Who Mixed the Fuel?

3:1, 1:1, 3:2? What’s the right ratio for burn juice?  If you don’t have an opinion on drip mix you must not be very cool.  The more adamant you are the more likely you are to talk loud about how everyone else does it wrong – no matter the topic.  Wait…what were we talking about?  Oh yeah…drip mix.  Amanda Stamper shares her view on the matter, and gives us a bit of a history lesson as well.

Torch Mix

By Amanda Stamper – Oregon Fire Manager, The Nature Conservancy

A recent podcast about drip torch leg burns got me thinking about drip torch fuel mix ratios. It is no coincidence that I make this association. Last October my pants caught on fire while I was burning gamble oak in New Mexico. After having learned during briefing about how to properly extinguish Nomex on fire by grabbing your pants with a gloved hand and pulling them away from you to extinguish rather than smothering the burning fuel against your skin, and just before my pants combusted, we engaged in lively debate about the proper drip torch mix ratio. And I thought the mix was too cool!



So what is the proper drip torch mix ratio? Does the likelihood of one’s pants catching fire change with different fuel mix ratios? Have you ever wondered how bio-diesel might work in a drip torch? How were burns ignited before the various combustible liquids were at our disposal? These and other questions arise the further one probes.

Ask Ten Fire Managers

Ask ten fire managers from across the country for the ratio of diesel to gasoline in drip torch or slash fuel mix, and you are bound to get at least two if not three or four different answers. Not sure about the ratio of agreement vs disagreement, but suffice to say that drip torch mix ratios depend on the fuels, burning conditions, and perhaps nothing more than past practice of the organization or local area.

Where longevity of combustion is more important than temperature, as in pile burning or broadcast burning for reduction of larger diameter fuels, a higher percentage of diesel may be desired. More diesel than gasoline is perhaps the only cardinal rule when it comes to mix ratio, with somewhere between 3:1 and 4:1 being the most common. The most volatile mixture, according to the U.S. Forest Service, is 3:1, and is recommended for use only in appropriate fuel types (such as grass) during periods of high humidity.


A 5:1 fuel mix ratio is reported to have been used on the Saddle Prescribed Fire, where a burn injury associated with pants igniting occurred in 2012. My pants caught fire with the 4:1 ratio being used on the burn in New Mexico, that I had deemed cool given that I had long been using 3:1. Is longer-burning fuel a contributing factor? Does gasoline vaporize more readily and thereby contribute less to pants igniting? More research to this end may be needed.

More on Bio-Diesel

As for bio-diesel, it works just fine with drip torches and has been utilized in both hand pile burn and broadcast burn situations since early 2006. The Medford District BLM has used over 1,200 gallons of bio-diesel in slash mix during prescribed fire operations to date. The mix is made by using 99% bio-diesel and regular unleaded gasoline in a 3:1 slash fuel mixture. Bio-slash fuel burns similar to regular petroleum diesel/gas mix, but with less toxic wick smoke, with more of a cooking oil smell instead of sulfur or diesel fumes. The liquid is also less toxic for personnel and the environment during mixing and handling. The cost when using the “off road” discount is comparable to diesel #2. Bio-diesel has a solvent effect on the slash tanks and drip torches and seems to prevent sediment build up, as well as a slightly higher flashpoint than regular diesel.

Other Firing Devices

Before flammable liquids were being used in wildland fire operations, fire was ignited using materials largely obtained from the same environment being burned. Among the most notable in North America is the fatwood from longleaf pine, from which the fat lighter used for setting the woods on fire is made. The rich and resinous smell of its smoke only adds to the pleasure of burning.

Fire-stick farming refers to the burning practices of Australian Aboriginals to enhance the productivity of the land., Many wooden matches have been struck and tossed by sheep herders on their way down from the mountains to rejuvenate meadows for grazing. Recreational burners everywhere use lighters if that’s all there is.

Would you feel comfortable throwing matches instead of dot firing? What are some other traditional or unconventional firing devices that we could and should be using?

8 thoughts on “Who Mixed the Fuel?

