Class B Fires and Spills
As a review, we’ll go over Class B fires. Simply put, Class B fires are flammable and combustible liquids and gases. The difference between a flammable and a combustible liquid is the temperature at which vapors are given off. Combustible liquids have a flashpoint above 100 degrees Fahrenheit, while flammable liquids give off ignitable vapors (have a flashpoint) below 100 degrees Fahrenheit.
For example, gasoline is a flammable liquid and gives off flammable vapors well below 100 degrees Fahrenheit. Some common sources, such as the International Fire Service Training Association’s (IFSTA) Principles of Firefighting Foam, 2nd Edition, use a flashpoint of -45 degrees Fahrenheit. For different blends of gasoline, check out the various sources available. The specific characteristics can differ from source to source.
Diesel fuel is a combustible fuel and gives off ignitable vapors over 100 degrees Fahrenheit. Sources such as IFSTA’s Principles of Firefighting Foam, 2nd Edition, use 126 degrees as the flashpoint. As an interesting side note, during the writing of this series my research found various credible Web-based sources and several Material Safety Data Sheets (MSDS) that identified the flashpoint of diesel fuel from 100 degrees to over 160 degrees.
Based on the facts for gasoline and diesel fuel, we could never cool gasoline to the point where we could prohibit vapors from being released. Only in the most extreme settings on the planet could the temperature be so cold that gasoline stops giving off vapors. A combustible liquid, on the other hand, can be cooled (such as through environmental conditions like a very cold winter day) to be rendered relatively safe. Nevertheless, there is always the potential for danger and any fuel spill should be given a wide berth. While we can minimize the danger, either through knowledge or actions, there is always a danger when dealing with any type of Class B fuel incident.
The different types of Class B fuels are numerous to say the least. Class B fuels can include everything from propane, natural gas, gasoline, paint, oils, lacquers, paint thinners, ethanol, kerosene, alcohol, and countless other types of liquids and gases. The potential threat to the fire service is varied and numerous. This fact alone should translate into more training time because there are so many dangers out there that can harm us!
The lower the temperature at which the fuel gives off vapors, the greater the potential for ignition. In addition, on a hot summer day for example, fuels are even more volatile and more likely to give off ignitable vapors. This is another size-up factor that has to be considered as part of the response.
One interesting point about Class B fires is that it includes both liquids and gases. Thus a propane leak has the potential to become a Class B fire. But, because of its gaseous properties and its three-dimensional expansion after being released from its vessel, propane would not be fought with foam. Foam application would be ineffective in such a situation.
For fires involving similar types of fuels, whereby the fuel converts to a gas immediately upon escape from the pressurized vessel (such as liquid propane), it is best to extinguish such a fire, or prevent ignition, by shutting off the supply. The same principle applies for any fire or leak involving other types of gases, such as a leak of natural gas. Foam is not the tool of choice; shutting off the fuel supply from a safe location is the tactic of choice. Furthermore, fires that involve a third dimension, such as a fuel being discharged under pressure and cascading downward or spraying outward, is very difficult to extinguish using a typical foam stream. Again, knowing the importance of fuel shutoffs can be of enormous value towards the mitigation of the incident. Take for example, the fuel shutoffs that you might see at the local gas station. Fuel spewing out under pressure may be easily controlled through pre-incident knowledge of such a shutoff. Not all of our incidents have to be front-page headlines. In many cases, a serious incident can be prevented through simple techniques.