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Abstract. Computational fluid dynamics (CFD) simulations were performed for a 12.20 m wide x 30.49 m long barn located above a full-sized manure pit with a fully-slotted cover. A tunnel ventilated barn configuration was studied to determine how manure pit-safety ventilation fan configuration (location and flow rate) affects the distribution of hydrogen sulfide (H₂S) gas in the barn airspace during a barn and manure pit-safety ventilation event. Simulation results were analyzed to determine the affected area in the barn and the duration of time when the concentration of H₂S gas was 50 ppm or greater, the maximum H₂S concentration in the barn airspace, and how much time was required to reach safe H₂S gas entry levels in the manure pit. During pit-safety ventilation, the maximum concentration in portions of the airspace within tunnel ventilated barns was equal to the initial manure pit H₂S concentration (C₀), requiring animals and personnel to be evacuated from those zones when C₀ ≥ 50 ppm. This work demonstrates the potential for evaluating alternative pit-safety ventilation configurations to reduce the need for animal evacuation from portions of barns located above positive pressure safety ventilated manure pits. The protocols developed for this study can be used by engineers when designing and evaluating manure pit-safety ventilation systems to reduce the risk of creating hazardous conditions inside the barn during pit-safety ventilation.