SOME NOTES ON FOAM APPLICATIONS ON HAZARDOUS MATERIALS
The choice to use foam at the Cooper County phosphorus incident—alcohol-resistant concentrates in particular—was indeed an excellent one. The agent, especially at 6% concentration and applied through air-aspirated equipment, produces a good-quality foam with good stability allows firefighters to operate at a safe range during initial attack and control, and allows a meager water supply to be maximized.
White (or yellow) phosphorus is not particularly aggressive toward this foam; however, the flame and resident heat in the molten phosphorus takes its toll. As the molten mass is cooled to below 84 to 86°F, the frequency of foam applications diminishes and a sixto eight-inch blanket survives much longer.
Foams used in hazardous-material mitigation/control generally evoke some reaction control (e.g., gradient dilution) or mechanical mechanism (e.g., membrane formation) that gives the foam a chance to contain the substance until remedial steps can be taken. We can speculate that this was the case at the Cooper County phosphorus incident. The unfoamed solution provided the initial fire knockdown and cooling that extinguished the fire. The foam blanket essentially kept additional water in place while the foam drained slowly to continue the cooling and oxygen depletion and prevent reignition. Solution draining to a hot surface such as the molten phosphorus often will turn to steam, producing a dense, moist atmosphere at the fire origin.
Where a long-term, on-site remedial program is anticipated, the foam application could be converted to use through a medium-expansion nozzle, whereby more efficient solution conversion yields a foam with considerably longer staying power (medium expansion here refers to foam at about a 50:1 ratio). The foam would be used as a 6% solution — that is, six parts of concentrate and 94 parts of water. This approach is especially useful where water and/or foam supplies are limited.
The Cooper County phosphorus incident demonstrates how quick action and proper choice of controlling agents can lessen the magnitude of an incident.
