I've just inspected a batch of FD60 fire doors in a large block of flats, each of which has been retrofitted with a single 15mm intumescent fire and smoke seal.  As far as I'm aware, unless otherwise stated on the fire certificate or if a certificate cannot be identified, FD60 default intumescent seal configurations should comprise either a single 20mm  or 2 x 15mm.

Does anyone know if historically, a single 15mm intumescent seal was ever acceptable on an FD60 doorset and if so, when did this change?

Thanks in advance.

In my experience FD60 require 20mm minimum (in one or two strips).  Are you sure they are FD60?  Sometimes 54mm thick doors are used for other reasons than their fire resistance properties.

Neil - apols for delayed response.  Yes I am sure.  By some miracle, given the age of these doors and the extent to which they'd been 'butchered', I found a couple with the following fire cert label intact (See attached).  I realise one has to be careful assuming that all doors in a residential block are identical but those that appeared original had certain aesthetic and constructional features that led me to believe they were from the same manufacturer.  Furthermore, some doors did have a single 20mm seal so I'm reasonably certain this is a consequence of contractors, who are unfamiliar with fire doors, assuming they were FD30 rated.

I just wanted to ensure, before I report back to the housing authority concerned, that 15mm seals on FD60 doors wasn't some legacy standard.

Thank you as always.