"At risk" is a strange term, at risk of what, who, when?
In my opinion it should be something like
"potentially dangerous, use at your own risk"
Then a disclaimer something like
"The engineer who attended to this boiler has found potentially hazardous elements. This gas appliance should be repaired as soon as possible as it may develop into a more serious problem"
Immediately dangerous is self explanatory and could even be labelled
"This is a dangerous gas appliance and has been isolated from the gas supply for your safety"
I'm lucky in that I generally work for regulars but if your working on large contracts, for the council for example, I bet you get some very awkward situations.
Its bad enough just trying to explain how a filling loop works!