How is the fire hazard class of the mixed gas determined?
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How is the fire hazard category of a mixed gas determined? Nitrogen is produced by pressure swing adsorption, with oxygen being released directly. Oxygen is classified as Category B; then how is the fire hazard category determined for such a mixed gas environment? Well, pure oxygen is classified as Category B; then what is the fire hazard category for 50% oxygen?
1) According to GB 50160, the Fire Protection Design Code for Petrochemical Enterprises, the fire hazard classification of combustible gases is determined based on the lower explosive limit of their mixtures with air; values below 10V% correspond to Class A, while values equal to or above 10V% correspond to Class B. Therefore, to determine the fire hazard level of a gas mixture, it is most important to first find out what the lower explosive limit of that mixture is compared to air. 2) The lower explosion limit for each type of pure substance can be found in relevant experimental literature. The explosion limit of a mixture composed of various flammable gases can be calculated based on the explosion limits of each component. Using Le Chatelier’s principle, the formula for calculating the explosion limit of the original mixed flammable gas is as follows: Lm = 100/(φ1/L1 + φ2/L2 + φ3/L3), where Lm represents the explosion limit of the explosive mixture in %, and L1, L2, L3 are respectively the explosion limits of each component in the mixture in % ； φ1, φ2, and φ3 represent the concentrations of each component in the mixture (%v), respectively. 3) It is basically impossible to eliminate the risk of fire and explosion in the process flow by controlling the concentration of flammable components. Therefore, controlling the Limiting Oxygen Concentration (LOC) is commonly used to prevent combustion and explosions. The calculation of the limiting oxygen concentration for combustible gases requires simplifying the gas composition by considering only the proportion of combustible gas components, thereby normalizing multiple combustible gas concentrations. The limiting oxygen content of the combustible gas after mixing can be determined using the following formula: (LOC)mixt. = ∑XiRi / (∑XiRi/(LOC)i). The LOC values for each combustible component are determined according to Table 5 in Section 5.1 of GB/T 27862-2011, \"Test methods for classification of chemical hazards – Combustibility and oxidizing capacity of gases and gas mixtures\".
I didn’t understand; study hard*:):)