13 June 2014

How We Infuriated Two Generals and a Town Mayor

by Dixon Hill

(For those wondering why my comments disappeared for a while this week, all I can say is that I was recovering from horrifying flash-backs brought on by Leigh’s kidney stone post. LOL)

Two weeks ago, I posted here asking what readers thought of mixing romance and mystery genres.

I wondered: When do the two genres make a good fit, why does this happen (or not), and how can a writer mix the two genres to best effect? I received many excellent comments, which I’ll talk about in my post on June 27th.

I’ve also thought a lot about those comments, as well as other ideas associated with genre mixing, and have formulated an idea I’d like to submit here. That, too, will have to wait until my next post, however, if you don’t want to read something seven pages long.

So, in the interest of brevity (he said, a bit deceptively), I will first tell you a humorous story that is very important to the idea I plan to submit for your comments on the 27th. It’s about how explosions create sine waves, and ways in which the amplitude of these sine waves may be manipulated—which probably sounds as entertaining as doing the laundry. But, please: bear with me. I think you’ll like this.

A Quick but Important Explanation 

Harmony and resonance are two terms most people probably identify with music. Being more comfortable with explosives than music, however—as my grade school band leader could undoubtedly attest!—I’m probably more inclined to think of harmony and resonance in relation to shockwaves created by the carefully synchronized detonations of properly located charges.

These shock waves, created when explosives are detonated, manifest themselves as sine waves that travel through those items targeted for demolition. In fact, according to explosive theory, they are largely the force that does the dirty work: tearing steel girders apart, punching holes through reinforced concrete, or throwing dirt high into the air while creating large holes in the ground.

They don’t just travel through the demolition target however. These explosion-created sine waves travel through the surrounding earth and air (or, in some cases, water), and can sometimes be felt miles away from the blast site, usually manifesting themselves as a rumbling roar and causing plates or windows to rattle, walls to crack, or glass to shatter. 

How I Learned to Play With Sine Waves 

Using sine waves to proper effect is an important part of explosives theory, of course, which I learned in the demolitions portion of the Special Forces Qualification Course.

Years after I graduated the Q Course, however, and was on an A-Team, we had a fellow from a civilian blasting company come out to share information about how he used explosives to break up rock at a nearby quarry. Around twenty of us (SF Demo Sgts.) went down to one of the demolition ranges at Ft. Bragg, where we met a nice young man. His boss had sent him down there, saying the young guy might learn something, too, if he kept his eyes and ears open while working with a bunch of SF guys. He proudly showed us the sausage charges and “nonel” ignition system he used, as well as his computer.

Then, we monkeyed around with them in a manner that really freaked this guy out, and got us in trouble.

What We Played With

The “sausage charges” he brought were well named. These low-order explosive charges really did look like oversize Jimmy Dean sausages—the kind that come stuffed in plastic tubes at the grocery store. Each tubular plastic-wrapped charge was probably about two feet long by four inches in diameter.


nonel fuse
The nonel fuse ignition system, which he commonly used to set off his charges, came with a blasting cap factory-installed on one end of each short fuse section. This fuse was tiny, compared to standard time fuse, probably about a sixteenth-inch in diameter and bright orange. It was also a bit stiffer than time fuse.

“Nonel” is considered an instantaneous non-electric firing system because that thin, orange plastic-tubed “fuse” carries a powder train designed to ignite at the rate of around 2000 meters per second. Thus, the person doing the blasting (called “the blaster”) connects a firing machine to one end of the nonel, then pulls a trigger, or pushes a button, which creates a spark that ignites the powder train. The flame shoots down the length of the fuse at around 2000 meters/second, finally shooting a brief spit of flame into the blasting cap at the far end and—BOOM!

Nonel is not really instantaneous, of course. It takes a little while—maybe half-a-second, or a second or two—from the time the blaster hits the button, to the instant of explosion, depending on distance from blaster to initial charge. But, nonel ignition is fast enough; it’s generally considered instantaneous.

Nonel clipped together for firing.
Nonel fuse is available in large rolls, so the blaster can get some ‘standoff distance’ before detonating his/her charges. As I mentioned earlier, however, it also comes in short sections. These sections can be rapidly and easily clipped together, and the ones we were using had 25-millisecond delays built into them.

The photo above, right, shows a short segment of nonel with a blasting cap at one end and the clip at the other. The photo at left shows multiple nonel fuses linked together.


How It’s Supposed to Work

Our visiting quarry blaster normally used his computer to create a model, which told him where to place his charges and how many milliseconds to delay each detonation by, in order to reduce the impact on people or structures in the local area.

