I believe the focus on this requirement is that these exterior spaces (decks, balconies, whatever you call thems) represent an appreciable risk to the building due to human activity. There have been some losses of mid-rise 13R properties that were spectacular to watch as an exterior fire on the balcony from cigarette or cooking traveled the often times combustible exterior finish and made quick work of access an unprotected truss void or attic. While 13R systems were not created for property protection this still warranted some attention and the sidewall offers an affordable option. Generally speaking the piping exists only a few feet away in the ceiling so there is not an exceptional cost when weighing risk / benefit.
For calculations - well frankly I don't see a calculation problem. First of all the exceeding the 4-head design argument goes out the window since the deck is clearly outside the 'compartment' for design area purposes in 13R. Secondly I'm not aware of that many 13R systems that are eligible to calculate two heads based on compartment size so typically its 3 or 4 heads calc'd. The exterior head (k5.6) is within the water demand already in place on the project and if it is effective at preventing an exterior fire from penetrating the building envelope and running the concealed combustible spaces then we really saved since we didn't operate more than one head - versus the 3 or 4 we designed for. If the exterior head doesn't suppress the fire until FD resources arrive OR if it never goes off because the heat zoomed past it and took hold of the attic above then we still didn't loose anything we didn't have already. Remember this is a 13R system and if you're in a place that doesn't use the IFC then you don't protect these spaces anyway and burning the building down with no life loss is still a 13R success. Sounds like a little cheap insurance. I also find in the installations I've seen so far that even the top floor balcony with no roof over still has some type of projection / soffit over the area where the head is located. If the heat of a top floor fire is escaping freely into the atmosphere and the head doesn't operate then it also supports the fact that the building envelope wasn't being exposed to temperatures that would indicate compromise and vertical spread. On the other hand if the fire is close to the building wall on the deck and possibly vertically exposing the envelope there is a much greater chance that the heat will rise and fire can spread easily into the attic by way of the soffit .. Likely also activating the head in the mean time and delivering water to suppress the heat release until manual FD resources arrive. My final thought is that this kind of 'exposure' or impromptu window sprinkler was where the authors were heading and nothing more since they did not include this requirement for full 13 systems which likely would contain concealed combustible space / attic protection. The authors simply did not want to chance a fire penetrating the building envelope and went with the original premise of early water close to the base of the fire. Personally I would like to see it added as a requirement for 13 systems as well in the IFC since it is possible and fairly common to have wood framed multiple dwellings that have 13 systems for various modifications but a fire on a deck is still hot enough to penetrate the building envelope. Thanks again Dave, _______________________________________________ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: techsupp...@firesprinkler.org To Unsubscribe, send an email to:sprinklerforum-requ...@firesprinkler.org (Put the word unsubscribe in the subject field)
