You have nothing to be worried about. Here's why:
1. At the voltage/amps that flexwatt runs at electricity on it's own cannot catch a rack on fire.
2. The copper bars are insulated with a sheet of plastic which should insulate them from anything that the flexwatt comes into contact with.
3. Melamine is not a conductor of electricity. This means that even if the flexwatt's plastic coating is damaged and the electrical pathways come into contact with the rack absolutely nothing will happen.