Posts Tagged ‘personal injury’

Forensic Engineering Focus On Electrical Fires

Sunday, October 4th, 2009

     Property damage and loss of lives, these are often the result of fires.  But did you know that one of the leading causes of fire is electricity?  Residential electrical fires claim the lives of nearly 500 Americans each year and injure another 2300.  Annually, these fires result in over $800 million in property losses.

     Approximately one third of the nearly 70,000 home electrical fires that occur each year are traceable to design and manufacturing defects in electrical products.  The rest are caused by the misuse and poor maintenance of electrical products, overloaded circuits and extension cords, and incorrectly installed wiring.

     The three components that must be present in order for a fire to manifest and sustain itself are well known.  These components make up the “Fire Triangle,” a potentially lethal combination of heat, fuel, and oxygen.  If any one of these three components is missing from the triangle, a fire can’t be started or sustained.  In the case of an electrical fire, it’s electricity that creates the heat component of the Fire Triangle.


The Fire Triangle

     How does electricity contribute to fires?  One example would be an overloaded extension cord.  Homeowners are sometimes unaware that extension cords must be sized appropriately for their ultimate usage.  If not, they can overheat, particularly if they are damaged.  Damage to cords can result from a myriad of factors, from factory production errors to kinking when heavy furniture is carelessly placed on top of them.

     The same principle holds true for electrical products.  If their internal wiring or a component is insufficiently sized or damaged, overheating can result.  If things get hot enough and there is sufficient airflow (oxygen) and combustible material (fuel) in the vicinity, then the fire triangle is complete.  The fire starts internally and can soon spread to other objects in the area.

     Electrical arcing can occur when an energized electrical circuit is broken.  For example, suppose a wire carrying current is suddenly broken in two.  If the voltage is high enough, the electricity will want to continue to flow through the air across the break to form an electrical arc.  If the power flowing through the arc is great enough, heat can once again complete the Fire Triangle, resulting in fire.

     Forensic engineering analysis of evidence collected from a fire scene often yields telltale signs of overheating due to overloaded electrical circuits or damaged wiring in components.  Under close examination by an experienced professional, even the smallest strand of wire can point to the cause of an electrical fire.

     CSI skills aren’t only employed at crime scenes.  Forensic engineers also use similar techniques to get to the true story of cause and effect.


Machine Safety, Operator Safety, And Keeping Those Fingers

Sunday, September 27th, 2009

     Crushed fingers, amputations, burns, blindness, these are all too common undesirable occurrences involving moving machinery.  Eliminating the risk of such accidents is an integral part of the engineering design process, where risk assessment goes hand and hand with industry standards in order to provide adequate machine safeguards and protection to operators as well as bystanders.

     Machine safeguards fall into three basic categories: Guards, Devices, and Distance.

     Guards are physical barriers that are added to machines with the goal of keeping body parts, clothing, etc., separated from potentially hazardous areas.  An example would be a metal cage surrounding drive belts and pulleys.  Guards can also serve to keep material fragments and debris from flying out of machines while in operation, such as when an enclosure is built around the grinding wheel of a bench grinder.

     Devices can consist of automatic controllers, often connected to sensors on machine componets.  These controllers use a form of “safety interlock logic” to monitor the operating state of machinery.  They must act quickly and automatically to stop the normal operation of a machine if they sense that an undesirable object, say a person’s forearm, is in danger of entering a hazardous area.

     Controllers can be in the form of hard-wired electromechanical relays, embedded microprocessors, or programmable logic controllers (PLCs).  Their sensors can include electrical switches embedded in floor mats or mounted on movable guards, incorporated into control handle grips, or linked to an access door latch.  Still other sensors are more elaborate, using more sophisticated methods to maintain safety, such as photoelectric devices known as laser curtains.  These act by spreading beams of light across an opening which may be a gateway to a dangerous area.  If the beam is broken by an object, the controller takes appropriate action and renders the machinery inoperable.

     Distance safeguards operate as you would infer them to, by designing machinery so that hazardous areas are kept a great enough distance from body parts, etc., so as to eliminate any danger of them being drawn into an unsafe area.  An example of this factor at work would be when machinery is developed so that moving gears and other potential hazards are kept far out of the reach of someone by virtue of their overall design. 

      Sometimes even the best machine safeguard designs can be rendered ineffective after a piece of machinery is put into actual operation.  The reasons for this are varied, from poor maintenance of equipment, to lack of training for operating personnel, to inadequate supervision of workers, or perhaps the machine has been modified to operate outside the parameters of its design capacity.  Whatever the reason, people can be put at risk for serious injury and even death if machine safeguards are bypassed, eliminated, and defeated.