Calibration Error or Communication Failure?

John R. Yannaccone, P.E., Principal Mechanical Engineer

Case Summary:  A worker, at an agricultural coop, was assisting the operator of a large agricultural spreader in order to configure the machine in preparation to spread a different product.  Part of this process required the spreader to be calibrated so that it would drop the proper amount of fertilizer for the desired application rate.  The calibration involves manually adjusting the opening in the hopper above the spreader’s spinners.  While the worker was starting this process, the operator turned on the spreader.  The worker’s arm became entrapped, which resulted in significant injury.

Expert Analysis:  The investigation of this incident focused on identifying which part of the spreader moved, thus entrapping the worker’s arm, and why that part moved during the calibration process.  The available materials indicated that the worker was reaching into the rear of the spreader as part of the calibration process when the spinners began to turn. It was determined that the spinners rotated because the operator had turned them on while teaching a new employee how to operate the spreader.

There were numerous errors that led to this incident, primarily, the failure of personnel to follow instructions and clearly communicate with each other.  When the three employees went out to the spreader, the operator and the new employee went to the cab to discuss operation of the spreader.  The other worker went to the rear of the spreader in preparation to perform the calibration process.  

When the worker was ready to begin, he stepped to the side of the spreader and gave a thumbs up to the operator to confirm it was clear to start work.  The operator responded with a thumbs up, so the worker went behind the spreader and reached into the spinner area.  The operator presumed the worker’s thumbs up was given to signal it was all clear to turn on the spinners, so he acknowledged with a thumbs up and activated the spinners.  Clearly, the two men failed to effectively communicate their intended actions with each other.  

Their miscommunication was not the only issue that allowed the resulting incident to occur.  The manufacturer’s manual for the spreader included a detailed calibration process and repeatedly warned that the spreader’s engine should not be running simultaneously.  Since the spreader’s spinners are driven by a hydraulic motor supplied by a hydraulic pump powered by the engine, there is no way for the spinners to rotate when the engine is off.  Warning labels on the spreader also indicated to stay clear of the rear of the spreader when it is running.  

The worker knew the cab was occupied and the engine was running, so he should have stayed clear of the spreader’s rear.  The manual also indicated that anyone working on the mechanism should be in possession of the spreader’s ignition key which provides lockout of the spreader.  The worker did not have control of the key and should have been aware that the key was in the ignition since the engine was running.  The manual further indicated that the control valve for the spinner motors should be unplugged as part of the calibration, thus adding another measure to prevent the spinners from operating during the process.  This step was not done.

Mechanical inspection of the spreader confirmed that the systems were operating properly and that, if the proper steps for calibration were followed, there would be no way for the spinners to rotate and cause a person to become entangled.  Additionally, proper communication between the worker and operator would have prevented the operator from turning on the spinners when the worker was reaching into the mechanism.

Result:  The case resolved with all parties prior to trial.

Categories: Case Studies | John R. Yannaccone, P.E. | Mechanical Engineering | Principal Mechanical Engineer

Tags: Agriculture | Calibration | Fertilizer | Hopper | Manufacturer's Manual | Spreader | Worker's Comp | Workplace Safety


Have A Question About This Article or Want to Contact the Expert?

Request An Expert

Fill out the form below so we may refer an expert

Do you have a question for us? We’re here to help!

James Schmidt Expert Spotlight