In many places, water is plentiful, relatively inexpensive and easy to obtain in large quantities. It’s also very effective when combating heat and flame, which makes it the agent of choice for firefighting in many applications. However, water does have its down sides:
- There are many areas where it isn’t easy to obtain.
- Often, we use more water than needed since all of it doesn’t always reach our intended target.
- It can take a lot of work and resources to obtain water and apply it in large quantities.
Smart firefighters have looked to improve the efficiency of firefighting operations since the early 1900s. As part of their efforts, they’ve experimented with a wide range of substances that could either replace water or be added to it to make it more effective in fighting Class A fires (those involving ordinary combustibles) or Class B fires (those involving flammable/ combustible liquids).
In 1999, the National Institute of Science and Technology’s Building and Fire Research Laboratory published a report, “Water Additives for Increased Efficiency of Fire Protection and Suppression,” on its study of seven agents that at the time met U.S. Forest Service specifications for Class A firefighting. The study’s conclusions:
- The additives improved water’s ability to provide exposure protection on vertical wood surfaces;
- The agents more quickly extinguished Class A and piled tire fires; and
- When using the water/additive solution, they used approximately one-third the amount of solution to extinguish test fires versus plain water.
Class A foams generally fall under the purview of the National Fire Protection Association’s (NFPA) standard 18 or 18A. In this article, I’ll discuss agents/tactics designed for Class A firefighting, and I’ll explore the benefits of using these agents in fighting Class B fires.
Passing the Test
Firefighters should use only extinguishing agents that meet independent testing or standards, and the best available standards for firefighting come from the NFPA. Agent selection should also be based on the manufacturer’s recommendations and which classes of material the agent has been tested on.
Wetting Agents
Today’s wetting agents are designed to reduce the surface tension of water and increase water’s ability to penetrate burning materials and spread. To meet NFPA 18: Standard on Wetting Agents requirements, agents are tested for their effectiveness on deep-seated Class A fires, as well as their ability to reduce the amount of runoff they produce. These agents may be used on Class A and some Class B fires, depending on the specific tests the agent has successfully completed. Note: NFPA tests for wetting agents are small in scale.
Class A testing is performed by using a 2 1?2-gallon fire extinguisher on a live fire. The intent of the test is to allow the agent in the extinguisher to meet the 3-A rating for fire extinguishers.
Wetting agents tested for Class B firefighting are tested on a 50-square-foot, 10-gallon pan of heptane–certainly not on something larger than an automobile fuel tank. Two to three tests lasting just a few minutes each are performed using a nozzle recommended by the manufacturer in minimal wind.
Water Additives
Water additives are defined by the NFPA as “any agent that, when added to water in proper quantities, suppresses, cools, mitigates fire and/or vapors, and/or provides insulating properties for fuels exposed to radiant heat or direct flame impingement.” NFPA 18A: Standard on Water Additives for Fire Control and Vapor Mitigation addresses water additives used for the control and/or suppression of fire and mitigation of flammable vapors. Additives can materially reduce water’s surface tension, increase its penetrating and spreading abilities, and might also provide enhanced cooling, emulsification and foaming characteristics.?
Water additives are tested on a slightly larger Class A hazard than wetting agents, but don’t get the same testing for deep-seated fires.
Testing additives for a Class B hazard also involves a 10-gallon pan, but it’s up to you to specify/verify which of the following tests have been successfully completed:
- Spill fire test–achieves 100 percent extinguishment in an average of 60 seconds or less at 5 gpm.
- Pool fire test–3-minute test at 5 gpm?with complete extinguishment and no reignition when additive is tested with a torch.
- Three-dimensional fuel fire test–applies additive to Jet A fuel or heptane or both. Check the manufacturer’s listing information before purchasing any additive for this test. The test uses 40—60 gpm of solution, and fire should be extinguished in 45 seconds or less, but only three of six tests must be successful.
- Vapor mitigation test–verifies via emulsification that the following are rendered noncombustible: heptane, gasoline, 90/10 gasoline/ethanol, 82/18 gasoline/MTBE, No. 2 diesel and Jet A fuel. Testing is done 1 minute after agitation and 2 hours after agitation.
