In any energy-transfer weapon, from a club to a bullet to a grenade to a nuke, the critical elements are:

1. How much energy is released?

2. Over what time period?

3. In what forms?

4. At what distance from the target / victim?

A bullet which misses you by a millimeter might as well be 1,000 km away. It requires direct contact with tisue to transact damage. Where it hits you also matters, and in many cases, a light interaction with an extremity (hand, foot) may do little damage, whilst a trunk or head shot will be critical or instantly lethal. Much of that comes from the transmission of fluid shock through the body. (Watching super-slow-motion video of bullets impacting various targets on YouTube is ... interesting and informative.)

A nuclear bomb delivers energy to the target in four major forms:

1. Prompt ionizing radiation. This is a pulse which lasts for a tiny fraction of a second, and is rapidly absorbed even by the atmosphere. It can be lethal or disabling at relatively close range.

2. Thermal pulse. Depending on the size of the weapon, this will ignite directly exposed flammable materials at ranges from a few hundreds of meters to a hundred km or so. This can be mitigated with white or reflective paint, or intervening structures.

3. Blast wave. This is the physical shockwave of the weapon (as well as any material picked up by it) which causes much of the direct damage.

4. Radioactive fallout. This is long-term radiation delivered generally downwind of the blast site. Exposure follows the seven-ten rule. For each increase by a factor of seven in time, the radiation falls by a factor of ten. A 1,000 rad dose 1 hour after the blast is 100 rads 7 hours after, 10 rads 2 days (49 hours) later, and 1 rad after two weeks.

The detonations of nuclear weapons are fast, on the order of a microsecond (on one-millionth of a second). In large part it's the ability to deliver all its energy virtually instantly which gives a bomb its power. An alternative understanding comes from the idea of "generations" of nuclear interactions and their timescale -- a typical nuclear blast occurs over about 50 generations, after which the core has generally spontaneously disassembled past the point of sustainable reactions.

(There's a pretty good Quora article on that point here: https://www.quora.com/How-long-does-a-nuclear-explosion-take)

Chemical explosives are far slower -- I believe closer to milisecond (thousandth-of-a-second) range. Or: a nuclear explosion is as much faster than a chemical explosion as a chemical explosion is to change taking a full second.

A table of chemical reaction velocities peaks at 10,000 m/s, or 1 km/s, or 1m / 0.001s, suggesting a typical deonation period of 0.001ms - 1ms.

https://en.wikipedia.org/wiki/Table_of_explosive_detonation_...

Meteor and meteorite impacts are often described in terms of megatons or Hiroshima-bomb equivalents. The Chelyabinsk meteorite is estimated to have released the energy of 20 - 30 Hiroshima-sized bombs, approximately 400 - 500 kilotons of TNT. However:

1. It did so primarily at an elevation of ~30 km,

2. over a period of 5 - 10 seconds,

3. in the form of light, heat, and sonic blast

Much the same as you experience the same total change in kinetic energy whether you decelerate from 100 kph in 10 seconds or 0.01s, the difference is in the total shock and stress, as well as the energy delivered.

TL;DR: a modest-sized nuclear blast high in the atmosphere or above it could have relatively modest ground impacts whilst delivering a strong EMP effect.