A hydrogen fuel cell is a device to oxidize hydrogen to produce electrical power. Maybe you mean hydrogen pressure vessels? Well-ventilated low-pressure LH2 ta

A hydrogen fuel cell is a device to oxidize hydrogen to produce electrical power. Maybe you mean hydrogen pressure vessels? Well-ventilated low-pressure LH2 tanks are not especially dangerous. What would be dangerous is enclosing them in a poorly ventilated space, such as an aircraft cabin.