Aspiration Smoke Detection (Avoiding Unwanted Alarms)

[deenee]

I am recommending an Aspirating Smoke Detectors on a listed building project where it serves both life safety and property protection (yes, insurers choose it over sprinklers) in addition to the aesthetic appeal. The building will have a very good management system.
However the potential users of the building will be smoking within the aspiration-protected areas (a fait accompli): obviously this will conflict with the early detection the system will afford.
We looked at different options of accommodating these things and arrived at incorporating a timer and relay logic where the system will have two sensitivity modes normal and smoking mode with push button in those areas where smoking will be taking place. Before smoking is started, the smoking mode (low sensitivity) will be activated by the push button and that will give the smokers certain time to smoke and will automatically return to normal mode upon elapsing of the set time.
all this sounds good, except it may take longer for the smoke particles to clear from the affected room (we'll be unable to use mechanical system to evacuate the particles) and therefore the system might be susceptible to false alarm upon returning to normal mode. This is the client's concern, as similar problem was encountered in one of their buildings. – We don’t want to set longer time for the smoking mode 
I am wondering whether somebody in this forum has encounter similar problem and how s/he went about resolving it. And also if other members can help with idea on how to resolve or improve the above option or if there is a better solution out there. Any idea is welcome.

[Galeon]

Treat the smoking area as separate , and then use a reference pipe / to monitor the exhaust of the air sampler covering the other areas .

[kurnal]

I am curious about the geometry of the space and how much they will be smoking. Is it fairly confined?
We know of warehouses with HSSD and a ceiling at only 6m with LPG fork trucks running round and diesel engines backing up to the loading bays and never yet had an unwanted signal.

[David Rooney]

Treat the smoking area as separate , and then use a reference pipe / to monitor the exhaust of the air sampler covering the other areas .

How will that work?

You'll need a separate detector to act as a reference detector and all you are referencing is the relatively "clean air" exhausted from one of the other ASDs... I don't see how that's going to help ?

[deenee]

I am curious about the geometry of the space and how much they will be smoking. Is it fairly confined?
We know of warehouses with HSSD and a ceiling at only 6m with LPG fork trucks running round and diesel engines backing up to the loading bays and never yet had an unwanted signal.

The geometry varies depending on where they find themselves smoking - ranging from an enclosure of, say, 25m2 to about 100m2, all with average ceiling height of 4.5m. Upto 7 people can be smoking at any giving time.

On the warehouses, do you think they tune down the sensitivity to avoid unwanted signal?
Talking to one of the HSSD manufacturers recently, they told me some of their clients actually used it to nab smokers in an otherwise non smoking area where HSSD's are installed. 

 

[Phoenix]

Being slightly intrigued by the initial post, could I ask, deenee, are these people smoking legally? 

And would it be correct to assume that there would be no one present with sufficient responsibility to conduct an investigation if a two stage alarm system were used?

Stu

[kurnal]

But Phoenix- Could what they are looking for be found in every single rose?

deenee its three years since I last looked at the spec but if I recall the installation I was referring to was made by airsense technology and I think it had five preset "states", we chose the default mid settings. But I see your problem - these are small volume compartments with low ceilings and  a lot of smokers.

[deenee]

Being slightly intrigued by the initial post, could I ask, deenee, are these people smoking legally? 

And would it be correct to assume that there would be no one present with sufficient responsibility to conduct an investigation if a two stage alarm system were used?

Stu

Phoenix, One of them is actually paying the bill, and and you can guess who the rest might be.
And the issue of person with suffficient responsibility re alarm investigation and necessary action is not in doubt, it is one of the reasons the insurer is happy to do without active suppression.

 

[Phoenix]

OK - sorry if I'm missing something - is the reason that you can't just have an investigation time (prior to giving the evacuation signal) because you wouldn't be able to reset the system immediately after a false actuation by smoking smoke (smoking smoke! - I don't half trot out some rubbish sometimes - but you know what I mean)?  Or is there some other reason for not just going down the investigation time route?

Stu


[kurnal - every single rose.  Have you looked?]

[kurnal]

Yes but I pricked my fingers on the thorns.....

[deenee]

OK - sorry if I'm missing something - is the reason that you can't just have an investigation time (prior to giving the evacuation signal) because you wouldn't be able to reset the system immediately after a false actuation by smoking smoke (smoking smoke! - I don't half trot out some rubbish sometimes - but you know what I mean)?  Or is there some other reason for not just going down the investigation time route?

Stu


[kurnal - every single rose.  Have you looked?]

Phoenix - we are going down investigation time but thought is not ideal to equate investigation time and smoking time.
Smoking time might take longer than neccessary and can lead to complacency so we think better not to use that route.
We are using investigation time to investigate potentially real fires.

[Smoking smoke - that is exactly what come to me mind when I'd wanted to explain. Thot is only me!]