Do metal objects attract lightning?

Question

I have come across various sources that claim that you should stay away from metal objects (umbrellas, bikes, etc) during thunderstorms because they "attract lightning". One example would be this text from ARD, a public and well respected German TV station.

Sobald ein Gewitter aufzieht, Finger weg von metallenen Gegenständen. Walking- und Wanderstöcke, Golfschläger sowie Eispickel und Karabiner gehören mindestens fünf Meter weit weg. Das gilt natürlich auch für einen ganz normalen Regenschirm - auch wenn es regnet. Der Regenschirm zieht wegen seines Metallskeletts Blitze an.

My rough translation (emphasis also mine).

When a thunderstorm approaches, hands off any metal items. Walking-sticks, golf clubs, ice picks or snap hooks have to be put at least 5m away. This of course also applies to normal umbrellas - even if it rains. The umbrella attracts lightning due to its metal skeleton.

I have a hard time believing that a small metal object like an umbrella will have a significant impact on where lightning strikes. There are als official websites that state that it is a myth that metal attracts lightning, although some acknowledge that being in contact with metal objects can cause more severe injuries if one is struck.

I am looking for recent, trustworthy sources, preferably peer-reviewed, scientific publications, that answer the following questions:

1. Does being in touch with a metal object like an umbrella or a bicycle increase the odds of you getting hit by lightning?
2. Does being in touch with a metal object increase the severity of injuries if you are hit by lightning?

PS: I am aware of this question regarding use of mobile phones during thunderstorms but did not find the answer to my exact questions there.

Answer 1

From Lightning Science: Five Ways Lightning Strikes People:

Metal does not attract lightning, but it provides a path for the lightning to follow. Most indoor lightning casualties and some outdoor casualties are due to conduction. Whether inside or outside, anyone in contact with anything connected to metal wires, plumbing, or metal surfaces that extend outside is at risk. This includes anything that plugs into an electrical outlet, water faucets and showers, corded phones, and windows and doors

and Lightning Myths:

Myth: Structures with metal, or metal on the body (jewelry, cell phones,Mp3 players, watches, etc), attract lightning.
Fact: Height, pointy shape, and isolation are the dominant factors controlling where a lightning bolt will strike. The presence of metal makes absolutely no difference on where lightning strikes. Natural objects that are tall and isolated, but are made of little to no metal, like trees and mountains get struck by lightning many times a year. When lightning threatens, take proper protective action immediately by seeking a safe shelter and don’t waste time removing metal. While metal does not attract lightning, it does conduct it so stay away from metal fences, railing, bleachers, etc.

Trying to make this simple: Lightning is lazy: while it's still in the air it will follow the shortest path to ground and when it has struck it will generally continue the path of lowest impedance until it has dissipated.

The location where lightning strikes will almost always be determined by the shortest path to ground. This will often be any "sticky outy" object that's near by: tall buildings, church steeples, trees, posts, ship's masts, etc. This is completely independent of what material this strike point is made off, it only matters that it is the shortest path.

Metal can make a difference on what happens next. The reason we have lightning rods is that they provide a very low impedance path for the lightning to go into the Earth. So the lightning travels mostly through the metal lightning rod and not through more valuable or vulnerable objects. Touching metal that is connected to Earth ground is generally not a good idea since this is preferred path for lightning. Touching isolated metal objects makes no difference whatsoever.

Does being in touch with a metal object like an umbrella or a bicycle increase the odds of you getting hit by lightning?

That depends a bit on the detail. If the metal objects have good ground connection and/or are sticking out above other nearby objects, than yes. Sticking out your umbrella with a metal tip when standing on a flat field is not so good. Holding the same umbrella when standing on the ground between two skyscrapers is perfectly fine.

Umbrellas don't have ground connectivity. Bicycle tires are good insulators but other parts like kick stand, frame touching a post, chain that connects it to a metal fence are not.

Does being in touch with a metal object increase the severity of injuries if you are hit by lightning?

Again, that depends a lot on the details: what exactly is the metal connected to and how high does it protrude. House wiring is very well grounded and it protrudes high in the house, so this is a concern. Holding a metal pen is no concern at all.

One more note based on the comments (if that's ok)

The physics behind lightning are rather complicated. It's guided by Maxwell's laws, material properties (under normal and high energy conditions), a highly dynamic and nonlinear set of equations, and the exact boundary conditions (geometry, material, layout) of the environment, which is dynamically changed by the lightning itself during its discharge.

