Permissble gap around the bottom of a fire door

[Suttonfire]

Hi All,

I have seen the above discussed before, but can not find any consistent guidance. Would anyone be able to confirm if there is any current guidance concerning the maximum allowable gap at the bottom of a fire door. In particular I am interested in the front entrance doors to blocks of flats (to which the bottom edges have not been fitted with any form of seals).

Thanks

[Tom Sutton]

BS 8214:2008 Code of practice for fire door assemblies is the relevant standard and it states,

"9.5.3 Under-door (threshold) gaps

Under-door (threshold) gaps should be in accordance with the manufacturer’s installation instructions for the particular doorset design. When fitted, smoke seals should give an even contact with the floor but should not exhibit significant increased frictional forces that could interfere with the closing action of the door (see BS 5588-112))."

I would be surprised if any final exit door required smoke seals.

[jokar]

The ASDMA guide, free download will give a specific figure for this for internal doors.  Fire exit doors to external aresa will probably not be covered as indicated by the above post.

[Paul2886]

I don't think the first post was referring to final exit doors. The doors from flats discharging onto the means of escape could be referred to as internal doors and may need to meet certain standards

[Tom Sutton]

The above comment says "see BS 5588" but as you know that has been superseded by BS 9999 which says,

A fire door having suffix S, should either have a leakage rate not exceeding 3 m3/h per metre, when tested in accordance with BS 476-31.1 with the threshold taped and subjected to a pressure of 25 Pa. When installed, the threshold gap should where practicable be sealed by a (flexible edge) seal either with a leakage rate not exceeding the above or just contacting the floor, giving an even contact with the floor but not interfering with the closing action of the door. Where this is impracticable, the threshold gap should not exceed 3 mm at any point.

When other methods of smoke control are provided in buildings, this might not be applicable, depending on the design of the system. Smoke leakage control can be applied to non-fire-resisting doorsets.

[Dinnertime Dave]

I was asked this question during an inspection a while back, the answer varies with whichever guide/ standard you use -

BS 8214:2008 - as above
Building Control Alliance - edge gaps to the jambs 4mm, threshold gaps to unfinished floor 22mm and to the finished floor 10mm
TRADA recommends 10mm

However, from a practical point of view as small as possible, but theoretically could have effect on an ventilated fire forcing fire gases under the door.

From a risk assessment point of view I would look on its position within the building, if it is a flats/storerooms/plant rooms door it may have a greater fire loading behind them than cross corridor or staircase door. And untimely is any relevant person likely to be at a significant risk.

[Tom Sutton]

Another to add to the list BS 4787-1:1980 Internal and external wood doorsets, door leaves and frames Specification for dimensional requirements.

Also another consideration is, are the doors FD or FDs because the latest guidance recommends fire doors with cold smoke seals should fit them to the threshold (bottom) of the door, if it is possible, if not the gap should not exceed 3 mm and yes you can buy special ones for this purpose. I think FD doors are a different matter, because the air flow will be travelling from the protected side to the risk side to feed the fire.

[Suttonfire]

Thanks for the responses.

Just to clarify, in my original email I did mean to refer to individual flat front entrance doors, rather than final exit doors.

I think that if we were to treat anything beyond a 3mm gap at the bottom of a door as unacceptable for existing doors, then a large number of the 'notional' fire doors (which do not need to be FD30s - i.e. flats in lower rise blocks) which we are guided to accept under the Purpose-built flats document would not be acceptable.

However, I would be very uneasy with recommending that an otherwise decent notional fire door at the entrance to a flat should be replaced/altered as the gap at the bottom of the door is 6,7 or 8mm.

What are peoples views on this?

[Tom Sutton]

I believe the final exit door do not need to be fire resistant and they are only there for security purposes therefore the threshold gap is irrelevant.

I remember being told many moons ago there is always an inch layer of fresh air at floor level. If this is not a myth then is the threshold gap so important and has there been real life research carry out?

[Paul2886]

Me thinks some should read the original post so we can stay focused on the correct issues.

[Dinnertime Dave]

However, I would be very uneasy with recommending that an otherwise decent notional fire door at the entrance to a flat should be replaced/altered as the gap at the bottom of the door is 6,7 or 8mm.

What are peoples views on this?

Remember the phrase "is any relevant person at significant risk" I would suggest strongly that there isn't the doors should be identified but nothing needs to be done until any future replacement is due. The same is true with letter boxes. I see improvement notices from housing officers telling the RP to change the door or have intumescent material fitted in them. Total waste of the RP money, most fires in flats won't activate the the material and let's face it 10 mins after the fire starts the fire service opens the door to fight the fire.

Let's change the above scenarios around - I send you a Notice telling you to change the doors because of a 12 mm gap not 10 or 3. What would your reaction be?

[Owain]

I believe the final exit door do not need to be fire resistant and they are only there for security purposes therefore the threshold gap is irrelevant.

What about arson risks? A gap under an external door could allow ingress of liquid accelerant.