By placing his charges where the computer told him to and using the computer-suggested time delay between detonations, he was able to cause the explosive sine wave created by one detonation to be cancelled out, when it collided with the sine wave created by the next detonation, and vice-versa.

You may recall, from my earlier posts about explosives, that ‘low order’ explosives may be thought of similarly to ‘low gear’ in a truck—they push and heave heavy things, like dirt and rock. This means their sine waves are very powerful. So, using distance and time-delay to cancel-out the sine waves created by these explosions strongly muted what, otherwise, would have been a series of long, deep sine wave vibrations created by low order explosives, from shaking up people in the surrounding areas or potentially damaging buildings hit by the deep sine wave’s rumbling THUMP!

Roots of an Idea

The first time we took the explosives down-range and set them off, we did it the way the guy suggested. We wanted to see how well the technique worked. And, it worked pretty well. In fact, the result was rather boring.

Each man set up two charges, for a total of around forty charges. Since the blaster had only brought a limited amount of ‘standoff’ nonel fuse along, that day, we used time fuse to detonate the initial charge, daisy chaining the rest of our charges with those nonel sections that incorporated the 25-millisecond delays.

Forty charges went off, each about 25-milliseconds apart. Nothing to write home about. There wasn’t even a satisfactory big THUMP! in the ground beneath our feet, because the charges had canceled out each other’s sine waves.

While walking down to plant those charges, however, a few of us, who’d been talking it over, asked the visiting quarry blaster if he thought adjusting the calculations for charge location and timing, in ‘thus and so’ manner might result in something a bit more exciting.

“Oh, you wouldn't want to do that,” he said. “That might increase the amplitude of the sine wave instead of canceling it out.”

“Exactly!” we responded, smiling. At this point, we reached the location where we had to fan out and start planting our charges.

We couldn't ask him more questions on the way up the range to the bunker, before firing that first shot, however, because he wasn't with us. Evidently, he’d used nonel all his life, and never dealt with time fuse before.

When we ignited the time fuse, to set off the initial charge, his eyes went wide and he said, “What are you doing?”

“Igniting the time fuse.”

“While we’re still here? Standing beside the charges!?!”

“Well, we’ve got four and a half feet of time fuse. That’s enough to let us get back to the bunker.” 

“But … we aren’t leaving!”

“Right. We have to make sure the time fuse is burning, first. Then, we’ll remove the mechanical matches from the fuse, so we can reload them.”

“WHAT!?! The fuse is burning? NOW?

“Yeah, see how it’s melting here? That’s good. In just a minute we’ll be able to remove—”

But that guy was gone, buddy! He looked like a character on Scooby Doo, legs churning wildly as he smoked-it back up the hill to the bunker.

The rest of us followed at a leisurely pace, a few of us discussing our idea of increasing the sine wave’s amplitude. We figured the idea made sense, but we had to decide how to calculate for it.

How We Pissed-off A Lot of People

When something happens that changes the size of a sine wave, it’s called Amplitude Modulation. When the quarry blaster used his charges to cancel out his explosions’ sine waves, that was just another example of amplitude modulation. And the small group of us, who’d been discussing how to increase the amplitude of the sine wave, were really discussing just that—amplitude modulation.

By now, we’d formulated a few ideas about how to accomplish what we wanted. So, while standing in the bunker, waiting for the time fuse to burn down, we quizzed our visiting blaster about what he thought.

He professed not to know, saying there was no way to tell what the result would be. He even kept claiming he didn’t know what formulas his computer used to arrive at its conclusions. Naturally, a bunch of guys who walked around, on a daily basis, with umpteen charge formulas, relative effectiveness factors, and other arcane explosives details in their heads, found this claim a little suspect. Besides, he kept interspersing this claim with the statement: “You guys are scary. You’re really, REALLY scary!”

Unfortunately for this fellow, he’d chosen the wrong words.

His repeated “You’re scary” encouraged us to believe we were on the right path, so we continued with our discussion. And, other guys heard this repeated phrase and came over to find out what he was talking about. After all, they wanted to be scary too.

By the time our first set of charges had disappointingly gone off, everyone was discussing the idea. In the end, about fifteen of us decided to experiment with a rudimentary formula on the next shot, while the rest decided to just adhere to the original plan.

We ran our calcs, then took our charges (two per man, again) down-range and planted them. This time, our visiting blaster decided not to accompany us, staying at the bunker and trusting the sergeant in charge to connect his standoff line to the daisy-chained line segments.

With everyone back up in the bunker, the visiting blaster hooked up his blast machine and fired.

The charges of the first five guys—ten charges total—went off, cancelling each other’s sine waves.

