JAN 2017

Issue link:

Contents of this Issue


Page 21 of 83

SAFETY & SURVIVAL Purlins are horizontal roof beams that run perpendicular to the sloping rafters. Purlins are usually found in commercial peaked roofs supported by trusses because this is where timber trusses can be spaced 15 or 20 feet apart, so purlins are needed to sup- port the roof deck. The other rare construction feature is a collar beam. Collar beams are designed to tie opposing roof rafters of a low slope together. Collar beams strengthen roofs by helping the sloping rafters resist the outward thrust of the rafters at the eaves. Purlins and collar beams are important for firefighters who operate above and below peaked roofs. When above the roof, stay close to the purlins, as they provide additional support for the roof deck. When below the peaked roof, do not cut or remove the collar beams because they keep the roof rafters from collaps- ing on top of you. Primary structure roof members A primary structure is a beam that supports another structure. Pur- lins and collar beams can be considered primary structure roof members because purlins support the roof deck and collar beams support roof rafters. Firefighters must be able to identify primary structure mem- bers in a peaked roof. Primary structure members should not be cut when venting with a power saw, and they should not be pried loose during overhaul to extinguish smoldering fire. If they are destroyed by fire, precautions should be taken to shore them up before overhauling begins. In a gable roof, for example, primary structure members are the ridge rafters, the collar beams and the wood plates resting on top of bearing walls to which roof rafters are connected. The plate is an important intermediate primary structure between the rafters and the bearing wall. A ridge rafter connects rafters together at the peak and provides stability to the roof. When operating on a sloping peaked roof, it is good to stay close to the primary structures like the ridge rafter because it provides additional support beneath a roof deck and can provide a high point to grab onto if you suddenly lose balance and slip down a sloping roof. Firefighters should be able to identify the location of primary There are some peaked roofs with slopes that are too steep to walk upon, forcing firefighters to use other types of equipment, such as ladders. Photo by Glenn Duda ® UTO CRIB-IT 1-800-PWR-HAWK Taller, Wider for SUV's and Light Trucks! Model AC-17 "The Standard" Model AC-14 Lift-an-Inch, Crib-an-Inch • Super Compact • Lightweight & Portable • Automatically Adjusts • Piston Actuated Rapid Intervention & Collapse STABILIZE I N SECONDS! Vehicle Stabilization POWER HAWK Technologies, Inc. Request information at e-inquiry 22 l Firehouse l January 2017

Articles in this issue

Links on this page

Archives of this issue

view archives of Firehouse - JAN 2017