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“8000 megatons is nothing to worry about. It’s a very quick way to die.”

Only if you’re relatively close, or on a coast that gets hit by a tsunami. On the grand scale of things, 8,000 MT isn’t so bad. The Chixclub (dinosaur killer) impact was 100,000,000 megatons.

If you’re over 100 mi. away you’ll escape without a scratch if it’s a land strike. At 62 mi. (100 km) here are the results from the U of A impact calculator:

Your Inputs:
Distance from Impact: 100.00 km ( = 62.10 miles )
Projectile diameter: 476.00 meters ( = 1560.00 feet )
Projectile Density: 3000 kg/m3
Impact Velocity: 20.00 km per second ( = 12.40 miles per second )
Impact Angle: 60 degrees
Target Density: 2500 kg/m3
Target Type: Sedimentary Rock

Energy:
Energy before atmospheric entry: 3.39 x 1019 Joules = 8.09 x 103 MegaTons TNT
The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 1.3 x 105years

Major Global Changes:
The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the tilt of Earth’s axis (< 5 hundreths of a degree).
The impact does not shift the Earth’s orbit noticeably.

Atmospheric Entry:
The projectile begins to breakup at an altitude of 56600 meters = 186000 ft
The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 19.7 km/s = 12.2 miles/s
The impact energy is 3.29 x 1019 Joules = 7.87 x 10^3 MegaTons.
The broken projectile fragments strike the ground in an ellipse of dimension 0.767 km by 0.664 km

Crater Dimensions:

Crater shape is normal in spite of atmospheric crushing; fragments are not significantly dispersed.

Transient Crater Diameter: 6.77 km ( = 4.21 miles )
Transient Crater Depth: 2.39 km ( = 1.49 miles )

Final Crater Diameter: 8.73 km ( = 5.42 miles )
Final Crater Depth: 568 meters ( = 1860 feet )
The crater formed is a complex crater.
The volume of the target melted or vaporized is 0.254 km3 = 0.0609 miles3
Roughly half the melt remains in the crater, where its average thickness is 7.05 meters ( = 23.1 feet ).

Thermal Radiation:

Time for maximum radiation: 325 milliseconds after impact

Visible fireball radius: 5.63 km ( = 3.49 miles )
The fireball appears 12.8 times larger than the sun
Thermal Exposure: 1.33 x 10^6 Joules/m2
Duration of Irradiation: 1.39 minutes
Radiant flux (relative to the sun): 15.9 (Flux from a burner on full at a distance of 10 cm)

Effects of Thermal Radiation:

Much of the body suffers second degree burns
Deciduous trees ignite

Seismic Effects:

The major seismic shaking will arrive approximately 20 seconds after impact.
Richter Scale Magnitude: 7.2
Mercalli Scale Intensity at a distance of 100 km:

VI. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.

VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.

Ejecta:

The ejecta will arrive approximately 2.4 minutes after the impact.
At your position there is a fine dusting of ejecta with occasional larger fragments
Average Ejecta Thickness: 1.88 cm ( = 0.739 inches )
Mean Fragment Diameter: 5.49 cm ( = 2.16 inches )

Air Blast:

The air blast will arrive approximately 5.05 minutes after impact.
Peak Overpressure: 26700 Pa = 0.267 bars = 3.79 psi
Max wind velocity: 56.7 m/s = 127 mph
Sound Intensity: 89 dB (Loud as heavy traffic)
Damage Description:

Interior partitions of wood frame buildings will be blown down. Roof will be severely damaged.

Glass windows will shatter.

About 30 percent of trees blown down; remainder have some branches and leaves blown off.

I guess the model is now hosted in the UK, it’s pretty fun to play around with:

http://impact.ese.ic.ac.uk/ImpactEffects/

I doubt you want to be a lot closer than 62 miles... ;-)