Forensic Engineers and Consultants

Archive: Machinery and Equipment

Danger Lurking in the Hot Tub

Several dangers involving the use of a hot tub (spa) may readily come to mind, such as the risk of shock or electrocution, or the risk of drowning for unsupervised young children.  Not so readily apparent is the effect of overheating the human body, or “hyperthermia”.

Some individuals are more susceptible to the effects of hyperthermia, including the elderly, young children, and those in poor health.  The effects of hyperthermia, or overheating of the human body, cause direct responses such as headache, nausea, heat exhaustion, increased cardiac output, lethargy, confusion, heat stroke and unconsciousness.  The onset of hyperthermia is defined as being at 99.5° F; if the body temperature reaches 104° F, a life-threatening medical emergency exists.  Read More

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box bailer

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.

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Figure 1: A typical warning found on a confined space.

Permit-Required Confined Spaces – What You Need to Know to Safely Enter (and Exit!)

According to the OSHA regulations, a confined space is anyplace that meets the following criteria:

(1)   Is large enough and so configured that an employee can bodily enter and perform assigned work; and
(2)  Has limited or restricted means for entry or exit; and
(3)  Is not designed for continuous employee occupancy. Read More

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Graphitic Corrosion – Difficult to determine before a failure!

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Graphitic corrosion is a process that may happen in equipment made of iron, particularly grey cast iron, but also ductile cast iron. Graphitic corrosion can lead to unexpected catastrophic failure of the affected part because the cast iron can lose its strength without a visible warning such as a change in size, shape, or appearance. Read More

Figure 1:  A view of the blower machinery.

Improper Design Leads to Fatigue Failure In Blower Shaft

Author

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 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

Author

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

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

Author

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

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