Originally Posted by
ThePenIsMightier
For home heating etc, it's not about pressure, at all. It's about molecule size and something called hydrogen enbrittlement... H2 is the smallest and lightest molecule on earth, so it really really wants to leak out of the horse shit, threaded connections in and around your house. It also can actually migrate into the microscopic lattice structure of carbon steel and mess it up, basically making it less bendy and more breaky. (Ultra Science terms).
The trial testing of using supplemental hydrogen are only going to start at 5% and if that's successful, they'll try 10%. They know that they can't go much higher than that without the risk of leaking and pipe damage becoming too high.