Assuming this question relates to the roof of the enclosure, there are no design criteria on this topic to the Panel’s knowledge. The key to the design would be ensure that the exhaust ventilation inlet is located at the highest point and that there are no pockets that can capture hydrogen (restrict flow to the exhaust inlet).

Information on Toyota’s repair garage approach is available at Toyota Mirai Hydrogen Fuel Cell EV- Repair Garage Design & Safety. CFD modelling could also be used to anticipate the flow of released hydrogen based on either natural or forced ventilation.