## 1 Introduction  
The effectiveness of water curtains in relation to clouds of hazardous substances depends on the solubility of the given substance in water, the reactivity to it or to components comprised by it, and the rate of diffusion to the droplet interior [1]. This is reflected in experimental data, as the significant effectiveness of water has been observed for the elimination of vapours of such compounds, as ammonia, hydrogen fluoride, or hydrogen chloride [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11]. However, in the case of chlorine occurs a low water curtains efficiency [9].  
An extensive study was also performed with respect to possibilities of using water curtains to eliminate hazards connected with vapours of hydrocarbons and hydrocarbon mixtures [12; 13; 14; 15]. Given the very low solubility of hydrocarbons in water, no significant reduction in vapour concentration is observed. There is also a possibility of using curtains as barriers to limit the shifting of hydrocarbon vapour clouds, or, at appropriate intensity and direction of playing, as an element that facilitates dispersion. The dilution effect would depend among others on the intensity of jet playing, the distance between the nozzle and the point of release, and the type of nozzle [16].  
A much better effectiveness of water curtains than in the case of hydrocarbon vapour was recorded for organic compounds soluble in water [11]. An additional advantage of water in events of uncontrolled release of substances mixable with water is also offered by the possibility of their becoming diluted, which allows achieving a point for which the spill ceases to pose a fire hazard.  
There was no unified system for assessing the effectiveness of water curtains due to diversified research methodology and needs of end users. A different purpose is served by fire sprinklers installeddownwards in the ceiling spaces of warehouses (internal curtains) and other ground firefighter curtains used in activities of specialized chemical rescue groups or ordinary first-order fire units [3]. In addition to these sorption properties, the firefighting curtain also creates a barrier that limits the spread of substances outside the zone. It can also be used as protection against thermal radiation, which was noticed very early [17]. Drops created from a ground firefighting curtain have twice the duration of sorbing, because they rise and then fall, which increases curtain efficiency [3,18]. Their modeling, as well as conducting field testing, are much more difficult because atmospheric conditions have a significant impact on their effectiveness [3,4]. Research conducted for fire curtains has shown that they can be an effective means of reducing the risk during uncontrolled releases of ammonia. [PERSON] et al. examined a water curtain with a capacity of 730 dm\({}^{3}\)/min forming a wall with a height of 8 m and a width of 20 m placed 5 m from the place of release of ammonia. It has been shown that it reduces the ammonia concentration by up to 90% at a distance of 10-20 m from the release point of ammonia at the outflow intensity of 6.5-13.47 kg/min [3]. Internal downwards curtains (sprinklers) in closed spaces have stable working conditions. [PERSON] described this type of curtain by means of the pseudo first order kinetic equation [19].  
The paper presents results of tests related to the effectiveness of downwards water curtains in closed areas for substances, for which the rate of vapour reduction in air may have a measurable practical aspect. Studies were conducted of kinetics of vapour concentration reduction of ammonia, acetone, and selected low-molecular aliphatic alcohols with the use of water curtains.