Critical values of exposure time of сarbon monoxide effects on human during the fire in premises

The aim of this work was to create the mathematical model for calculation of the carboxyhemoglobin concentration in the human blood in case of fire. Tests were conducted in conditions of variable CO density, typical for the initial stage of indoor fire, and increased pulmonary ventilation rate. It is offered the criteria for determination of the critical values of fire duration under the terms of safe evacuation and people rescue. The methods of theoretical analysis of the content of carboxyhemoglobin in the human blood and calculation of the carbon monoxide (CO) concentration, in conditions of fire in premises, were used during the experiment. The mathematical model was created taking into account the concentration of CO in the inhaled air, the mass of hemoglobin in the blood, the pulmonary ventilation rate, the volume of respiratory dead space and the CO exposure time. Critical time of safe evacuation for people under the effects of CO is accepted when the content of carboxyhemoglobin in the blood reaches the 20 % by mass (minor poisoning). Critical time from the initial stage of fire and until the moment when people, which stay in premises without protection means against CO (respirators, gas masks, self-rescuers, etc.), and, with high probability, are unable to leave the premises independently, is accepted when the concentration of carboxyhemoglobin in the blood reaches the 50 % by mass (moderate poisoning). The model premises were in the form of parallelepiped with dimensions (m): 4´5´3, 4´5´6 and 24´12´3. As combustible materials there were used the wood building materials, PVC sheath of cables and transformer oil. The results of numerical experiments on determination of the carboxyhemoglobin concentration using the analytical solution of the integral calculation model for the thermal and gas dynamics of fire are presented. The estimated values of CO exposure intervals prior to various degrees of human intoxication are obtained. The comparison of critical durations of fire (considering CO effects), obtained using proposed model and existing approach, is made. The critical duration of fire, obtained using proposed model, was significantly greater than the corresponding value determined by existing methods (for example, in case of burning of the transformer oil in the room with dimensions of 4´5´3 m). The main conclusion is that existing scientific and regulatory literature contains the calculation methods for critical duration of fire, considering CO effects, which may lead to qualitatively and quantitatively wrong results. The proposed criteria for determination of the critical values of CO exposure time and the calculation methods for the content of carboxyhemoglobin allow defining the time of safe evacuation and people rescue more reasonably than existing approach.

пожар, моноксид углерода, критическое время, карбоксигемоглобин, интоксикация человека, время воздействия СО, fire, carbon monoxide, critical time, carboxyhemoglobin, human intoxication, CO exposure time

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