If the arc was triggered by the exhaust, the most likely place the arc would be drawn to is the stack itself. If the stack and other components of the smokebox are not well bonded electrically and if the locomotive is equipped with a front end throttle, there might be a chance that the throttle could be "hot".
The arc itself would present a hazard to those nearby from a combination of UV rays and possible molten metal.
- Erik
Semper Vaporo The metal that something is made of does not "attract" lightning.... <enormous snip, to save some other electrons... ;-} > So what happens when a large hollow metal volume (Locomotive or Car, etc.) becomes part of the path that lightning takes? The electrons will tend to stay on the outside of the conductor because they are pushing away from each other. They would only go to the inside of the cab if there was enough positive charge there to let them in. There is not much volume inside the cab to produce much positive charge, so the electons will continue to the earth, jumping whatever air gaps are conducive to conduction as part of the path to connect the two charges that are being equalized. I've rambled enough.
The metal that something is made of does not "attract" lightning....
<enormous snip, to save some other electrons... ;-} >
So what happens when a large hollow metal volume (Locomotive or Car, etc.) becomes part of the path that lightning takes? The electrons will tend to stay on the outside of the conductor because they are pushing away from each other. They would only go to the inside of the cab if there was enough positive charge there to let them in. There is not much volume inside the cab to produce much positive charge, so the electons will continue to the earth, jumping whatever air gaps are conducive to conduction as part of the path to connect the two charges that are being equalized.
I've rambled enough.
I humbly suggest that you could have summed up the whole of the relevant answer in two words: Faraday Cage.
As long as you stay inside the cab, it's comparatively unlikely a leader would propagate to you, or that a stroke would then propagate around your body (the voltage is far too high to go 'through' you) even at the open rear of a typical cab, without bridging to an adjacent 'grounded' metal surface first. (I wish you'd explained electron mobility in metals vs. in air to explain why this would happen...)
Here's perhaps a better question:
There have been a number of discussions over the years as to whether certain British steam locomotives, operating under 25kV catenary depressed very low in stations, might cause an arc to strike from the catenary to the locomotive under certain situations (excess carbon in the exhaust, or priming causing excess water in the exhaust) with the arc then possibly sustaining itself to the 'nearest' reasonably-conductive part of the locomotive structure.
Let's see if anyone has a good answer -- based on what you have learned in this thread so far -- about whether this poses a danger, and if so, to whom on or around the locomotive?
(I do think the 'can lightning cause a boiler explosion' subject might deserve a little better consideration than it received, if for no other reason than that it would get people thinking about what is involved in a boiler explosion rather than just jet effect from something like a crownsheet failure...)
RME
As mentioned above, presumably the water vapor and soot in the exhaust of a steam locomotive or the plume formed by the safety valves act (at least at low speeds) as a giant funnel above the locomotive as far as lightning is concerned?
Eugene Crowner
A rule of thumb about how raised metal objects and lightning is that the metal object will provide a zone of protection for a distance from the object of twice the height of the object. A 15' tall steam locomotive would provide protection for 30 feet on each side.
Blaming lightning for a locomotive boiler explosion seems far fetched.
http://books.google.com/books?hl=en&lr=&id=e-QpAAAAYAAJ&oi=fnd&pg=PA5&dq=Pennsylvania+Locomotive+Explosion&ots=jLLTH8CS9M&sig=JsIewDQuPxgBVg0BsqcSsk8mJwU
The metal that something is made of does not "attract" lightning. Any conductor of electricity will conduct lightning, including water, so a wet plastic stick can conduct lightning, but there are no "things" that "attract" lightning.
When two areas or volumes of space, whether air, clouds, land masses of rock or soil or even volumes of water become electrically charged at different levels, there is the possibility that the media between the two areas will breakdown and conduct electrons between the two so the charges will equalize.
