Automatic Release Mechanisms.

[colin todd]

It happened when I was still young, I-doll.  When CFOA, who may even have been CACFOA at the time it is so long ago, told people to stop putting detectors only on each side of the door but to at least string them down the whole corridor.  It was a rare moment when CFOA came up with something that showed an inkling of technical understanding; that's why it is so memorable.

This was reiterated but taken further in BS 7273-4 in 2007, though some members here like to pretend it doesnt exist and will do so until it bites them in the rear end big time.  Current guidance is string them down a non fr the corridor at half spacing (unless there is already an L3, L2 or L1 system). If the corridor is a protected corridor with FD 30S doors to rooms, you can keep to normal spacing as in L4.

[Tom W]

Is no-one thinking about where such devices are fitted?   If there's an overhead closer fitted then any hold open device should be fitted at the same level as the closer to stop the leaf distorting - anything fitted at the sole, be it wedge or Dorgard, has the potential to distort the leaf so that it doesn't fit the frame properly if and when it's closed.

BRE conducted some research on this a few years ago. Found plenty of warped doors equipped with magnets but found no doors fitted with Dorgard to have warped doors. The point being all retainers have the potential to distort.

The weekly and night time release features in built into Dorgard certainly helps relieve the potential for warping.

[kurnal]

OK I found Colin's response  typically cryptic so I will stick my head above the battlements and have another bash at this point.

If the building has a compliant  BS5839-1 , L1, L2 or L3 alarm system then BS273-4 accepts that the siting of detectors will be satisfactory to meet the requirements for the warning of fire and for the hold open devices to operate in a timely manner to protect the means of escape.

If there is not an L1, L2 or L3 fire alarm and detection system installed then the siting of detectors to control the hold open devices requires further consideration.  As a minimum an L5 system will be needed and BS7273-4 gives recommendations on the siting of these detectors in respect of corridors, staircases and in particular the proximity of detectors to door openings between corridors and staircases and between rooms and corridors or rooms and staircases. The standard refers to a  distance of 0.5m - 1.5m horizontally between  at least one detector and the centre line of the door opening fitted with the hold open device. 

Where there is an L4 system then in corridors that are sub divided by doors on hold open devices it's ok to have  non FR doors to rooms, (which may be open or closed at any time) but to ensure that the cross corridor doors close in a timely manner  the detector spacing in the corridor is reduced to 8m rather than the normal 15m. However if the door to a room on that same corridor  is a fire door and is fitted with a hold open device then  Clause 13.2.5 applies and detection should be provided in the room. 
 
Now as I see it in simple terms (which is where I came into this discussion) does this not mean  that detection should be provided  on both sides of any fire door that is held open using an electromagnetic or acoustically triggered hold open device?

[colin todd]

Kurnal, if the doors to rooms are FD, why do detectors need to be fitted in the rooms. That doesnt make sense. And the 1.5 does not always apply. You cant simplify it quite as much as you would like.  Why not give up and tell people to buy the wretched standard.

[kurnal]

I always thought the same but that's not what the standard says. Of course a taking risk assessment approach I would come to the same conclusion as you. My simplified approach was an attempt at advice aimed at those who would buy a Dorgard on eBay and fit it anywhere without thought.  Have come across this more often than I would care to remember.

[colin todd]

Big Al, that is what the standard says.