Fighting fires with neutron science

14 November 2018

Researchers at the University of Bristol are using the ISIS Neutron and Muon Source at Rutherford Appleton Laboratory, to investigate the properties of chemicals used in fire-fighting foams in a bid to make them more efficient and environmentally friendly.

When you think about putting out a fire, chances are that the first thing you’d think of is water, and water is great at putting out a blaze, but if it’s an oil fire, then water is, at best, ineffective and, at worst, dangerous. It’s ineffective because water has a higher density than oil so, rather than smothering the flames, it just sinks though the burning surface where it turns into steam, expands and throws flaming oil in all directions.

So in order to tackle oil fires, firefighters use foam-based extinguishers. Foam is low density (so it won’t sink beneath the surface) and it expands to create a nice flame-dampening blanket that starves the fire of its oxygen supply. These foams are created by chemical compounds called surfactants, which are soap-like molecules. But you can’t use any old bubble-making soap – it has to be able to survive the heat of the fire long enough to cover the fuel source and starve it of oxygen. Scientists have spent decades trying to find the most effective formulation of fire-retardant chemicals. In the past, some of these formulations have included ingredients ranging from liquorice to extract of animal hoof!

Today, the most effective formulations are fluorocarbon-based surfactants, which have superior thermal stability (the foam molecules are less likely to break apart in extreme heat) – thanks to the strength of the bond between the carbon and fluorine atoms, which is one of the strongest in organic chemistry.

Unfortunately, many of these fluorocarbons are hazardous pollutants that degrade into toxic substances and, thanks to the strength of their chemical bonds, do not easily break down – meaning they can persist in the environment and even accumulate within living organisms (bioaccumulation). Recent advances mean that, by altering the way they are made, the fluorocarbons used today are no longer toxic or bioaccumulating, but they do still persist in the environment.

This has prompted researchers from the University of Bristol, in collaboration with Angus Fire Ltd. to investigate fluorocarbon surfactants to aid in the design of a more sustainable and less hazardous alternative. To achieve this, they have used the neutron beams at ISIS Neutron and Muon Source to study the molecular structure of potential replacement surfactants. By studying the scattered neutrons they have been able to see how a variety of surfactant molecules behave and interact. They also studied how changing certain properties of those molecules could make them more effective fire-fighting tools.

This research could lead to developments in the design of more environmentally-benign chemicals, such as those with a low fluorocarbon content, for use in fire-fighting formulations.

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Last updated: 25 February 2019


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