Forensic Engineers and Consultants

Blog Posts by: Jeff Warren

Author Jeff Warren

Expertise Includes:

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

Conveyor Backstops: Sometimes One Isn’t Enough, Part 2

This is the second in a two-part blog series about conveying equipment that severely injured a worker at a mine. In case you missed it, click here to read Part 1 where I describe the incident and the mining equipment. In this part, I will discuss my engineering analysis of the incident and the machinery involved and share the conclusions I reached.

The injured miner was a front-end loader operator. He was not a maintenance worker. He simply responded to a radio request for help with the conveyor. Power to the electric conveyor motors was locked out, but none of the maintenance workers did anything to lock out or block the hazardous gravitational potential energy in the heavy load of stone on the belt.

Figure 1: A view of the head pulley showing the north and south side speed reducers. Only the north side speed reducer had a backstop. When the north side torque arm was disconnected, there was nothing to stop the belt and its load from running downhill due to gravity. The moving belt caused the partially disconnected north side speed reducer to unexpectedly rotate and repeatedly strike a miner.
Figure 2: A composite view of two speed reducers. The speed reducer on the left has a backstop as indicated by the red arrow. The speed reducer on the right has no backstop.

The mine relied on an outside company to properly design and install all components of the hill conveyor including the motors, speed reducers and the backstop function. The mine agreed that the backstop on the hill conveyor is a safety device but did not understand its importance. If the outside conveyor design company had recommended two backstops for the hill conveyor, one for each side, the mine would have purchased two backstops. The conveyor design company did not warn or instruct anyone at the mine that the hill conveyor and the north side gear reducer would move suddenly and unexpectedly if the turnbuckle on the north side was removed. The conveyor company did not train, warn or instruct anyone at the mine about how to prevent the conveyor from rolling backwards. The conveyor company did not warn or provide instruction that there was only one backstop on the hill conveyor drive. The conveyor company also confirmed that the backstop is a safety device to prevent backward rotation of the conveyor belt. The conveyor company agreed that two backstops on the hill conveyor would have made the hill conveyor safer.

The conveyor company agreed that it was technologically and economically feasible to add another backstop. The conveyor company agreed that the hill conveyor would not have released if there was a functional backstop on the other side of the hill conveyor. The cost of an additional backstop was negligible in comparison to the total cost of the conveyor company’s work.

As a result of my investigation of the incident, I concluded that:

  1. The hazard that injured the miner is a hill conveyor with two motors, two speed reducers and two turnbuckles but with only one backstop located on the north side speed reducer and no backstop on the south side speed reducer. When the turnbuckle on the south side is removed, the belt will not move because the north side backstop prevents the north side speed reducer from turning in reverse. If the turnbuckle on the north side is removed, the north side backstop becomes ineffective, and the south side gear reducer has nothing to prevent it from turning backward. As a result, the belt and its load run downhill, and the north side speed reducer rotates hazardously about the head pulley shaft.
  2. The single backstop on the hill conveyor with two motors and two speed reducers does not adequately control the hazard of unexpected movement of the belt, load, and machinery. The turnbuckle on the south side of the head pulley can be loosened or removed safely but removing the turnbuckle on the north side will produce disastrous consequences.
  3. It was technologically and economically feasible for the outside conveyor company to adequately control the hazard of unexpected movement by installing a backstop on each of the two speed reducers so that either turnbuckle could be disconnected without the conveyor moving due to gravity.
  4. It was or should have been foreseeable to the outside conveyor company that the hill conveyor would need to be serviced while the belt was loaded. The outside conveyor company could have and should have provided an adequate protective device to prevent the hill conveyor and speed reducers from moving during servicing operations.
  5. The hill conveyor is defective because:
    1. It contains an inadequately controlled hazard of unexpected movement due to gravity.
    2. There is a high and foreseeable risk of severe injury from uncontrolled movement of large, heavy power transmission components including the speed reducer and its turnbuckle.
    3. There is a high probability of occurrence of harm any time the large, heavy, uncontrolled rotating components strike a worker.
    4. It was technologically and economically feasible for the outside conveyor company to install a second backstop on the south side speed reducer that would have prevented the hill conveyor, north side speed reducer and turnbuckle from moving unexpectedly.
    5. The risks associated with the hill conveyor outweighed its benefit.
    6. Adequate warning or instruction was not provided.
  6. The defective condition of the hill conveyor was a cause of the miner’s injury.

