by Dixon Hill
A Quick Recap
1.The Explosive Train is a chain of explosions used to detonate a large, stable charge though what’s known as “Sympathetic Detonation” (one explosion causing another).
2.The first explosion in the chain is usually quite tiny; the next a little larger … and so on … until you manage to generate a walloping BANG!
3. The little explosive gadget most often used to initiate the Explosive Train is a Blasting Cap.
4. Blasting Caps come in two primary types: Electric and Non-Electric.
5. Last time, we covered general practices for using an Electric Blasting Cap.
So, this time we’ll be turning our eyes toward:
Non-Electric Blasting Caps
Note: Should anyone be familiar with a product or firing system known as NONEL, please be forewarned: NONEL is not what we’re going to look at today; it’s a completely different kettle of fish, which permits a blaster to fire a charge almost instantaneously (in fact it’s so nearly instantaneous, that’s it’s often referred to as being “an instantaneous firing system”). Standard non-electric blasting caps work differently, using Time Fuse, which is NOT an instantaneous ignition source, so it’s important not to confuse the two.
The picture on the left shows a bundle of non-electric caps rubber-banded together.
I’m sure we’ve all seen action heroes light a fuse that’s connected to a bundle of explosives, in a movie. When a character lights a fuse to set off an explosion, that person is — generally speaking — using a Non-Electric Blasting Cap to set off the charge. Technically, the first non-electric blasting cap was patented in 1867 by Alfred Nobel (because he needed something that would set off the dynamite he’d also invented).
Below are a couple of “cutaway” drawings that should give you a serviceable idea of what’s inside a non-electric blasting cap. One picture is a little more detailed than the other, but both clearly reveal how a non-electric cap is contained within a metal tube, which holds a primary explosive (also sometimes called a “booster”), and a secondary or output explosive — just as an electric blasting cap has. But, they also have an initiating charge that starts the explosive ball rolling.
The diameter of the blasting cap’s metal tube usually runs about a quarter-inch wide by two to three inches in length. (A quarter-inch equals 0.25 inches, versus the 0.241-inch measurement at the base of the cap [right side] in the lower drawing, and the 0.260-inch dimension at the open [left] end in the same drawing.) In both cases, the area to the left of the ignition charge (the charge labeled Pyrotechnic Ignition Mix in the color drawing) is hollow. This hollow section of tube is there so you can slide your Time Fuse into it, butting the end of the Time Fuse up against the initiator, and crimping the fuse in place so it won’t slip out.
The idea, of course, is that one lights the far end of the Time Fuse, then the powder train inside the fuse burns slowly along its length, until that flame spurts out at the other end — right into the initiator (or Pyrotechnic Ignition Mix), which is highly volatile and explodes because that tiny little spurt of white-hot flame is enough to set it off.
The initiator’s small explosion sets off the Primary Explosive (AKA: intermediate charge, or “booster”), which makes a greater explosion, which in turn sets off the Secondary Explosive ( AKA: base charge; AKA: output explosive), which is large enough to (hopefully) detonate the dynamite, TNT or C-4 (or whatever) that the blasting cap is snuggled up inside of. And . . . WHAMMO!
Generally speaking, one sets off a non-electric blasting cap by lighting a fuse. That fuse runs into the blasting cap, so the fire from the lit end of the fuse can find the place where it can set off the explosive chain.
Fuses come in many different types, depending on what you want to classify as a fuse. A fuse is essentially anything with black powder (or other well-burning substance) running through the middle of it. If you’re like me, you may have disassembled the fuse of a Black Cat fire cracker in your youth, and discovered that it was primarily a black powder train running through (wrapped in a tube of) something similar to newsprint. That’s a pretty simple fuse.
But, what makes a fuse, a fuse?
When Richard Sharpe (of the Sharpe’s Rifles series, set during the Napoleonic era) pours a line of black powder along the ground, from an ammunition dump, then lights the far end of that powder line in order to blow up the ammo dump — is this a fuse? Well, maybe. But, the word “fuse” usually connotes the idea that the “burning agent” (such as black powder) is combined with some sort of fibrous material to make it more reliable.
