The use of firefighting foam containing per- and polyfluorinated alkylated substances (PFAS) has impacted soil, ground and surface water across the U.S. at manufacturing sites and Department of Defense bases. PFAS are difficult to remove from impacted water or soil, because there is no known degradation for perfluorinated substances in these sites. The objective of this Limited Scope effort was to develop a PFAS-free firefighting formulation based on hollow glass microspheres and evaluate their application in extinguishing pool fire that could potentially replace PFAS-containing aqueous film forming foams (AFFF).
AFFF products used in fuel fire-fighting are made up of air bubbles dispersed in a continuous aqueous medium. The AFFF replacement PFAS-free products lack the foam stability which is critical for the functioning of fire quenching foams. If the air bubbles of PFAS-free products are made up of solids, they can form “extremely stable” foams on top of hot fuel. Hollow glass microspheres are stable solids which are also of low density like air bubbles. Therefore, PFAS-free foam formulations can be made using hollow glass microsphere (HGM). In this project, the fire suppression performance of the HGM containing formulations were tested to meet the firefighting performance requirements of the MIL-F-24385F standard. The film-forming and fire suppression abilities of the hollow microsphere foams were evaluated. The tests included foam stability over hot fuel and benchtop fire suppression test. Based on the lab-scale tests, the potential formulation were down selected for further research.
Hydrophobic and hydrophilic hollow glass microspheres were prepared using surface coatings. Hydrophobic microspheres sank to the bottom of gasoline layer while hydrophilic microspheres floated on top of the gasoline fuel, though both types of microspheres had similar density lower than that of gasoline. The spray application of glass microspheres on top of burning fuel was complicated by their floating on top of water layer due to their low density. Addition of surfactants and additives to homogeneous microspheres in water was not successful. Application of dry HGM powders on hot fuel did not result in fire quenching, because they are not able to form tight seal. Interestingly, the hydrophilic glass microspheres could seal the gasoline from evaporating. Therefore, glass microspheres could be used in the firefighting to prevent the burnback along with other PFAS-free foams. When glass microspheres are applied, after quenching of the fire using PFAS-free foams, they could seal the fuel layer and can increase the burnback time response to meet the military specification.
PFAS-containing fire-fighting foams need to be replaced immediately because they are not environmentally sustainable due to the growing awareness on the environmental impacts and enormous cost expected from cleaning the impacted areas. The safe alternate to AFFF will mitigate these environmental and human health concerns associated with current PFAS-containing firefighting formulations. (Project Completion - 2022)