I work in an independent retirement living complex over 50 vulnerable people.  As they couldn't go into the communal lounge where before COVID  they did their exercises they decided to have an exercise class in the car park but couldn't understand that when I said they couldn't  do it again all hell broke loose.  

they still don't get it.  Any ideas as to how i can make them see it is dangerous.  They wouldn't understand the risk assessment even if I showed it.

I am assuming you work in a safety-related capacity as you refer to 'the risk assessment' but I don't know what risks this covers. Why is this dangerous? Is the car park busy? All of it, all the time? Or is this Covid related? It's not clear to me where the danger is coming from. As said, close the car park or a section of it. 

Your residents are private citizens entitled to make decisions for themselves, even if those decisions may appear unwise. The benefits of an outdoor exercise class include improved physical and mental health, vitamin D from sunlight, fresh air, birdsong, freedom . . . Please find a way to say 'yes' not 'no'.

the issues that immediately stand out (and not all).

Weather (cold and too hot)

car park needing to be closed off (and not just some cones as they might not be seen) - if its closed will this move the parking problem elsewhere and cause more risks?

getting the clients to and from the car park (access, confinment in corridors etc)

will any be left alone whilst others are escorted out (could wander off)

first aid requirements

what if they need the loo, who takes them and what about the others who remain, are they alone?

jsut a few thoughts

I would start by asking why they cannot go in to the communal lounge? They were there before Covid, they are in an independent living complex - essentially an island away from the general population.

Is it because some jobs worth is insisting these people who effectivley live together must separate by 2m in accordance with government guidelines for separate households?

I too am with the residents - with less travelling and social interaction why would the car park be so busy as to be dangerous (unless it is also used by a take-away drive through that has just re-opened).

The fact the residents are rejecting your proposal tells me they have the mental ability to consider consequences, if they did not I doubt they would be allowed to be in independent living.

If your audience cannot understand your RA as written have you considered you may not be the correct person for the job?

Independent living is exactly that an opportunity away from a closed institution to develop by experiencing life and its many risks.

 Kinning- can you clarify why they cannot use the lounge in smaller groups and what the problem is with car park?

We need to think differently about how we do things, particularly when a group need to meet in real life not just via a screeen. for example  we have a small communal garden which we have just re-designated as an out door meeting room ( when not raining) as it seemed an opportunity to get more than 3 people together ( small meeting rooms).

I have also suggested that the nearby park is used for 1-2-1 meetings ( maybe walk and talk).

Using a carpark seems like a good idea unless there are safety concerns that cannot be mitigated.