, hydrogen and propylene, 2006
See also:
    Maximum rate of pressure rise (dp/dt)max
    KGex value at a defined concentration

Relative gas density
More
Unit:
    None  (no unit)
Definition:
    The relative density of a gas is the ratio of its density over the density of air at the same temperature and pressure.
References:
    [1] W. Berthold, U. Löffler; Lexikon sicherheitstechnischer Begriffe in der Chemie, 1981, Verlag Chemie
See also:
    Wobbe index

Stability pressure limit
More
Unit:
    bar  (Bar)
Definition:
    Minimum pressure limit at which the decomposition of a chemically unstable gas in the absence of air or oxygen just barely fails to initiate.
Special Notes:
    The stability pressure limit depends on:
    - temperature
    - shape and size of the explosion vessel
    - type and energy of the ignition source
    It is therefore necessary to specify the experimental conditions under which the stability pressure limit is determined.
References:
    [1] Lietze,D.; Pinkofsky,H.; Schendler,T.; Schulze,H.P.; Stability Pressure Limit of Acetylene, Chem. Ing. Tech., 1989, Chem. Ing. Tech.
    [2] Schendler,T.; Schulze,H.P.; Stability Pressure Limits of Acetylene-Gas Mixtures, Chem. Ing. Tech., 1990, Chem. Ing. Tech.
See also:
    Maximum stability ratio
    Ignition energy at decomposition of gases

Stoichiometric fraction of combustible in mixture with air
More
Unit:
    Mol%  (Amount-of-substance  fraction in %)
Definition:
    The stoichiometric fraction of a combustible in mixture with air is the amount-of-substance fraction of a combustible that is needed for complete combustion.
Special Notes:
    The stoichiometric fraction depends on the chemical reaction equation of the overall reaction. In most cases the reaction yields completely oxidized products (e.g., water and carbon dioxide).
References:
    [1] M. Molnarne, M. Bulin, G. Viczian, K. Kollar-Hunek; Triangle - ein Computerprogramm zur Darstellung und Auswertung der Explosionsbereiche von Dreistoffsystemen, 2003, Springer-VDI-Verlag
See also:
    Stoichiometric fraction of combustible in mixture with oxygen

Stoichiometric fraction of combustible in mixture with oxygen
More
Unit:
    Mol%  (Amount-of-substance  fraction in %)
Definition:
    The stoichiometric fraction of a combustible in mixture with oxygen is the amount-of-substance fraction of that combustible needed to achieve complete combustion.
Special Notes:
    The stoichiometric fraction depends on the chemical reaction equation of the overall reaction. In most cases the reaction yields completely oxidized products (e.g., water and carbon dioxide).
References:
    [1] M. Molnarne, M. Bulin, G. Viczian, K. Kollar-Hunek; Triangle - ein Computerprogramm zur Darstellung und Auswertung der Explosionsbereiche von Dreistoffsystemen, 2003, Springer-VDI-Verlag
See also:
    Stoichiometric fraction of combustible in mixture with air

Triple point
More
Definition:
    The triple point is the point in the phase diagram of a pure compound at which three phases (e.g., vapour, liquid, solid) co-exist in invariant equilibrium. The triple point consists of a triple point temperature (°C) and a triple point pressure (bar).

Upper explosion limit
More
Unit:
    Vol%  (Volume fraction in %)
    Mol%  (Amount-of-substance  fraction in %)
    g/m3  (Gram per cubic metre)
Definition:
    The lower and upper explosion limits define the bounds of mixture explosibility, i.e., the range of the content of combustibles in mixture with an oxidizing agent within which a flame can separate from the ignition source and propagate. The explosion limits are not part of the explosion range. In CHEMSAFE the amount indicated in vol% or the equivalent concentration indicated in g/m³ refers to the total mixture. If an oxidizing agent other than air is used, this is indicated in a description text.
Measuring Method:
    The explosion limits of gases and vapours are determined according to EN 1839.
    The explosion limits generally refer to an initial pressure of the mixture of about 1013 mbar (atmospheric pressure). For gases the initial temperature of the mixture is normally 20 °C (ambient temperature).
    In the case of liquids, the initial temperature of the mixture is selected to lie at a point well above the condensation point. The indicated value is then calculated from the measured value using the reference temperature of 20 °C.
Special Notes:
    The conversion of vol% to g/m³ and vice versa can lead to deviating results, as all data are rounded in the direction of greater safety.
Dependencies:
    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 vapour pressure curve.
See also:
    Lower explosion limit

Upper explosion point
More
Unit:
    °C  (Degree Celsius)
Definition:
    The upper explosion point of a flammable liquid is the temperature, corrected to 1013.25 mbar, at which the concentration of a saturated vapour/air mixture equals the upper explosion limit.
Standards:
  • DIN EN 15794:2010-02; Determination of explosion points of flammable liquids, German version of EN 15794:2009
Special Notes:
    For pure substances this definition is sufficient. But it is possible to measure different explosion points of mixtures depending on the volume ratio of the gaseous and liquid phases (h ratio). The upper explosion point of mixtures must therefore not be given without the h ratio.
Dependencies:
    The upper explosion point of a pure compound is the point where the vapour pressure curve intersects the upper explosion limit curve [1].
References:
    [1] E. Brandes, W. Möller; Safety Characteristic Data, 2008, Wirtschaftsverlag NW-Verlag für neue Wissenschaften
See also:
    Lower explosion point
    Upper explosion limit

Wobbe index
More
Unit:
    kWh/m3  (Kilowatt hour per cubic metre)
Definition:
    The Wobbe index is a criterion for the quality of gaseous fuels. It is the quotient of the calorific value based on the volume (gross or net) and the square root of the relative density of the gas. In CHEMSAFE the Wobbe index uses the gross calorific value as the reference value, which is given in the same unit (kWh/m³).
Standards:
  • DIN EN ISO 6976:2016-12; Natural gas - Calculation of calorific values, density, relative density and Wobbe indices from composition, German version EN ISO 6976:2016, revision of DIN EN ISO 6976:2005-09
See also:
    Net calorific value
    Gross calorific value
    Relative gas density