Panteras competing in the early days had to run cut-off heater flow valves because of the number of failures and injuries to drivers from rupturing that little 3" heater hose under the dash. High rpms on overage hoses were the cause. Passengers have been injured as well depending on how the hose blew. Some owners didn't even realize there was a breakable hose down there.
We had to use TWO VISIBLE manual valves when competing because Tech Inspectors had no time to have you pull the firewall door and trace out the plumbing to be sure the valve(s) actually cut off the heater feed. Sure, one valve would theoretically be enough but again, Inspectors were often not Pantera owners. So electric valves were illegal and thus very uncommon.