As a tech geek and data analyst who loves gaming and streaming, topics involving electricity really energize me (pun intended!). The third rail in subways is particularly fascinating due to the dangers involved. Many riders don‘t realize that it carries up to 750V DC – easily enough to kill on contact. In this comprehensive guide, I‘ll provide more details and insights into the technical and historical aspects of third rails. My goal is to thoroughly explain the science behind these high voltage systems and satisfy any reader‘s inner nerd!
Diving Deep on How Third Rails Deliver Power
The electrified third rail is typically powered by a 750V DC power supply feeding into it through multiple electrical substations adjacent to the tracks. These convert high voltage AC power (often 11-33kV) from the electrical grid down to the 750V DC needed for the third rail.
The rail itself is normally made of steel with an alloy high in nickel content. The nickel limits corrosion and helps conduct the electrical current. The third rail is supported on insulating ceramic standoff insulators which prevent the electricity from leaking into the ground.
According to Maxwell‘s equations, this current creates an electromagnetic field around the third rail. When a train‘s sliding shoe contacts the rail, it forms a closed circuit allowing current to flow through the train‘s motors and propel it forward. The third rail is also divided into multiple sections that are only powered when a train is over them. This helps isolate power failures.
Here‘s a diagram showing the components involved:
Now let‘s get into more technical details on why the third rail is so dangerous!
It‘s All About the Amps – Calculating Lethal Current Levels
According to Ohm‘s Law, the current flowing through a conductor is equal to the voltage divided by the resistance (I=V/R). The human body‘s resistance varies between 300-100,000 Ω depending on contact area, moisture, and other factors.
Using 750V as a typical third rail voltage, a body resistance of 1000 Ω would result in 0.75 Amps of current when touched. However, resistance as low as 300 Ω is possible, which could induce 2.5 Amps.
How much current is dangerous? According to a study in the Journal of the American College of Cardiology, as little as 100 milliamps (0.1 Amps) across the heart is sufficient to cause ventricular fibrillation – an often fatal heart rhythm disturbance. The resulting cardiac arrest stops oxygenated blood circulation and leads to death within minutes.
Resistance of 750 Ω or less leads to current flow exceeding 100 mA, as this chart shows:
| Body Resistance (Ω) | Current from 750V Third Rail (Amps) |
|---|---|
| 300 | 2.5 |
| 500 | 1.5 |
| 750 | 1.0 |
| 1000 | 0.75 |
So a wide range of body resistance values can have lethal consequences when contacting third rails. This helps explain why most accidental or intentional contact proves fatal. The principles of physics unfortunately work quickly to kill.
Nerding Out on Notable Historical Third Rail Accidents
I couldn‘t resist doing some deep research into famous third rail fatalities through the years. Here are a few interesting cases:
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1909, Paris – An engineer was electrocuted trying to retrieve a lost hammer near an exposed third rail carrying 600V DC. This spurred the spread of insulated third rail covers.
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1923, Sao Paulo – Three young boys aged 10-12 were killed by a 600V DC third rail while walking along tracks on their way to school. Tragedy struck as they used the rail as a bridge over a puddle.
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1935, Toronto – A line worker survived after his stainless steel watch band contacted an 1100V DC third rail, though the watch melted. The material‘s high resistance limited current flow through his body.
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1950, Montreal – A Dalhousie University physics professor purposefully touched a 600V DC third rail to demonstrate the absence of "ground" allowing him to survive the shock. He repeated the risky stunt multiple times.
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1971, London – A man attempted suicide by cutting his foot to lower resistance, then contacting the 630V DC rail. He died instantly, becoming engulfed in flames according to witnesses.
These cases illustrate that third rail dangers lurk worldwide and date back over a century. They also show that under very specific conditions, improbable survival is possible. But would-be daredevils should not bet on being so fortunate!
Now let‘s switch gears and get into more recent innovations in third rail safety…
Modern Safety Developments – Preventing Future Accidents
In response to accidental and intentional deaths involving third rails over the years, transit agencies have developed an array of solutions aimed at removing risks:
Insulated Rail Covers
Third rails are now required to be fully covered by insulating composite boards in stations, yards, and any locations where workers may pass by. This prevents accidental contact with the energized rails. Materials like FRP (fiberglass reinforced plastic) are durable, weather resistant, and non-conductive.
Platform Screen Doors
These have grown popular worldwide as an added safeguard to prevent riders from falling or jumping onto tracks. Platform doors create a floor-to-ceiling barrier the full length of stations, with openings that align only with train doors. This approach has worked well in cities like Singapore, Tokyo, Paris, and São Paulo.
Third Rail Heat Sensors
Systems have been tested that use thermal imaging to detect when foreign objects like humans make contact with third rails. When a heat spike is sensed, power can be automatically shut off in milliseconds. This technology could help prevent electrocutions or fires resulting from track falls.
All-in-One Power Rails
Some agencies are switching to composite third rails that integrate traction power, insulation, fire barriers, and touch detection – eliminating the need for separate cover boards. Vienna‘s metro is one system using this safer consolidated "third rail in one" design to reduce accident risks.
So modern third rail safety is clearly an area of ongoing engineering innovation which gives me hope that future systems may avoid the deadly pitfalls of the past. We can leverage technology to overcome the lethal legacies of physics when power generation and human frailty intersect.
Summing it All Up – Respect the Rail!
I hope this guide has scratched your intellectual curiosity about all things related to third rails while also serving as a warning. The sobering reality is that contact with live third rails often kills quickly and gruesomely. No smartphone is worth such a risk!
Despite urban myths and a handful of miraculous exceptions, anyone venturing onto the tracks should follow safety advice and never touch a third rail under any circumstances. Your life literally depends on respecting these electrified technological marvels.
Yet I remain fascinated by third rails and other electrical applications. Hopefully new engineering solutions can continue to make subways, trains, and infrastructure safer in the years ahead. But for now, let‘s just agree to stay off those tracks!
