Case Study: Fatality Servicing Unsupported Excavator Boom


Expertise Includes:

    • Machine Design & Safeguarding
    • Machinery & Equipment Analysis
    • Products Liability
    • Risk Assessment

A mini-excavator at a job site developed a leak at a hydraulic fitting at the base of the cylinder that raises and lowers the boom. A subcontractor foreman at the site raised the boom to search for the leak. The foreman found and attempted to tighten the leaking fitting. When he did, the fitting separated from the base of the cylinder, releasing the hydraulic pressure that held the boom aloft. The boom fell and the bucket struck a nearby superintendent for the general contractor.

Orange mini excavator

Figure 2 below shows the damaged hydraulic fitting after the incident. The fitting supplies hydraulic fluid under pressure to the cylinder that raises and lowers the boom. When the fitting fails there is nothing to keep hydraulic pressure inside the cylinder. The weight of the boom collapsed the cylinder and expelled the hydraulic fluid through the opening created by the failed fitting.

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Figure 2: A view of the damaged hydraulic coupling located at the base of the mini-excavator boom. The coupling separated and allowed the hydraulic fluid in the boom cylinder to escape when the subcontractor foreman attempted to tighten the fitting.

Figures 3 and 4 below are excerpts from a Construction Industry Manufacturers Association (CIMA) manual on excavator safety. Figure 3 in particular is a drawing illustrating a falling-boom incident very similar to the one in question. My copy of the CIMA excavator safety manual is copyrighted in 1986, approximately 20 years before the incident. Unsupported hydraulic equipment falling during servicing is a hazard that owners of such equipment and their service personnel need to be and should be aware of.

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Figure 3: Construction Industry Manufacturers Association Safety Manual for Users, Operators and Maintenance Personnel, Hydraulic Excavator, p. 37. [emphasis added]

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Figure 5 below is a drawing from the Operation and Maintenance manual for the mini-excavator involved in the incident in question. Figure 5 shows a hazardous situation similar to the incident.

In Figure 5, the arm of an excavator moves and strikes the worker servicing it because the bucket wasn’t lowered to the ground. The Operation and Maintenance manual for the mini-excavator reads in part: Always lower the bucket and blade to the ground before doing maintenance.

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Figure 5: Excerpt from the Operation and Maintenance manual for the mini-excavator involved in the incident.

If the foreman had lowered the bucket of the excavator to the ground and then tried to tighten the fitting, the fitting would, more likely than not, still have failed. However, an excavator bucket that is already on the ground will not fall on another worker if hydraulic pressure is suddenly lost. The foreman who attempted to service the fitting with the boom raised should have been educated about the danger of servicing unsupported hydraulic equipment and should have been trained to always lower the bucket and blade to the ground before doing maintenance.

A proper procedure to repair a leaking, damaged hydraulic fitting in the excavator includes:

  1. Lowering the bucket to the ground;
  2. Stopping the engine;
  3. Moving the control levers to dissipate any hazardous stored energy;
  4. Disassembling the fitting;
  5. Replacing the fitting and associated seals as necessary;
  6. Reassembly; and
  7. Testing.

Some excavators have pilot operated valves that may require a different procedure than moving the control levers with the engine off to dissipate hazardous stored hydraulic energy. A proper energy dissipation procedure should be documented in the machine’s manual. It is important for personnel who service hydraulic machinery like excavators to have access to and read operator’s, service and other manuals for the equipment they service.

My investigation demonstrated that the cause of the incident in question was the foreman’s failure to lower the bucket to the ground before attempting to service the fitting. The subcontractor failed to properly train their foreman. The subcontractor did not act in a reasonably prudent manner when they didn’t lower the bucket, didn’t properly train their foreman, and allowed an improperly trained foreman to attempt a repair.

If you have a claim involving construction equipment and you want to know the cause of the incident, consider making the assignment to an engineer at Warren. We would love the opportunity to consult with you and your team to get to the facts.

Jeffery H. Warren, PhD, PE, CSP, is the chief engineer and CEO at Warren specializing in mechanical, machine design and safety.  His deep expertise in machine design and safety analysis makes him a frequent presenter, trainer and expert witness. In addition to investigating more than 2000 claims involving property damage and injuries related to machinery and equipment since 1987, Jeff has an undergraduate degree in Mechanical Engineering from the University of North Carolina as well as a Master of Science and a Doctorate in Mechanical Engineering from Virginia Polytechnic Institute and State University — both with machine design emphasis.

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