Forensic Engineers and Consultants

Archive: Electrical and Control Systems

Hazards Can Lurk Anywhere … Watch Your Step …

While on a lunch stop during a recent vacation trip through Tennessee, I happened across a safety hazard that required immediate attention.  The establishment had a raised concrete patio at the front with a steel railing around the perimeter.  At one edge of the patio was a set of stairs with a continuation of the steel railing used as a handrail.  The top edge of the patio had light strings wrapping the top metal bar as accent lighting for the perimeter.  The light string continued down the stair handrail wrapped in the same manner as the rest of the patio. Read More

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Tom_Kelly_WEB
Gas Appliance testing lab

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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Figure 1: A typical Ground Fault Circuit Interrupter (GFCI) Receptacle.

Testing…testing… Is this thing on?

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Many people just take for granted that something is just going to work, and in many cases assume that it will work forever.  One such device that does not get enough attention is the Ground Fault Circuit Interrupter (GFCI).   Simply put, a GFCI is a protective device that compares the current flowing on the hot and neutral wires of the circuit and will “trip” to disconnect power to the circuit if a small imbalance of current is detected.  The imbalance of current is an indication of a dangerous alternate path for the current to flow from a damaged line cord or a fault inside an appliance and constitutes a shock hazard to a person. Read More

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Ready, Set, Fly! – Understanding Another Technology for Forensic Investigations

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This is the first blog in a series on integrating new technologies into the process of forensic investigations.  Documenting the scene of an incident accurately, efficiently, and safely is a key step in every investigation.  Busy roadways and unstable structures present hazards to the investigator during the investigation process. The use of remote sensors can reduce these risks and provide data that otherwise could not safely be obtained. Read More

Ground rod installed in the earth with clamp.

Grounding versus Bonding – Understanding the Difference in Building Electrical Systems

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While a teenager might be very familiar with being “grounded”, there is confusion over the meaning of the word in the electrical sense. In building electrical systems, “grounding” and “bonding” are two terms that are often misunderstood. Improper application of the concepts of grounding and bonding may create lethal shock and fire hazards. “Earthing” is a term which comes from the European International Electrotechnical Committee (IEC). Earthing is synonymous with grounding but often thought to have a different meaning. Read More

flooded-electrical-outlet

Flood Damage to Electrical Equipment

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As a result of the recent weather, those of us in South Carolina have gained a renewed appreciation of the damage that can result from flooding. Even a few inches of flood water can result in property damage and a loss of services in addition to the immediate risk of physical harm. Read More

Figure 2: A view of a typical PLC.  The blue and red wiring to the right terminate at the PLC’s input / output wiring connections. The processor is to the left at the keyed switch.  This PLC has capacity to communicate over an Ethernet data link.

Forensic Examination of Losses that Include Programmable Logic Controllers (PLC’s)

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Many modern machines and processes are controlled by Programmable Logic Controllers (PLC’s).  PLC’s are essentially computers that have the ability, properly connected and programmed, to interface with the outside world and control the actions of a machine like a robot or conveyor.  The PLC has a processor for processing the user programmed logic, and also has input / output (I/O) wiring provisions for both analog (e.g. temperatures and pressure transducers) and digital (e.g. limit switches and indicator lights) devices.  Read More

Gas valves from a process furnace that experienced an explosion. The final gas safety shut off valve has its wiring cover partially open. This can be an indication that someone was directly powering the valve and bypassing the control system safety logic. Open wiring covers on controls should be fully investigated.

Stay in Control: Manipulation of Electrical Controls Can Lead to Fires and Explosions

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We have a saying at Warren, “When we go to work on a new case, usually someone else has had a very bad day.” If you are a plant manager at a factory, you know it’s a bad day when you hear the fire alarm or a loud explosion emanating from the back of the plant. Read More

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