Deluge System

[Goodsparks]

Im involved with a number of works to a 20 year old Civic Centre building. Its a four storey building which houses around 800 staff, but has a large central full-height atria. The curtain walling between the internal offices and the atria is not FR and from what I understand, the deluge system was installed as an engineered solution to this. The system is configured with a 125mm wet rising main which feeds eight 'zones' of pipework with open heads positioned every couple of metres in the atrium over the glazing line. The water is held back by a 24v solonoid between the main and the first sprinkler head in each zone.

Thats the easy bit...

Within the offices there are 10 'zones' of of 1/2" pipework fitted with standard sealed sprinkler heads which, again follow the glazing line. Each zone is fitted with a non-return valve and a pressure switch, upstream of the valve/switch the zones are connected to a main and in-turn a compressor. Activation of one of the zones, causes the pressure to drop, closing a relay in the panel. A fire signal is required from the FAP to close a second relay and open the solonoid valve to the coresponding deluge 'zone'.

Theres very little info on the system, the installers only have as fitted drawings, what I`d like to know is:

Is there a standard for such installations (Curent service provider seems to think not)?
Does the system need to have a mechanical detection, or could the pneumatics be replaced with smoke / heat detectors on the existing addressible FA mounted on both sides of the glazing configured for double / tripple knock ?
Are such systems still installed ?

Paul

[John Webb]

This installation is, I presume, to stop fire spread from a fire in one office up through the atrium to the offices above. You do not mention if the building is fitted with any form of smoke extract, as per the advice from BRE, ADB and BSs on atrium buildings. (Although BR 258 on atrium buildings was only published in 1994, so the building design is likely to be prior to much of this advice.)

Most articles I've seen in the past few years have been aimed at covering the atrium by spray nozzles actuated by double-knock IR or other flame detection to allow the atrium to be used for various purposes.

One possible alternative is to make the separation from the atrium fire resisting by replacing the current glazing with FR glazing; you might then be able to remove the deluge system altogether.

[Ashley Wood]

Approved Document B gives some advice on the use of sprinklers in atria. it does state that for the purpose you have described it should be activated, as John says, by electronic detection not by sprinkler bulbs as the delay would be too long.

[kurnal]

How many heads are fed by the 1/2 inch pipework? I dont know anything about such a system but flow rate must be very limited. It cant be a deluge zone if the heads then have standard sealed sprinkler heads and in any case if you assume approximately 80litres/min/rootP per head you will very quickly run out of flow using half inch pipes.

I would be very surprised if the original spec is not sitting in the archives somewhere. 20 years is not a long time in terms of civic buildings especially where engineered solutions were involved. I think without access to the original concept and justifications you will struggle to make sense of it. If it were my job I would point out the potential concerns over the system and reserve any comment unless they can come up with the original data

[John Webb]

It's OK, kurnal, the 1/2 inch pipework is feeding the office sprinkler heads with air and is acting purely as the means of communicating when an office sprinkler head actuates purely as a heat detector. So there is no problem with water flow rate 'cos there isn't any water.

I'd be inclined, if the addressable FA system is reasonably recent and therefore hopefully easy to reprogram, to substitute heat detection in the offices in which any two heat detectors near each other are required to reach alarm levels to operate the appropriate part of the deluge system. That would do away with the pneumatics and pipework but should still keep the likelihood of accidental operation to the minimum.

[kurnal]

Thanks John- got you now.
Wow sounds quite a system- bit like steam radio.

[Goodsparks]

Its ok Kurnal, it took me a while to get my head around it to.

There are a couple of large smoke extract fans in the top of the atrium, they are currently configured to start when the bms shuts down on receiving a fire signal, only snag is that the fire relay was shorted when the conventional FA panel was replaced and never re-connected.(That`ll be sorted in the next couple of weeks :-) )

I`ll take a look through ADB and BR258.

Thanks guys.

Paul

[John Webb]

Goodsparks, one factor often overlooked with smoke extract is the replacement or 'make-up' air, particularly in buildings which have been around for a while. There is also the risk that vents to provide this make-up air may have been interfered with over the life of the building because their function may not be obvious. If the make-up air is not readily available, the atrium becomes lower in pressure than the rest of the building with the risk that any leakage from the area on fire is intensified.

But with the newer smoke detectors the building appears to be fitted with means that you should get an alarm well before the fire develops sufficiently to actuate the sprinkler heads and trigger the drencher system.

Thinking a bit further about this, modern heat detectors will probably give an alarm well before a sprinkler head would (even a fast-response head) so you may need to trigger on a fixed temperature (as a sprinkler head nominally does) rather than 'rate-of-rise' sensing to avoid any awkward false alarms.