- Fuel in-depth fire test–determines whether additive meets Underwriters Laboratory (UL) 162: Standard for Safety for Foam Equipment and Liquid Concentrates.?
- Polar solvent fire test–This protocol has not yet been developed, however, during special 2007 tests on ethanol fires at Ansul (sponsored by the IAFC, IAFF and others), the only agent that passed was the UL-listed AR-AFFF. Class A, emulsifiers, protein foam, etc., all failed.
All these tests are performed with both fresh water and (synthetic) seawater. Burnback resistance is also tested.
Agent Limitations
The testing for both wetting agents and water additives on flammable liquids is relatively small scale, and there may not be much test information on larger scale applications of these agents on flammable or combustible liquids, so it’s not recommended they be utilized for this purpose. It’s interesting to note that although wetting agents and additives are often more effective than water alone, they have most of the same limitations as water: They create additional hazards when they contact water-reactive chemicals; they don’t work well on water-soluble Class B hazards or combustible metal (Class D) hazards unless specifically listed to do so; and they present the same hazards as water when applied to electrical (Class C) fires.
Additionally, just like foams, wetting agents and water additives and their solutions should not be mixed with other wetting agents or water additives or their solutions, although finished solutions generated separately can be applied to a fire together or consecutively. Remember: Completely flush systems before changing foams, wetting agents or water additives, as these concentrations should not come in contact with any others.
Class A Foams
When Class A foam application and compressed air foam systems (CAFS) are discussed, NFPA 1145: Guide for the Use of Class A Foams in Manual Structural Firefighting is an indispensable resource. The application of Class A foams normally indicates an additive or agent concentrate is mixed with water at 0.1—1.0 percent. “Foam” refers to the finished product applied to the fire.
Foam Addition/Generation
Making foam involves mixing water, concentrate and air. Water temperature or quality has little affect on the firefighting capability of foam, although it can present challenges to foam generation and the characteristics of the concentrate itself. Firefighters may prefer to do “batch mixing” of foam–preloading the vehicle’s water tank by adding foam concentrate. Another alternative when using a tanker (tender) shuttle with portable tanks: Batch mix the foam right into the portable tanks.
The problem with batch mixing is the product’s bio-degradability, which tends to reduce the foam’s effectiveness over time. Further, the system can’t be easily recharged until the tank is empty. But batch mixing works when eductors or similar appliances are unavailable.
Batch mixing is best done at the time of the incident, unless the manufacturer has specified it’s permissible to do otherwise. When batch mixing, be careful not to violently agitate the solution (via tank recirculation at pressure) or too much foam will develop inside the tank, causing a variety of problems, up to and including loss of pump prime. When refilling the tank, add the water first, then the foam.
Other methods of adding foam concentrate include using portable eductors and cans/containers (traditional foam concentrate addition mechanism), nozzle sticks or proportioning from onboard tanks. When using eductors, it’s important to match the nozzle with the eductor. Failing to do this might result in insufficient foam concentrate being added to the hose stream, or no concentrate at all. Tip: When using any of these methods, make sure the system is fully flushed after use if a different concentrate might be used in the tank/eductor/system in the future.
Compressed Air Foam Systems
During an incident, wetting agents/water additives can be applied in various manners. Standard firefighting nozzles and foam-generating nozzles, or CAFS, can be used. CAFS adds air at the mixing point at the pump mechanically, while non-CAFS systems add air generally from aspiration at the nozzle. The energy added by the CAFS at the pump helps the agent mix more effectively with water through the hoseline, which makes the best foam.
The use of a foam nozzle on a non-CAFS system generally makes better foam than a standard nozzle because of the nozzle’s air aspiration. Note: High-expansion generation equipment can mechanically add air to foam solution. A few departments have had success with using Class A foams and this equipment.
One major benefit to CAFS: The hoseline contains a large percentage of air, making the hoseline much easier to handle and move. It will also have a propensity to kink, but this can actually improve the finished foam. Tip: During a fire attack, Class A foam flow rates and hoseline sizes should be no different than the flow rates and hoseline sizes used with a water-based attack.
One of the biggest challenges to effective application of CAFS is slug flow, an alternate flow of air and water that occurs when air is inserted into the water stream without foam solution present. To avoid this, the pump operator must confirm continuous flow of foam solution.
