| I’ve been talking about how I was asked to be a subject matter expert for an upcoming series on The Discovery Channel titled Curious and Unusual Deaths. Most of the accidents discussed involved electrocutions, and in each case the electrocution occurred because the victim’s body, usually their hand, inadvertently contacted a source of current. When that happened their bodies essentially became like a wire, providing an unintended path for current to travel on its way to the ground. Why does it travel to the ground, you ask? Because electric current, by its very nature, always wants to flow along a conductor of electricity from a higher voltage to a lower voltage. The ground is the lowest voltage area on our planet. When electricity flows to ground along an unintended path it’s referred to as a “ground fault,” because that’s where the electricity is headed, to the ground, or Earth. By “fault” I mean that something in an electrical circuit is broken or not right, allowing the electrical current to leak out of the circuit along an unintended path, like through a person’s body.
For example, in one of the Curious and Unusual Deaths segments I was asked to explain how a fault in wiring caused electrical current to flow through a woman’s body to the ground that she was standing on. This happened when she unintentionally came in contact with a metal door that was, unbeknownst to her, electrically charged from an unanticipated source. The current was strong enough to cause her death. Where did the electric current originate from? Watch the program to find out, but I’m sure you’d never guess. To say that it was an unlikely source is an understatement. When ground faults pass through a person’s body, bad things often happen, ranging from a stinging shock to stopping your heart muscle to burning you from the inside out. The severity depends on a number of factors, including the strength of the current to the amount of time your body is exposed to it. It might surprise you to know that if your skin is wet at the time of contacting a current, you risk a greater chance of injury. Water, from most sources, contains dissolved minerals, making it a great conductor of electricity. But what exactly is electrical current? Scientifically speaking it’s the rate of flow of electrons through a conductor of electricity. Let’s take a closer look at a subject close to home, a power cord leading from a wall’s outlet to the electric motor in your kitchen hand mixer. That power cord contains two wires. In the electrical world one wire is said to be “hot” while the other is “neutral.” The mixer whirrs away while you whip up a batch of chocolate frosting because electrons flow into its motor from the outlet through the hot wire, causing the beaters to spin. The electrons then safely flow back out of the motor to the wall outlet through the neutral wire. Now normally the number of electrons flowing into the motor through the hot wire will basically equal the number flowing out through the neutral wire, and this is a good thing. When current flow going in equals current flow going out, we end up enjoying a delicious chocolate cake. Since the human body can conduct electricity, serious consequences may result if there is an electrical defect in our hand mixer that creates a ground fault through the operator’s body while they are using it. In that situation the flow of electrons coming into the mixer from the hot wire will begin to flow through the operator’s body rather than flowing through the neutral wire. The result is that the number of electrons flowing through the hot wire does not equal the flow of electrons flowing through the neutral wire. Electrons are leaking out of what should be a closed system, entering the operator’s body instead while on its way to find the ground. Next time we’ll look at a handy device called a Ground Fault Circuit Interrupter (GFCI) and how it keeps an eye on the flow of electrons, which in turn keeps us safe from being electrocuted. _____________________________________________ |
Archive for June, 2011
Ground Fault Circuit Interrupters
Sunday, June 26th, 2011Green Screens and Makeup Chairs
Monday, June 20th, 2011| Imagine being a typical guy, the kind that hates to shave and would never dream of wearing anything that even remotely resembles makeup. That was me, before being contacted by The Discovery Channel to act as a subject matter expert on the topic of steam power plants and electrocutions, part of a series they’ll be airing in the near future to be called Curious and Unusual Deaths. Little did I know when agreeing to appear on the program that I was also agreeing to venture into an area of human experience most males would like left to the females, that of donning facial makeup.
Upon my arrival in Toronto to meet up with the producers I was treated like a celebrity. A chauffer had been sent to greet me at the airport, and I was driven to a fancy downtown hotel. The next morning I was driven to the video studio and spent some time in the makeup chair to get gussied up. My imperfections muffled, I was invited to take a seat in front of a green screen, and for those of you who don’t know what the function of this marvel of photography is, let me briefly explain. The green screen enables the editors to digitally impose any kind of background behind me at a later time of their choosing, anything from the Grand Canyon to footage of World War II. As of this time I have no idea what images will be shown in back of me as I speak. It’ll be interesting to see where I end up! Once the cameras and lights were adjusted in the studio, there was a clack from the director’s clapper board, accompanied by a shout of “roll ‘em!” And we were off shooting, just like in Hollywood. Two video cameras shot me simultaneously, one placed directly in front and one to my left. One of the show’s producers sat next to the front-positioned video camera during shooting. She needed to be within earshot, because she soon proceeded to ask me pointed questions about the science behind each incident being investigated. It was up to me to ad-lib the responses, bearing in mind that the subject matter was technical and had to be conveyed to an audience of average technical background in a manner in which they could understand it. Every now and then we’d take a break from filming so the crew could tend to the video equipment. It seems that adjustments had to be continually made to both cameras and lighting. Videotapes had to be changed, and the makeup artist would use these as opportunities to tweak my makeup. All in all it was an enjoyable experience. Everyone acted professionally and was easy to work with, and the producers expressed their satisfaction with the part I had played. I was told that I explained the technical subject matter in a way that anyone could understand, and I thanked them. But after all, as I shared with them, that’s my job! It was nice to hear that I was doing it well. Next time we’ll get into how GFCI outlets help to prevent you from getting electrocuted and from becoming a potential subject on Curious and Unusual Deaths. _____________________________________________
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Just Call Me Expert
Sunday, June 12th, 2011| Last week I said we’d talk about ground fault circuit interrupters (GFCI), but before we get to that let me provide a little background on how I recently came to be a subject matter expert for The Discovery Channel.
