The gas will be fine, it'll not be flammable. German airships like Hindenburg used hydrogen because helium (that it was originally intended to use) was relative

The gas will be fine, it'll not be flammable. German airships like Hindenburg used hydrogen because helium (that it was originally intended to use) was relatively rare and there was an export ban from the US (who were producing and holding the majority of what was available). Modern devices won't use flammable gasses. The problem will be the heat for a different reason: changing the dynamics between the gas in the device and the atmosphere inside making buoyancy much more difficult to maintain. Also, the engines used to move them around might be susceptible to the same concerns as helicopter engines & blades.