Many of the res-care premises that I come across do not appear to have sufficient staff at night to carry out an effective evacuation - even to an adjacent protected area - and so the idea of losing one or more members of staff to stay with residents would be impossible and may not have been thought through from a risk assessment perspective. Of course this may be a wealthy provider, well able to supply one member of staff for each resident, plus additional staff to respond to the alarm, investigate the zone, coordinate staff placements, liaise with the fire service and carry out any other associated duties... but I suspect not.
As stated in the previous posts, if the protection is required to the appropriate level, including additional protection if the nature of the occupants dictates it, then staff should not need to be set aside for this task.
Have you considered the use of a sprinkler system as a further risk reduction measure?
Paul