And how would officials know, a nuclear reaction is happening?
I suppose they would transport the reactor to the White Sands Missile Range and apply every known diagnostic instrument to determine whether a nuclear reaction is occuring, and what sort of reaction it is.
But you miss the point. You really miss the point! Suppose there is no evidence that a nuclear reaction is occuring. In that case, the energy is appearing out of nowhere, apparently in violation of the conservation of energy. That is totally inexplicable. For all anyone knows, the unknown conditions that cause energy generation might suddenly change and allow, say, 5 orders of magnitude more energy production. Kaboom! Since cold fusion reactors have exploded, and since they have no chemical fuel in them, this cannot be ruled out.
Once many experts think they understand where the energy is coming from, and once they can assure the public the energy level will not suddenly increase to catastrophic levels, then it will be safe to use the machines.
Again, I do not think Rossi's large machines produce any excess energy. I base that on Rossi's own report and his testimony in the lawsuit. However, if they do produce energy, we cannot depend on Rossi, and Rossi alone, to assure the machines are safe.