Can air itself be theoretically considered as a (very poor) wireless ESD grounding strap?

Question

There are many kinds of questionable ESD wriststraps available which claim to provide ESD protection "wirelessly". When asked about how exactly they work, they cite dubious claims about physics as their theory of operation. Many experiments have repeatedly shown that they're ineffective at preventing ESD from the human body for the purpose of electronics manufacturing. One can find many publications from both trade journals and personal blogs. In fact, a teardown showed some "wireless" ESD wriststraps are just regular wriststraps without a wire installed - even the megaohm resistor was kept as-is, making them a big joke among engineers.

But thinking from here, it makes me wonder whether the air itself can be theoretically considered a "wireless ESD grounding strap" - although a very poor one with negligible effect in most applications and are certainly not a practical device for ESD protection during electronics assembly. It's based on the following ideas:

1. Air is an insulator but its conductivity is non-zero.

2. It's possible to define an electric potential from air to Earth ground. Above an idealized Earth ground or seawater, there exists an electric potential gradient around 100 V/m (when the field is not distorted by a conductive object).

3. When equipotential grounding is impractical, an air ionizer can be used as a workaround to increase the conductivity of air, thus reducing the occurrence of ESD by allowing charged objects to discharge to ground. Similarly, increasing the humidity of a room has the same effect.

4. Some applications discharge ESD directly into the air. For example, on aircraft, high static potentials can build up on airframes due to triboelectricity, so they include sharp static discharge wicks to discharge ESD into the air in a controlled manner. (This discharge takes place even without a wick, the purpose of a wick is to ensure that it originates at a predictable location instead of a random piece of metal).

Thus, one can imagine the following thought experiment:

Imagine an ESD-safe room. In this room, its floor and all of the workbenches are covered by ESD mats, and are all bonded to the power ground, and thus, the Earth ground. Now imagine an object is suddely magically created, insulated from ground and with an extremely high potential with respect to the Earth ground. Now the experiment is started. Initially, an electrostatic discharge to air occurs. If an object has a sharp point, it would occur at this location, if it does not, it occurs at a random location. After this discharge, its potential is equalized to the potential of the air at this height, perhaps 100 V plus a residue value.

Question

1. Does it make sense? - Is the thought experiment correct, at least in a rough sense?

2. Would it work? - Theoretically, does the same thought experiment work for the human body? If so, is it correct to say that air is a ESD grounding strap? (but with negligible effect in practice, of course).

3. Would it really happen? - Is there any theoretical scenario that would create a static potential on the object (or human body) so high that it would spontaneously discharge into the air, with or even without a sharp point? Entirely hypothetical scenarios are acceptable, such as assuming the humans are spherical and initially charged in a vacuum.

4. If it does work, how practical is it? - If such a scenario indeed theoretically exists and the "ESD protection from thin air" theoretically works, how much static potential does the object (or human body) need to have before a discharge takes place, and how much residue potential is still on the object after the discharge takes place? From my experience with spark gaps, I think the voltage involved is around many kilovolts, but I'm not sure how a ESD discharge from an object into the surrounding air can be analyzed (unlike the case of discharging to ground, which is a simple dielectric breakdown problem), pointers to relevant books and papers would be appreciated.

In summary, the question is whether an electrically-charged object can be spontaneously be discharged to air.

Answer 1

Does it make sense? - Is the thought experiment correct, at least in a rough sense?

Air has about 10^9Ω to 10^13Ω depending on conditions like humidity and composition and the amount of ions in the air, so it's a very bad pathway for current. Yes 'high' points create a better pathway by shortening the distance and by creating a higher electric field gradient for elections to jump off of/onto.

ESD can occur without an ESD event, some gates of mosfets (not usually these days because they have ESD protection built in) can be blown out just by exposing it to an electric field - the gates are nanometers thin and it doesn't take much voltage build up to exceed Vgs and blow them out. The whole point of ESD safety and protection is to make sure nothing in the room is at a high potential vs ground, because it's the electric fields that can also cause problems. In an aerospace ESD bench, you can't even have materials like paper or certain types of plastic because they can develop charge. Another problem is humans, they develop charge and touch a device and then cause damage. ESD safety is also to keep humans at the bench potential.

Would it work? - Theoretically, does the same thought experiment work for the human body? If so, is it correct to say that air is a ESD grounding strap? (but with negligible effect in practice, of course).

No. Air is definitely not an ESD grounding strap. Even with ionizers and humidity control to help make air more conductive, it's not sufficient to replace an ESD strap.

Would it really happen? - Is there any theoretical scenario that would create a static potential on the object (or human body) so high that it would spontaneously discharge into the air, with or even without a sharp point? Entirely hypothetical scenarios are acceptable, such as assuming the humans are spherical and initially charged in a vacuum.

It's really the potential that matters and the breakdown of air, at a certain point the air ionizes itself to the point it becomes a plasma and then it becomes very conductive. Sharp objects help this process, but its really the breakdown of air that makes a spark, not the object.

If it does work, how practical is it? - If such a scenario indeed theoretically exists and the "ESD protection from thin air" theoretically works, how much static potential does the object (or human body) need to have before a discharge takes place, and how much residue potential is still on the object after the discharge takes place? From my experience with spark gaps, I think the voltage involved is around many kilovolts, but I'm not sure how a ESD discharge from an object into the surrounding air can be analyzed (unlike the case of discharging to ground, which is a simple dielectric breakdown problem), pointers to relevant books and papers would be appreciated.

For the reasons listed in the first question having any electric field potential near a bench or in an ESD protected space the idea of the use of air as a way to mitigate ESD is a non-starter.

Answer 2

Does it make sense? - Is the thought experiment correct, at least in a rough sense?

I'm not clear what part of your question is "the thought experiment". But you are correct that it is possible for highly charged objects to discharge through the air.

Would it work?

Yes, it is possible to discharge objects through the air (you yourself mentioned the use of ionized air curtains). But no, without the use of ionized air, it won't discharge the object completely and reliably enough to fulfil the function of an ESD strap, which is to prevent damage to the object or to other sensitive devices nearby.

Would it really happen? - Is there any theoretical scenario that would create a static potential on the object (or human body) so high that it would spontaneously discharge into the air, with or even without a sharp point?

Of course it is possible. We have photographic evidence:

(source: Physics Stackexchange)

If it does work, how practical is it? - If such a scenario indeed theoretically exists and the "ESD protection from thin air" theoretically works,

It is entirely impractical as ESD protection. The discharge itself is likely to cause the damage that we normally use ESD protection to avoid.