Example—Process Jet Fire

The heat release rate, Q, of the resulting fire is calculated [Equation (5-17)] as  

Assuming relatively still air, the flame height, L (m), is first calculated [Equation (5-18)] as  

The ratio of L/D (flame length to the gas exit diameter) is calculated and found to be 139, which is less than 200. Therefore, the jet flame is buoyancy-controlled and the calculated flame length of 13.9 m is appropriate. 

With aflame length of 13.9 m, the jet flame will impinge on the steel structure overhead. Consequently, the steel will see high convective and radiative heat fluxes on the order of 200 kW/m. Since the structure will be exposed to direct flame impingement, the expected failure time would be 3-4 minutes (Table 5-7) or less due to the high heat flux from the jet fire, depending on the type of steel structure and design factor of safety. 

To estimate the impact of the jet fire on process equipment located 20 m from the source, the point source model can be used to determine the incident heat flux from the jet flame to the equipment. The incident heat flux per unit surface area of target, q is calculated as follows. 

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