Forensic Engineers and Consultants

Archive: Machinery and Equipment

Danger Within Reach

How far away from a hazard should you stay?  Your parents or grandparents would probably have told you to stay far away, but what are you to do when a hazard is present, and you must work around or near the hazard?  And what exactly is a hazard?  ISO 12100 Safety of machinery – General principles for design – Risk assessment and risk reduction defines a hazard as a “potential source of harm.”

Where would a designer of a machine or product start if they wished to protect the user from a known hazard?  Consensus standards are a great place to begin the quest for safety. Read More

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Interpreting Industrial Incident Data – Lesson Learned

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This is a case study about an incident I investigated involving a major upset in a distillation column.  This blog builds on the previous blogs about the Distributed Control System, DCS – Data is the Key.

Distillation is a method of separating mixtures of compounds with differing boiling points.  Uncle Bill with his still on the hill separates ethanol, that boils at 173°F, from water that boils at 212°F.  If the mixture is heated to above 173°F, but below 212°F, the ethanol will boil, the vapor will travel up out of the unit and then can be condensed and served over ice with an olive…   Any mixture of two or more chemicals with different boiling points can be separated in this way.  The distillation Read More

Stress Corrosion Cracking of Stainless Steel in Marine Environments

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Stress corrosion cracking involves the slow growth of small, often microscopic, cracks through a metal part in a corrosive environment.  The cracking can continue to the point that the part fails suddenly and unexpectedly even though it still appears new and in good condition.

My first experience with stress corrosion cracking happened in the Charleston harbor when the stainless steel rudder suddenly separated from a sailboat during moderate winds. What had been a pleasant evening sail turned instantly into being in a difficult to control boat in the middle of the busy shipping channel. The rudder remained attached only Read More

Load Holding Valves in Hydraulic Cranes

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Hydraulic cranes absolutely rely on the integrity of their high-pressure fluid systems for safe operation.  A crane can become out of level when an outrigger cylinder leaks over time, possibly leading to a tip over.  A boom can collapse if a hydraulic hose ruptures.  It is not possible to absolutely prevent hydraulic cylinders from developing leaks or prevent hoses from rupturing during the life of a typical crane, therefore crane manufacturers provide load holding valves at key components to prevent these dangerous incidents.  In fact, ASME B30.5, Mobile and Locomotive Cranes, requires load holding valves or equivalent devices at outrigger cylinders, boom support cylinders, and boom telescoping cylinders. Read More

Machine Guarding and Risk Assessment

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The Occupational Health and Safety Administration (OSHA) “Top 10 for 2018” violations once again have Machine Safeguarding earning a position on the list. Machine safeguarding was the 9th most cited standard as noted in the list below:

  1. Fall protection, construction (29 CFR 1926.501)
  2. Hazard communication standard, general industry (29 CFR 1910.1200)
  3. Scaffolding, general requirements, construction (29 CFR 1926.451)
  4. Respiratory protection, general industry (29 CFR 1910.134)
  5. Control of hazardous energy (lockout/tagout), general industry (29 CFR 1910.147)
  6. Ladders, construction (29 CFR 1926.1053)]
  7. Powered industrial trucks, general industry (29 CFR 1910.178)
  8. Fall Protection–Training Requirements (29 CFR 1926.503
  9. Machinery and Machine Guarding, general requirements (29 CFR 1910.212)
  10. Eye and Face Protection (29 CFR 1926.102)

(Source: www.osha.gov/Top_Ten_Standards.html)

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Unguarded Shear Point on Force Tester Amputates Worker’s Finger

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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

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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.

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Testing As Part of Gas Appliance Incident Investigation

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Equipment and appliances supplied with fuel gases like natural gas, propane and butane are a common and convenient part of most of our lives.  Such devices as gas grills and ranges, ovens, furnaces, space heaters and water heaters usually perform without incident.  However, when they malfunction the potential for incidents such as fires and explosions, carbon monoxide (CO) poisoning and burn injuries may occur. These incidents may be due to design and manufacturing defects in the product, or improper installation or operation of the device.

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

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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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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

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