Calculation of dibromomethane atmospheric lifetime is carried out, as well as an experimental assessment of its fire extinguishing efficiency. Calculations show that methylene bromide atmospheric lifetime is 15.8 days so it rapidly decomposes in the troposphere. The main mechanisms of the removal of CH2Br2 from the atmosphere are its reaction with hydroxyl radicals and the processes of physical removal from the atmosphere. Special experimental equipment allowing to measure fire extinguishing concentration of gaseous fire suppressant having high boiling point is described. Experimentally measured minimum extinguishing concentration of methylene bromide for n-heptane is 2.5 % vol. According to this, CH2Br2 is close to the most effective gaseous fire extinguishing agents, such as C3F7I and C2F4Br2. LOAEL value for CH2Br2 is predicted at the level of 0.3-0.4 % vol. Due to the high boiling point of methylene bromide and its relatively high toxicity, the most appropriate way to use it in fire suppression is to create fire extinguishing mixtures, in particular, with fluorinated hydrocarbons. This approach allows to diminish application of greenhouse gases in fire protection and also to solve the problem of toxicity of extinguishing substance.

One of possible ways to reduce the volume of the use of hydrofluorocarbons (HFCs) as gaseous fire suppressants is studied in the paper. Extinguishing mixtures of HFCs and some fluoroiodocarbons are investigated. It is theoretically predicted that fluoroiodohydrocarbons are effective inhibitors of conversion of fluorinated alkanes in a flame. Special experimental equipment allowing to measure fire extinguishing concentration of gaseous fire suppressant having high boiling point is described. Experiments show that fluoroiodohydrocarbons are effective means of reducing the use of gaseous fire extinguishing agents based on fluorinated alkanes, which are greenhouse gases: in the presence of insignificant addition of iodized substance the volume of fluorinated alkanes required for the extinguishing decreases several times. Creation of mixtures with the content of iodized components higher than 5 mass. is impractical because in this case the iodine-containing substance will exceed safe level of its use from the point of view of toxicity

Показана нехватка современных веществ для газового пожаротушения, вызванная борьбой с глобальным потеплением. Описаны подходы к поиску перспективных газовых огнетушащих веществ (ГОТВ), применявшиеся ранее. Предложен новый подход и найдены с его помощью принципиально новые огнетушащие вещества, полностью удовлетворяющие современным экологическим и токсикологическим требованиям. The paper is devoted to investigation of perfluoro-isohexenes as new gaseous fire suppressants. The current situation in the field of fire protection with chemically active gases is analyzed. The problem of greenhouse gases replacement during fire suppression is discussed. The disadvantage of existing alternative agents is short atmospheric lifetime. It is also shown that the existing approach to development of new gaseous fire extinguishing substances is almost exhausted. New group of gaseous agents for fire suppression - perfluoro-isohexenes - is proposed based on new approach. These substances are non-toxic and have very short atmospheric lifetime. Two types of experimental equipment were used in this work to investigate properties of aforesaid substances as extinguishing agents. It was implemented to determine flammability limits of gaseous mixtures and fire extinguishing concentration of gaseous fire suppressants having high boiling point. It was shown that perfluoro-isohexenes are non-flammable and their extinguishing properties are substantially better than properties of the nearest equivalent - perfuoroethyl-isopropylketone. These results are discussed from the point of view of the features of transformation of considered fire extinguishing substances in a flame.

Ecological properties of perfluorohexenes are studied in the paper. C6F12 atmospheric lifetime of 17.4 days was obtained using one-dimensional photochemical model. It was shown that the substance disappears in the atmosphere due to its reactions mostly with OH radicals. Absorption spectra of C6F12 in the short-wavelength ultraviolet region of 110-200 nm and in the infrared region were calculated using the Gaussian 09 quantum mechanical calculation program. Calculations revealed that C6F12 has significant absorption in the infrared region but due to short atmospheric lifetime of this substance its global warming potential GWP is as low as 28.64. Ozone depleting potential (ODP) of perfluoroisohexenes is equal to zero due to short chain length for the chain processes of ozone destruction involving fluorine atoms. Thus, perfluoroisohexenes with their zero ODP, short atmospheric lifetime and low GWP meet all modern environmental requirements and can be considered as effective substitutes for high-GWP HFCs in fire suppression.

It is shown that for determination of tanks stability to explosion of gas-air mixtures it is important to calculate explosion pressure in dynamics (at filling or emptying of the tank) depending on level of filling. A method for determination of explosion pressure in the tanks is proposed, taking into account the dependency of the volume of hazardous area from time. It is shown that the formation of the zone of explosive concentrations is divided into three types depending on the ratio of saturated vapor concentration to the lower and upper flammability limits, and for RVS-5000 tanks the type II is characteristic. The results of calculations of explosion pressure from the time of evaporation taking into account the volume of explosion-hazardous area for a tank of 5000 m3 are presented.