Flash point
The flash point has been used in Germany for safety considerations for more than 130 years (1882: Ordinance of 24 February 1882 on the commercial sale and offering for sale of petroleum, Reich Law Gazette (RGBl.) No. 7, page 40-41).
“The flash point of a flammable liquid is the lowest temperature at which vapors are generated from the liquid to be tested in a closed cup (…) under specified conditions and in such quantities that a vapor/air mixture flammable by positive ignition is formed in the cup.”
Today the flash point is decisive for the designation and classification as a hazardous substance or in accordance with the Industrial Safety Regulation (BetrSichV).
Flash points are not physicochemical constants of the substance being tested. They depend on the dimensions of the test facility, the conditions of the test facility used and the implementation. For this reason, the flash point is in a strict sense only valid with reference to the respective standard, and valid correlations cannot be proven between the results of the various procedures to determine the flash point or with test facility other than that required by the standard.
Various equipment and methods are used for the determination:
Rapid equilibrium closed cup method (EN ISO 3679:2015)
The test item is heated in a closed cup (recess in an aluminum block) by means of an electric heater placed under the cup. The cup is heated to a predefined temperature and held there for a defined time (e.g. 60 or 120 s). Then, an attempt is made to ignite the vapor/air mixture with an ignition source (flame), which is introduced through an opening in the lid. The temperature at which ignition is observed on the surface of the liquid is designated as the flash point. The determination of the flash point with the Rapid Tester is carried out within a temperature range of -30°C to 300°C.
Pensky-Martens method with closed cup (EN ISO 2719:2016)
The test substance is heated and continuously stirred in a closed cup using an electric oven with a hot air bath (with air space between the oven and cup). While slowly increasing the temperature, attempts are made at fixed intervals to ignite the vapor/air mixture with an ignition source (flame) inserted through an opening in the lid. The temperature at which ignition is observed on the surface of the liquid is designated as the flash point. Determination of the flash point according to Pensky-Martens is applicable in a temperature range from 40°C to 370°C.
Abel closed-cup method (EN ISO 13736:2013)
The test substance is heated and continuously stirred in a closed cup using an electric oven with a hot air bath (with air space between the oven and cup). While the temperature is slowly increased, attempts are made at fixed intervals to ignite the vapor/air mixture with an ignition source (flame) inserted through an opening in the lid. The temperature at which ignition is observed on the surface of the liquid is designated as the flash point. Determination of the flash point according to Abel is applicable within a temperature range of -30°C to +70°C.
In all cases, the measured flash point must still be corrected to the standard pressure of 1013 hPa. The following formula is used:
Flp. = C + 0.025 x (1013 – p)
with
Flp. = corrected flash point in °C
C = measured flash point in °C
p = barometric pressure in mbar
The flash point corrected for barometric pressure is rounded with an accuracy of 0.5 °C. This flash point is then used to classify the substance according to the current guidelines [1], [2], [3]. Furthermore, the safe handling temperature in a plant can be estimated:
– 5 K below flash point for pure, non-halogenated liquids,
– 15 K below flash point for solvent mixtures without a halogenated component.
We will gladly support you in determining flash points and evaluating the results in connection with your process. Simply discuss this with us.
Sources
[1] Globally Harmonized System of Classification and Labeling of Chemicals (GHS) / Regulation on Classification, Labeling and Packaging of Substances and Mixtures (CLP) / Regulation (EC) 1272/2008
[2] UN transport directive: UN Recommendations on the Transport of Dangerous Goods: Manual of Tests and Criteria, Rev. 7 (2019) and UN Model Regulations, Rev. 21 (2019)
[3] Dangerous Substances Directive 67/548/EEC