Those last two posts from Pat and Duane were great! Good job guys, that is so helpful.
Scott Office: (763) 425-1001 x 202 Cell: (612) 759-5556 -----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 _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
