The Effect of Humidity on the Atomization Process and Structure of Nanopowder Designed for Extinguishment

Abstract

Increasingly, firefighting aerosols are being used to extinguish fires. It is assumed that the extinguishing mechanism involves breaking the chain of physicochemical reactions occurring during combustion by binding free radicals at ignition. The radicals are most likely formed from the transformation of water molecules, with the active surfaces of aerosol micro- or even nanoparticles. The aerosol extinguishing method is very effective even though it does not reduce oxygen levels in the air. In contrast to typical extinguishing powders, the aerosol leaves a trace amount of pollutants and, above all, does not adversely affect the environment by depleting the ozone layer and increasing greenhouse effects. Depending on how the firefighting generators are released, the aerosol can act locally or volumetrically, but depending on environmental conditions, its effectiveness can be variable. The article presents the influence of environmental humidity on the atomization of aerosol nanosize, which confirms the radical combustion mechanism. This paper presents the effect of environmental humidity on the atomization of aerosol superfine (nano) particles. The main focus was on the grain distribution and its effect on the surface activity of the FP-40C type firefighting aerosol. Changes in the characteristic parameters of the particle size distribution of RRSB (Rosin-Rammler-Sperling-Bennet) are presented.

Application of Nanotechnology in Extinguishing Agents

“…The use of these measures has an impact on the environment, as they leave a trace of contaminants at the site of the fire. In the products generated in the production of aerosols, there are substances such as ammonia, nitrogen oxides, carbon monoxide and hydrogen cyanide which have a harmful effect on the human body and the environment [32].…”

“…environment, as they leave a trace of contaminants at the site of the fire. In the products generated in the production of aerosols, there are substances such as ammonia, nitrogen oxides, carbon monoxide and hydrogen cyanide which have a harmful effect on the human body and the environment [32]. Although the extinguishing aerosols do not contain any corrosive substances, in an aqueous environment they can reach a pH of 8-10, which can damage materials and equipment sensitive to high pH.…”

“…However, the reduction of the particle size affects the possibility of agglomeration of the particles, which may result in the difficult contact of the particle surface with the flame radicals. Biel et al [32] also found that one of the parameters determining the atomization of the nanosize of an aerosol is environmental humidity, which has an effect, inter alia, on the grain distribution and thus on the surface activity of the FP-40C type extinguishing aerosol [32]. The results of the research showed that in dry (30% humidity) and very humid (90% humidity) environments the number of aerosol nanoparticles decreases with time due to both aggregation and lumping, and the most favorable conditions for extinguishing aerosol atomization occur in an environment with a humidity of approx.…”

“…70%. This may be related to the more effective capture of water radicals from chain reactions taking place in the flames [32]. Although the extinguishing aerosols do not contain any corrosive substances, in an aqueous environment they can reach a pH of 8-10, which can damage materials and equipment sensitive to high pH.…”

“…Fire extinguishing sprays are based on potassium carbonates and nitrates. They have a grain size in the range of 200 nm and at aerosol release temperatures, i.e., > 1000 • C, they can be active centers and react immediately with radicals supporting the flame combustion reaction [32,34].…”