The cost per gallon of dropping retardant

We calculated the cost per gallon of delivering retardant on a wildfire for several different models of air tankers

MD-87 drops on the Round Peak Fire
An MD-87 drops on the Round Peak Fire east of Springville, Utah. Photo by Jocelyn Marie Cooley.

This article first appeared on Fire Aviation

On February 12 I wrote a lengthy article about exclusive use Next Generation 3.0 air tanker contracts, the Aerial Firefighting Use and Effectiveness study, air tanker availability since 2000, and the contracts that were awarded recently for Call When Needed (CWN) large and very large air tankers.

The next day I added some calculated data to that article about the cost per delivered gallon from the CWN air tankers. In an effort to ensure this additional information does not get lost, I am including it again here.

Keep in mind the costs only apply to CWN air tankers which can be more than 50 percent higher than an exclusive use air tanker that is guaranteed several months of work. The initial dollar figures supplied by the Forest Service are based on the contracts that were awarded in December, 2019.

The U.S. Forest Service refused to give us the actual daily and hourly costs that the government agreed to when issuing the new CWN contracts to the six companies, but did supply the chart below with estimates based on the contract costs. The data assume the tankers were activated 36 days a year, for 4 years, and flew 100  hours each year. The dollar figures also include the estimated fuel costs based on each aircraft’s fuel burn rate at a fuel price of $5.21 a gallon.

Call When Needed large air tanker contracts
The companies that were awarded Call When Needed large air tanker contracts in December, 2019. Data from the US Forest Service.

In comparing the dollar figures, note that the listed air tankers can carry up to 3,000 to 4,000 gallons in each load, except the DC-10 and 747 which can hold up to 9,400 and 19,200 gallons respectively.

With the very different capacities of the seven models of air tankers receiving the CWN contracts, using just the USFS data above it is difficult to analyze and compare the actual costs of applying retardant. I did some rough back-of-the-envelope cyphering assuming 3,500-gallon retardant capacities for all aircraft except the DC-10 and 747, and 9,400 and 19,200 gallons respectively for those two very large air tankers. Other assumptions were, 36 days availability a year for four years and one load per hour for a total of 400 hours. The approximate, ball park costs per gallon delivered by a Call When Needed air tanker that was awarded a USFS CWN contract in December, 2019, rounded to the nearest half-dollar and including fuel but not the costs of retardant, are:

Retardant Cost Delivered Gallon CWN

These dollar figures are very, very rough estimates. In some air tankers the amount of retardant carried varies with density altitude and the amount of fuel on board. The cost of retardant would add several dollars per gallon.

Call When Needed air tankers are usually much more expensive per day and hour than Exclusive Use Air Tankers which are guaranteed several months of work. CWN air tankers may never be activated, or could sit for long periods and only fly a small number of hours. Or, they may work for a month or two if the Forest Service feels they can pay for them out of a less restrictive account.

In 2017 the average daily rate for large federal CWN air tankers was 54 percent higher than aircraft on exclusive use contracts.

New fire retardant gel developed that can remain effective for months

It could be used to pretreat areas at high risk of fire ignitions to make them fire resistant

long term gel fire resistant
Overhead time-course images of 3 m × 3 m unmowed (standing) grass plots that were untreated or treated with different coverage levels, dried, weathered, and allowed to dry again over time in the environment prior to burning. The normalized area burned over time demonstrates that CL2 (coverage level 2, or 2 gallons per 100 square feet) is sufficient to preclude spreading of the fire. Air tankers use the same unit of measurement, coverage level, to specify how much retardant will be dropped. Figure from the research.

A group of scientists and engineers have developed a new fire retarding chemical, actually a gel in this case, that they say can be effective for months after being applied to vegetation.

The millions of gallons of red fire retardant that air tankers drop every year is usually made from ammonium phosphate or its derivatives. It has  been called “long term fire retardant” because even after it dries, the chemical can interfere with the combustion process and may still retard the spread of  a vegetation fire to a limited degree. However research and experience in the field has shown some formulations can be toxic to fish.

