In a house to flat conversion, where the front doors to each flat (FD30's) are technically internal doors, can I fit a door security chain / bar and if so would this need to be fire rated, as it's inside each flat? I've fitted thumb turn locks to each door, but would like some form of extra security for each tenant if this is allowed.

Thanks

The flat entrance door as well as being a fire resisting door is essentially a security door too because it opens onto the common area. Therefore a face-fixed security chain like the one in the image below below is allowed.

It does not need to be fire rated because its purpose is solely security and it has no contribution towards the fire separation qualities of the door BUT it must not interfere with the self-closing action of the door.  

You are right to fit thumb turns on the inside so as to aid safe escape from the flat in an emergency.

Would it be acceptable to fit the chain at a higher than normal height to stop small children unlocking flat door via thumb turn. Allowing the parents to engage the chain whilst inside flat to stop children from opening font door when their backs are turned?

A query that’s come up recently by a few tenants who have young children who can open the front door via thumb turn when their old door had a night latch and deadbolt lock. 

The chain, as described with the image above, could be fitted at approx. 1500mm above floor level.