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.