Gels have been used by firefighters for several decades on structure fires occasionally on vegetation fires. The products can be more effective than plain water due to their ability to stick to a vertical surface or vegetation. Water can remain in the gel for an hour or more depending on the ambient temperature, wind, and humidity. GelTech Solutions recently received a contract from the Oregon Department of Forestry to supply a blue-colored version of FireIce HVB-Fx gel to be used in air tankers. The company says the product passed the U.S. Forest Service’s newly revised, more challenging requirements for wildland fire chemicals. But the safety data sheet for the product says, “Titanium dioxide [a component of the product] has been classified by IARC as a possible carcinogen to humans (Group 2B) through inhalation of particulate dust.”  The safety data sheet goes on to say, “This classification is based on inadequate evidence for carcinogenicity in humans, but sufficient evidence of carcinogenicity in animals (rats). It should be noted that recent studies have demonstrated that the rat may be particularly sensitive to high levels of toxicity dusts such as titanium dioxide. Epidemiology studies do not suggest an increased risk of cancer in humans from occupational exposure to titanium dioxide. The conclusions of several epidemiology studies on more than 20,000 TiO2 industry workers in Europe and the USA did not suggest a carcinogenic effect of TiO2 dust on the human lung.”

This is not the first time blue gel has been used in air tankers. The photo below was taken in the Black Hills of South Dakota August 15, 2006.

blue gel air tanker fire retardant
A single engine air tanker drops blue gel on a fire near Shep’s Canyon in the Black Hills of South Dakota August 15, 2006. Photo by Bill Gabbert.

The scientists who developed the new fire retarding gel that they claim has “persistent retention”qualities said their formulation is environmentally benign, nontoxic, and will “biodegrade at desired timescales.” After application, it will retain its ability to prevent fires throughout the peak fire season, even after weathering that would sweep away conventional fire retardants. The cellulose-based gel-like fluid stays on target vegetation through wind, rain and other environmental exposure, they said.

“This has the potential to make wildland firefighting much more proactive, rather than reactive,” said Eric Appel, the study’s senior author and an assistant professor of materials science and engineering.

Treating wildfire prone areas prophylactically could provide a highly targeted approach to wildfire prevention, but, until now, long-lasting materials have not been available.

The researchers have worked with the California Department of Forestry and Fire Protection (CAL FIRE) to test the retardant materials on grass and chamise — two vegetation types where fire frequently starts. They found the treatment provides complete fire protection even after half an inch of rainfall. Under the same conditions, a typical commercial retardant formulation provides little or no fire protection. The researchers are now working with the California Department of Transportation and CAL FIRE to test the material on high-risk roadside areas that are the origin of dozens of wildfires every year.

“We don’t have a tool that’s comparable to this,” said Alan Peters, a CAL FIRE division chief in San Luis Obispo who monitored some of the test burns. “It has the potential to definitely reduce the number of fires.”

The Stanford-developed treatment contains only nontoxic materials widely used in food, drug, cosmetic and agricultural products, according to the developers. The unique properties of these gel-like retardant fluids allow them to be applied using standard agricultural spraying equipment or from aircraft. It washes away slowly, providing the ability to protect treated areas against fire for months as the materials slowly degrade.

Link to the research paper, “Wildfire prevention through prophylactic treatment of high-risk landscapes using viscoelastic retardant fluids”.

Thanks and a tip of the hat go out to Tim, Carl, and Kelly. Typos or errors, report them HERE.

DC-10 air tanker delivers 373,600 gallons of retardant

Tanker 911 dropping Poco Fire
Tanker 911 dropping on the Poco Fire in Arizona, June 15, 2012. Photo by Ian James.

One of DC-10 gallons retardant deliveredthe DC-10 air tankers has dropped about 373,600 gallons of retardant during 33 sorties on seven wildfires in Arizona and New Mexico over the last 10 days. The fires were: Little Bear fire, 257 fire, Grand fire, Poco fire, Six Shooter fire, Fox fire, and 177 fire.  They were all in Arizona except the Little Bear which was in New Mexico.

Eight of the nine air tankers currently on exclusive use contracts with the U.S. Forest Service are 50+ year old P2Vs designed for maritime patrol. Their average retardant load is 1,948 gallons according to a 2007-2009 air tanker study. If all of those 373,600 gallons the DC-10 dropped in those 10 days had been delivered by a P2V it would have taken about 192 round trips to the fires.

The U.S. Forest Service has a call when needed contract with one of the two DC-10 air tankers. Yesterday and today the pilots are on mandatory days off, making it unavailable. The USFS is not interested in awarding exclusive use contracts for the DC-10 or the 747 air tankers. The 747 can carry 20,000 gallons of retardant, more than 10 times more than a P2V, while the DC-10 almost always carries 11,600 gallons, more than five times the average load of a P2V.

We originally posted this video shot by KASA TV of the DC-10 dropping on June 14, but in case you missed it….

(the video is no longer available)

 

Thanks go out to Trish and Ian.