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FIRE SERVICE AND GENERAL FIRE SAFETY TOPICS => Fire Safety => Topic started by: Tom Sutton on January 19, 2016, 03:04:54 PM
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I had inquiry about Automatic Release Mechanisms (ARM), Dorgard in particular, did a little research and found out, providing they are category A then they can be used anywhere subject to a fire risk assessment. I had a little problem trying to find out what category Dorgard is, it appears to be cat C, but even that you can use them on staircase enclosures providing it is not a single staircase. Are ARM's used extensively?
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Yes all manner of ARMs are very widely used. Many people who install them are much less diligent than you Tom and have no awareness of BS7273-4. You will find Dorgards in many buildings with no automatic fire detection including local authority premises. A nearby local comprehensive school has them on fire doors protecting a single staircase without any detection at all (manual break glass alarm system), a nearby private school has more of the same and the local council uses them in its main buildings to hold open the alternative exit doors from the function rooms, again in a building with a cat M alarm system.
You can tell em but they can't see the problem!
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There is also a Dorgard X
http://vserver.firecoltd.com/fire/dorgardx.aspx (http://vserver.firecoltd.com/fire/dorgardx.aspx)
Supposed to be category A when transmitter is hard wired into the fire alarm.
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Interesting the original DorGard which was a Cat C Product for years was re-classed as Cat B (now Standard) a year or two ago increasing the options for it's use.
Whilst recent years have seen them used in Cat M premises the phenomenon isn't new, I've seen traditional hard wired magnetic hold opens in similar situations.
Whilst it's important to use the right category device for the risk I'd still rather see a correctly fitted DorGard with a correct category of FD&W system (& proximity of sounders) than a door wedged with wooden wedges, extinguishers, etc (consigned half a dozen to wedge heaven today...)
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Tam, Dorgard is not Cat C.
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I said it appears to be cat C because I could not find its category designation, except one that stated cat C but now AB says was re-classed as Cat B (now Standard) and DD with his link the Dorgard X is cat A, thanks to everybody for your help. When ARM's where first introduced there was a great distrust which has now completely evaporated, now they are using Dorgards in premises with only manual BGU's not much use for smoke control and fire come to that, how things have changed not to the good always.
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Tam, if there is no AFD, it is irrelevant as to what sort of door hold-open device you use.
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Colin my point is if there is no AFD you shouldn't use any AMR's, which appears to be happening.
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Yes Tom you are right but it has been happening for a long time and as AB points out with magnets as well as other devices. Till BS7974-4 was published there was little definitive guidance on such devices, where they should be used and how they should interface with an alarm.
Perhaps the Dorgard and other similar acoustically triggered devices, by their simplicity and free availability, tended to be more likely purchased and installed by building users without regard to the provision of detection though.
For the benefit of others reading this forum Without automatic fire detection - ie smoke detectors either side of the door- such devices have only the smallest of benefits compared to a wedge. All things being equal the door should close when the fire alarm sounds - ie its a wedge that removes itself - but until the fire is detected by a human and the alarm is operated there is no barrier to smoke and fire spread through the door so the open door provides no protection to the means of escape.
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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.
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Lin, don't tell them that you are destroying the fire door replacement industry!!
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They are normally fitted to improve freedom of movement around the premises e.g. Care homesetc., obviously this freedom of movement isn't so important at night when the residents are tucked up in bed or no occupation I.e. Schools, and therefore if the doors are then shut as they should be then the warping of the door is not such an issue I.e. "Automatic fire door keep clear close at night" signage.
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Big Al, having detectors only immediately on each side of the door went out with old fashioned concepts like friendly and helpful enforcement.
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Thanks Colin my comments were aimed at the 100 or so casual users of the forum who are browsing at any time and who are more likely to just buy a Dorgard on eBay and screw it a door without thought.
Bearing this in mind I would be grateful if you could suggest a form of words to replace mine without going into the nuances of BS7273-4?
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Big Al, having detectors only immediately on each side of the door went out with old fashioned concepts like friendly and helpful enforcement.
When did all this happen Colin?
So, what's the new minimum benchmark standard for a single Dorgard on a cross-corridor door in a small single storey office with two-directional escape?
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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.
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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.
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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?
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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.
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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.
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Big Al, that is what the standard says.