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Later, engineer Dick Karsky at MTDC was asked to provide material strength data to assure that the tripod system could handle heavy loads safely. Kent Niles, a local welder and fabricator, built a set of tripods. Niles altered the top plate assembly design slightly (figure 3), made the foot and plate assembly one piece, and used trailer hitch pins with locking hairpin cotters (figure 4) to adjust the legs. Niles delivered the tripods during the summer of 2003.
Bitterroot National Forest employees have used these tripods many times, transporting loads weighing up to 1,200 pounds. Any organization that needs to move heavy loads over short distances using equipment that can be packed to a remote location (figures 5a and 5b) should consider trying this versatile piece of equipment.
Safety and Training
Rigging operations can be dangerous. Equipment failure can lead to serious injury or death. Equipment must be inspected frequently to ensure it is in good, safe working condition. Pay special attention to frayed, bent, or kinked cables. They need to be repaired or replaced.
Employees working on or near rigging operations must be informed of the hazards and receive proper training. A Job Hazard Analysis must be completed and signed before starting a rigging operation and a safety briefing should be held before the start of each day's work.
Currently, the Forest Service does not have a certified Rigging Training Program. On-the-job training should be done by only those experienced in the type of rigging operations required and using equipment with which they are familiar. All rigging operations will follow applicable OSHA guidelines, such as 1910 Subpart N--Materials Handling and Storage. Private industry, State, or local technical schools may offer training or classes in rigging operations. Consult with your forest's safety officer before conducting a rigging operation.
Building and Using the Portable Tripod
The tripod is made from steel tubing and plates that are welded. It breaks down into sections that can be transported easily and that can be reassembled quickly using hitch pins with locking hairpin cotters. The leg sections are just 6 feet long so they can be packed on a horse or mule.
MTDC Drawing No. 1035 (PDF - 759 k) was prepared based on the Bitterroot National Forest's tripods. Fabricators must adhere to accepted welding practices and comply with the callouts in the drawing's materials list to assure that the tripod can support heavy loads safely.
The tripod was designed to be used with a materials handling winch, such as the Griphoist-Tirfor model TU-28 (pulling capacity of 4,000 pounds). Operators must ensure that the wire rope, blocks and fittings, and anchor points are in good working condition and are compatible with this load. They must observe all Occupational Safety and Health Administration guidelines for the use of cable clamps, safety latches, chains, and slings.