What is a significant hazard of using hydrogen-oxygen fuel cells in vehicles?

The significant hazard of using hydrogen-oxygen fuel cells in vehicles lies in the flammability and explosive nature of hydrogen. When hydrogen gas is mixed with oxygen in the right proportions, it forms a highly combustible mixture. If ignited, this mixture can lead to fires or explosions, posing a serious risk during operation or in the event of a leak.

Hydrogen's low ignition energy means that it can ignite easily from a spark or a heat source, making safety precautions critical in the design and operation of hydrogen fuel cells and their associated storage systems. This hazard necessitates robust safety measures in vehicles powered by hydrogen fuel cells to mitigate risks and protect both users and the environment.

While other options mention factors related to hydrogen, they do not encompass the immediate danger posed by its flammable and explosive characteristics. Understanding this risk is essential for ensuring safe application and widespread acceptance of fuel cell technology in transportation.