Spiral external escapes and evacuation chairs

[Demontim]

Scenario: Two similar buildings of three floors, steel frame with brick walls panel cladding (cladding not an issue) and a barrel roof, built in late 90's in accordance with ADB so MOE is ok but...

Both have a central protected staircase along with an external spiral at either end (the larger building has two additional internal protected staircases equidistant rom the centre and externals), are predominately open plan and all staircases are provided with refuges and comms.

Question: Is it reasonable to just provide standard Evac chairs and only utilise the internal stairs or do chairs with the capability of being used on the external spirals need to be provided?

[Fire Monkey]

What are the travel distances?

I have not seen an evac chair that is designed to be used on a spiral staircase - they tend to be on rubber tracks that glide down on the stair nosings. On a spiral staircase there would need to be a twisting action and I can't see how that would work with treads - surely they would just jam due to friction. Also the gradients of spiral stairs tend to be greater that what evac chars are designed for. There are other ones that are designed to be carried by two people but just think of trying to carrying someone down - that can't be safe and they may be too narrow to turn the chair as well.

[Demontim]

The chair works on a similar principle to a stair climbing barrow (3 wheels each side), but has a small bogey wheel which locks the mechanism preventing forward movement when it loses contact with the tread surface. You then rotate the chair around using the handles (approx. 1.5m) as levers until the bogey regains contact and then continue to move forward before repeating the process on the next step (its best to come down the centre of the staircase rather then the widest part in order to get enough rotation).

[Animal]

Is the evac chair suitable for all forms of mobility impaired disabilities?
Is any EVC in place?
I assume there are no members of the public in the buildings.

[Phoenix]

Is there a lift in the building?  If not then there is no problem.

However, assuming that there is a lift (otherwise I guess you wouldn't have asked the question), it's what Fire Monkey said, it depends on the travel distances.  People with impaired mobility will be in dead ends while able bodied people next to them will have choices on which way to go.

In the smaller building, if it's only about 18 - 20m from the furthest point to the storey exit then this is ok.  It's similar in the larger building for those parts of each floor that are beyond the intermediate protected stairs.
 
Also, in the smaller one, if the travel distances are ok to accept the protected route as the only way out for mobility impaired people, the stairs will be very important and will need at least 'door and smoke' protection if not lobbies.