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Teacher accused of using Tesla coil to burn 'I love mom' into students' arms

Posted by on May. 7, 2015 at 12:50 PM
  • 6 Replies

 KRMG – Tulsa, Okla.

SALEM, Ore. —

A science teacher in Salem, Oregon, is under fire for allegedly burning students with a Tesla coil, KRMG reports.

A prosecutor says he isn't filing criminal charges "at this time" against South Salem High School science teacher Samuel Dufner, who is accused of burning phrases like "I love mom" into students' arms. The students reportedly volunteered for the experiment.

Dufner was arrested Tuesday at the school. He has been placed on leave.

The Tesla coil transmits electricity without wires at high frequency and high voltage levels.

Read the full story here.

by on May. 7, 2015 at 12:50 PM
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by Gold Member on May. 7, 2015 at 12:51 PM
by on May. 7, 2015 at 12:53 PM

Whaaat the fucccck??

by abides on May. 7, 2015 at 12:55 PM
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by Anonymous 1 on May. 7, 2015 at 12:56 PM
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The 'skin effect'[edit]

The dangers of contact with high-frequency electrical current are sometimes perceived as being less than at lower frequencies, because the subject usually does not feel pain or a 'shock'. This is often erroneously attributed to skin effect, a phenomenon that tends to inhibit alternating current from flowing inside conducting media. It was thought that in the body, Tesla currents travelled close to the skin surface, making them safer than lower-frequency electric currents.

Although skin effect limits Tesla currents to the outer fraction of an inch in metal conductors, the 'skin depth' of human flesh at typical Tesla coil frequencies is still of the order of 60 inches (150 cm) or more.[61][62][63][64][65] This means high-frequency currents will still preferentially flow through deeper, better conducting, portions of an experimenter's body such as the circulatory and nervous systems. The reason for the lack of pain is that a human being's nervous system does not sense the flow of potentially dangerous electrical currents above 15–20 kHz; essentially, for nerves to be activated, a significant number of ions must cross their membranes before the current (and hence voltage) reverses. Since the body no longer provides a warning 'shock', novices may touch the output streamers of small Tesla coils without feeling painful shocks. However, anecdotal evidence among Tesla coil experimenters indicates temporary tissue damage may still occur and be observed as muscle pain, joint pain, or tingling for hours or even days afterwards. This is believed to be caused by the damaging effects of internal current flow, and is especially common withcontinuous wave, solid state or vacuum tube Tesla coils operating at relatively low frequencies (tens to hundreds of kHz). It is possible to generate very high frequency currents (tens to hundreds of MHz) that do have a smaller penetration depth in flesh. These are often used for medical and therapeutic purposes such aselectrocauterization and diathermy. The designs of early diathermy machines were based on Tesla coils or Oudin coils.

Large Tesla coils and magnifiers can deliver dangerous levels of high-frequency current, and they can also develop significantly higher voltages (often 250,000–500,000 volts, or more). Because of the higher voltages, large systems can deliver higher energy, potentially lethal, repetitive high-voltage capacitor discharges from their top terminals. Doubling the output voltage quadruples the electrostatic energy stored in a given top terminal capacitance. If an unwary experimenter accidentally places himself in path of the high-voltage capacitor discharge to ground, the sudden pulse of current can cause involuntary spasms of major muscle groups electric shock and may induce life-threatening ventricular fibrillation and even cardiac arrest. Even lower power vacuum tube or solid state Tesla coils can deliver RF currents capable of causing temporary internal tissue, nerve, or joint damage through Joule heating. In addition, an RF arc can carbonize flesh, causing a painful and dangerous bone-deepRF burn that may take months to heal. Because of these risks, knowledgeable experimenters avoid contact with streamers from all but the smallest systems. Professionals usually use other means of protection such as a Faraday cage or a metallic mail suit to prevent dangerous currents from entering their bodies.

The most serious dangers associated with Tesla coil operation are associated with the primary circuit. It is capable of delivering a sufficient current at a significant voltage to stop the heart of a careless experimenter. Because these components are not the source of the trademark visual or auditory coil effects, they may easily be overlooked as the chief source of hazard. Should a high-frequency arc strike the exposed primary coil while, at the same time, another arc has also been allowed to strike to a person, the ionized gas of the two arcs forms a circuit that may conduct lethal, low-frequency current from the primary into the person.

Further, great care must be taken when working on the primary section of a coil even when it has been disconnected from its power source for some time. The tank capacitors can remain charged for days with enough energy to deliver a fatal shock. Proper designs always include 'bleeder resistors' to bleed off stored charge from the capacitors. In addition, a safety shorting operation is performed on each capacitor before any internal work is performed.[66]

by Dra til helvete on May. 7, 2015 at 12:56 PM
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Now, it's been quite a while since I've taken any sort of science class, but it's my understanding that tesla coils don't hurt and the "brands" fade after a little while. So I'm not really seeing the issue here besides clever wording used to enrage people.

by Gold Member on May. 7, 2015 at 12:58 PM
1 mom liked this
I think he is a cool teacher who made science interesting.
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