I?ve come across similar issues in residential care homes in England where residents, who pay for their own rooms and care, refuse, and in some cases are unable, to go outside to smoke. The governments of all of the country?s of the UK have made specific exemptions to their respective smoking prohibition legislation. These include residential care homes, prisons, mental health units, adult hospices and, some Hotel rooms.
In short, the rules are that the smoker is allowed to smoke in their own demise but not in common parts or shared areas. If in a prison cell, inmates are only allowed to smoke if they have their own cell or share a cell with another smoker.
The one work place were the employees are still permitted to smoke is the theatre where actors can smoke on stage during performances, if the performance demands it in the script. They are not however permitted to smoke during rehearsals.
In my experience Risk Assessments for smokers tend to focus on the health issues for both the smoker and members of staff who have to interact with the smoker. It is rare to find a risk assessment that looks at the fire risks arising from smokers and the use of smoking materials in confined places within larger premises.