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09/01/2004
OSHA Relations Committee Update
There is an effort at the National Institute of Occupational Safety and Health (NIOSH) to undertake another Industry Alert on a safety hot point: structural modifications.
When each of us hears about a tower that collapses, the first thing we ask is, "Was anyone working on the tower?" Many times over the last few years, the answer has been, "Yes."
Replacing "in-service" structural members is deceivingly complicated. The loads carried in the horizontal and diagonal members cannot be determined without an investigation performed by a structural engineer.
When planning for the replacement of a damaged member or replacing a member with one of greater capacity, procedures must be closely followed to prevent a catastrophe. The common element in many tower accidents has been the lack of a detailed procedure and the use of a proper temporary support device.
As with many of the activities we face when working on towers, most begin with a structural analysis. When steel of larger capacity is required to enhance a tower for new or different equipment, the location is always specifically identified, where each piece of new or larger steel is required. This is when the replacement process is initiated.
A tower crew is contacted. Replacement parts are ordered. The scope of work is defined. What does not necessarily happen each time is that a detailed replacement process is developed. A structural engineer must assess the work and develop the temporary support device that will be used to take the load off the tower, while the structural member is being removed and replaced.
Each structural member to be replaced is under a static load or stress with the tower just standing still without wind. As wind forces are applied, the stresses created in the member rises. When considering the design of the temporary support frame or support device, the structural engineer will need to consult with the engineer of record to verify the safety factor required for the temporary support frame or support device.
Then the structural engineer can design a temporary support device that will provide a suitable safety factor while the steel is being replaced. Then specific procedures need to be developed. The procedures should simply state each step of the process to replace the subject tower member.
As an example, the various steps of the procedure may include these topics and should go into sufficient detail to fully explain each task:
• Pre-job hazard survey and if needed, abatement;
• Pre-climb meeting, crew assignments and safety protocols;
• Rig the tower;
• Locate the member to be replaced;
• Install the temporary support frame or support device, secure and check;
• Visually verify suitable weather for the expected duration of the replacement;
• Verify size of materials and verify correct size of new bolts;
• Loosen the structural member to be replaced;
• Verify no residual strain;
• Remove and replace the structural member;
• Secure the new piece in place; and
• Remove the temporary device.
It is hoped that another Industry Alert published by NIOSH will bring awareness to a safety issue that is well known and understood by seasoned professionals.
Proper advance planning with qualified experts as well as proper execution of the plan should assure that the structural modification can be done in the way it needs to be done and result in the desired, enhanced tower.
Don Doty serves as Chairman of the NATE OSHA Relations Committee as well as Vice Chairman of the Association. He is the Vice President of Doty-Moore Tower Services, Inc. of Cedar Hill, Texas and can be reached at 215-631-1300 or don.doty@stainlessinc.com
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