Then, one by one, the next thirty charges went off …
… the sine waves building on each other as they went along.

Each time another charge went off, the blast got louder, deeper and more satisfying. Soon, though we wore earplugs, we had our hands over our ears, and the ground beneath our feet was dancing a nice jig. Finally, it all came to an end. The final shot was not visually exciting, but the roaring cacophony and deep thump in our feet were truly GLORIOUS!

Amid an extended round of whistles, yells and cat calls, I turned to look at the young quarry blaster. I can still see him in my mind’s eye: blonde hair sticking up on one side, where he’d yanked on it with his hand, face ashen, eyes wild. He looked as if he’d just survived a strafing run by an A-10.

I was still laughing when the field phone in the bunker went off. People were making a lot of excited noise, but the instant the sergeant in charge, who’d answered the phone, popped to rigid attention, all noise cut off abruptly. We knew what his behavior meant. It was Pavlovian, and we’d all responded in similar manner in the past. Every man in the bunker knew: somebody BIG was tearing into the sergeant on the phone.

In the sudden silence, we could hear the angry voice bellowing on the other end, but not what he was yelling. On his end, the sergeant just kept answering with things like: “Yes, Sir!” “Only twenty charges, sir!” “I’m sorry, sir. That wasn’t planned.” “No, sir. It wasn’t intentional.” “I understand, Sir!” “It won’t happen again, sir!” “Yes, sir! Yes, sir!”  He concluded with the phrase: “Crystal, sir!”

After he hung up, the sergeant turned his back to us, asking: “So, I know most of it’s missing, because it just got royally chewed off, but . . . have I got ANY ass left?”

He explained that the caller had been the General commanding the 18th Airborne Corps and Fort Bragg. In other words, this was the guy who issued the commanding generals of the 82nd Airborne and 101st Airborne Divisions, and several other major units, their marching orders. He had none-too-gently informed the sergeant that his staff was receiving reports concerning our little science experiment from across Ft. Bragg and the gate town of Fayetteville, as well as personal phone calls from the commander of Pope Air Force Base next door, and the Fayetteville mayor who was upset that shop owners were complaining of damaged merchandise.

To top it off, the 18th Airborne Corps Commander’s wife had called him directly, to complain of a house that rocked from the blasts and windows that had threatened to shatter—as well as an expensive antique China tea set that had been bounced around, and which she was currently inspecting for potential damage.

“Pray the tea set has no cracks,” said the sergeant. “The general said he’d call me back, if it was damaged.”

Thus, our little science experiment ended— at the direct orders of the 18th ABN Corps Commander.

Thankfully, the sergeant in charge never got a call about the tea set. But, I never forgot what I learned about amplitude modulation that day, and the way it can depend on location and timing.

And, that’s the take-away I want you to remember for my next post, on June 27th.

See ya’ then!
—Dixon

13 comments:

Leigh Lundin said...

Dixon, it is entertaining! I seldom LOL– usually a quirk of the lip implies I find something funny. This time, I grinned through most of the article in appreciation and when the sergeant hung up the phone, I really laughed.

Throughout, I kept recalling my old college, not NYU but Rose Polytechnic, now called Rose-Hulman. It’s a top science and engineering campus with some ultra-brainy guys– think Big-Bang Theory with a thousand cast members. How admissions screwed up and let this joker in, no one seems to know.

Brainy guys pull brainy pranks (or geeky if you prefer), like using studio speakers to create standing waves to blast open doors. As I read your article, Dixon, I kept thinking thank God we no one had built major explosives.

Dixon, a question: Can nonel or time fuses have different topologies? In other words, can’t one fuse line feed multiple dependent lines, like one column of dominoes triggering two, which trigger four in a chain reaction? Assuming that’s true, how does that affect demolition planning?

Fran Rizer said...

Dixon, I enjoyed this tale and will remember it until the 27th (possibly even longer). I think I know where you're headed, and I'm eager to see if I'm correct. I'm dealing personally with a situation involving genre which I'll save until the 27th to share.

Anonymous said...

Oh man! You know what this made me think of (pedestrian by comparison as it is), is that when I was restoring an antique tractor and got on an online forum, I heard tons of stories about "blowing up things" from all these guys. Their favorite and best thing to do was find a way to get a really satisfying THUMP (as you say) and simultaneously see something fly into the air high enough to threaten local airspace regulations. Roger Welsch, who was on CBS Sunday Morning with Charles Kurault for years and wrote books about his own experiences restoring old tractors, claims that "blowing things up" is men's primary mode of amusement, genetically in-built. I think I'm going to have to share your blog post with him!