Air, at standard temperature and pressure will go from an insulator to a conductor at a particular difference in charges. The amount of charge that will break down the insulating properties depends on the distance and particular elemental makeup of the air. The shorter the distance and the higher the humidity (water is a better conductor than air) the higher the possibility electrons will pass through it. It is usually considered that it requires about 20,000 Volts of charge to break down 1-inch of air. e.g.: if you build a static electric generator (van De Graf generator, or Whimhurst machine) and it will spark over a 1-inch gap, then it is producing 20,000 Volts. (Once the air gap has been breached, the air is then ionized and the Voltage required to continue the spark is then lower and the spark can go farther, but the initial Voltage to spark over a 1-inch air gap would be around 20,000 Volts.)
If you shorten the distance between the two areas, or reduce the insulating properties by inserting a good conductor (metal, such as iron, copper, aluminium, etc.) in the gap between the areas, then the Voltage required to jump the distance will be reduced. Higher humidity will reduce the resistance between the two points considerably and allow a much lower Voltage to push electrons across the gap. So the air associated with a rain storm will conduct electricity much more easily (lower electrical potentials will produce lightning) than clear dry air.
If you are standing on the fareway of a golf course and there is a large electrical charge difference between the ground you are standing on and somewhere in the sky, there is the chance that lightning will jump from the sky to the ground (or vice versa). Even on a clear sunny day! But more likely in a storm. If you raise a metal club (or an umbrella) over your head, then you have introduced a good conductor between the two areas of charge and reduced the insulating properties of the total media between the two. If the metal is, say 3 ft long then you have reduced the distance between those areas by 36-inches, and reduce the necessary Voltage to jump the distance by 36 * 20,000 Volts or 720,000 Volts, give or take a tiny fraction of a Volt required to make the golf club or umbrella to conduct.
Remember that the air gap between the ground and some arbitrary area of the sky is an amorphous conglomeration of gasses (nitrogen, oxygen, carbon dioxide, radon, etc.), water and other vapors, and dust of various content, all in varying concentrations and all with various conductivity and suceptability to breaking down their resistance to conduction; so the straight line distance between the two areas is not necessarily the distance that presents the lowest resistance to the conduction of electricity. This is why lightning is often so jagged in its path.
ANYTHING that is inserted into the area between two electrical charges, will change the amount of Voltage required to conduct electricity between the two areas. Might cause the Voltage to go up in order to conduct or might make it go down. Doesn't matter whether it is a Steam Locomotive, Diesel locomotive, Automobile, bicycle, human body, golf club, umbrella, tree, wire, spray of water from a garden hose, etc.... doesn't matter, it will change the level of Voltage at which conduction will occur. Metal and wet things tend to reduce the necessary Voltage to conduct; plastic, glass, dry wood and other things tend to increase the necessary Voltage to conduct.
Note also, that "like charges" repel. Electrons, all being negatively charged, are always pushing away from each other. To get two electrons to get close together requires the equivalent positive charge of the two electons in that place, or more electons around the two pushing them toward each other.
Lightning often branches out because the electons, in their travels, are pushing away from each other and if there is a path that presents an easy way to get farther apart, they will take it (obviously firm believers in what Yogi Bera said; "When you come to a fork in the road, take it!").
Semper Vaporo
Pkgs.
Ya, I can't say I've ever heard of an engine being hit by lightning. If engines were made of copper they might attract lightning, not sure about steel attracting lightning.
I have a book that Dad bought from Frisco that had a lot of stories about the RR over the years. Steamers did have a problem with tornadoes and high winds. One steamer was not even able to move forward because of the wind, the wheels just kept spinning but they were not going anywhere.
No mention of any problems with lightning.
Speaking as an electronic technician, if a crew member happened to be touching bare metal when the lightning struck, they MIGHT have gotten a shock, possibly even a burn, but probably not fatal, unless directly struck!, If wet, they may have sustained a greater injury, but STILL not fatal! However, being knocked out, or reaction to the current can cause MORE injury! And, as mentioned, the frame and chassis would conduct the great majority of current AROUND them, to the wheels and rails, to ground. In addition, unless on a fairly flat plane where the engine stuck out higher, more than likely, trees and hills would get the strike. Lightning tends to go the most convenient, shortest route!
