From my days working in Telecommunications and IT, where I had responsibility for staff - I was introduced to the Act of Parliament that set out safe working conditions and temperatures for staff. Then I was trained as a Fire Marshall. In most of the buildings where I worked, I was part of the team that checked for safe evacuation of staff and customers in a fire etc. as I had to provide emergency communications equipment. In the early 1980s I was involved in numerous fire drills and very much for real on one occaision due to an IRA bomb.
Those stairwells do not need a major event like a fire - they only need someone to lose their balance at the top, or faint and fall forwards ...