A motor vehicle accident has occurred at the intersection of a heavily traveled area of a commercial downtown area. It has involved a commercial tanker truck holding about a thousand gallons of diesel fuel, most of which has spilled. The occupants are standing nearby their vehicles and appear shaken. It is a hot, sunny July afternoon with temperatures approaching the 100-degree mark. The sun has baked the asphalt streets and the spilled diesel is pooling against the curb and other low areas. The area of the spill is about 30 feet x 30 feet. The pooled area of fuel is not threatening to spread much beyond its present location, but continues to get deeper. No drains or storm sewers are near the spill, but occupied buildings and spectators are in the area watching your every move, some with video cameras in their phones!
On arrival, the first due company officer has his work cut out for him. First off, the company officer initiates the incident command system, sizes up the situation, calls for the appropriate resources that are and could be needed (being proactive!) and orders the apparatus and crew to take up a position upwind and uphill from the spill. This is an important part of the strategy. While no fuel is presently running downhill and appears to be “pooling,” what happens when the finished foam starts to build up? Could the additional flow cause liquids to run downhill?
Next begins the task of making sure the engine company establishes a sustained water supply. Real quick, our company officer can determine a few critical points as it relates to this incident:
- The spill is a hydrocarbon (diesel fuel)
- It requires an application rate of at least .10 gallons per minute (gpm) per square foot
- The spill is about 30 feet x 30 feet or a total of 900 square feet of fuel
- This requires an application rate of about 90 gpm of foam solution (foam and concentrate mixed at the proper ratio)
- The foam being used in this case is the typical 3% x 6% Alcohol Resistant Aqueous Film Forming Foam (AR-AFFF) concentrate (3% on hydrocarbons and 6% on polar solvents)
- The company has to be able to deliver this flow rate for at least 15 minutes in a worst-case scenario of the spill igniting. For a simple spill, the 15-minute application rate may be overkill, but better to be safe than sorry.
- The company is equipped with a 95 gpm eductor with a 95 gpm air aspirating nozzle, which is above the 90 gpm flow rate required.
- At the 95 gpm rate, the company will be using concentrate metered at 3%. This equates to almost 3 gpm of concentrate and about 92 gallons of water. For 15 minutes this translates into: 45 gallons of concentrate and just less than 1,400 gallons of water
- A backup line that is flowing the same volume would also require a similar amount of concentrate and water. Most forget about the need for a backup line as it relates to foam operations, but like with any building fire, it does offer added protection, an insurance policy of sorts!
The company officer coordinates with the other responding units to set up the foam operation, to mass the needed amount of concentrate and to establish the needed water supplies. These are all important tasks that have to be done quickly and, more importantly, must be done correctly!
The company officer chooses to break the hose lay down into the following setup:
- The apparatus is positioned 200 feet from the spill in an upwind and slightly uphill position and connects to a hydrant
- A 50-foot section of 3-inch line is stretched to the 95 gpm eductor and from the eductor another 200 feet of 1¾-inch hose is attached with a 95 gpm nozzle with a low-expansion, air-aspirating attachment
- Doing the math, we know that the engine pressure should be just over 200 pounds per square inch (psi). This allows for the eductor to receive the necessary 200 psi inlet pressure as there is practically no friction loss in 50 feet of 3-inch hose when flowing only 95 gpm
- After the eductor is positioned, the company officer orders 200 feet of 1¾-inch hose, thus providing enough hose to advance beyond the crash scene if needed
- Of the 200 psi that we are supplying at the eductor, 65% of this can be used for friction loss, elevation (if needed) and for nozzle pressure. Thus, in this case we have 130 PSI as follows: