Must we follow heat pump instructions?

Do we need to follow ALL the instructions when it comes to R290 heat pumps?

R290 (propane) is fun stuff. It's heavier than air. There's a very good reason that LPG (propane) cars aren't allowed in underground car parks or the lower decks of ferries. Korean YouTube explains all:

https://www.youtube.com/watch?v=j9H45wmBlf0

(and that's just combustion rather than detonation of a fuel air mix)

Some heat pumps use R290. They include instructions on "protective zones" around the heat pump where there musn't be source of ignition (fair enough) or indeed windows/doors that might allow R290 inside a building.

This seems a little excessive given that you're allowed to pipe unlimited quantities of R50 (methane) into a house controlled by little more than a human controlled mechancial valve; and you're allowed to store 30 kg of R290 inside your house in two 15 kg cylinders; and you can have as many aerosols with R290/R600 (butane) in your house as you like; with an LPG fuelled vehicle parked in the garage.

If it's deemed safe enough to pipe natural gas into a house or store are much propane inside the house as you like (as long as it is little tins); it seems a little excessive to require heat pumps be located such that extra R290 really can't get inside the building.

Fair enough if you have a basement. Although legal to fill that with methane/propane/butane it would definitely be dumb. Perhaps fair enough if the heat pump is above a window and it could conceiveably leak a material quantity of R290 into the house if you speared a hole through the evaporator.

But restricting placement next to ground floor doors? This doesn't feel in the slightest bit proportionate given the volumes involved.

1) Where do these instructions come from? (is there a standardised risk assessement that the manufaturers are copy pasting from that's worth reading?)

2) Do we actually have to follow these? The MCS process appears to allow deviation from manufacturer instructions where justified. Has one every heard of "sorry; that clearance requirement is excessive for properties without a basement; at least until such a time as natural gas supplied are banned alongside aerosols with hydrocarbon propellants..." or words to this effect being presented?

I ask because, as one of many with a pish piddly little terrace house (6 metres wide) one can't actually put an R290 heat pump at the front or rear of the house thanks to these (3.1 metre width) clearance requirements.

The option to overrule these, citing far greater idiocy that's clearly still considered an acceptable risk by the gas industry, would be useful.

Adam Chapman Brendon Uys TMIET Graham Hendra Damon Blakemore et al - I iamgine you must have asked this question of the vendors at some point?

Pertinent excerpts from MIS3005 below:

Note the "should" in 5.3.1 here - this isn't mandatory if reasonable justirication can be given - and is key to R290 by the back door.

Note also the arrogance of clause 5.3.2 - what the authors of the MCS standard state is deemed true without any proof; whereas doing what the manufacturer requires needs proof of performance/safety/durability.