In that Sharpe’s Rifles example, for instance, the powder train could easily be disrupted by kicking apart the loose powder on the ground. If that were to happen, the flame would burn along the black powder train right up to the point where it ran out of any more flammable material, at which point the flame would fizzle — and that ammo dump wouldn’t blow up.
If you soaked a string in kerosene or gasoline, you’d have a rudimentary sort of fuse that couldn’t be so easily disrupted. Nobody could just kick it apart, for instance; they’d have to take additional time to cut it apart. However, it wouldn’t have a long life (because things like kerosene or gasoline evaporate fairly quickly), and it wouldn’t necessarily burn at a steady rate. Black powder, however, doesn’t lose its efficacy as quickly, and it does tend to burn in a fairly uniform manner. As noted earlier, though, a black powder train — in and of itself — can easily be disrupted.
One obvious solution is to weave a line of black powder into a line (string or rope) as the line is being braided. (In case you’re not familiar with the term, “braiding” a rope means making a rope by twining several lengths of twine or string together. If anyone is interested in the details, let me know and maybe I can do a post about Pioneering [the use of rope, for lashing poles in the construction of towers, derricks, or cranes, for instance].)
When a black powder train is woven into a line (string, rope), in a manner that insures the powder train runs all the way through without interruption, the result is a strong, flexible fuse that has a fairly consistent burn rate and is not easily disrupted. It’s also easy to carry (coiled in a backpack, for instance) and can be cut to any desired length. And this is basically all that a fuse really is.
Non-electric caps can be set off in other ways, but this post will deal primarily with the use of Time Fuse, when it comes to setting off blasting caps.
The fuse used to set off a contemporary blasting cap is normally called either Time Fuse, or Safety Fuse. It comes in spools similar to the one seen above.
I’m used to calling it Time Fuse, since that’s what the Army calls the stuff it uses. However I’ve worked with Safety Fuse in other countries, as well as when dealing with civilian blasters here in The States. The two fuses are really interchangeable, and are composed of a black powder core that’s protected by a fiber wrapping (or wadding) encased in a water-proof plastic or waxed coat.
Imagine you took a brown paper lunch bag and fed it through a cheap paper shredder (one strong enough to shred a paper bag, that is). You know the sort of shredder I mean: it cuts the paper into long, skinny strips — almost as if making thin ribbon, or paper fettuccini. Now, imagine you waxed the interior and exterior of the brown paper bag before feeding it into the shredder; the strips of waxy brown paper that came out would be very similar — in both appearance and feel — to the braided wadding inside of Time Fuse.
The black powder is sort of “woven” into the braided twists of waxy brown paper strips to make a long braided cord. In some types of fuse, this cord is then encased inside something very much like a thick, hollow cotton shoestring for added durability when bending the fuse. Then, this cord is covered with a plastic coating. In civilian versions, this plastic coating may be day-glow green, or pink – even orange. With military Time Fuse, this coating will be olive drab (OD) green, with twin yellow hash marks every foot-and-a-half or so.
(You may be interested to know: When movie actors handle bombs with powder-blue Time Fuse, that powder-blue color is actually a telltale indicating the fuse being used is inert. Nearly all military training explosives — fake TNT blocks, Time Fuse, Det Cord, etc. — are this powder-blue color, making it easy to differentiate the real stuff from the practice materials. Blue, training materials show up in a lot of movies. You might find it fun to watch for them.)
Lighting Time Fuse
Time Fuse just needs heat, to be ignited. But, it needs quite a bit of heat.
You can light it with a match, if you hold the match to the fuse long enough. Or, with a Zippo or Bic lighter. You can also use a cigar, because cigars burn in excess of 700° f. You can’t light Time Fuse with a cigarette or pipe, because they don’t burn hot enough.
But, the surest way to light Time Fuse is by using a Mechanical Match.
