This really winds me up. A CO alarm can only be used for the internal safety of those on board. I was repeatedly told by the examiner of my boat this year that the BSS is there to prevent my boat causing issues to others like catching fire, so like others have said here, this seems yet another example of nanny state mission creep. BUT the one thing that can really ruin your day and of those around you is if the boat blows up because of an internal gas leak. I come from the yachting world and have never sailed a boat in recent years without a gas alarm. They are cheap and easy to fit. I normally put the sensor as low as possible and near the cooker. When I mentioned this to the examiner he had no idea what I was talking about. The reality is that all the incredibly detailed BSS gas safety precautions can't stop a leak happening if it wants to. The only way to find out is to light a match (not a good idea) or fit an alarm. Heres a simple one: https://www.force4.co.uk/pilot-single-sensor-gas-alarm-12v.html?sqr=gas alarm&
I'm not trying to widen the debate or suggest that BSS should adopt these merely using it to illustrate, to my mind, why the BSS is losing its way.