Fire suppressants have been around since the first time that water was used to put out a campfire. Water remains the most available, cheapest, and highly effective direct attack suppressant available to the wildland fire community, but as we all know water evaporates and volume is lost upon contact with the heat from a fire. In aerial applications, this evaporation is increased with the shearing action of the drop.
So it begs the question if water is the most effective fire suppressant then how do we prevent its evaporative loss so as to have maximum direct attack suppression capabilities?
The good news is that this capability exists today and is widely taken advantage of by many wildland fire agencies using naturally occurring, non-toxic, non-corrosive polymers.
The USDA Forest Service Wildland Fire Chemical System’s program at the Missoula Technology Development Center in Missoula, Montana is charged with the evaluation of wildland fire chemicals. The results of the evaluation are published at: https://www.fs.fed.us/rm/fire/wfcs/index.htm
There you will find a section entitled ‘Qualified Products List’ or QPL that identifies ‘Fire Retardants, Foams, and Water Enhancers’. The website states ‘All wildland fire chemical products must go through an extensive evaluation before they are qualified for use by federal firefighting agencies’. These lists are used extensively by all U.S. Federal wildfire management agencies and many state and foreign government programs as an effective means to ensure that the safety, health, and effectiveness of product use has been evaluated.
The benefit of mixing water enhancers into loads of water are multi-fold for the following reasons:
- When enhanced water is dropped from an aircraft the typical problems of wind shear and evaporative loss are significantly reduced due to increased viscosity and increased molecular bonding of water molecules. Further, as a result of ‘binding’ the load of water together the resultant accuracy is praised by both pilots and ground personnel due to the increased amount of water reaching the ground and resultant fire suppression.
- The next major benefit of enhanced water with some of the products on the QPL is, unlike retardant, the load migrates downward through the overstory canopy effectively reaching the ground fire found below in the understory.
- Lastly, and most importantly, the polymeric action of the water enhancers requires significantly greater heat energy to convert the water from its liquid state to steam. That translates to a direct reduction of the heat side of the fire triangle.
However, not all water enhancers are the same. There are two major categories of water enhancers, Super Absorbent or crosslink style polymers and Linear Chain or Elastomeric Polymers. The difference in chemical makeup, functionality and performance are important to understand so that the firefighting agencies select the best product to meet their requirements.
Super absorbent polymers
These polymers, or ‘Gels’ as they are commonly described, absorb water molecules into the larger cells. The mixed product is applied directly to the fire as a ‘Direct Attack’ tool after the polymer cells absorb the maximum amount of water molecules. The effect is that the polymer cells shield and then release their water molecules once the product comes into contact with the fire.
The primary limitation of these products is the negative impact that both salinity and pH have upon the ability of the polymer cells to effectively absorb water molecules. These limitations are overcome by the addition of more polymer concentrate, based upon measurement of the water source by the user of either salinity, pH, or both. Assuming that measurement is possible, operators must be careful when adding additional polymer concentrate because one can add too much concentrate resulting in a super thickening of the load. In extreme cases, the load may not release from the aircraft or ground equipment tank. Interchanging loads of retardant with the Super Absorbent gels is not advisable due to the concerns over the negative effects of salinity.
One additional and very important consideration when using super absorbent gels is the significant mechanical shearing that is required to mix the enhancer with the water.
Linear chain (also known as elastomeric polymers)
These polymers physically strengthen the naturally occurring bond between water molecules resulting in a 3-dimensional matrix. Like Gels, this water enhancer is also applied directly to the fire as a direct attack tool.
Mixing of Linear Chain polymers occurs readily with little to no shearing required. Salinity and pH DO NOT affect the ability of the Linear Chain polymer to mix with water; therefore, no adjustments in dilution level is necessary.
The ease of mixing lends itself to airborne injection of Linear Chain Polymers. Existing foam injection tanks in helicopters and fixed wing aircraft (approved by Simplex, Isolair, and fireboss) have been proved to be effective at airborne injection of these polymers due to the simple agitation requirement.
These polymers do not mix well with fire-fighting foam resulting in a combined product that will clog systems and require cleaning. That is the reason that Linear Chain polymers must not be used interchangeably in foam injection systems. But elastomers can be used interchangeably with retardant with no negative effect in either products.
Ground Use of water enhancers
Use of water enhancers in ground equipment is approved by the QPL as well. The significant shearing that is required by Super Absorbent polymers is a hindrance to its use, but can be pre-mixed in a batch plant and pumped into ground fire equipment. Linear Chain polymers can be released into the tank through the filler port and agitated through the re-circulation pump system. One complete re-circulation of the tank volume is sufficient in mixing of the product with water.
Tactical use of water enhancers
Deployment of water enhancers requires that fire managers change their use of retardant as a suppressant. Retardant is a highly valued part of an indirect attack tactic, but when used as a direct attack suppressant the water component of the retardant mixture and its mediocre ability to reduce evaporative loss upon delivery are mildly effective when compared to gels and water enhancers. The water content in the retardant is the effective suppressant component and approx 15% are compounds that have no benefit as a direct attack suppressant at a significantly higher price per gallon.
Millions of gallons of water are delivered for direct attack by helicopters and fixed-wing water scoopers. Use of water enhancers would greatly increase the effectiveness of the water that is delivered resulting in fewer ordered missions and the associated financial savings.
A reduction in the number of missions will result in a decrease in hours flown. A reduction in hours flown decreases the risk of flight in a high-risk environment.
An obvious result of decreased flight hours is the resultant decrease in associated flight costs to the fire agency. When comparing the high cost of retardant when used as a direct attack suppressant the cost savings of using a much lower cost water enhancer can be significant.
In summation, wildland firefighting continues to increase in both intensity and duration resulting in ever expanding costs to the public and the environment. Safe, effective, and efficient wildland firefighting operations are the goal for all agencies charged with suppression. Use of water enhancers is an available, safe, effective, and efficient next-generation firefighting tool and should be considered by all agencies.
For more information, go to www.biocentral-labs.com