I have a client who has a 3 storey office building with several fire escape staircases. Each door leading from the office space has a lock with thumb turn operation for security as it is a multiple tenancy building. We have been asked to find out if a double throw lock is acceptable in this application. I am struggling to find an answer and wondered if you could help and point me in the direction of some literature that I can send her.
Many thanks
Paul

I am not sure about the type of lock you are proposing to install but as it is a fire exit it should comply with BS EN 179:2008. 

The standard says, the handle shall release a door at all times from the inside, when the premises are occupied, in less than 1s, by one single hand operation only  and not require the use of a key or other similar object. It should enable immediate exit from the inside at all times and not be hindered by any additional locking such as a deadbolt or outside access device.

There is a lot more in the standard but if it meets the above criteria then it should be satisfactory to any enforcing authority.

heck out http://firecode.org.uk/Code_of_Practice_hardware_for_fire_and_escape_doors.pdf

 

I'm assuming it's the thumb turn escape mortice deadlock where you have to complete two full rotations of the turn to unlock the door instead of one or less.

I don't like these personally as it's easy to think the door is locked and the turn failed to release the lock if you don't know how to open it.

Depending on the location of the door, signage and the number & type of people using it the thumb turn type lock remains acceptable subject to risk assessment, although certain storey and final exits do require an EN approved exit device.