Up to this point, we have covered a lot of valuable points. The proper proportioning of foam concentrate is another critical piece in the foam application process. Our goal is to mix the foam concentrate with the water in the proper ratio so that after it leaves the nozzles and is mixed further with air, it will offer a protective barrier that will separate the fuel vapors from the air.
There are several ways for this mixing to occur. For the purposes of this series, we’ll simply concentrate on the inline portable eductor. The inline portable eductor is a very simple appliance that allows any engine company to engage in a simple foam operation. An eductor works on the Venturi principle, whereby the appliance (the eductor) picks up concentrate and adds it directly to the hose stream without water diverting from its intended course. Eductors have various ratings of how much foam solution they flow at the proper pressure. For example, some of the more common flows are 60, 95, 125, and 250 gallons per minute (GPM). This is a mix of both water and concentrate at the proper ratio.
For example, if a 125 GPM eductor is in operation with the required pressure and 3% foam concentrate is being used, then the foam solution mixture will consist of approximately 3.75 GPM of concentrate and just over 121 GPM of water.
The portable inline eductor offers quite a punch to the engine company’s arsenal. We have the ability to flow for small spills and fires right on up to the larger incidents we could typically encounter. For even larger incidents, nozzle-mounted eductors can be used to deliver even larger quantities of foam solution. With the nozzle eductor, there is less maneuverability, but much greater punch. For our purposes, we’ll stick with covering the simple portable inline eductor.
The inline eductor is placed somewhere in the hoseline layout, hence the name “inline” eductor. It could be attached to a discharge on the side of the engine company or could even be installed between two couplings as part of a longer hose layout. The option for acquiring a foam stream from a lengthy distance away is possible, so long as the principle of this appliance is understood.
They say that where the eductor goes, so goes the foam supply. Foam concentrate in five-gallon pails, for example, are brought to the point where the eductor is. The “pick-up” tube of the eductor is placed into the foam supply and, at the proper inlet pressure to the eductor, the foam concentrate is pushed (via atmospheric pressure) up the pick-up tube and added into the water stream. Each eductor has a check valve to prevent water from back flowing into the foam supply.
Many departments place the pick-up tube into the five-gallon foam pail. With the higher rates of proportioning, the pick-up tube has to be placed into a new foam pail every few moments. For example, a 250 GPM foam stream at 6% would mean 15 gallons of concentrate every minute. This is a five-gallon pail every 20 seconds. The firefighter assigned to the foam supply at the eductor has to pay careful attention to ensure a continuous foam supply. The last thing the nozzle team would want to experience is a loss of foam. The danger of diluting the foam blanket would be a very real threat.
Rather than this tedious process of a firefighter moving the pick-up tube every so often, try using a container such as a wash bin or other open top vessel that holds 20 or 30 gallons. The logistics of this is a relatively simple concept…keep the pick-up tube in the metal wash basin and keep adding pail after pail after pail. A steady supply of foam is readily available and visible, and with a bit of common sense, no concentrate will overflow the basin.
Each eductor has a manual control or metering valve that varies the orifice size to take in foam concentrate. The metering valve has a series of numbers on it such as 1%, 3%, and 6 %. Some of the newer portable inline eductors have percentage settings that are even lower, such as ¼ or ½ of a percent. These smaller fractions of 1% are for use with Class A foam concentrates and allow for a more versatile engine company.