Constructing fireline with high-expansion foam

Chief Charles Scripps of Painted Rocks Fire and Rescue in Darby, Montana conducted what they call a “foam experiment”. Here is their description of the video:

We flowed foam using a Chemguard foam generator to see if it would have value in the wildland environment. We used 1000 gallons of water with a 2% foam solution (Hale digital foam system). The test took about ten minutes. The foam line was about 1000-1200 feet, 20-40 feet wide and 2-4 feet deep. Further testing for ‘foam and roll’ as well as different percents of foam will take place.


I have seen photos of this procedure before, and it has been used on prescribed fires, but has anyone ever seen it used on a wildfire?

In order to do this, you need a high-expansion foam generator, as opposed to a much smaller medium-expansion foam nozzle which is about 8-12 inches in diameter. Some high-expansion foam generators are so large they are mounted in the back of a pickup truck and most use either a water motor or a gasoline engine to drive a fan, which introduces a large quantity of air into the water/foam solution.

Thanks Chief Scripps and The Latest.


UPDATE September 15, 2009

From The Latest, we have more information from Chief Scripps:

The unit is a Chemguard model 300WP. This is a water driven unit so the engine does not need extra equipment. There are units that are electric or gas driven but neither develops the rpms of the Pok water motor.

I chose this one as it weighs 115 lbs and the next size up weighs 225 lbs. There is a limit to what I can get old volunteers to load, unload and carry safely. The foam was Silvex at 2% as measured by a Hale digital unit. The engine holds 1000 gallons so that was the limit of the trial. The factory recommendation is to run it at 80 psi. So for our first test that’s what we did.

I had seen the YouTube videos of high expansion foam filling aircraft hangers. What intrigued me was when they opened the hanger doors and the foam flowed out on the apron. I wanted to see how it would flow down a mountain. It seems to do this very well. High expansion foam lacks the durability of the denser stuff but it makes a very fast wetline. I think it would be excellent for ‘foam and roll’ in low fuels. I am trying to engineer a method to mount it to my engine so it would function off either side. One of the difficulties for testing is we are running out of summer weather so testing in hot weather conditions is getting difficult.

This is the engine we used.


Author: Bill Gabbert

After working full time in wildland fire for 33 years, he continues to learn, and strives to be a Student of Fire. Google+

5 thoughts on “Constructing fireline with high-expansion foam”

  1. WOW. If you lived in the interface above Darby and had a roadway above your house, they could blanket your homesite pretty quickly. Can they foam from the back of a moving truck? How long’s the foam last? Have they tried pushing a little fire through it? And can you imagine a private pilot flying over the area and wondering WTF was going ON down there???? 😀

  2. Our department has been using foam and CAFS for a long time and we love it. I have assisted the USFS with our ODIN truck 500 cfm and 500 gpm in a fire line the Feds burned right off the line and it held nicely. We also use it in structure attacks. I recommend playing with the foam and all of the different appliances we do have a high expansion and low expansion, you can use these with out a compressor. And to answer the question of driving with the high expansion yes we hook it up from our monitor and and drive very slowly we also hook up an low expansion off of the panel this will make a great fire break. Play with the % and pressure and find what will work best for the RH and the fuel.

  3. Looks like a useful enhancement on the basic wet line or foam line, with the advantage that the volume of foam would eliminate one of the problems using a foam line, of fire sneaking under it. Definitely much faster than digging an equal amount of handline for a quick firing operation or direct attack, but wouldn’t last as long if the fire isn’t going to hit it right away. Not a cure-all, but a great tool in the tool box.

  4. Ron Rochna, retired from National Interagency Fire Center, has been teaching this technique for about 20 years. Some things take awhile to catch on. High potential for use where all safety factors for downhill line construction with crews cannot be met. Also useful for blanketing burned areas for smoke abatement. Creating firelines in sage and grass with a Hi-Ex generator on the truck (mounted on a hitch receiver works well) for burnout in sage and grass is commonly used. 2% is above the 1% maximum approved use rate for Class A foam and will tend to make a slower draining foam – so if you follow too closely with the drip torch for burn out it may still be holding water above the fuels instead of draining to wet fuels below – overcome this by reducing percent, using a generator that has a low volume (3-7 gpm) straight stream straight down into the ground fuels, and/or allowing more time before following with burn out. Lots of other useful stuff, too.

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