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Foam-based fire suppression for fuel storage facilities

13th November 2017

     

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DoseTech (Pty) Ltd  (0.02 MB)

Fighting fire with foam concentrates

Fuel storage fire protection is critical and even more so when it is done underground. Detection systems for early response to a fire outbreak are essential. In this article, fires safety specialist, Mike Feldon, discusses the use of firefighting foam as a means of fire suppression and extinction.

There are basically two types of fire that utilise firefighting chemicals to enhance or to make firefighting with water more effective: 

‘A’ class fires which are solid fuel based
‘B’ class fires which are liquid fuel based

In A class fires you use chemicals called wetting agents or A class foam concentrates which increase the boiling point of the water and breaks the surface tension of the water which allows it to penetrate the material, making the fire fighting far more effective.  This allows the water to penetrate deeply into the internal pile of solids and the higher boiling point allows the water to sustain its firefighting capabilities for much longer. These A class chemicals are added to the water   at 0.1% and 1% for wetting agents and 2- 5% for foam.

In B class fires there are two types of concentrates namely:   Hydro carbon liquids (non-polar solvent) and alcohol based (polar solvents) liquids.

To effectively manage a hydro carbon based liquid fire an Aqueous Film-Forming Foam (AFFF) concentrate is used to enhance the water capability and provide foam to fight the fire.

Alcohol based liquid fires on the other hand are more complexed, and another layer of chemistry is added to the fire fighting chemicals in order to provide the correct weapon to attach these fires and are called Aqueous Film-Forming Foam with Alcohol Resistant polymer added or AFFF-AR. These complexed chemicals are Thixotropic and Pseudo plastic

There are two genres of chemical foam available to the market:

  • Protein Based Foams
  • Synthetic Based Foams

The trend worldwide is to move towards synthetic foams which is newer modern technology with improved stability and life span, in addition, included in this new trend is a move towards fluorine free foams which offer an environmentally friendly solution for some types of B class liquid fire applications.

When selecting a foam chemical the amount to be added to the water or dosage percentage is a critical selection factor. When selecting the dosing rates, there tends to be confusion based on the difference between 6% foam concentrate, 3% foam concentrate and 1% foam concentrate and the related costs.  1% foam concentrate is taken as being more diluted and therefore less effective than a 3% or 6% foam, however, in fact the reality is exactly the opposite.  The 1% is a more concentrated formula and therefore is required in far less quantity to provide the same effect.

When 1% foam is added to 99% of water it equals 100% and 3% foam is added 97% water it equals 100%, and 6% foam added to 94% water equals 100%.

The end result is that each compound blended with its relevant amount of water equals 100% - meaning that there is absolutely no difference between a 1% foam concentrate, a 3% foam concentrate and a 6% foam concentrate once you have produced the premix solution. Taking this a step further in most cases when using 1% AFFF the end result to the project costing will be a more cost effective solution to your project.

At this point, all that is happening is blending the water and the firefighting chemicals together, it is at the end of the line on presentation of this pre-mix to the fire that the foam is formed. This is achieved by aspirating air into the water/chemical mix via a form of venturi at the nozzle which sucks the air into the mixture and an expansion rate is achieved. This expansion rate is dependent on the type of end of line equipment and on whether low, medium or high expansion ratios are required. The expansion ratio required will depend on the risk been protected for example, on tank farm bunds medium expansion equipment is installed, for air craft hangers high expansion equipment is common so that a vast area can be very quickly filled to extinguish the fire.

ChemSystems have been manufacturing Fire Fighting foams in South Africa since the early seventies and have been manufacturing Dr Sthamer foams under license from Dr Sthamer in South Africa since the late seventies.

DoseTech (Pty) Ltd introduced the German manufactured FireDos foam dosing system into the local market in 2000, now 18 years later they have successfully supplied a large number of foam dosing systems into a vast cross section of industries with a wide variety of dosing for most foam concentrates and dosing rates. Recently, FireDos GmbH introduced monitors [water cannons] to their range which increased the fire protection capabilities offered including mobile foam dosing and monitor systems.

Contact Mike Feldon on 0832519346 or view www.dosetech.co.za for more information.

Edited by Creamer Media Reporter

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