A second concern when using CAFS: Energy can build up when compressed air is inside the hoseline, causing a significant nozzle reaction to occur when it’s first opened. To prevent this, open the shutoff slowly from a balanced position, and consider using pistol grip nozzles.
One final concern: If the intake pressure to the pump exceeds 70—80 psi on a CAFS pumper that’s not designed to compensate for this, the capacity of the CAFS?compressor can be surpassed, which won’t allow CAFS to be produced. On these apparatus, keep intake pressures below 70—80 psi to ensure high-quality compressed-air foam.
The Finished Product
The percent of concentrate used and the amount of air entrained into the foam affects the finished product and how it’s best utilized on the fireground. “Drier” foam normally has a greater expansion ratio, longer drain-off time and more of a shaving-cream appearance, which provides better exposure protection and has Class B applications. “Wetter” foam is just the opposite, but the greater water content may result in better fire extinguishment. Some water additives differ from these products, as they may not have a traditional “foamy” appearance. Remember: More foam concentrate in the mix isn’t always better; in fact, it becomes expensive when used in large fire attacks.
Class B Foam
Some Class B foams can be used as concentrations below 1 percent to provide the same properties as Class A foams, but some are quite viscous and hard to proportion below 1 percent. Further, most are much more expensive than Class A foams. However, they’re very effective on Class B fires, and crews only have to carry one type of foam, eliminating any confusion about which foam to use on the fireground.
Notes on Nozzles
Using standard firefighting nozzles, such as a smooth-bore or combination nozzle, won’t add a lot of air to a Class A solution, thus creating a wet foam that works best for fire attacks and overhaul because it penetrates more rapidly and creates protective fog streams.
Adding an air-aspirating nozzle increases the foam expansion ratio, making a drier foam that works even better for fire attack and exposure protection, although the nozzle reach will likely decrease.
The greater the expansion ratio of the foam, the more likely the stream and the finished foam will be affected by winds on the fireground. However, using low-expansion foam nozzles may provide minimal protection from radiant heat, which presents safety issues for interior attacks and Class B attacks.
Medium-expansion nozzles are generally limited to overhaul and exposure protection, but they can also be used for blanketing the hazard if the foam has expansion limitations or must be discharged a short distance.
For CAFS applications, a full-flow ball valve or smooth-bore nozzle works well, and the larger the discharge, the drier the foam.
Safety & the Environment
Most concentrated firefighting wetting agents/water additives aren’t much different than household detergents and shampoos. As with any chemical, every fire department should have a current Material Safety Data Sheet on the water additive concentrate it uses, and all personnel should be familiar with the concentrate’s safety and environmental hazards and limitations, particularly because firefighters use large volumes of concentrate for long periods of time.
Keep the following tips in mind when using foam on the fireground:
- Avoid contact with all concentrates, as they irritate the eyes and skin. Rinse any areas of the body that come in contact with a concentrate.
- Never ingest any concentrate.
- Remain cautious on the fireground when using foam, as foam can hide building damage and structural weaknesses, although it will likely apply less weight to the structure than plain water (but foam is more likely to stay in place/soak in rather than run off).
- Watch for slippery floors and reduced visibility inside the fire building.
- Exercise extreme caution when using or checking electrical equipment as wetting agents are more likely to leak into electrical equipment, even equipment that’s “water-tight.”
- Rapid fire knockdown may cause an increase in heat due to steam inside the fire building, therefore, make sure you have effective ventilation and/or continued agent application before making entry.
- Although most agents are biodegradable, avoid getting concentrate in or near bodies of water, and clean up concentrate spills in accordance with local/state regulations.
Storage
When storing wetting agent/water additive concentrates, keep them in closed containers, as some of their ingredients are capable of evaporating, and keep the room temperature above 40 degrees F (4 degrees C), unless the manufacturer advises otherwise. And at least once a year, inspect (look for crystals) and test the stored concentrates.
Summary
If you want to use Class A foams, read through NFPA 18, 18A and 1145. They will help you better understand the diversity of the agents on the market and the many ways you can apply them.
