Aspiration detectors

[Goodsparks]

Just a quickie. Got a large room with an ornate ceiling which is to be protected by a vesda. About 1/3 of the way into the room is a large decorative beam, which, in height just exceeds 10% of the room height (like 12 - 15%). Now, if we were using standard point detectors, would treat as two rooms and install two. Is it any different with aspirators ? Have just looked through 5839 and it seems to indicate that theres no difference.

I`m trying to get hold of the BFPSA CoP at the mo, but no joy as yet.

Any help appreciated.

Paul

[Peter Wilkinson]

It is my understanding that the aspirating sampling points are required to be located as you would locate traditional point detectors, therefore, I would say yes, you need two sampling points fort the room you describe.

I can forward a copy of BFPSA CoP if you send your email address (about 600KB file size)

[Allen Higginson]

Each sampling port is treated in the same way as a point smoke detector and it's coverage is therefore the same.

[Goodsparks]

Thanks All, They`ll have to rip up some more oak floorboards :-)

Paul

[kurnal]

Yes goodsparks if you want to issue cert to BS5839 with no variations on the commissioning certificate you had better get the saw sharpened.

Lets not forget though that the aspirating detector is a very different beast than a conventional point detector which relies entirely on the convective energy from the fire in order to sample the atmosphere in the room whereas the aspirator does impart some energy to draw the smoke in - response is therefore much faster, even though the analysis  is done remotely.

It would not be too difficult to calculate the delay that would arise as a result of not siting a detector beyond the beam, working on a range of fire sizes.
But depending on the reason for the installation of the detection equipment your client may be happy to offset a few seconds in response time in return for less disruption.
I have seen some aspirating systems that use small bore tubing in heritage building in the past. Cant find it on google at the moment but it may be worth digging around.

[Mr. P]

The only time I have seen aspirating systems work well is for specific point protection i.e. in electrical kit, computer banks and the like.  In these situations the quick pick up of the smallest nasty particle can lead to a quick shut down of effected item saving more expensive down time and cost of equipment/people replacement.  Not a good system for open/larger space detection.  But, that is my experience, others may put up a good case for this use.

[Graeme]

Mr P

That is a bit of an old fashioned view of asd now. You don't happen to work for an insurance company i am having a arguement with? They are insisting that asd can only be installed in extreemly sterile small rooms as they are super sensitive.

check here

http://www.vision-fs.com/opencms/opencms/system/modules/com.vfsportal/default_bodies/apac/int_en/products_fire_sevenreasons.html

[Mr. P]

Graeme, yes that was a long while ago, and I have checked out the site you posted. Noo, no, no, NO - no. Never say never, but, I would not work in that line.  Personally I thought the system I was involved with was good. (I was involved with some trials back in 80's.)  Due to great controlability and trigger levels, not many false calls, and you could go direct to the affected point even if smoke was still not visible.  Engineers were able to isolate in most cases before anything got out of hand.  The remaining problems were the gases given off by 'popped/fried' components.
The systems are even better now and can be used to pick up on a variety of substances.  I guess there is a whole debate there waiting as to the pros & cons betweeen system types. Again, for large open spaces... but what is being protected and what is being looked for?  I keep open minded!

[Thebeardedyorkshireman]

Guys
Things have move on a lot from the early days. We have protected large open spaces using Vesda with fantastic results.
Just over a year ago we protected an underground/ underbuilding car park. Running fine, no problems. Occasional flow faults on days of very high winds and changing atmospheric pressures but settles down again very quickly. Client loves it, the engineers think it the dogs..... it is the future.
Dave

[kurnal]

I know of a system in a very large warehouse 400mx120mx15m high- no problems most of the time, a huge number of flow faults when the weather is extremely windy - but thats only happened once, it was rather extreme,  blew a few of the vents off the roof and stopped all the lifts working they were shaking in their shafts with the wind pressures, various internal fire doors could not be shut- thank goodness we didnt have a fire that day.

Obviously easy access for  maintenance to relatively small numbers of sensors is a huge advantage in such a hig shed.

[Mr. P]

So, are they still having to use single tubes from det point back to analyst/sample equip?

[Allen Higginson]

The pipe network is still the case but the sampling ports can be extended from the main pipe to small capillary tubing into flat "discs" mounted on the ceiling which are ideal for the likes olde architectured buildings or cells etc. (as long as the little buggers don't block them up with wet tissue paper or sudocream, as I experienced at a local young offenders centre!).

[Earlyfox]

Guys,
Does somebody has copy of BS5839? This would help me clarify a lot of issues which was long dominated by UL standard.

Thanks

[Wiz]

Further to Graeme's and Thebeardedyorkshireman's posts I can confirm that I have also successfully used aspirating detection to cover rooms rather than just cabinets.

There is also now a very cost-effective Vds approved aspirating product available that allows you to use the automatic fire detectors of your choice in the sensing chamber, and air is sucked in from your protected area and then sampled. I am considering using this in shafts and risers so that no access by engineers is required into the top of the shaft for installation and maintenance.

[wee brian]

Easy access is a big selling point for aspirating detectors. I got involved with a regional shopping centre with sampling points at ceiling level over the two storey mall. The gubbins is accessed by an access walkway. Much better than smoke heads that require a cherry picker to get to them.