Why isn't voltage of electric chair higher?
I recall vividly a story told by my grandfather who worked with high voltage power lines. A worker drove heavy machinery into 700kV line and then jumped out of the truck, instantly combusting upon touching the ground.
I recently read about executions by electric chair, and got curious as to what voltage is used, since the described process seemed to last upwards to a minute, which seems incredibly unnecessary. Various sources indicate that voltage ranging from 1400V-2300V is used, most often figuring around 2000V. If we know that it is current that kills, it seems intuitive to use much higher voltage to achieve higher current, in effect speeding up the process.
Are there any considerations from electrical perspective, such as safety regulations, fuse ratings etc. that could be a reason for using this particular voltage and not going higher?
2 answers
After some research I found some reasoning behind the voltage range:
1500V is sufficient to destroy the somatic nervous system, which is responsible for consciousness and feeling of pain. After applying the voltage, within 4ms the subject becomes unconscious faster than the nervous system can register pain. The autonomic nervous system (which is responsible for basic functions such as breathing and heartbeat) requires >2000 volts to stop the heart. Allegedly, 20% is added to "be sure". Furthermore, after voltage is applied and the body saturates, there is a 10% voltage drop that varies based on the electrode resistance and the body resistance. It was also noted that the current should be below 6A to prevent burning, since that is not the goal.
Fred A. Leuchter Associates, Inc., which made these devices seems to be the only company in US, however, the owner had no formal engineering experience and was dropped as a manufacturer, so it is unclear whether these numbers are accurate and make sense at all.
If this is accurate, it seems that properties of the human body are the primary drivers of design choices, and not safety concerns.
If anyone has any more information regarding the accuracy of this, please do share.
I feel that I also have to say that my interest in this is purely out of curiosity, and I do not plan to build one or sit in one. From the perspective the question is asked, this is an electrical appliance that has specs, and the reasoning behind these specs needs clarification.
I think your grandfathers story is, shall we say, apocryphal.
You should know that electrocution kills by stopping the heart (or causing fibrillation), and the heart must be kept from beating long enough for the person to die. It only takes a few mA to accomplish this and there is no benefit...no speedup...in using drastically higher voltages or currents.
Some people have been struck (or nearly struck) by lightning and survived. The high voltage stopped their heart but the heart started beating again without intervention.
On the other hand, using higher voltages requires more expensive equipment and presents a greater risk to bystanders.
Please don't interpret anything I have said here as support for capital punishment.
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