Why would defusing a WWII "1.8 ton" bomb require a 1.5 km evac radius?

See query–in Frankfurt, a “British bomb,” while in Koblenz, with apparently a similarly wide evac zone, for a “500 kg US bomb.”

(Both numbers are weird, the US reference obviously, and that’s all I have from AP. I did find a nice “Bombs of WW II” research page, though.)

Fragments can go a long ways.

There was a building demolition that killed a child a quarter mile away.
Royal Canberra Hospital implosion

We have to differentiate between the effective radius and the safe radius. The effective radius is the radius at which there is a sufficiently high probability of the desired effects so as to be useful to the chosen tactics. Being out of the effective radius doesn’t mean you’re completely safe. For example, a 1lbs hand grenade may have an effective radius of 15 meters but you might still get hit with fragments up to 250 meters* if you’re unlucky. So, with a 500kg bomb, they’re playing it safe to avoid even low probability cases of injury.

Like a lot of things in life, Murphy’s law provides the explanation. If you’re dropping a bomb and trying to take out enemy soldiers in a war, you concern yourself with the radius where the bomb will have a high chance of taking out enemy soldiers. If you don’t hit the targets, then they’re around to shoot back at your guys later. So if there’s a distance from the bomb where 95% of enemy troops will be unscathed, you should just consider the bomb useless at that distance when you drop it. In peacetime, in contrast, you don’t want anyone to get injured, and there isn’t a strong reason for people to be in the area - it’s not like they’re holding a bridge against enemy troops. So you evacuate a larger area, maybe out to where there is a 99.99% chance of people surviving uninjured, because you can and you don’t want injuries. Murphy’s Law is relevant because if you’re trying to bomb the enemy, you should expect not to get lucky and hit them with long-range fragments, but if you’re trying to protect civilians you should expect that they will happen to get hit.

While the effective radius of the bomb is much smaller than the evacuation area, the authorities now are trying to have zero serious injuries if the bomb goes off, they don’t want a bunch of people hanging around in the “95% safe” zone.

Plus people don’t like being hit with body parts.

Nor whale parts. https://www.youtube.com/watch?v=GkZottYDpEE

However far away you think you need to stand, double it. :smiley:

Nor trains.

There is a whole science area devoted to explosive quantity distance and related arcs. Long story short - someone has calculated the required distance for evacuation based on standard quantity-distance tables. If you have X amount of explosives in the bomb; you must evacuate non-essential personnel to this distance and fudge a little longer. The basic distances are:

Magazine distance - an explosive magazine or bomb detonates and adjacent magazines/bomb to not detonate immediately (see: sympathetic detonation). How much explosive determines needed distance. Conversely, if you have a fixed distance - that distance limits the amount of explosives that can be present. Everyone dies at that distance - strictly to prevent immediate transmission of detonations from magazine/bomb to mag/bomb.

Intraline distance - specifies the required distance between operating explosive line buildings that have dissimilar operations, i.e. explosive melt pour in one building and projectile painting in another. Protects against sympathetic detonation and limits building loss. People will be killed or seriously injured at this distance - property protection.

Public Traffic Route distance - Specifies distance from explosive locations to auto routes, trains, ship channels, etc… Provides a fair degree of personnel protection due to transitory nature of exposure to the explosive site and that a car or other conveyance has structural elements that mitigate the effects of an explosion (shock - fragments). Personnel expected to survive except for driving off the road from surprise/shock.

Inhabited Building Distance (IBD) - provides protection to personnel in the open or in structures. Then there is additional distance factor in for substantial glass exposure (more distance) and way more distance required for accidental or designed demolition operations such as the bomb defusing in this case.

For light (not) reading on this subject you can download incredibly large PDF files of DOD 6055.9 (multiple volumes) or DA Pam 385-64 from the inter-tubes.

There are computer assists now but still a lot of hand calculator work. The equations and constants have multiple exponents stretching into long decimal numbers. I did this stuff for years and it can be mind-numbing. Year-to-year change are also a headache.

Anecdote: We (US contractors and I) are destroying decaying munitions in Iraq after Desert Storm II. Based on calculations for 4 - 25,000 pound net explosive weight pits being donated; we needed 2.7 miles distance for us observers. The guys triggering the explosion just under a mile in a bunker. That worked for several weeks until a different method of stacking and priming the explosives was tried. Undetonated projectiles were thrown and landed beyond where we were standing. We moved back to 4 miles minimum from the “daily” detonations. Our experience also altered the book value equations when we reported our little mishap.

Here is a quote from the DA-PAM 385-64 regarding rogue fragments:

“These calculated fragment throw distances are for individual items and do not apply to stacks. They also do not address “rogue” (non-case) fragments
produced by sections of nose plugs, base plates, boat-tails, or lugs. Rogue fragments can travel to significantly greater distances (for example, greater than
10,000 ft [3,048 m]) than those shown”.

Thanks all.

smithsb, great specialized info. Yet again SD reveals the bestest with the mostest.

So now I have to worry about nose plugs and boat-tails. Let alone stacks. More to add to the list of I-have-no-idea-what-they-are things that can kill me.

Forewarned is forearmed.

There was an episode of mythbusters when they were blowing something up, I think it was the cement truck.

The explosives expert refused to look at the explosion, even though they were at safe distance, but told the others they were free to. It was an odds game. If you are out there once to watch an explosion, you are pretty safe. If you are blowing stuff up on a regular basis, the unlikely starts becoming more likely.

It doesn’t take much of an explosion to start shattering windows.

1.2 tonne might shatter windows quote some distance out.

That was reportedly a British 4000 pound bomb - IIRC the one called the “Blockbuster”. You’d want to be a very long way from that block.

German man reports WWII bomb, police find zucchini

No More Zukes!

It was even an aerially delivered Zuke. Them’s the worst kind.

Maybe it was a zukkelin.

Damn that’s funny!

This is a technology the world must come together to squash.