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« Foam - 106 Discharge Devices and Nozzles | Main | Foam 104-How Foam Works »
Tuesday
Oct012013

Foam 105 - Foam Proportioning

Now that we understand “how” finished Foam "functions" the question becomes how do we get the Foam concentrate and water mixed into a Foam solution at the proper percentage? There are many varying ways to accomplish this task. After working and teaching in the industry and Fire Service municipalities for 30 years, I would like to share my two favorites. All portable systems operate on the same principles of premixing, venturi, balanced pressure, flow control, and conductivity. Regardless of the operating system you have or may endorse, realize that their operation and correct function shall be driven by the manufacturers design and the specific recommendations for your system.

NFPA 11 provides the industry standard for proportioning, and application of low expansion Foam operations for flammable liquid risks. These risks require greater accuracy than class “A” fuels and should be noticed, recorded, and practiced in your SOP (Standard Operating Procedure).

Accurate proportioning through any proportioner is critical. If the proportioning is too “lean” (less than the % intended) finished Foam quality decreases. This influences everything from extinguishment to personnel safety.  If the proportioning is to “rich” (more than % intended) finished Foam will show stiffness, non-fluidity, and reluctance to flow around obstructions preventing extinguishment and vapor suppression. In addition Foam concentrate supply is depleted more rapidly demonstrating a waste of your resources. The NFPA minimum application “times” may not be achieved prior to depleting your Foam concentrate supply.

My first choice are line educators which are the least expensive and simplest pieces of proportioning equipment available, however they are also the most misunderstood. The in-line proportioner or Eductor is a "venturi" type device that manipulates the incoming water velocity. This function creates a vacuum within the device to which a pick-up tube is connected. This tube is then inserted into any size container of Foam concentrate, drawn into the hand line, creating Foam solution. This type of device has many benefits such as;

1] Low cost

2] No moving parts

3] Minimal maintenance

4] Portability

5] Simple operation

Because they are portable, line proportioners are easily set-up remotely from apparatus to separate Foam supply operations any distance from the apparatus. Hose sizes can be varied to increase the desired distance between the Eductor and the attack nozzle. Relay operations can be utilized when longer distances become necessary. Common Eductor failures on-site are;

1] Mismatched Eductor and nozzle

2] Air leaks in pick-up tube or connection

3] Improper flushing after use

4] Kinked discharge hose line

5] Nozzle elevation

6] Hose length between Eductor & nozzle

7] Incorrect inlet pressure to Eductor

8] Partially closed nozzle

9] Pick-up tube length

The best training for this study is hands-on field exercises where students set-up and participate in the operation of an in-line Eductor. This allows for a simulated Eductor failure, and for students to experience failures, evaluate, and find a remedy BEFORE they are faced with this challenge on an emergency scene.

My second choice is the external “around-the-pump” proportioner. This simple device, converts any municipal Fire Engine “Pumper” into a Foam proportioning Engine capable of hand line or aerial attack streams. This by the way is an excellent way to turn an Aerial “Quint” into master stream Foam device. Also, the use of Fire Engine “deck-guns” creates master stream devices from the common Fire Department Pumper. This portable device connects to the auxiliary intake suction which is fed by a discharge port line. This feed, allows the pick-up tube to replicate the venturi affect like the in-line device. The drawn solution then is passed through the main water pump where it is mixed and sent to all opened discharge ports. Attentive flushing to the main water pump “post” operations must be done to prevent corrosion or future blockage issues. Since this device is portable, it can be stored in a compartment when not in use. It can also be set to flow at any percentage setting desired by the operator.

                                     Haz Mat Mike

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