What is a foam proportioner?

Fighting fires with foam is a relatively new phenomenon. It has become more widespread in the Oil & Gas, Mining industry since the 1950's.

A brief history of Fire-fighting foam

As better firefighting techniques developed, fire-fighting foam has developed from its original state called chemical foam, a mix of powders used to smother a fire. This subsequently led to protein foam being developed in the 40's. Industry now has a wider range of foam types developed for specific fire classes, such as Fluoroprotein, Aqueous Film-Forming Foam (AFFF), Alcohol Resistant-AFFF (AR-AFFF) to the recent development of Fluorine Free Foam (FFF).

Foam has a very simple purpose:

• Blanket the fire - thereby smothering it
• Blanket the vapours - preventing Oxygen getting to it
• Cooling - reducing the flashpoint to eliminate ignition or re-ignition

However, the challenge has been and remains to produce foam in its correct consistency to extinguish fires.

Foams are generally mixed with water at pre-determined admix or proportioning rates. These can range from 0.1% (for wetting agents) to as high as 6% (adversely, this means the water is 99.9% for a 0.1% ratio to 94% for 6% ratio). Economically, the lower the ratio the less foam has to be transported or stored for any given fire. Therefore the trend has been to reduce the proportioning rates as much as possible. Typical oil & gas fires are extinguished generally with specific foams at 1% to 3%

If the proportioning rate is too high, the foam will not flow properly (too stiff). If the rate is too low, then foam is not produced effectively (extinguishing class B fires with water does not work).

The production of foam means pumping foam concentrate via a delivery mechanism into water with a proportioning device and aspirating (adding air) at the discharge device to produce foam.

The foam discharge device could be a simple fire hose nozzle, to a foam pourer (for tanks) or a monitor.

Foam Proportioners

The Grandmother of foam proportioners is probably the simple Eductor, which uses a Venturi to induce foam concentrate into a water stream to a discharge device.

The problem with venturi based eductors means any change to the flow & pressure affects the concentrate pick up which changes the proportioning rate. Remember, we need consistent foam quality for the foam to extinguish effectively.

Modern proportioning

More modern proportioning devices developed to overcome the limitations of Eductors or anything using the venturi principle have ranged from:

• Dedicated foam pumps combined with balanced pressure proportioners: A valve is balanced with the water pressure to give a consistent foam flow
• Electronically controlled valve systems: Water & concentrate flow is matched with electronic flow sensors and;
• Premix systems, where premix foam & water concentrate is stored in a tank under pressure
• Water driven foam proportioners

There is a lot of detail surrounding the pros & cons of each system. A simple venturi based proportioner combined with a bladder tank for a small, constant flow & pressure system is ideal & a very competitive solution. However, when changing conditions such as different heights, lengths of hose, constant on/off operation of hoses and partitioned/zoned sprinkler systems then other systems need to be considered, especially which match the foam pump flow with the main extinguishing water flow

Water driven foam proportioners

A relatively simple concept & elegant in its simplicity is the use of a water motor where the firewater main drives a water motor, in turn driving a foam pump.

When using a positive displacement pump the water volume, driven through the motor can be matched exactly with the foam pump, ensuring the ratio is kept at an even rate regardless of flow or back pressure (for example from a variable height hose, such as a ladder).

As the water flow increases the foam pump changes in speed to match & a constant proportioning rate is achieved.

Every system is a compromise to some degree. For example, the investment cost of a water motor-driven proportioner can be relatively high in comparison to a bladder tank. However, the additional benefits of utilising the positive displacement ability mean testing foam concentrate without discharging is easy.

Environmental concerns & periodic testing

In many countries, it is an offence to discharge any firefighting foam without a specific permit. All foams are toxic. Either because of their Biochemical Oxygen Demand (BOD) or they are not bio-degradable.

Oxygen Depletion (BOD)

The aim of the foam is to smother & eliminate the ability for Oxygen to reach a fire. This means discharging foams into rivers can kill off marine life as it depletes the oxygen in the water on a short term basis, even those which are bio-degradable.

Bio-degradable / PFAs / Fluorine Free Foam

Many traditional foams use Fluorine based surfactants (the family of Per- and polyfluoroalkyl substances), also known as 'forever chemicals', which do not degrade & cannot be cleaned up as easily.

This means testing foam without discharging becomes even more important & could potentially meet some large firms environmental targets.

Summary

When considering a foam system keep updated on the latest technology. FireDos are manufacturers of innovative fire-fighting equipment designed to overcome many of the challenges faced by the industry.

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Based in Germany, FireDos GmbH we have delivered over 13,000 water driven foam proportioners Worldwide.