My department has been using CAFS since 2003 with a UL-listed wetting agent made by a major international foam manufacturer. The manufacturer also indicates that the agent will emulsify hydrocarbons, but it’s not applicable for polar solvents (alcohols, etc.) and may not be effective on gasoline additives, which are becoming more common. Despite these limitations, we’ve found it to be quite effective at several working structure fires, maximizing attack, minimizing water use and improving overhaul on various outdoor fires.
CAFS is always our primary agent of choice unless there’s some hazard that prevents it. We’ve also found that using CAFS requires extra training and vigilance on the part of the pump operator, as they must complete up to six steps to engage the CAFS, and they must watch for adjustments needed between wet and dry foam.
So do your research, talk to folks already using it, and carefully choose which agent works best in your community and which appliances are most appropriate for your styles of fire attack.
References
NFPA 18: Standard on Wetting Agents, 2006 edition
NFPA 18A: Standard on Water Additives for Fire Control and Vapor Mitigation, 2007 edition
NFPA 1145: Guide for the Use of Class A Foams in Manual Structural Fire Fighting, 2006 edition
Class B Foam Attack Tips
John Sachen, the 2006à2007 Fire Rescue Instructor of the Year at the University of Missourià•s Fire and Rescue Training Institute, offers the following pointers exclusively to FireRescue readers for making a foam attack on Class B fires:
- Use an appropriate foam, remembering that many vehicle fuels now utilize various additives that are polar solvents and require alcohol-resistant foams.
- Attacks on vehicle fuels require greater foam expansion, which can only be achieved through the use of air-aspirating nozzles, not standard fire-attack nozzles.
- Foam must be applied gently onto the hazard to be most effective. Plunging the stream into flammable liquid presents several problems, not the least of which is wasting finished foam. A simple method for making a gentle foam application into a melted tanker compartment or other partially enclosed hazard is to find a nearby downspout (copper, if possible) and remove it for use. Then insert the foam nozzle into one end and discharge the foam onto the hazard from the other end. Doing this also keeps firefighters farther away from the hazard.
- Remember: Class B foam should be utilized on Class B fires!
Foam & Fire Attack
For each of the following fireground scenarios, NFPA 1145 recommends the following types of foam, nozzles and strategies, and my experience confirms these recommendations:
Exterior Structure Fire Direct Attack
Wet or fluid-type foam
Non-CAFS–Prefer combination nozzles for reach and penetration
CAFS–Adjust for wet foam
Exterior Structure Fire Overhaul
Start with wet or fluid-type foam for cooling/penetration and transition to dry foam for blanketing and filling void spaces
Non-CAFS–Prefer low- or medium-expansion aspirating nozzle
CAFS–Adjust to dry foam, use large orifice nozzle/ball valve
Exterior Structure Exposure Protection
Start with wet foam to wet the material, then follow with dry foam to blanket the exposure
Non-CAFS–Prefer low- or medium-expansion aspirating nozzle
CAFS–Adjust to dry foam, use large orifice nozzle/ball valve
Interior Structure Fire Direct Attack
Wet or fluid-type foam
Non-CAFS–Prefer combination nozzles for reach and penetration
CAFS–Adjust for wet foam, use combination nozzle if possible
Interior Structure Fire Indirect Attack
Wet or fluid-type foam
Non-CAFS–Non-aspirating combination nozzle
CAFS–Adjust for wet foam, use combination nozzle if possible. If directing stream from outside, smooth-bore nozzle is effective
Interior Structure Fire Overhaul
Start with wet foam to wet the material then follow with dry foam to blanket the material
Non-CAFS–Prefer low- or medium-expansion aspirating nozzle
CAFS–Adjust to dry foam, use large orifice nozzle/ball valve
Vehicle/Mobile Equipment Fire Attack
Same tactics as exterior structural fire attack. Consider using penetrating-type nozzles where appropriate. Use caution if Class B materials are involved, unless your additive/wetting agent is listed for this purpose. Do not apply to Class C fires, and apply to Class D fires only if your additive/wetting agent is listed for this purpose.
General Class A Fires Outside
Start with wet foam to wet the material, then follow with dry foam to blanket the exposure
Non-CAFS–Prefer non-aspirating nozzle for reach and penetration
CAFS–Adjust to wet foam, use combination nozzle
