Physical Danger
Zap. Pow. Bang. Slash. Kablooey. These and more are the sounds you will come to dread working the life of an engineer. They're sounds that will accompany the moderate-to-severe amount of pain that you'll go through on a seemingly endless basis. Fuel cell engineering is a research & development specialty, and both the R and the D have dangers involved.
Such hazards will be all around you. The various tools you'll use, from the simple hammer to the complex and scary power cutting tool, will have the ability to change your life if you're not careful. Three hundred volts of electricity may not sound like much, but it most certainly feels like something. That doesn't even take into account the experimental prototypes you'll be building with your own hands. While no one wants their project to "blow up in their face," for you that is an actual, literal possibility.
You'll want to pay special attention to the rules you learned in shop class (or from Bob the Builder). This means using things like safety goggles, gloves, slip-proof shoes, and any other safety equipment intended to prevent your mistakes from becoming painful mistakes.