From my limited understanding, Fire Exit Doors and Emergency Exit doors are demarcated as doors that are one way.
Management choosing to lock off door poses a concern whether or not the nearest exit in case of emergency is less than 20sqm away.
Thats why it is always recommended to have at least 2 ways of escape: (In this case)
1) Emergency Fire Escape
2) Normal entry exit to and from your own place (resident's access)
In the case that there is a fire that is cutting off the resident's regular stairway access out of the building on their level, they'll all have to be trapped?
That doesn't make sense. Any building plan drawn up with their emergency evacuation exit doors usually use that as a main route or alternative route of escape.
Check with them what the fire evacuation plan is, clarify that that particular exit door will not be used in case of an emergency.
Get them to confirm in writing then you check with SCDF.
my 2 cents