Forensic Engineers and Consultants

Archive: Machinery and Equipment

Improper Design Leads to Fatigue Failure In Blower Shaft

A blower used to exhaust air from an industrial process stopped functioning when the blower wheel drive shaft fractured.  The process, and thereby most of the plant, had to operate at a reduced volume until the blower wheel could be replaced.  The blower wheel had been installed during a shutdown a week before the incident.  The blower wheel was a spare installed when the existing blower wheel was sent for scheduled remanufacturing. Read More


Figure 2: A close view of the opening of the heat sealer. A person’s hand will fit in the opening below the guard to the left. Two "Danger" stickers are visible.

Injury Involving Packaging Machinery


From time to time, I and other engineers here at Warren are asked to evaluate a case involving an injury that has been caused by machinery designed to produce or fill packaging. The hazards associated with packaging machinery are often similar to other commonly-used industrial machinery, but packaging machinery has its own voluntary consensus standard for machine safety. Read More

Figure 2: A view of some of the undersize anchors used to secure the capstan winch. The anchors at the upper right failed by pulling out of the concrete slab. The one at the lower left failed by bending and pulling out.

Injury Involving a Capstan Winch


Co-Authored with Jeff Warren, PE   

A capstan winch uses a mechanically powered rotating cylinder, called a capstan, to apply pulling force through a rope. When the rope is looped around the rotating capstan and tightened, friction between the rope and capstan allows the winch to apply force to pull a load. A typical capstan winch is shown in Figure 1 below. Read More

A clevis pin with the spring clip attached.

Defective Clevis Pin Culprit in Runaway Trailer


A large agricultural trailer had been connected to a truck using a clevis pin with a spring locking clip.  The trailer became disconnected from the truck and collided with an oncoming vehicle.  The trailer was in poor condition, did not have safety chains, and had substantial recent modifications by the owner. Read More


Are You Prepared for Emergencies? Your Generator Set Should Be!


Emergency generators are often called into service during catastrophic events like hurricanes, floods, tornadoes or fires, but also during more mundane events like thunderstorms and other things that may temporarily interrupt the public power grid. Can you rely on your generator to perform at those critical times? Read More

Figure 2.  A view looking into the mixer. The grate and ribbon are visible. The grate openings are large enough to admit a worker's leg.

Case Study of an Injury Involving a Soil Mixer

Co-Authored with Aron Olson, P.E.

In May, 2014, a plant farm worker was seriously injured when he fell into the hopper of an electrically powered soil mixer.  The mixer in question used a rotating steel ribbon powered by a 7-1/2 hp electric motor to mix batches of materials such as sand, mulch, wood shavings, fertilizers and other landscaping materials to create potting soil. At the top of the hopper sidewalls, within 6 inches of the ribbon, was a steel grate. Read More

Figure 2: A self-propelled roof bolter similar to the one described in this post. The canopy is on the extreme left of the image.

A Case Study in a Coal Mine: What are a Machine Rebuilder’s Responsibilities?

Co-Authored with Aron Olson, P.E.

In November of 2010, a miner was injured by a roof bolting machine (roof bolter) in an Alabama underground coal mine. The roof bolter in question had undergone a complete rebuild intended to return the machine to the original equipment manufacturer’s (OEM’s) specifications. Warren was hired to analyze both the design of the roof bolter and the actions of the rebuilder to determine if either contributed to the unfortunate coal miner’s serious injury. Background information on coal mining and roof bolters, as well as an analysis of the roof bolter and the actions of the rebuilder are included. Read More

Figure 2: A Webshare photograph from a scan captured from the safety of a balcony in the workshop. The scanner operator never had to climb directly above the forklift to create the shot in Figure 1. The Webshare user can pan, zoom, and measure from the photograph. The grey target icons represent other scan locations on the ground.

Another Dimension of Engineering, Part 2: Visual Demonstrations Can Clarify the Issue


Co-Authored with John Phillips, PE, CFEI

In our last post on 3D scanning, we introduced Warren’s new Faro Focus X 330 three dimensional scanner.  To recap, the Faro scanner combines three dimensional laser measurement with automated photography to capture 360-degree data from the real world. Potential applications include vehicle accident scenes and damaged vehicles, structural collapses, fire scenes, flood damage scenes, and machinery and equipment analysis, among others. In this post, we will highlight some of the outputs that can be created from the detailed data captured by the scanner. Read More

Figure 1: A Faro 3D scanner.

Warren Adds Another Dimension of Engineering


Co-Authored with John Phillips, PE, CFEI

We at Warren are pleased to announce our recent purchase of a Faro Focus X 330 three dimensional scanner with FARO Scene image processing software. The scanner takes up to 976,000 data points per second and can scan objects at distances to 1000 feet.  The scanner forms a point cloud of millions of data points while also capturing 360 degree panoramic photographs.  By combining a series of scans, a three dimensional representation can be created that enables precise measurements, animations, and demonstrations. The scanner can capture imagery indoors, outdoors, and even in darkness. Read More

An example of a non-contacting RFID interlock device. The switch, left, detects when its key, right, is sufficiently close that the guard must be closed. In well-designed interlock systems, the use of a unique RFID key discourages defeat of the system.

Interlocking Guards: A Glossary of Terms Often Used


As a part of Warren’s ongoing blog series on interlocking guards, I’d like to provide a brief glossary of selected terms frequently encountered in the context of interlocking guards. To review, interlocking guards are commonly found on machines that have a hazardous function that needs to be guarded, but frequent access to the danger zone is needed. These definitions are paraphrased from a number of voluntary standards including those described in my glossary of codes and standards that apply to interlocking guards. Read More

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