Abstract: The mechanism of liquid nitrogen foam fire extinguishing system was introduced and foam expansion, drainage time, micro image of liquid nitrogen foam were studied. Long distance pipe system was established to study the transportation of liquid nitrogen foam. Multi-scale tank fire tests were conducted to test the fire extinguishment of the foam. The results showed that the even diameter of liquid nitrogen foam bubbles was 20 ~ 50 μm and the foam bubbles were even. Foam expansion was about 7 to 8 and the 25% drainage time was about 3 to 5 minutes. The liquid nitrogen foam can be transported to 1 000 meters without foam layer drainage, and the performance of the foam remains the same. The fire extinguishment capability of liquid nitrogen foam was about 1.6 times of that of compressed air foam and 2.5 times of that of aspirating foam. The large flow liquid nitrogen foam system can be widely applied for large tank fires, floor pool fires, flowing fires and some large equipment fires.

Key words: liquid nitrogen foam; compressed air foam; aspirating foam; fire extinguishment