Fire-extinguishing agents comprising microscopic drops of water micro- encapsulated in flame-retardant polymers have been proposed as effective, less toxic, non-ozone- depleting, non-global- warming alternatives to prior fire-extinguishing agents. Among the prior fire-extinguishing agents are halons (various halocarbon fluids), which are toxic and contribute both to depletion of upper- atmospheric ozone and to global warming. Other prior fire-extinguishing agents are less toxic and less environmentally harmful but, in comparison with halons, are significantly less effective in extinguishing fires.

The proposal to formulate new water-based agents is based on recent success in the use of water mist as a fire-suppression agent. Water suppresses a flame by reducing the flame temperature and the concentration of oxygen available for the combustion process. The temperature is reduced because the water droplets in the mist absorb latent heat of vaporization as they evaporate. The concentration of oxygen is reduced because the newly generated water vapor displaces air.

Unfortunately, water mists are difficult to produce in confined spaces and can evaporate before they reach the bases of flames. The proposal addresses both of these issues: The proposed fire-extinguishing agents would be manufactured in microencapsulated form in advance, eliminating the problem of generating mists in confined spaces. Because of the microencapsulation, the droplets would not evaporate until exposed directly to the heat of flames. In addition, the proposal calls for the introduction of free radicals that would inhibit the propagation of the chemical reactions of the combustion reactions.

Manufacturing of a fire-extinguishing agent according to the proposal would begin with the formulation of a suitable polymer (e.g., a polybromostyrene) that would contribute free radicals to the combustion process. The polymer would be dissolved in a suitable hydrocarbon liquid (e.g., toluene). Water would be dispersed in the polymer/toluene solution, then another hydrocarbon liquid (e.g., hexane) that is not a solvent for the polymer would be added to the mixture to make the dissolved polymer precipitate onto the water droplets. The resulting polymer-coated droplets would be removed from the coating mixture by filtration, dried, and stored for use.

This work was done by Clyde F. Parrish of Kennedy Space Center.

This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Technology Programs and Commercialization Office, Kennedy Space Center, (321) 867-8130. Refer to KSC-12236.

NASA Tech Briefs Magazine

This article first appeared in the October, 2003 issue of NASA Tech Briefs Magazine.

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