Alcohol Resistance in Firefighting Foam - March 2018

 

The videos that go along with this issue can be viewed on our Testing Videos page.

 

There are some important differences between firefighting foams that are alcohol resistant and foams that are not. Alcohol resistant (AR) foams work on both polar (alcohol) and non-polar (hydrocarbon) solvents whereas non-AR foams, such as standard Aqueous Film Forming Foam (AFFF) or protein-based foam, only work on non-polar solvents.

Foam blankets are mostly water.  Water, which is polar, will mix with polar hazards, like alcohols, thus causing the foam blanket to collapse and be rendered useless. Therefore, a barrier is often needed to prevent the foam from collapsing.  Most AR foams currently contain a high molecular weight polymer ingredient which gives rise to the foam’s alcohol resistance. The polymer forms an insoluble membrane between the foam blanket and the flammable hazard, as in Figure 1.

Figure 1: Diagram representing how most AR foams work.

 

When placing AR foam concentrate that utilizes a polymer ingredient in an alcohol, the polymer will separate out, as seen in Figure 2. For comparison with an AFFF concentrate, see the demonstration video.

Figure 2: Polymer separating out of solution when AR foam concentrates that contain this ingredient are placed in an alcohol.

 

There are two methods that Dyne uses to verify alcohol resistance. One is by measuring viscosity because the amount of polymer present in a foam is proportional to the viscosity. Since viscosity is an important indicator of the presence of polymer in AR foams, Dyne will fail an AR sample if the viscosity is less than one half of the lower acceptable value provided by the manufacturer. Note that there are some listed AR foams on the market today that do not utilize any polymer ingredients and have the same viscosity as non-AR foams.  For these foams, viscosity cannot be used to indicate alcohol resistance.  The second way to check for alcohol resistance is to perform alcohol resistance verification tests.   These tests include the Acetone Stability Test and IPA Burnback Test. Dyne performs alcohol resistance verification tests on all non-viscous AR-AFFF samples. When not required, these tests can also be requested for all other samples for an additional charge.  For AR protein based samples tested to International Maritime Organization/US Coast Guard (IMO/USCG) standards, Dyne is required to perform the Acetone Stability Test and the IPA Burnback Test to ensure continued alcohol resistance. IMO requires this extra level of testing for only AR protein based foams due to their higher failure rate in the past.

The IPA Burnback Test setup is shown in Figure 3. Like with non-AR foams, the concentration of foam to water is very important for alcohol resistant foams. Foams that are marked 1/3% AR-AFFF should be used at 1% on standard hydrocarbon fuel fires and 3% on polar solvent/alcohol fires. Dyne compared a new 3/6% AR-AFFF foam at 3% and at 6% using the IPA Burnback Test to demonstrate the importance of proportioning at the correct percent.  Since the test done at 3% is not at the correct percent for the hazard, we would expect the foam to fail this test.

Figure 3: The IPA Burnback Test.

 

The requirement for passing the IPA Burnback Test is for the foam blanket to remain at least 50% intact for at least 54 seconds after being exposed to the fire, which occurs when the center ring in Figure 3 is removed.  The 3% foam dissolved before the fire was in direct contact with foam blanket whereas the 6% foam lasted for 70 seconds after direct exposure to the fire. The approximate time at which the fire took over 50% of the pan can be seen in Figure 4.

Figure 4: IPA Burnback Test of a 3/6% AR-AFFF proportioned at 3% and at 6%. Note the time difference between them.

 

To demonstrate the problems sometimes seen with AR protein based foams, a failing 3/3% AR protein based foam that was stored on board an overseas vessel was also included in the study.  It lasted for 25 seconds after direct exposure to the fire. The protein based foam performed better than the 3/6% AR-AFFF sample that was proportioned at the hydrocarbon level (3%) but still failed to meet the requirement.  Therefore, it is important to follow periodical testing guidelines to ensure the foam is going to continue to work for the hazard. All of the results of the IPA Burnback Tests can be seen summarized in Table 1.

Table 1: A comparison of IPA Burnback Test times of an AR-AFFF proportioned at two different concentrations and an AR protein based foam.

These results demonstrate why it is imperative to have the correct foam for the type of hazard that is present, to proportion it correctly, and to follow periodical testing guidelines.  Standard AFFF finished foam will almost immediately dissolve when placed onto an alcohol and therefore should never be used where alcohol or polar solvents are stored. Similarly, the difference between foam proportioned at the correct percent and the incorrect percent is drastic. For this reason, it is important for Dyne to know what type of foam customers have so it can be accurately tested and it is vital to always be aware if new hazards are introduced into an environment. These additional hazards may not have the same requirements and therefore may need different foam and equipment.

View videos of the polymer in alcohol and the IPA Burnback Tests. If you have any questions about these results or fire foam testing in general, please contact Dyne at (800)-632-2304 or lab@dyneusa.com.

©2018 Dyne Technologies, LLC