Which is known as "skin effect" and will be even more pronounced in a locomotive due to it being sheathed in steel (ferromagnetic). IIRC, the wiring on a steam locomotive is encased in conduit, which should provide for a fair amount of protection for the wiring, though I wouldn't want to have my hands anywhere near a switch when the lightning struck.
And actually, the lightning will travel along the surface of the locomotive since it is the path of least resistance. This happens all the time with the airline industry. A plane gets hit by lightning, but lands as if nothing happened. Instruments are intact and everything. It is only in the worst case scenario that the instruments are messed up. And since a steam engine is run on steam with almost no electrical wiring (ignoring the electricity generated by the generator) there is almost nothing for the lightning to mess up on a steam engine anyway.
The Lehigh Valley Railroad, the Route of the Black Diamond Express, John Wilkes and Maple Leaf.
-Jake, modeling the Barclay, Towanda & Susquehanna.
If a locomotive is hit by lightning, a little bit of the lubricant in the axle bearings might get fried - but not enough to matter.
People who work with Tesla coils (those gadgets that throw off lightning bolts) either stay inside the dome and watch instruments or put on metal mesh suits and play with the multi-megavolt discharges. There's a popular act here in Las Vegas that features such a performance.
Back when the Brits were running open-cab locos those crews might have been in danger. (That, incidentally, is why our friends in the UK call a cab a, "Footplate.") Once enclosed cabs became common the danger pretty well went away. Even a wooden cab wet with rain would probably carry the discharge on its outside surface. Since, on locos with wood cabs, the stack was usually the tallest piece of grounded metal, the cab was unlikely to take a direct hit.
Chuck
I remember reading a story about how a railfan was watching a couple sets of Milwaukee road box cab electric locomotives, pulling a train out of a yard when the overhead wire broke and landed right on top of the cab of the electric locomotive. He said sparks were flying at least 30 feet in every direction, with huge flashes of blue light. When everything was over he talked to the engineer and asked him if he was ok. He said he was smoking a cigarette just like nothing had happened and told him one of the wires must have broke. As we all know, electricity always takes the shortest route to ground. Since the locomotive is already grounded to the rails nobody would feel a thing.
A steam locomotive (or any vehicle) is not likely to "outrun lightning"! As for outrunning the storm to get away; that would only happen if the tracks are in the right direction. The train is just as likely to "run IN" to the storm as away!
But as for danger to the crew inside... if all arms and legs (and heads!) are "inside" the cab, the crew is in no more danger than you are in your car. The metal frame will tend to carry the electrical charge around the cab and not to the interior. In electricity, "like charges" repel each other. Electricity is a negative charge so it tends to spread away from itself rather than come into a space. (the branches of lightning are not individual bolts coming together; it is one bolt spreading out to follow the paths of least resistance). The interior of the cab would have to have a high more positive electrical charge for the lightning to enter into it.
Being a large (tall) metal object (and all "wet" if in the rain) connected to rails laying on the ground does present a low resistance to the flow of electrical charges and so, like a golf club or umbrella held over your head would tend to be a part of the path an electrical discharge would likely follow.
The crew IN the cab "SHOULD" be relatively safe from the lightning... but static electrical discharges tend to go in odd directions and can sometimes infiltrate into areas one would think benign and not normally a carrier of electricity.
I'm curious about if there were problems in the days of steam that engine crew members where zapped by lightining in the cab. After all, steam locomotives are like 99% steel which conducts electricity. Also, I would assume that the railroad wouldn't stop the trains just because of the lightining storm. On the flip side, wouldn't the trains be able to "outrun" the lightining for the lack of a better word?
Lone Geep
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