Improving water spray efficacy for fire suppression via CO2 addition at high pressures and low temperatures:: Evidence for CO2 clathrate hydrate formation

This paper describes a technique for achieving a compact aqueous spray that incorporates CO2 into the spray at low temperatures (T < 10 degrees C) and high pressures (P > 10 MPa). A high-pressure spray apparatus was used to explore the effects of temperature (4-25 degrees C), nominal CO2 mole fraction (0-0.12), in-line filter pore size (0.5-7 mu m), and additives on the high-pressure (12-19 MPa) water spray patterns. Divergence of the high-pressure H2O-CO2 spray was significantly reduced at low temperatures, with addition of sodium lauryl sulfate or aqueous film-forming foam (AFFF), and with a small-pore-size (0.5 mu m) filter. The observed trends, based on digital images, can be explained by the formation of CO2 clathrate hydrate within the continuous-flow system. The concepts discussed herein may be applied to conventional H2O/AFFF fire-suppression systems, where the introduction of CO2 as a foaming agent can increase fire-suppression efficacy.