The program I was asked to contribute to is titled, “Curious and Unusual Deaths,” where I will be discussing a variety of tragic occurrences, including deaths by electrocution. It’s actually slotted to be a series of half-hour segments presenting, you got it, some of the strangest, most grizzly, tragic, or simply avoidable deaths from across the globe and throughout time. The episodes use actors to recreate the incidents, which take place in a variety of locations, from the home to the workplace. After presenting a graphic portrayal of the unfortunate event, experts, including myself, provide an explanation of the science behind it all. Cinematic recreations and high quality computer generated imagery are used to recreate how the deaths occurred as well as illustrate the experts’ explanations. It all started when I was contacted by a researcher for the program. She had discovered me through this very blog site, the Engineering Expert Witness Blog, and was impressed with my diverse background, which as my loyal readers know covers both mechanical and electrical engineering. She also liked the fact that I’ve worked professionally within many different industries. Needless to say, I was flattered. She went on to explain that she was interested in discussing with me the technical aspects of four particularly unusual but actual incidents that had proven to be deadly to those involved in them. The deaths were due to a variety of factors, from a steam pipe failure, to contacting high voltage electronics through a seemingly benign unplugged appliance, to succumbing to carbon monoxide poisoning produced by a propane heater, and finally, the one I thought to be most unusual of all, a death caused by touching a hotel room door that was, unbeknownst to the person inserting the key in the lock, charged with stray electrical current from an unlikely source. Sound interesting? Look for the series to air in the near future to find out more. We discussed the incidents by phone for awhile, and then a week later I received another call inviting me to fly up to Toronto, Canada, to be videotaped as an expert for the series. Now, although I do not have a ham bone in my body, I do enjoy sharing my knowledge of technical things with others, so I gladly took her up on the offer. Tune in next week to read the insider’s track on the making of a quality television series. _____________________________________________
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Industrial Ventilation – Local Exhaust Ventilation Exhaust Stack Design
Sunday, June 5th, 2011| Imagine how nasty it would be if some of the dirty water draining into your sink was allowed to leak back into the fresh water coming from your faucet. Yuck! Now imagine looking up at a factory’s exhaust stack and noticing that it’s located just inches from the intake pipe, the one that’s supposed to suck in fresh air for the workers inside. Even a novice can see that this is an unhealthy situation. Some of the airborne contaminants exiting the building are sure to be sucked right back in.
Last week we discussed the importance of location with regard to intake and output pipes, an integral part of a local exhaust ventilation system. The placement of these stacks is governed by various industry standards that present guidelines to insure that ventilation systems work properly and protect the health of people in the workplace. These guidelines have been determined by scientific study to equate to a safe minimal standard, as determined by a body of experts that have come together to form a consensus committee on the subject. Generally speaking, the standards set recommend that exhaust stacks extend upward a minimum of 10 feet above the highest point of the roof. As for discharge velocity, the rate at which contaminated air blows out of the stack, the standards recommend that operation take place at a minimum of 3,000 feet per second. Separation distances between exhaust stacks and air intakes vary according to dilution requirements set out in the standards, but basically the separation must be great enough so that airborne contaminants leaving the exhaust stack get safely diluted by outside air so they will pose no hazard should they ever reach the air intake ducts. This combination of height, velocity, and distance factors allows contaminated air to be dispersed far enough from the building to avoid downdrafts created by wind passing over the roof, thereby preventing undesirable consequences like the smoke that re-entered my house through its fireplace on windy days. One device that is sometimes incorporated into the scenario to keep workplace air clean is the inclusion of rain caps on the roof. These look like conical shaped hats, and they’re supposed to keep rain from falling into the exhaust stack. It seems like a good idea, but they unfortunately do not work very well. To begin with, they don’t do a good job of keeping out rain, especially when it’s driven by strong winds. Another drawback is that they can actually direct contaminants exiting from exhaust stacks back down to the roof and into the building’s fresh air intake ducts. Yet another drawback of rain caps is that they often result in the local exhaust ventilation system fan working harder than it has to because the contaminated air slams into the rain cap, thereby slowing its rate of exit and causing it to lose velocity energy. This means a fan must be selected to work harder to compensate for the resistance. Well, that’s it for our series on local exhaust ventilation systems. Next time we’ll switch gears and discuss how those outlet covers in your home with the cute little red and black buttons work to protect you against death by electrocution. They’re usually positioned near water sources and are known as “Ground Fault Circuit Interrupters,” or GFCI. I’ll be discussing topics like this on an upcoming show to be featured on The Discovery Channel, where I’ll be acting as a subject matter expert. The series, titled “Curious and Unusual Deaths,” will cover a wide range of potential threats that are present in our everyday environments. _____________________________________________ |
