A comparative study of the effects of chemical additives on the suppression efficiency of water mist

• Water mists of several chemical compounds in aqueous solution were studied.
• The relative suppression efficacies of the additives were quantified by time taken to extinguish a small heptane fire.
• Two different laboratory-scale set-ups were used.
• Strong suppression effects were shown by alkali metal compounds.

This paper reports the results of a comparative study of the effects of various salt additives on the flame extinguishing efficiency of fine water sprays. The relative suppression efficiencies are gauged by comparing the extinguishment time of a heptane flame. Preliminary tests are performed in a reduced scale cup-burner; major results are obtained using the closed reduced compartment set-up.The addition of NaCl, KCl or KHCO3 resulted in large improvements of the suppression efficiency of the water mist. Potassium compounds show the greatest effect as 10% solution of KHCO3 reduces the average extinction time by up to 96% compared to pure water. The other additives tested have a less noticeable effects, with aqueous solutions of MnCl2, ZnCl2 and CuCl2 showing minimal improvement over water, whereas (NH4)2HPO4, (NH2)2CO and FeSO4·7H2O actually increasing the time taken to extinguish the flame.