Scientists at ITMO University in Saint Petersburg, working with Russian research company SOPOT, have produced a new ceramic firefighting foam based on inorganic silica nanoparticles. The foam increases in strength with a rise in temperature, and was shown to improve on current foams in terms of fire extinguishing capacity, thermal and mechanical stability and biocompatibility.

Large fires are typically extinguished with firefighting foam types based on synthetic substances such as pre-fluorinated surfactants. The problem is that these can be very harmful for living organisms, and can take up to 200 years to fully biodegrade, with residues penetrating far into soil and surface water, leading to the accumulation of toxic elements in the food chain. Some countries have even decreased or stopped using these fire extinguishing agents.

However, this new study, as reported in ACS Advanced Materials & Interfaces [Vinogradov et al. ACS Appl. Mater. Interfaces (2015) DOI: 10.1021/acsami.5b08653], demonstrates a silica-based ultrafast-gelated foam that is completely biodegradable and has a fire extinguishing capacity greater than that of existing analogues currently being used. The silica nanoparticles create a polymer network that, when exposed to air, adheres to the burning object and momentarily cools it down while also hardening. The inorganic origin of this polymer network means it can resist temperatures above 1,000oC.

"the foam creates a hard frame that not only puts out the fire, but also protects the object from re-ignition"Alexandr Vinogradov

As lead research Alexandr Vinogradov said, “Most existing foams are made of organic materials and quickly deteriorate when temperature approaches 300 degrees Celsius. In our case, the foam creates a hard frame that not only puts out the fire, but also protects the object from re-ignition.” Also, once a fire is extinguished, the substance then actively absorbs water, becomes softer and breaks down into bioinert silica particles. If the foam were to inadvertently enter a living organism, it would not prove harmful.

The team carried out a range of experiments on the hardening foam, including imitating a real forest fire, where the foam was used to create a flame retardant belt to constrain the fire from spreading. This found it could localize the fire, ensure that adjacent territories were safe and also remain active during the entire fire season. The tests found that the sol-gel foams exhibit an almost 50 times higher extinguishing efficiency than ordinary water, and was 15 times better than the best existing fire-extinguishing agent.

The next step for the team is to develop a comprehensive system of fire protection with the new generation of foams, analyze the extinguishing of other areas using the foam and also work with industry to develop the technology further.