Basic Foam Operations - Part 7

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...

  1. 100 psi for nozzle pressure
  2. 0 psi for elevation loss (actually a slight gain because we are uphill)
  3. Up to 30 psi to overcome friction loss in the 200 feet of 1¾-inch hose flowing 95 gpm, this is about 22 psi friction loss (depending on the age, maker, and condition of the hose, all determine what the friction loss could actually be. The only sure way to confirm the friction loss in this stretch is to flow test it during training)

  • The foam is brought to the eductor’s location and at least 9 x 5 gallon pails are made available, then the attack line has a sufficient amount of concentrate (if each engine carried 5 x 5 gallon pails, a first-alarm assignment could provide a great initial foam-attack capability)

During this preparation phase for foam application, many other tasks can be completed simultaneously, but again, this requires adequate staffing levels, so be proactive and call for assistance early. These other tasks include, but are not limited to, air monitoring, establishment of zones, isolation and denial of entry, identification and confirmation of the product that has spilled and monitoring nearby exposures. Once the logistics associated with the hose stretch and foam staging are complete, the order to charge the line is given. With water flowing at the correct pressure, there are a few things to keep in mind:

  • The time for foam to actually be picked up into the stream and delivered to the nozzle (transit time) can be 15 seconds or more, therefore point the nozzle in a direction other than the spill. Once foam is being discharged, then begin the application
  • Remember not to plunge the stream into the product, rather bank the stream off the street in front of the spill and allow the finished foam blanket to gently push across the product, creating the required foam barrier that separates the fuel vapor from the air
  • The idea of also banking the stream off of a distant object and allowing the finished foam to cascade down and spread out onto the spill is another means of safely applying the finished foam.
  • The greater the expansion ratio, the thicker the foam blanket and the longer the “drain time”
  • Foam may have to be reapplied as the finished foam blanket begins to break down, so make sure the foam line is at the ready with sufficient amounts of concentrate
  • Continue to monitor the surrounding air for an increase in flammable limits. This is an indication that the foam blanket is deteriorating and reapplication is required.
  • Check the exposures for a buildup of vapors including the low areas. Full personal protection equipment (PPE) / self-contained breathing apparatus (SCBA) is a must during the recon for explosive mixtures!
  • Make sure that the logistics are adequate and enough foam concentrate is available for not only the attack line, but also for a backup line

Problem solving is also a critical part of foam operations. It’s important to remember certain key rules of thumb. If you fail to get foam, try these simple solutions:

  • Make sure the inlet pressure is at the correct pressure (usually 200 psi) and then compute that you are not using more than 65% of this number for nozzle pressure, friction loss, and elevation
  • Make sure that the nozzle matches or is greater than the eductor in gpm
  • Is the nozzle open all the way?
  • Are there any kinks in the line that could create additional backpressure?
  • Did you allow for enough transit time? Don’t expect finished foam to come out instantly. Transit time could be 15 to 30 seconds!
  • Is the eductor pick-up tube more than 6 feet above the concentrate supply?

Other problems could be due to a clogged or blocked eductor or a thick concentrate that is having difficulty being picked up through the strainer on the end of the pick-up tube. To prevent some of the problems associated with clogging, it is critical that the eductor be properly cleaned after each use. As a minimum, the eductor and other appliances in the layout should all be flushed for at least 5 minutes with fresh water after each use. This can pay dividends the next time you go to use it. An ounce of prevention is worth a pound of cure!