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FIRE SERVICE AND GENERAL FIRE SAFETY TOPICS => Fire Safety => Topic started by: asl on January 21, 2008, 11:48:35 AM
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Hello all.
Can anyone confirm whether a Vesda detection pipe can be extended by a couple of metres to detect an additional area without running a feed back to the original panel please and would the panel have to be recalibrated?
Just general opinion please as we are getting different advice from different installers.
Many Thanks
asl
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I am not technically competent so take this with a pinch of salt.
IMO a couple of metres should not make much difference to the flow levels in the pipe, my justification for saying this was that recently a sensor pipe was completely broken in half about 45m out from the panel and no faults or flow errors were detected by the panel (on an air sense technology quadra unit) .
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If you want to protect an additionl area, then an additional run should be made. It will be a different address etc.
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Many thanks for the response guys.
Just to clarify we are fitting an additional comms cabinet in an existing computer room so its not truly another area.
Is this a "try it and see" situation or is there more technology involved? (we havent at this stage got a supplier seriously involved as we wanted to get a handle on it ourselves first.
Many thks for the advice
Regards
asl
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I looked at this one for a while before making a responce as the answer could range from very simple to very hard.
There are a number of VESDA products on the market but let us assume you have a lazer plus device and not a scanner. If the design of the vesda system protects the room with seperate units and the cabinets with seperate units then adding a short length of pipe and another hole will increase the dilution and reduce the sensitivity. This can be compensated for in the settings and the sensitivity increased ( assume it is not on max now). Simple answer.
Vesda works by drawing air through a sampling chamber by an air pump ( fan) from the risk, via pipes. At commissioning the whole thing will be balanced by the engineer. I have seen people get the design totaly wrong such that the pressure differential between the exhaust and the sample holes has defeated the pump and the air has flowed the wrong way thus rendering the whole thing useless. Thus the answer will be dependant on the static and dynamic pressures achieved inside the cabinet with the a/c running and off. You may invalidate the protection to the existing cabinets by making your proposed alteration. Hard answer!!! Why not get your problem looked at by somebody you can trust?
Beware of the many cowboys that are in our industry. Must dash now as I have to get a letter on the deadwood stage or butch and the boys will have no vesda pipe to throw in ( sorry install ) next week. More pills please matron and I didn't mention ASPIRE once HA!
Dave
Dave
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Many thanks for the response guys.
Just to clarify we are fitting an additional comms cabinet in an existing computer room so its not truly another area.
Is this a "try it and see" situation or is there more technology involved? (we havent at this stage got a supplier seriously involved as we wanted to get a handle on it ourselves first.
Many thks for the advice
Regards
asl
I'm confused.... you will either have primary detection, or secondary or both. That is, you will have vesda pipework installed in front of the return air grilles thereby sampling air from the entire room and therefore no need to extend pipework. Or you will have pipework installed at ceiling level or in a void (possibly above the ceiling and in a floor void) and again you will be sampling air from the room - spacings determined by BS6266 etc therefore no need to extend because you are installing a cabinet.
The only other option is that you have specific in cabinet detection. In which case extending a pipe a couple of metres and adding a sampling hole will make very little difference.
However, you should get a competent company to check out the existing design and run it through the design software supplied by the system manufacturer in order to verify the flow, balance and sensitivity and basically re-commission the system.
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Dave,
what are you aspiring to?
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Dave,
what are you aspiring to?
Oh dear.... someone fetch Jokars funny file.......... yes thats it.... the very thin one.......!!!!
:D
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50 metres is the max length..if ur happy to keep the room on one zone then no harm done!
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Well done Steve_gb you nearly remembered. To extend the pipework of a VESDA detector you should use the ASPIRE software program to ensure that the detector will work to the required sensitivity and timings. Thats the correct and responsible way of doing it.
Here's some rules of thumb though. A VESDA LaserPLUS (VLP) has four pipes but does not distinguish between which pipe detects the smoke. Each pipe could cover the return air grilles, known as primary detection, the room space or voids, known as secondary detection or be installed with a sampling point into each cabinet, known as cabinet protection.
If all four pipes are used, each pipe can be a maximum of 50m in length. If only two pipes are used each pipe could be 100m in length. For room detection hole spacing should be 5m apart (BS6266) or 10m apart (BS5839).
To answer the question above, assuming that the addition of an extra cabinet means that it is cabinet protection that is being implemented, as long as the pipework is under 50m in length and any capillaries used are under 2m in length, and as long as there are no more than 10 holes in a 50m length of pipe you will probably find that adding one aditional hole will not create any problems.
If it does create a problem it will probably be that it affects the flow rate which will more than likely only reduce transport time from the end hole. This could be corrected by increasing the fan speed of the detector. Sensitivity can also be easily adjusted to take account of the extra hole (although i suspect this would not be required)
You may also find that if the transport time is increased it is still within parameters. BS allows for a max of 120 secs for the transport time. Xtralis, the manufacturers of VESDA, recommend 60 secs. You will probably find that the origional calcs were done to meet this 60 sec target and therefore an additional hole wouldn't make much difference.
