The flash point of coalescing agents for water-borne paints

Flash point is a parameter that is usually associated first with solvents and solvent-based paints. Flammability pictograms are usually found on such products. It should also not be forgotten that the coalescents present in many water-borne paints are also organic compounds showing vapor pressure, which under appropriate conditions show a flash point.

Flash point tester – small scale closed cup at Spektrochem Paint Laboratory

These tests are very important when it comes to the safe use of coalescing agents, as well as the use of paints with their participation in various industrial painting processes. While in DIY architectural paints for walls, zero-VOC coalescents or practically non-volatile plasticizers with very high flashpoints are usually used, in industrial water-soluble paints for painting wood or metal, various coalescents with different flashpoints are used. Their use is associated with the need to form the coatings in appropriate conditions, giving appropriate strength properties, and often it is also about regulating the drying time.

Flash point is required as parameter in Safety Data Sheet (SDS), to classify material to ensure it is handled, stored, transported and disposed of correctly, for correct labeling of products according to CLP and applicable to all modes of transport and governed by relevant legislative bodies, whether by air (IATA), rail (COTIF), road (ADR) or maritime (IMDG).

Many coalescents’ technical data sheets contain flash point determinations carried out using different test methods (e.g. small scale cup, tag, cleveland open cup, etc.) How are they different?

Example of TDS of Daplad A coalescing agent with flash point value marked

The principles and test methods cited here do not only apply to coalescents, but are widely used.

Small scale closed cup

Methods: ASTM D3278, ASTM D3828, ASTM D7236, ISO 3679 and other

The test methods are used to determine whether the flammable liquid will have a flash point at a given temperature (flash/no flash – method A) or to search for the flash point (method B) in the range from -30 to 300 °C (-22 to 572 °F). The device is equipped with an electronic Flash detector and can also be used to determine the flash point of biodiesel like FAME.

Small scale testers are also used for shipping and safety regulations such as CLP to define flammable and combustible materials and classify them.

According to these test methods, the determination of the flash point is carried out in the Spektrochem laboratory.

Pensky-Martens Closed Cup (PMCC)

Methods: ASTM D93, ISO 2719

The flash point of petroleum products at a temperature of 40 to 360 °C (104 to 680 °F) is determined with the PMCC apparatus. The measurement is performed using a manual or automatic PMCC, and the methods are also used to determine the flash point of biodiesel in the temperature range of 60 to 190 °C (140 to 374 °F), using an automatic PMCC apparatus.

Cleveland Open Cup

Methods: ASTM D92, AASHTO T48

Open cup methods for determining the flash point for petroleum products using manual or automatic apparatus. The Cleveland Open Cup test methods are applicable to all petroleum products with flash points above 79 °C (174 °F) and below 400 °C (752 °F) except fuel oils.


Methods: ASTM D56, ASTM D3934, ASTM D3941, ISO 1516, ISO 1523

These methods are used to determine flash point using manual and automated closed cup apparatus for liquids with a viscosity below 5.5 mm2/s (cSt) at 40 °C (104 °F) or below 9.5 mm2/s (cSt) at 25 °C (77 °F), and a flash point below 93 °C (199 °F).


Methods: ISO 13736

The Abel method for determining the flash point is a closed cup test for flammable liquids with a flash point between -30 and includind 70 °C (-22 to 158 °F incl.). However, precision covers the range from -5 to 66.5 °C (23 to 152 °F).

Coalescing agents flash point

The following selected examples of coalescing agents used for water-based paints show the variety of flash points. The results of the ignition temperatures presented in the table concern their value determination using the small scale closed cup tester (except for the last item – Cleveland Open Cup)

Examples of coalescents for water-based paints and their flash points

The mentioned method of marking NFPA704 includes markings due to fire safety. The red section of the NFPA704 diamond identifies flammability and is classified as below:

Markings in the NFPA704 diamond in the red section

In the industrial painting process, the processes of drying at high temperature, pumping or mixing water-based paints and varnishes are also subject to restrictions due to ignition. One of the elements of such restrictions is the flash point. Coalescents are often an overlooked element of these restrictions and although they do not constitute such a danger when increasing the vapor pressure as e.g. toluene, it should not be forgotten that although they are in relatively small amounts in recipes, the flash point parameter and the associated risk are also exists.

Related topics

Published by Artur Palasz

Scientist, paint formulator and testing expert.

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