If you have a case involving an injury caused by conveying equipment, please give us a call. We at The Warren Group would be happy to help you determine the cause of the incident.

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 UNC Charlotte 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.

 

Conveyor Backstops: Sometimes One Isn’t Enough, Part 1

This is the first of a two-part blog series describing an incident involving conveying machinery that seriously injured a miner. Part 1 describes the machinery and the incident. In Part 2 I will summarize my engineering analysis of the incident and share the conclusions I reached.

A loaded, inclined conveyor belt may contain hazardous levels of energy due to gravity. To protect workers, anti-reverse devices called backstops are installed on inclined conveyors to prevent unexpected downhill movement. The Conveyor Equipment Manufacturer’s Association (CEMA) defines a backstop as: Read More

Staying Connected on the Loop: Two by Two’s Mobile Internet Setup

After completing the sit-stand workstation in the guest stateroom of our 47’ Nova Scotia pilothouse trawler, Two by Two, that I reported in a previous blog, I found I needed an internet connection with reasonable speed and reliability.  While almost every marina will give you a password for their WiFi, the quality of most marina connections is unreliable and too slow to effectively work as a forensic engineering consultant. When I tried to download a simple photograph through any type of remote connection to the Irmo, SC office, I could go make a cup of coffee and come back before the download finished.  To upload a group of photographs Read More

Working on the Waves While Working the Waves…

The rumors of my pending retirement have been greatly exaggerated…..

Ever since I heard about The Great Loop I have wanted to cruise it (www.greatloop.org).  To successfully complete the Loop, one needs to have 3 things: adequate equipment, adequate time, and adequate health. I had the first and third.  To secure the second, I had floated the idea of a two-year sabbatical.  A year to complete any existing cases and a year to execute The Great Loop.

With the arrival of COVID-19, our firm went to remote work. Read More

Unguarded Shear Point on Force Tester Amputates Worker’s Finger

A worker was injured while testing gas springs similar to the type that hold the hatchback of an SUV open. The hazard that injured the worker was an unguarded shear point. The tester contained a mounting plate that was raised and lowered by a pneumatic cylinder.

The pneumatic cylinder lowered the mounting plate while the worker’s fingers were in the hazardous, unguarded shear point. Read More

Case Study: Fatality Servicing Unsupported Excavator Boom

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.

Read More

Defective Vertical Baler Causes Serious Crush Injury to Operator’s Arm

I recently worked on an interesting case involving a box baler. An employee of a butcher shop put some empty cardboard boxes in a vertical box baler and pushed the control switch to compact the boxes. After the 30 by 60 inch platen weighing 851 pounds returned to its raised position, the employee reached into the open space above the bottom door on the baler and began to clear cardboard from the bale tie slots in the bottom of the raised platen. Suddenly, and without warning, the steel pin attaching the platen to the raised hydraulic cylinder rod failed. The heavy steel platen fell and crushed his arm which was outstretched over the baler door into the compaction space.

Read More

Children Will Fall At Playgrounds. What Shall We Do To Protect Them? A Multipart Blog Series – Part III: An Overview of Selected Playground Safety Technologies

Welcome to the third and final post in our multipart series of blog posts about a young boy’s fall and serious injury at a public playground. In our first post we gave a brief overview of the incident and our investigation. In the second post we discussed some of the safety standards applicable to public playgrounds. In this post, we will examine some of the impact-absorbing playground surfaces available to protect children at playgrounds from injury. If you would like to read the first two posts, they are available here and here.
Read More

Children Will Fall At Playgrounds. What Shall We Do To Protect Them? A Multipart Blog Series – Part II: A Brief Summary of Playground Safety Standards

Welcome to the second part in our multipart blog series examining a young boy’s fall and injury at a public playground. If you missed the first part in this series, click www.warrenforensics.com/2017/10/11/children-will-fall-at-playgrounds-what-shall-we-do-to-protect-them-a-multipart-blog-series-part-i/ to read it. In this post, we will highlight some resources that designers of public playgrounds can use to help ensure their designs are reasonably safe. Read More

Warren Announces the Retirement of Dan Olson

With both pleasure and regret, Warren announces the retirement of Dan Olson. Dan has been a consulting engineer at Warren since its founding 20 years ago and has been a leader in the development of Warren and its culture from the onset. Read More

Type ofLoss

Not sure what you're looking for?
Browse All

Select Loss Category