The Mechanical Match in the picture on the left is lying on a plastic sheet of some kind. The device, itself, is a plastic tube with screw-on lids at both ends. If you look at the picture, you can see that the device is thinner in the middle, than it is on both ends. This is because those thicker ends are actually screw-on caps. The thin, middle part is the plastic tube they screw onto.
One end of the Mechanical Match has a pull-ring, similar in appearance to the pin on a hand grenade. This end contains a trigger, that’s hooked to the pull-ring pin (The pin is that short-looking shiny metal rod that runs out of the top of the screw-on cap and has a hole that the pull-ring goes through.). The trigger and a spring-loaded firing pin assembly are inside the tube. When the pull-ring is yanked out, it lifts the pull-ring pin, which fires the spring-loaded firing pin. The firing pin shoots across the inside of the plastic tube, to ram its pointy end into a shotgun primer that’s loaded into the other end. That shotgun primer detonates from the impact, igniting the Time Fuse.
Looking at the picture, you’ll also see an olive-drab (OD) green string or cord that comes out of the screw cap near the pull-ring, on the upper right side, then is laid across the front to the left side. If you look at the Mechanical Match, on the other side from where the string comes out (i.e.: the string comes out on the right, so looking on the left side of the device . . .), you’ll see a thin, straight line sticking out of the screw cap. This thing is actually the end of a cotter pin, which locks the pull-ring pin in place, acting as a kind of “safety.” To use the Mechanical Match, you first have to grab that OD green string (which is attached to the other end of the cotter pin) and use it to pull the cotter pin out. Only then can you pull the pull-ring.
The shotgun primer is actually held in one end of the thinner “tube part” of the device. And, the screw cap just below it has a hole in the end. In the picture, to the left of the Mechanical Match, you’ll see some small plastic doodads. Those are shipping plugs that normally block the hole in the end of the screw cap, so dirt doesn’t get in the hole and foul the shotgun primer.
To attach the Mechanical Match to Time Fuse, simply unscrew that screw cap a little bit (this loosens up two C-shaped plastic pieces inside the cap), then pull the shipping plug out. Then slide your Time Fuse up inside the hole until it bumps into an obstacle. That obstacle your Time Fuse just bumped up against is the shotgun primer. So, all you need to do is hold the Time Fuse in place – so it doesn’t slip back out – and screw the cap back tight. When you screw that cap tight, it causes those two C-shaped plastic pieces inside to tighten together, clamping your Time Fuse in place. Now you can let go, and your fuse isn’t going anywhere; it’s held fast against the shotgun primer. When you yank on the pull-ring, the firing pin will strike the primer, which will explode, and the Time Fuse will be ignited by the bang.
On the right is a picture showing a Mechanical Match hooked to Time Fuse. The pull-ring is folded back behind the device, near the top of the man’s hand. His other hand grasps the cotter pin string, preparing to remove the cotter pin "safety."
Cutting Time Fuse for Proper Burn Time
Time Fuse usually burns at about twenty to forty seconds per foot. In other words, it takes about half a minute for the flame inside to travel one foot along the powder train inside the fuse. However, it’s important to understand that Time Fuse has certain properties that cause it to burn at different rates under various circumstances.
For instance, if you compress Time Fuse while it is burning, it will burn faster. Essentially, by compressing it, you’re sort of squeezing the fire down the powder train at a faster rate. It’s similar in mechanics to what happens if you squeeze a garden hose. If you squeeze that hose, the water at the end shoots out with a lot more force, and it shoots much farther through the air. Doesn’t it? Well, this is roughly the same thing that happens when you squeeze Time Fuse; it really amps up the burn rate — the speed at which the flame travels along the powder train. In fact, you can even make the flame shoot out farther when it reaches the end. (I once used this idea to lend greater probability of success to a charge, when I had blasting caps that didn’t seem to have been made very well. The caps kept malfunctioning when I tested them out. Consequently, I covered the last couple of feet of Time Fuse with rocks, in order to amp up the power just before it hit the blasting caps used to set of my charge. My hope was that this would help boost the probability that the caps would get a bigger jolt from the fuse. It worked like a charm.)
