Air Sampling “VESDA” system

[Simon Morriss]

Air Sampling “VESDA” system

Does any one have any experience of using this type of detection as a "front line" detection system?  My experience has only been to use this in high risk areas to provide an early response from a trained team.  As such it would not instigate a building alarm this would be done by the installed point detection.

I have a proposal in front of me asking for the use of this type of system in a room with very high ceilings.  This will ensure that there will be no maintenance at high level.  

In the building we have a two stage system of alert and evacuation.  Evacuation is caused by a MCP or two detectors in one area going off at the same time.  

In principle I agree with the recommendation I am just working out how to link it into the cause and effects and weather to have it provide an alert signal or an evacuation signal considering the large area one units covers.  It is proposed to install two units.

Your help and experience will be greatly appreciated.

Simon

[Gary Howe]

I have experience of designing these systems, the key aspect is the set up, they can be adjusted to suit virtually any environment, with programmable sensitivity levels. The key to success is good commissioing, correctly matched to suit the risk (often they are left at the factory settings, and have a reputation for false alarms). One Vesda unit can cover up to 2000m2 with 4 pipes, alternatively there is a scanner version of this product which gives you an output for each pipe, that way you can quickly identify which area is in alarm, rather than searching the entire zone.
As for the cause and effect well it depends on what the risk is? and the proccess and operations that are going on in the building.
If you can provide some additional information, then further advice can be added.
I hope this helps.

Gary Howe.

[Simon Morriss]

Thanks Gary

The room is used to house very valuable pieces of historic art, not these tents and lumps of cow that people call art now.  These are original Michael Angelo’s and the like.

There are many 1000's of these all housed in cupboards on two levels, the second level is serviced by a balcony which is why the room is so high.  We have a VESDA type system already in place only giving a pre alarm but we are enhancing the lower areas with point detection.

Apart from storage the room is used to study the pictures.

I hope this helps.

Simon

[Peter]

There are two VESDA units providing detection in the atrium section of Norwich Millenium Library (http://www.theforumnorwich.co.uk/), which as far as I am aware have been in place for 2+ years without problem - low 'unwanted calls' - I am not sure if they have been actuated for real yet.
They are linked in to open natural ventilation to the area, I don't recall if they are singe or dual knock to activate alarm, the Management were helpfull when I was in contact with them so may be able to assist o0n cause/effect if you email them.

[Gary Howe]

BikerBoy,

Bearing in mind the risk, it is obvious that you need early detection, the system should be set up so that it is on a high sensitivity configuration, it does not sound like dust, working practices are going to cause you a problem.

I suggest this as a possible config:

1: Pre-alarm - investigation by trained staff, no sounders, limited to 5mins.
2: Alarm - investigation by trained staff, alert sounders 1 second on/off.
3: Upon activation of 2 above, a MCP will override the alert signal and move the sounders to cont.

Regards


Gary

[Simon Morriss]

Thanks Gary

Nice to have some clarification.

Simon

[wee brian]

Just back from a week off. Aspirating Detection systems are now commonly used in many "normal" risk type applications. As previous posts have said one of the benefits is that you can vary the sensitivity.

[Graham Horsman]

I am just wondering if you have been given as much advice as you need without knowing the precise dimensions etc.

The advice already given does allude to the capabilities of the detector but doesn’t detail the whole ‘system’ capabilities.

A Vesda LaserPlus detector provides 4 levels of alarm; Alert, Action, Fire 1 and Fire 2 all are software programmable for sensitivity, delay etc and can provide outputs from each alarm level into a cause and effect matrix to suit the circumstances that you require.

Probably more important than the detector capabilities is the system pipework design which will impact on the parameters you want to use the detector for. It is imperative that the ‘Aspire’ programme is used for this part of the system design and that the pipework is balanced and the share of the aspirated air is equalised otherwise you may find that parts of the system are not as efficient as others.  

Hope that helps

[FHT]

Have you given consideration to using Video Smoke and fire detection systems designed by DTEC?

[Fishy]

London Underground used aspirating detection systems in all their escalator machine chambers, post King's Cross fire.  I understand that they've replaced nearly all of them with point detectors.

[Chris Houston]

London Underground used aspirating detection systems in all their escalator machine chambers, post King's Cross fire.  I understand that they've replaced nearly all of them with point detectors.

Do you know why they changed to point detectors? Were they assessed to be better?  I am interested to hear people's opinions on the pros and cons of using aspirating where traditionaly point or beam detectors would have been used.

[Paul]

I am carrying out some work for a large industrial Bakery, that is in the late stages of construction.  It is a large factory of well over 15,000 sq meters.  As you would expect there will be a presence of dust in some of the plant, along with comprehensive coverage into the loading area, where there are obviously a good number of vehicles etc.

My point is that I can understand that VESDA is very good in high risk instances or to provide early warning for critical information storage facilities or infact storages with high value contents.  However, and please correct me if I am wrong, I thought that VESDA systems are really only designed to be used in areas that have a pretty constant atmosphere, as they are designed to give early warning of slight changes in conditions etc.

Does anyone have experience of VESDA being used so extensivley in such an environment that is not constant and does experience dust contamination etc??

I have seen VESDA used very well and without problems of False Alarms in other areas, but not so extensivley in an industrial premises as a Bakery??

Any advise would be gratefully recieved.

Thanks

Paul

[Gary Howe]

I would be very careful against using the VESDA system in such an environment, any form of dust is without doubt going to result in unwanted alarms. I have designed such systems for high bay warehouses on a normal point detector sensitivity, even so when stagnent pallets, cardboard box's have been moved after a long time in situ, it can result in the movement of dust/dirt and cause false alarms.

I would not recommend either 24hr point smoke detectors or VESDA for a bakery. They are much better suited to computer/electronic data processing rooms/under floor areas.

It sounds like a time related system may suit, whereby the detectors could be configured for heat or CO during the occupied period and smoke detectors during the unoccupied period.

This set up would optimise protection and mitagate the risk of false alarms.

Regards


Gary.

Regards


Gary.

[Paul]

Many thanks for this Gary,

You have confirmed what I thought.  I was a little surprised to see this being commisioned when I visited last week.

I have played no part in the design of this and would not of recommended such a design.  Its a first for the group and they will doubt have issues with the system designers.

Thanks for this Gary.

[Simon Morriss]

Have you thought about video detection.  This could be your best option, have a look at www.dtec-fire.com.

Simon