Any "rule thumb" will therefore require significant simplification and approximation and you will always be able to find or construct use cases where that rule is wrong or misleading. Hence my simplification "metal that's isolated is generally ok to touch. Metal that as good connectivity to ground or other low impedance thingies you should leave alone". It's not perfect but more useful then "lighting will follow the steepest gradient in the Electric Field which is dynamically reshaped by the discharge"

Answer 2

Lightning is complicated and I don't think there's a simple, straightforward answer to this. I found a really detailed paper about this and it has a lot of detailed content while also being relatively easy to follow. I encourage people to read the full paper here: The physics of lightning. I found it really informative and helped disabuse me of my own incorrect notions.

First off, the most lightning never reaches the ground:

All lightning discharges can be divided into two categories: (1) those that bridge the gap between the cloud charge and the Earth and (2) those that do not. The latter group as a whole is referred to as “cloud discharges” and accounts for the majority of all lightning discharges.

The question is about lightning strikes that might strike a person, who is presumably on or near the ground so we can focus on the minority: category (1) above.

Summarizing from the article:

• About 90% of cloud-to-ground lightning flashes are initiated by a negatively-charged, downward-propagating leader
• About 10% of cloud-to-ground lightning flashes are initiated by a positively-charged, downward propagating leader
• The remaining two types of cloud-to-ground (actually ground-to-cloud) lightning discharges are relatively uncommon and are upward initiated from mountaintops, tall man-made towers, or other tall objects, towards the cloud charge regions

The last point is interesting, I think, but upward lightning is rare and wouldn't typically be a risk to a person unless they were on one of these objects, and I think most people understand that the top of a cellphone tower during a lightning storm is a risky place to be. So we can ignore those as well. This leaves the 'downward strikes'. For brevity, we will also ignore the less common positive 'downward strikes' and focus on the most common cloud-to-earth strikes:

The physical mechanism for moving the negative charge to Earth is a propagating electrical discharge called the “stepped leader”.

This is mechanism is explained as:

The stepped leader’s movement from cloud to ground is not continuous, but rather it moves downward in discrete luminous segments of tens of meters length, then pauses, then moves another “step”, and so on.

Presumably, this gives lightning its characteristic zig-zag appearance. Skipping ahead, we get to the part that is relevant to the question:

When the stepped leader is near the ground, its relatively large negative charge induces (attracts) concentrated positive charge on the conducting Earth beneath it and especially on objects projecting above the Earth’s surface.

The key word 'attracts' appears but to be clear, it is not saying that the objects attract the lightning, but rather that the nearing negative charge causes the ground and objects on the ground to become net-positively charged. To understand this, it's crucial to understand that the earth is, in general, assumed to have a neutral charge. That is, negative and positive charges are balanced. When a large negative charge comes near the ground, that balance is disrupted as the negative charges in the ground are repelled and positive charges are attracted.

When the electric field intensity near ground from these charges becomes large enough, upward-going, positively-charged electrical discharges from the ground or from grounded objects will be initiated, ... One of these upward-going discharges will contact a branch of the downward-moving leader, thereby determining the lightning strike-point and the primary lightning current path (channel) between cloud and ground.

That last bit is important here. The final path to ground is determined by which object or point on the ground initiates the upward positive discharge. So it makes sense that an object that is taller is likely to be closer to the downward leader, in which case, the field strength will be stronger at points on that object that at the ground surface.

And finally:

Understanding the “attachment process” is critical to the proper design of lightning protection systems. Unfortunately, the attachment process is sufficiently complex and variable that it has not been possible to gain more than a relatively crude understanding of it.

So, the answer is complicated. Logically, though, conductivity of the object(s) in question would influence how easily an 'upward-going discharge' will be initiated through that object. So, while the initial claim may not be strictly correct, I think saying it is strictly false is more wrong. Holding a aluminum pole over your head in a lightning storm might be more dangerous than holding an insulating pole of the same length but neither is advisable.

Answer 3

No, metal objects do not attract lightning in the sense that a force is excerted on the lightning pulling it to the metal rod.

The physical process is this: A potential difference or voltage is build up between the clouds and the earth. When this voltage is high enough elektrons are pulled from their atoms in the air and propelled to the positive potential. The electrons are accelerated and then ionize other atoms in their path.The moving elektrons constitute an electrical current. In the path of the current electrical energy is converted to heat and the heated atoms produce light. This is what we call lightning.

Sticking a metal rod in the air shortens the distance between clouds and earth, and thus increases the possibillity of the atoms being ionized as the electrical field between earth and clouds increases. This will not happen with a insulator rod, as the distance between the clouds and lowest potential (earth) is not shortened.

See M.A. Uman. All about lightning, Dover Publications Inc. New York, 1986