Smoking shelter outside fire exit

[Guest Paul]

Hi,
One of the tenants on an industrial estate we manage has erected a smoking shelter immediately outside their fire exit door, this door exits onto the fire escape route for the terrace of units. By way of explanation, they are the tennant on the end. This doesn't sit right with me - please can you let me know if this is allowed and if not under which specific regualtions/guidance?
Many Thanks,
Paul.

[Tom Sutton]

Does the smoking shelter restrict people using the fire escape route and by how much.