June 12, 1991
The Directorate of Technical Support issues Hazard Information Bulletins (HIBs) in accordance with OSHA Instruction CPL 2.65 to provide relevant information regarding unrecognized or misunderstood safety and health hazards, inadequacies of materials, devices, techniques and engineering controls. HIBs are initiated based on information provided by the field staff, studies, reports and concerns expressed by safety and health professionals, employers and the public. Information is compiled based on thorough evaluation of available facts, literature and in coordination with appropriate parties. HIBs do not necessarily reflect OSHA policy.
The Denver Regional Office has brought to our attention that communication towers may collapse due to the corrosion and failure of the guy anchors resulting in serious injuries.
A 20 year old communication tower in North Dakota collapsed due to failure of the anchor system. The tower is described as a three-leg, triangular shape with each face measuring approximately 36 inches in width and 350 feet in height. It was anchored at the base with all three legs embedded in a concrete slab. In addition, it was guyed to three anchor points with 5 guy lines attached to each anchor point (Attachment I).
The accident occurred when three workers from a tower servicing company were conducting routine inspection and maintenance on the tower structure. The crew checked the tower plumbness and added tension to guy wires. Two workers ascended the tower to perform structural and antenna inspection. The tower fell while the workers were ascending the tower. Both workers suffered serious injuries.
The investigation revealed that the anchor shaft at one location had separated at the point where it entered the concrete block (3' underground). The separation occurred as a result of extensive corrosion activity on the galvanized channel iron used as an anchor shaft.
There are thousands of towers with this type of anchoring system that are susceptible to corrosion. Since corrosion can be caused by a number of mechanisms, it is essential that the type of corrosion mechanism at a given location be identified. An overview of the variables affecting corrosion is provided in attachment II (courtesy of the Bismarck Area Office). It is recommended that the inspection of a tower anchoring system includes regular checking for corrosion of the steel anchor rods.
Please distribute this bulletin to all Area Offices, State Plan States and Consultation Projects.Back to Top
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