  1. in the distant past, on the My Hood, tended to mix it hot to ensure the wick stayed lit. Since most torch use involved rain gear, we just wiped burning fuel off.
    I am not aware of any of my coworkers actually burning themselves during lighting ops. The drip torch is a tool, which has its hazards and must be used with care.

  2. I learned to do 3 to 1 from Sisters fire managers. I made my first batch in 80’s a little too hot but lighters loved it! If using an ATV that can get dicey/sporty especially if a log high center occurs. Yes, I’ve made that mistake also. Putting out the wand and your small fire while lifting your ATV off the log is a great exercise in quick thinking.

  3. This is great information! I’ve been using 2:1 and sometimes 1:1 mixes to get moist fuels to get the idea that I really want them to burn. I’m going to back off to a kinder, gentler mix. And always keep my clothing away from the stream!

  4. Did way more backfiring than Rx burning over my career. In ‘88 at Yellowstone, we dragged fire all night and day for days. I was one of those skinny, wiry, high endurance types, and was usually assigned as one of the lighters in my early Fire career (before I was supervising). There’s nothing more exhilarating and challenging than being one of 3 staggered lighters, and being the one furthest away from the control line. Only job I’ve ever had where I literally could not stop if I wanted too, or fall and get injured, because the entire area around would soon be burning. I sure loved that assignment. Ive dragged a lot of fire. On those IHC crews, and on engine crews, over 25 seasons, I did see a handful of torches start burning, or spewing flame as if pressurized, but I never seen anyone light their pants on fire. So this article was a surprise to me, I didn’t know this was a problem. If I was still in fire management today, and there were incidents occurring, I would first examine drip torch handling practices. What is being taught on the unit? Is recurring training happening to teach and reinforce proper handling of lit torches? I don’t say this to be disrespectful or glib, but fuel can’t land on clothing unless careless movements, habits, or practices are occurring.

  5. Geez is my memory fading badly or what? I’d forgotten saying this. Pretty fun I suppose. So in the FB question I said 2 and 1/2 to 1…

  6. Here is what it says in the FS Health and Safety Code Handbook-

    Select the best fuel mixture ratio for each burning job. AUTHORIZED
    mixtures are:
    a. 1 gallon (4 L) of gasoline to 3 gallons (11 L) of diesel.
    b. 1 gallon of gasoline to 4 gallons (15 L) of diesel.
    c. 1 gallon of gasoline to 5 gallons (19 L) of diesel.
    Caution: 1 gallon of gasoline to 3 gallons of diesel fuel produces a
    very volatile mixture. This mix should be used only in appropriate
    fuel types and during periods of high humidity.

    Might want to consult your agency/organizations guidelines before giving directions to or deciding to utilize a “hotter” mixture than 3 to 1 (2.875 to 1 Liter) as it seems to be pretty clear that AUTHORIZED mixtures are 3:1 – 5:1 (Forest Service).

  7. We have had great luck lately starting piles on fire with saw dust or wood chips in metal buckets. Pour in drip torch mix, get the chips saturated, and get a metal shovel with a long handle to scoop it out. We light the shovel and throw the lit chips into the pile. Alternatively you can put the chips in the pile and then light the shovel on fire and start the chips on fire. The chips provide a longer fire residence time and gets piles going quickly. It is nice to have a lid for your bucket in case it lights on fire (put the lid on and put the fire out quickly). I have also heard of people sitting on lit buckets to put them out (sounds a little risky to me, but I hear it works). I think people have been using this method in other parts of the country for a while. We just started a few years ago and it works great. We plan to continue using this method. We use 3:1 or 4:1 (depending on who is mixing it) for our burn mix ratio.

  8. Here on the Olympic Peninsula, we like to use propane torches for burning piles. By far the cleanest way to burn that I have experienced. No oil slicks in the back of the truck or fuel soaked gloves and pants. No worries about who mixed the fuel! It’s not always as easy to get as filling 5ers up at the local gas station but its worth it to me. Resonance time is as long as you want to leave the torch sitting there and it kinda acts like a little blast furnace, forcing air into the pile. Just make sure you don’t leave the tank sitting too close! Sure the tanks are a bit awkward but strap one on a pack frame and away you go.

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