Leigh Lundin said...

Anon, I'm curious. What kind of tractor? I bought my dad a 1947 John Deere model L that he restored. He found a company in Indianapolis that still had the molds to pour tires!

(Sorry, Dixon– my ADD sidetracked me.)

Dixon Hill said...

Leigh, with standard time fuse, I think you could carefully trim the ends and use electrical tape to seal them together so the powder train of one fuse is butted up against the powder train of the other, and this might result in a longer piece of fuse that worked for you. However, I wouldn’t recommend this approach, and I’d give such a hookup a fairly low probability of success—probably no more than a 50/50 chance of working right.

To use one standard time fuse line to set off multiple non-co-located charges, the preferred method is to run your time fuse to a blasting cap that’s taped to a det cord ring main, then run det cord lines from the ring main to caps in your charges. I’ll run a post some time about det cord ring mains, if you’d like.

NONEL: I’m not all that familiar with nonel, quite frankly. The occurrence I posted today was the only time I can recall working with it, and that took place over twenty years ago. So, I’m not really sure, but . . . the way I recall it, nonel fuse just had to be clipped together.

In truth, it may be that the standoff line, such as the one used on that second shot, was some form of specialized det cord. I seem to remember that our visiting blaster actually referred to the fuse as “firing line,” or “det cord,” or something like that—though it in NO way resembled standard detcord when it went off, because the cord itself did not blow apart. Instead, if memory serves me right, the powder train in nonel runs down just one side of the “fuse” interior, leaving most of the inner plastic tubing filled by air.

To clarify what I mean: imagine standing in a sewer line about six feet in diameter, with only about a 1-foot-deep stream of water running through it—this would be about roughly the ratio of the powder train to the inside of the “fuse” tubing, or at least that’s the way I recall the idea. I believe it’s intentionally set up this way, because the nonel tubing is closed at either end, which helps promote a sort of “flash over” effect, essentially sucking the flame down the tube, thus boosting the burn rate of the powder train, which helps explain how it gets that 2000-m/s burn rate without actually blowing apart.

Here’s a URL for a PDF concerning a little of what I’m talking about. Finding the main dyno nobel site may provide better clarification, and more factual information: http://www.dynonobel.com/apac/~/media/Files/Dyno/ResourceHub/Technical%20Information/Asia%20Pacific/Initiation%20Systems/NONEL%20MS%20HD%20Series.pdf

Incidentally, that sounds like a fun school!

Dixon Hill said...

NO problem, Leigh. As the song might indicate, it always helps if: "She finds my tractor sexy!"

Dixon Hill said...

Fran, I'll be looking forward to your comment!

Dixon Hill said...

ANON: Feel free to share the post! The more the merrier.

R.T. Lawton said...

Dix, great story. With your words, I could picture the events almost as if I were there.

Dixon Hill said...

Glad to hear it, R.T. Your posts are an inspiration.

Anonymous said...

Leigh, I was restoring a 1950 Ford 8N. Roger Welsch restored old Alice-Chalmers, I forget what years but I think from about that same time period. Might have been about the same age as your dad's John Deere. Fun stuff!!

Anonymous said...

There was one occasion with a crazy bunch of English Civil War re-enactors when a replica of a monmouth rebellion nine-pounder needed re-proofing. We arranged for this to happen on a military range, of course so he's loaded up with an excessive amount of powder and double-shotted and we all huddle behind the sandbags as the gun-captian uses an extra length linstock to touch off the gun from back there with him ducking down as soon as he gets the match into the touch-hole.

Now, we were not the only occupied gun pit on the range at the time. Some of Her Majesty's finest were exercising with their field pieces, making the typical flat "crack" of modern pieces using modern propellants.

Then ours goes off. There's this god-awful BANG! the ground shakes and (the piece being charged with black powder) huge clouds of sulphurous-smelling white smoke.

The range sergeant comes boiling up out of his dugout looking like he just had an accident in his BDU pants screaming at teh top of his lungs "WHAT THE F*** WAS THAT????"

The squaddies on the rest of the line bought us drinks all night, just for the effect we had on the range sergeant.

Leigh Lundin said...

Thanks, Dixon. Your articles are explosive and fun; we can't get enough of them.

Anon (American): Our little county celebrated Pioneer Engineer's Day, which today features vintage gasoline and diesel tractors of the era, but when I was a kid, focused on antique steam traction engines. There was something special about those huge machines with their acrid eye-stinging smoke, virtually silent except for their whistles and clanking parts.

Anon (British): What a great story to accompany Dixon's article. You make a deeper point, too, that as much fun as re-enactors have now, the battlefield was a frightening place.