Smoking would be bad because the fire would be amongst the tanks, but you'd have to open it almost on top of the motor to cause a fire that way, because the fire in contained, and the hot part (the exhaust) is under water. Plus the motor is not located where the people/supplies are.

So simply don't carry the tank over to the motor and open it there, and don't smoke. Even the most basic of safety practice would make this not a problem.

Do you not carry any fuel onboard? Hydrogen is safer than gasoline, yet people carry it without a second thought.