In 2024, Fauske & Associates had the pleasure of assisting University of Iowa chemical engineering student Ashley Sheehan in her research on the “outgassing” phenomenon of halogenated liquid fuels. The University of Iowa offers an excellent undergraduate course on chemical process safety (which includes the Fauske ARSST adiabatic calorimeter), and we are fortunate to collaborate with many Hawkeye students and alums. Go Hawks!
Outgassing (or masking) is a flammability phenomenon in which a material’s vapors “push” a flame away from a liquid sample by inerting the space around it with nonflammable vapors. It is seen most often in flash point testing, where the denser halogenated vapors fill the headspace of the closed sample cup of the flash point tester and expel the ignitable vapors. When this happens, the flash point tester’s pilot flame gets pushed out of the sample cup port as the flame enters the headspace instead of propagating into the cup - thereby “masking” the flash point of the material. A visual example of this phenomenon can be seen in Figure 1.
This result cannot be reported as a flash according to definitions incorporated in various ASTM flash point testing standards. Instead, the material is generally reported as not having a flash point. This can be misleading, as the material may still be ignitable under conditions not well represented by the flash point apparatus. A common way to test this hypothesis is to use alternate testing setups that represent other process or storage conditions.
The joint study consisted of testing three non-halogenated liquid fuels and two halogenated liquid fuels. The halogenated samples, which include such elements as chlorine or fluorine, represent the type of samples that have been seen to experience the outgassing phenomenon, while the non-halogenated samples acted as controls.
These samples were tested in accordance with two standardized methods: a closed cup flash point method, where a pilot flame is introduced into a small sample cup, and a closed glass flask method, in which an electrical discharge is used inside of a 5- or 12-liter glass flask.
Fauske & Associates performed all testing on the halogenated samples due to the toxicity of the reagents and their post-combustion products, while the University of Iowa performed the testing on the non-halogenated samples.
The results, as listed in Table 1, showed experimental values comparable to the flash point values reported on each material’s Safety Data Sheet (SDS) for the non-halogenated fuels. Examples of a standard non-ignition and ignition for the sec-butanol sample using the closed glass flask tester are shown in Figures 2 and 3, respectfully. An ignition in this method is defined as an upwards and outwards propagation of the flame.
For the halogenated fuels, no ignitions were found in the 5-liter glass flask. After switching to a 12-liter glass flask, the trichloroethylene ignited at 31°C, as shown in Figure 4. Despite this, that sample exhibited outgassing in the flash point apparatus, which prevented the sample from flashing there. Dichloromethane did not show an ignition in either method, though there were instances of flame propagating upwards but not outwards in the 12 liter glass flask.
The findings of this preliminary research indicate a need for further study of halogenated materials and their flammability, lest the safety of users and transporters of these chemicals be at risk. A confirmed ignition from trichloroethylene challenges the information found in its SDS, which states that the material is not flammable. When the information is presented in this way, the nuance of method is gone, and users of the material may unknowingly take on a greater risk than the SDS would otherwise suggest. Fauske & Associates hopes to share more studies on the topic in the future to better classify the flammable properties of these materials.
For more information on flammability testing services contact flammability@fauske.com.