A high-speed camera was used to record the change of flame shape during
the extinction of methane-air flame. The structures of the flame in
different time nodes during the fire-extinguishing process were shown inFig.S6 , in which the time nodes were defined as 10s after the
last time changing the concentration of the agent as the starting point
(to wait the new ratio mixture of extinguishant and air getting into the
cup-burner), and the flame being completely extinguished as the end
point. As the time went by, it can be found that the flame lost
stability and rapidly shocked, then the flame was suspended upward,
finally the suspended flame completely detached from the cup, and the
flame extinguished quickly. This process is similar to that of
HFC-236fa, which also suggests that CF3I has potential
as Halon replacement。
3.4. Theoretical analysis of fire extinguishing
mechanism
Extinguishing mechanism of fire extinguishing agent actually includes
physical and chemical extinguishing mechanism. Physical extinguishing
mechanism is realized by reducing temperature and isolating oxygen,
etc., while chemical extinguishing mechanism refers to the capture and
depletion of active radicals of hydroxyl and hydrogen by reactants
required for combustion reaction. Highly active free radicals and
molecular fragments generated by the pyrolysis of fire extinguishing
agents can capture a large number of essential free radicals OH· and H·
in the combustion reaction to block the combustion reaction and achieve
the purpose of fire extinguishing19. Based on the low
boiling point of CF3I at 1 atmosphere, it can be
inferred that CF3I will vaporize rapidly at flame
temperature and absorb heat at the same time, which indicates that
CF3I has the possibility of physical fire extinguishing.
In addition, all of the above decomposition reactions are endothermic
reactions, which can also reduce the temperature of the fire site. Based
on the geometry of CF3I, the most likely
fire-extinguishing free radical produced by CF3I is
CF3·. At present, a large number of literatures have
reported its reaction mechanism of capturing flame radicals such as OH·
and H·20-23, which confirmed its fire extinguishing
effect. Therefore, in this section, the research on the mechanism of
fire suppression in CF3I is mainly devoted to exploring
the formation path of CF3· in CF3I. The
research method is the same as the study of thermal decomposition
mechanism. The calculated fire-extinguishing mechanism is shown inFig.6 .