May 23, 2016
Small Orifice Sprinklers in an Attic “I have a combustible concealed space above a pitched roof with a slope of 8:12 where the sprinklers are spaced between 8 and 10 ft perpendicular to slope. The wet system does not work hydraulically with 5.6 K-factor sprinklers as it is flowing too much water. Can I utilize a 2.8 or 4.2 K-factor sprinkler at the minimum 20 psi in order to minimize the flow?” We have reviewed NFPA 13, 2010 edition that you indicated as the applicable standard. Our informal interpretation is that the orifice has no size restriction for light hazard occupancies for wet pipe systems including the attic application. The standard encourages that sprinklers be spaced 8 ft or less perpendicular to the slope using pressures to deliver a density for the light hazard occupancy. Spacing greater than 8 ft up to the maximum 10 ft has a minimum discharge pressure of 20 psi per Section 8.6.2.2.1.1. It is believed that this improves the distribution and effectiveness of the sprinkler discharge pattern while using the design pressure of 20 psi for these greater distances. Even if this were a dry pipe system you could reduce the K-factor to a K-4.2 sprinkler (see Section 8.3.4.4). This shows that the 20 psi is not linked to the K-5.6 sprinkler (and an assumption that the intent was the need for additional water discharge). This was best portrayed in the 2002 edition that identified the allowance to use a K-4.2 in Section 8.6.4.1.4.4 under the attic section and stated; “Nominal K-4.2 orifice sprinklers shall be permitted for use at the 20 psi minimum pressure option for wet pipe systems and dry pipe systems where piping is corrosion resistant or internally galvanized.” In the 2007 edition, this text was transferred to Section 8.3.4.3 where it stated that K-4.2 sprinklers could be used in dry-pipe system in corrosion resistant pipes. This shows that it is intended to apply to all dry pipe applications (not just attics) and that the corrosion resistant pipe and restriction to K-4.2 applies just to dry pipe system. Wet pipe systems in light hazard occupancies have been allowed to use smaller orifice sprinklers as dictated by Section 8.3.4 for a long time. The minimum 20-psi pressure requirement for attics does not affect this allowance. ------------ Technical Update is prepared by the Technical Services Dept. of the AFSA: Roland Huggins, a PE registered in fire protection engineering, Vice President of Engineering and Technical Services; and Tom Wellen, a PE registered in fire protection engineering. This is provided with the understanding that the AFSA assumes no liability for this opinion or actions taken on it and they are not to be considered the official position of the NFPA or its technical committees. Copyright 2016, American Fire Sprinkler Association. All Rights Reserved. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.firesprinkler.org/private.cgi/sprinklernotes-firesprinkler.org/attachments/20160523/570d00e4/attachment.htm>
