I struggle with these systems - at least when trying to work with various clients. My time at Factory Mutual taught me to simplify systems as much as possible. In this case, use double-interlock for only those systems where filling of pipe is itself a catastrophic event, like in freezer warehouse. Outside of that scenario, are we really that concerned about the pipe accidentally filling? We would still need the accidental pipe break or sprinkler activation to cause harm. Maybe if the occupancy contained a priceless painting - biut then maybe there are better protection schemes than sprinklers.
Too many clients are ignorant about fire suppression. They assume all sprinklers activate at once; or that any sprinkler activating in their 5,000 sq.ft. server room will result in total loss of all equipment. As a contractor, it's hard to argue if the client insists on spending more money. As an engineer, we don't directly benefit, unless we got stuck with a fee based on percentage of construction costs (which many engineers gladly take, partly explaining their complacency when it comes to knowing or doing too much with fire suppression - but I digress). The client needs to objectively consider actual risk and select (with our help) with most cost-effective approach to fire protection - including consideration of long term maintenance costs as well as reliability of the system. Nothing is more reliable than a wet-pipe sprinkler system, at least in terms of activation. Start there and tick off reasons why this system would be unacceptable. Also, consider supplemental systems what may improve the fire suppression, e.g. gaseous systems with a sprinkler back-up. Air sampling smoke detection as a means of activation or even as a total replacement of suppression (in some circumstances) can make sense, as Scot noted. As Duane said: It depends. Just MHO. Mark A. Sornsin, P.E. | Karges-Faulconbridge, Inc. | Fire Protection Engineer | Fargo, ND | direct: 701.552.9905 | mobile: 701.371.5759 | http://www.kfiengineers.com -----Original Message----- From: Sprinklerforum [mailto:[email protected]] On Behalf Of Duane Johnson Sent: Friday, November 13, 2015 7:29 PM To: [email protected] Subject: Re: Cross zoned preaction detection No problem Pat, good post. To sum things up, IT DEPENDS. For example, had one client that wanted a double interlock for a 200 sq ft server room. Just couldn't justify the added cost for two sprinklers. Other items that play a role in the decision tree are items such as area of protection, occupancy, ambient temperature, temperature fluctuations, ceiling arrangement, mission continuity, performance goals/objectives, etc. Special hazards opens up so many more things to discuss. Duane Johnson Strickland Fire Protection Sent from my iPhone > On Nov 13, 2015, at 7:02 PM, Pat Thompson <[email protected]> wrote: > > I agree on the whole with Duane, but for a couple of clarifications to his > statements that I'll hit on later. With over 40 years in the industry and 20 > years in special hazards here's my take: it is true, using different > detection technologies and cross zoning them gives better assurance against > false or unwanted activations. In most cases it is also true that this kind > of setup will delay the activation of the valve. My question would be - is > this critical, given that the water is not going to deploy until a head fuses? > > Modern technology in detection and control systems provides a range of > choices, I'll attempt to hit some highlights without getting long winded. > > In a setting where critical operations or artifacts are at risk we should as > an industry do what we can to ensure suppression is employed only when > needed, so double up on automatic detection via cross zone and even multiple > technologies. Or, as Duane suggests use double interlock. > > On the other hand, if protecting a generator enclosure an accidental dowsing > of water is probably not going to be catastrophic; here single interlock on a > single detector activation rather than cross zone works just fine. My > practice has been to use heat detection in this setting and preferably flame > detection as well. Sometimes these are cross zoned, sometimes not. Speaking > to Steve's comment about incipient fires and their rate of growth, Class B > fuels do not take long to woosh into fully involved; flame detection will > give the quickest reaction for these fuels. > > Some will point out that flame detectors have caused them misery and pain due > to false activations. The industry and technologies have come a long way from > the first UV detectors (which caused me misery and pain back when) to the > point that when properly applied they are very reliable. > > I would also mention that for automatic smoke or heat detection used for > suppression one should always reduce listed detector spacing by at least > half, sometimes more depending on conditions. > > Bottom line is that application of detection is application specific. Air > sampling smoke detection is a great solution and provides lots of flexibility > in design and implementation - I love it. Spot smoke detection works well but > has challenges in high airflow or dirty environments. Heat detection is > reliable but generally slower to respond unless the fire has moved beyond the > incipient stage. > > As an aside, FMG's take on pre-action is to use heat detection and NOT cross > zone; whether single or double interlock. > > As this is a technical forum I want to point out a couple misstatements in > Duane's info. Nothing personal Duane, just sharing info. Firstly, ionization > smoke detectors are no longer available from any of the system manufactures > (hazmat disposal issues). Second, alarm verification is not allowed in > releasing applications per NFPA 72. > > Cheers, > > Pat Thompson > NICET IV Special Hazards > ATS Alaska > Direct: 907-375-4176 > > -----Original Message----- > From: Sprinklerforum > [mailto:[email protected]] On Behalf Of > Duane Johnson > Sent: Friday, November 13, 2015 10:38 AM > To: [email protected] > Subject: RE: Cross zoned preaction detection > > Cross zoned works, but personally I like double interlocked over cross zoned > single interlock when you are discussing mitigation of damage. > > Cross zoned will not help 'detect' a wider range of fires, it helps 'reduce' > the amount of false activations. The more fire signatures you require (ie. > Heat, smoke, IR, etc) prior to activation, the less false activations you > will have. For example, a welders torch will activate both a heat detector > and sprinkler (seen it), but not likely a photoelectric smoke detector and a > sprinkler. So you add smoke detection as a way to mitigate non-fire heat > sources from tripping the system. There is a good range of smoke detector > types (ie photo, ionization, air sampling, etc) and fire alarm program > adjustments (ie. Alarm verification, dirty, etc.) that can help reduce false > activations. > > One type of detection that seems good, at least on paper, is video detection. > But I can't confirm field success. > > Duane Johnson, PE > Design Manager > Strickland Fire Protection > 5113 Berwyn Road > College Park, MD 20740 > 301-474-1136 Office > 301-455-0010 Cell > > > -----Original Message----- > From: Sprinklerforum > [mailto:[email protected]] On Behalf Of > Steve Leyton > Sent: Friday, November 13, 2015 12:37 PM > To: [email protected] > Subject: Cross zoned preaction detection > > Does anyone have any strongly held opinions about cross-zoning of detectors > for single-interlock preaction systems? I haven't done one, and have usually > fallen back on double-interlock when there is a heightened concern about > accidental activation (earthquakes and all that). My understanding is that > when two different types of detectors are cross-zoned, it can help to detect > a wider range of fires that may grow out of the incipient stages at different > speed and/or with different release characteristics. And cross-zoning with > the same type of detector can give a heightened level of fail safety, so that > seems more comparable to double-interlock. I'm interested in hearing any > suggestions, opinions of the value of this design (or not) and good or best > practices. > > Steve Leyton > > _______________________________________________ > Sprinklerforum mailing list > [email protected] > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkl > er.org _______________________________________________ > Sprinklerforum mailing list > [email protected] > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkl > er.org _______________________________________________ > Sprinklerforum mailing list > [email protected] > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkl > er.org _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. 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