- Cooling of the fuel. Most often this is done with water. For flammable liquids that generate vapors at very low temperatures, this is highly impractical and potentially unsafe. Foam does offer a cooling ability and can assist in cooling nearby metals that were previously exposed to fire.
- Inhibiting the chemical chain reaction. The use of specialized extinguishing agents can effect extinguishment, but this is geared toward more localized and limited spills that have ignited.
- Removal of the fuel. This could be as simple as shutting off the flowing fuel source, such as using the emergency shutoff that is strategically placed near a fuel pump.
- Eliminating the oxygen. This is a key feature of the extinguishing properties of foam. The ability to float a layer of foam on top of a fuel spill simply creates a barrier between the fuel and the oxygen; it excludes the fuel vapors from mixing with oxygen. The ignitable vapors are smothered, suppressed, and prevented from mixing with oxygen.
There are a variety of extinguishing agents out there that can be used on a flammable liquid fire. Carbon dioxide and dry chemical agents are just two examples. While these agents are effective, they do have their limitations. For example, both can knock down a fire by either excluding oxygen (carbon dioxide) or inhibiting the chemical chain reaction (dry chemical), but neither can prevent re-ignition. Foam offers us many advantages, but it is incumbent on the firefighter to know these.
Let’s review what we have covered. Firefighters should have a solid grasp of all classifications of fire. Knowing the four means of extinguishing a fire leads to efficiency, effectiveness, and safety on the fireground. Each classification of fire presents a hazard and each extinguishing agent has its advantages and disadvantages. Knowing how to use each extinguishing agent is critical.
We can now see that Class B fires are a bit more complex than what we might have previously envisioned. Knowing if a liquid is a flammable or a combustible liquid can help to orient our size-up. Furthermore, conditions can also affect our size-up. For example, a combustible liquid spill onto a blacktopped street on a cold February night would be less prone to giving off ignitable vapors than that same spill on a 105 degree sunny July afternoon. Such a condition would be more likely to heat up a fuel that normally would have been more stable. Again, knowing the basics of fire behavior and chemistry can gear your size-up in the right direction!
In addition, the firefighter has to understand that fuels are not all alike. Some can mix with water and some will shed water. As we start to discuss the basics of foam attack procedures, we’ll see that not all foams are created equal. To apply the wrong foam to a spill or fire can result in greater danger or at the very least, a waste of foam resources.
- Principles of Foam Fire Fighting 2nd Edition is available through the International Fire Service Training Association (IFSTA). This text is an exceptional resource on the entire foam process including Class A and B foams. This textbook and many other related topics can be found at their web site at: www.ifsta.org
- NFPA 11: Standard for Low-, Medium-, and High-Expansion Foam (2010 edition) has exceptional details regarding foam application for a host of incidents and can be purchased via the NFPA's website at: www.nfpa.org
- While not related to this series of articles, the author Dominic Colletti is one of the nation's foremost authorities on the topic of Class A foam. He has authored extensively on the topic and a downloadable report that he authored on Class A Foam for structural firefighting can be found at: http://www.cafsinstitute.com/pdf/CAFS_Briefing.pdf
- Kidde Fire Fighting - National Foam web site has additional details of different types of foam concentrates and other products. It offers very specific details to the firefighter and fire officer. The web link is: http://www.kidde-fire.com/utcfs/Templates/Pages/Template-50/0,8061,pageId%3D3513%26siteId%3D465,00.html
- Chemguard Fire Suppression Solutions offers information on many foam concentrates and other products. The link for this site is: http://www.chemguard.com/fire-suppression/catalog/foam-concentrates/aqueous-film-forming-foam-afff/
- Ansul's Firefighting Foam Products offers additional details like the web links above. It is another great source of data and can be found: http://www.ansul.com/en/products/foam_prod/foam_list.asp
- Task Force Tips Nozzles is a major producer of nozzles and appliances. Their web site has many downloads that are available on foam proportioning and other products. The web link can be found here: http://www.tft.com/
- Akron Brass Company is also a major producer of nozzles and appliances. Their web site offers details on foam proportioning systems and other resources. The link for them is: http://www.akronbrass.com/foam-equipment.aspx