March 5, 2014
Water is not the only tool some firefighters across the country are using to battle fires.
Consider this example: Firefighters who arrive on a scene have traditionally put out flames with water, which, after it splatters against trees and bushes, flows down and away from the fire. Until recently, water was the main flame retardant used on burning buildings.
But new advances in firefighting resources now allow departments to use different types of gels as the flame retardant of choice. Gels reduce water use and, subsequently, impose less water damage. When it flows from the fire hose it’s a liquid, but shortly after making contact with a tree or building, it solidifies into a gel, depleting the fire’s oxygen supply.
Here’s how it works: Water and a special kind of dry power are mixed into a gel before being pumped through the hose.
As this gel is pumped through the hose, the force of the flow results in a solid-to-liquid transition. The mixture remains a liquid until after it makes contact with a tree or building. Because it’s no longer being propelled, the mixture starts to form into a gel.
Firefighters and commercial distributors are testing these gels and are seeking the ideal properties — some of them not fully understood. For example, the gel is primarily composed of water because of its ability to absorb heat. However, the gels behave like solids when they’re not agitated, just like jelly or peanut butter behave. After a certain time, these non-Newtonian fluids become gels again.
Mechanical science and engineering assistant professor Randy Ewoldt and his team are trying to understand how different mixes vary in the time it takes to change state.
Ewoldt said the time scales aren’t zero. In other words, the change between solid and liquid or vice versa doesn’t happen instantaneously.
This is crucial because researchers are trying to determine when is it best for the gel to turn back into a solid. For example, they’re trying to learn how much time should elapse before the gel starts to solidify.
A longer amount of time between when the mixture hits the surface and solidifies into a gel gives the opportunity for the mixture to thin out or spread across the surface and extend the amount of area covered.
The change of state happens whether the mixture is dropped from a specialized aircraft to fight wildfires or deployed from a fire truck.
As time scale changes, “you would see how it sticks, spreads or splatters,” Ewoldt said.
This is important because gel or water absorb heat well, said Gavin Horn, who is the research program director at the Illinois Fire Service Institute, which is the state training and research organization for fire fighters.
But if that water doesn’t stay on the surface after it spreads, that heat is transferred elsewhere, fueling the fire and making it harder to contain for firefighters.
“It (the gel) can help to control exposure of fires, from downtown fires, where buildings are close together, to wild land fires,” Horn said. The gel “absorbs the energy instead of the energy (transferring) to the building.”
And containing the energy increases the firefighters’ safety, which has been a point of discussion between Ewoldt and the Illinois Fire Service Institute, which are working with each other to evaluate the practicality of the research.
This is one of the biggest selling points of EarthClean, which is among the leaders in the field for commercially developed fire-suppression gels and a research partner of Ewoldt’s.
Its TetraKO mixture promises a faster and more effective knockdown of the fire, effective suppression by removing the fuel source and a reduced chance of rekindling. In addition, the company says it’s non-toxic and biodegradable. It has all the properties that make it appealing to fire departments in the near future.
But Horn said the IIlinois Fire Service Institute has to have complete confidence in their performance before gels like TetraKO is commonplace in firefighting.
Darshan can be reached at [email protected]