There are a lot of ways to compress Time Fuse. You can bury it under dirt, or lay a line of rocks or bricks over the top. You can even squeeze it with your hands. But, watch out! That stuff’s hot! The plastic coating on the outside will bubble up and melt or burst as the fuse burns inside it. But, if you suddenly decide to abort your explosion, you’d better cut your Time Fuse about two or three feet beyond the point where that bubbling and melting is going on, because the fuse is actually burning about 18 inches ahead of that point.
The well-trained blaster takes this compression factor into account when camouflaging his/her Time Fuse, knowing that it will burn faster if it passes through a constriction such as a tight wall join, or mound of earth. Or if it’s hidden under layers of sticks or branches.
The compression factor also means that Time Fuse burns more slowly at higher altitudes (where there’s less air pressure) than it does at sea level. And it burns much more rapidly under water! (Remember: it’s water proof, and has it’s own oxygen source on-board, so it burns very well under water. In fact, you can even light it under water using a Mechanical Match!)
Ambient temperature can also effect Time Fuse’s burn rate. It tends to burn a little faster in a hot climate, and slower in a cold one. Other factors that influence burn rate include: its age, how well it was made, and how well it’s been cared for.
Because of all these variables, the good blaster doesn’t worry about the idea that this stuff is supposed to burn at around 30-seconds a foot. Instead, s/he knows this ratio is very mushy, and therefore conducts a test burn.
A test burn is (usually) a fairly easy thing to do, and can aid a blaster in getting his/her charge to go off within one second of when that explosion is desired. To begin with, s/he cuts 3 feet of fuse from the roll s/he plans to use when setting off the charge. Then, s/he carries this fuse (along with a mechanical match) to a setting that’s as similar to the location where the charge will be placed, as possible. If the charge is going to be used to blow down a train trestle that runs across a mountain pass high in the sky, then the blaster needs to take that test fuse up a mountain to the same elevation. If the charge is going to be set 300 feet below the ocean, the blaster needs to don a wet suit and air tanks, and take it down beneath the waves – preferably to 300 feet of depth.
Once the blaster has gotten as close as possible to the expected conditions, s/he then pulls out a stop watch, hooks up the Mechanical Match, and sets off the Time Fuse. The blaster times how long it takes, from the moment the Mechanical Match is fired, until that little spurt of flame shoots out the other end of the fuse.
Now, the blaster takes that number (the length of time it took to burn three feet) and divides it by 3 (the number of feet it burned in that time). The answer tells the blaster what this specific Time Fuse’s burn rate will be under those conditions.
If, for example, it somehow took 3 minutes to burn three feet, the blaster would divide the 3 minutes (time it took to burn) by the 3 feet (the length of the fuse tested) and arrive at a burn rate of 1 minute per foot. Since s/he now knows that this fuse will burn at the rate of 1 min./ft, if the blaster wants a 6-minute fuse, s/he will divide those 6 minutes by the burn rate. 6 mins. ÷ 1 min./ ft. = 6 feet of Time Fuse. In other words, s/he now knows to cut off six feet of Time Fuse, if s/he wants the fuse to burn for six minutes before the explosion occurs.
In reality, our blaster is much more likely to get a number like “1 minute and 18 seconds”, or “1 minute and 42 seconds” when s/he does the three-foot test burn. The easy way to handle this is to convert minutes to seconds and add it to the seconds left over. (For example, if our time was 1 minute and 42 seconds, we’d convert our 1 minute to 60 seconds, then add that to 42 seconds. 60 + 42 = 102. So, now we know it takes 102 seconds for the fuse to burn 3 feet. Dividing 102 seconds [the time] by 3 feet [the distance burned] gives us a burn rate of 34 seconds per foot.)
In the example above, if we wanted a 6-minute fuse on our charge, we’d divide 6 minutes (which is the same as 6 x 60 = 360 seconds) by 34 seconds/foot.
