I can't believe it was FM's intention to allow, say, a 47" duct to be located directly below the sprinkler and within only a few inches of the deflector. But I am having a hard time finding where something is written to refute that.
If it was NFPA 13, I think we'd be saying that it needs to be a minimum of 18" below the deflector before we apply that allowance to allow the pattern to develop. Kyle Montgomery [cid:image001.png@01DBA471.57FA6910] Pre-Construction Manager Aero Automatic Sprinkler Co. 21605 N. Central Ave. Phoenix, AZ 85024 Direct: 623.580.7820 Cell: 602.763.4736 kmontgom...@aerofire.com<mailto:kmontgom...@aerofire.com> From: Ed van Riel <evanr...@geelenfp.nl> Sent: Thursday, April 3, 2025 12:07 AM To: sprinklerforum@lists.firesprinkler.org Subject: [External][Sprinklerforum] FM Global obstruction You don't often get email from evanr...@geelenfp.nl<mailto:evanr...@geelenfp.nl>. Learn why this is important<https://aka.ms/LearnAboutSenderIdentification> Here below is a passage from FM 2.0 (2021-10) non-storage. (2.5.2.5.4.1 Any object up to 4 ft (1.2 m) wide, as measured in the object's least dimension and in a plane that is parallel to the floor, does not qualify as an obstruction to the sprinkler's discharge pattern.) Is anything up to 4ft. wide no obstruction? no matter what the vertical distance from the deflector (or themal element) is? Or do we have to respect the clearance of 3 ft (0.9 m)?
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