Or you may find, as suggested above, that it was done by cowboys in which case none of the above applies and you should just add your extra hole anyway.
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is this the Yorkshire Gaazzzaa?
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Hi asl,
The advice Gazzaaa has given you is very good. I work for Xtralis (the chaps behind the VESDA fire deteciton) and I will happily get in touch with you to provide any help or advice on any VESDA projects you have any niggles with. With regards to flow rate yes, while BS does allow for a max transport time of 120 seconds we as the manufacturer do suggest a shorter time 60 seconds. This all can be easily calculated from the ASPIRE pipe design program you can download and use for free at:
http://www.xtralis.com/opencms/opencms/system/modules/com.vfsportal/default_bodies/apac/int_en/products_fire_softwaredownload_aspire2.html
Sorry about the long web address! Either way take a look and see what you think, a lot of installers and fire system designers have found it useful when specing or installing the VESDA systems. Either way, any problems give me a call and I'll gladly speak with you!
Kevin Shea
KShea@xtralis.com
01442 206 429
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Do you still get unwanted alarms with these when someone decides to engage in a rather dusty activity within the room, Kev? My recollection is of building management having to switch off the system from time to time and then remembering to put it back on again - I ask in as much as extending a pipe to another room could have implications for fire detection in another should the system be switched off - so management would need to plan for this.
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Ey Up Steve_gb - Does that answer your question?
Ken, the Vesda detector you probably remember is the old style E70D. These detectors were designed for extremely sensitive early smoke detection and used a Xenon type strobe to detect the smoke particles.
The type that are around now are laser based and incorporate a dual stage filter that filters pretty much everything except smoke sized particles from entering the laser detection chamber. Unlike the old Xenon based product, the sensitivity is adjustable from around 0.005% to 20% obscuration per meter. Typically a standard smoke detector has a threshold of around 4% obscuration per meter. As you can see, you can make the Vesda detector extremely sensitive or a lot less sensitive than a standard point detector.
I do know of issues where the detector struggles in certain circumstances though, such as cement works. It would seem that powdered cement has the same particle size as smoke. On the other hand, i have seen false alarm testing carried out in an underground carpark with a Vesda detector installed. The test consisted of the oldest, most delapidated, Transit van being fired up and revved up to kick as much diesel fumes and smoke as it could into the underground car park. The Vesda detector did not go into alarm condition. After all the smoke & fumes cleared, a smoke pellet was lit which pretty much instantly triggered the detector.
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Thanks, Gaz. I've had this sort of issue with large rooms in historic listed buildings during maintenance works and the like.
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Hi Ken,
Sorry about the delay in getting back to you! Gazzaa is right about the old E70D Xenon detectors becase the sensitivity is unajustable they are not the right VESDA unit to use in a dirty environment with losts of air bourne debris. Also on a side note all of the Xenon detectors are now obsolete and we no longer support those types, we are offering an incentive for any xenon upgrades to our new detectors if people are interested.
Off the top of my head I cannot remember any circumstances where VESDA units have been used to protect areas that include cement works specifically. We have however had successful installations within a paper recycling facility which creates a huge amount of paper dust in the environment with out any problems. The detection sensitivity threshold will definately be set towards the lower end of the range. All I would suggest is to set the system for a autolearn period to establish what the general background dust levels. Fomr this you should be able to minimise false alarms but setting your alert, alarm and fire thresholds to suit the envirnment. Also remember that in these dirty environs the VESDA filters will need to be replaced at regular intervals to remain effective.
I hope this helps! Any questions just email me.
Kevin Shea
Xtralis Lts
KShea@xtralis.com
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Ken, I have seen aspirating systems installed in a couple of flour mills. They worked fine but needed an extra inline filter and lots of maintenance. Sorry Kev, it was one of your competitors but non the less an aspirating system.
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Ashley you wound me sir! Surely there is no other aspirating systems apart from VESDA!? But yes, you will need to do regular mainenance on any asd systems in environs like flour mills whether they are VESDA or others like Airsense.
VESDA Kev
KShea@xtralis.com
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Kev,
I always specifiy VESDA on my projects as I think you are the market leaders.
My opinion and I'm sticking to it :- )
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Ashley if I didn't know any better I would say you're angling for commision..
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Commission, Whats that then?
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Thanks, Kev.
I have tended to use the term 'Vesda' in much the same way as people refer to 'Thermos' instead of 'vacuum flask' or 'Evac Chair' instead of 'evacuation chair'. Sometimes architects, surveyors and builders wrongly conclude that you are using a colloquial generic term rather than a specific product name - so they need watching - but they do anyway.
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I always get my wife to hoover although it is made by Dyson. I can't get round the words I want you to do some dysoning. As regards the word vacuum, thats what I have been living in for a number of years.
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That would be a good for us if all asd was referred to as VESDA so long as they did specify and use VESDA which by the sounds of it some people don't. Maybe we could start using the term vesdering?? Mhhmmm.. what do you guys think?
VESDA Kev
Xtralis Ltd
KShea@xtralis.com
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Fortunately, I don't have to get my wife to do the vacuuming, Jokar, as she assumes it's her job anyway - just like she assumes that it's mine to operate the credit card.