360 seconds ÷ 34 seconds/foot = 10.5882 feet. But, what about the .5882 feet?
Well, now we multiply 0.5882 x 12 to get inches. 0.5882 x 12 = 7.0584 inches. So, now we have a fuse that’s 10 feet and 7.0584 inches long.
But … what about the .0584 inches?
Simply multiply 0.0584 x 16 to get sixteenths of an inch. 0.0584 x 16 = 0.9344
0.9 can be rounded up to 1, so … we’re going to measure out 10 feet and 7 & 1/16 inches of Time Fuse, then we’re going to cut off that hunk that’s 10 feet and 7 & 1/16 inches long.
That may seem complicated, but I guarantee that if you spell it all out, a reader will be convinced you know how to cut Time Fuse! And that will lend a sense of verisimilitude to your story — which is what I’m aiming for by writing this little reference guide.
If you don’t quite get how it works, feel free to use my numbers. Or, contact me and I’ll be happy to run whatever numbers you want. Either way, no one will doubt that your character knows what s/he is doing. And that’s what counts!
Cutting and Crimping (or “Romper, Stomper, Bomper, Boo!)
Do you remember an old kiddy show called Romper Room? I don’t know if it showed all over the country, but I’ve spoken to a lot of guys (particularly Special Forces Demolitions Sergeants) who remember that the lady who ran the show used to sit in her chair, holding a thing that (I think) was supposed to be a hand mirror (but had no glass, so that you could see right through it) in front of her face as she looked out at the audience (Okay! Actually, she looked straight into the camera lens. But, hey, I was just a kid!). She’d hold that thing up and look out through it, while mumbling something about the “magic mirror” and intoning: “Romper, Stomper, Bomper, Boo! I see Mary and Jacky and Mark and Lisa …” and she’d go on and name all these kids whom she could supposedly see watching the show, by looking through her magic mirror.
You remember that?
Well . . . Damn it, Jim! I’m a demo man, not a child psychologist! So . . . on with the penultimate phase of today’s post.
You can cut Time Fuse with a knife, but it takes a little finesse — and a lot of sawing to work through that plastic and cordage. The result is often a frayed mess that doesn’t bolster a blaster’s confidence in his/her charge going off right.
Consequently, one of the best ways to cut Time Fuse is to use Crimpers. The crimpers in the photo on the right (above) are military crimpers similar to the ones I had in the army. On the left, you’ll see an older set of civilian crimpers.
Crimpers are a little like wire cutters in a way. You know how wire cutters often have two functions: you can use one section to strip the plastic coating off of wire, and you can use another section to actually cut the wire? Well, crimpers are sort of similar. That hole near the end can be used to crimp a blasting cap onto Time Fuse (we’ll get to that in a minute), but the scissors jaws just below that hole can be used to cut the fuse. And this cut will be very clean, quick and efficient.
The scissors jaws — as the name implies — cut Time Fuse in the same way scissors would. However, because most scissors tend to be straight, the cutting action would shove the round, smooth-sided time fuse down their length, reducing their cutting effectiveness. Hence the term “scissors jaws”. The jaws part comes in, because the scissors jaws are curved. Sort of like the letter C and its mirror image, where the inner line on the C would be very sharp. This curved C-shape helps hold the Time Fuse in place while you’re cutting it. And the sharp edges slice cleanly through the tough fuse material.
To attach your Time Fuse to your blasting cap, you need to slide the fuse into the cap until the fuse bumps up against the initiator (pyrotechnic ignition mix) inside. Then, you have pinch the metal cap into the fuse, in order to anchor the fuse in place. This pinching process is called “crimping” the cap.
There are a lot of ways to crimp a cap, including the bite-down method, in which you squeeze the cap into the fuse by biting it between your teeth. I don’t suggest you try this.
The preferred method for crimping a blasting cap onto Time Fuse is to slide your fuse inside the cap as described above. Then pull a set of crimpers out of your pocket and hold them up in front of your place. As a mnemonic device, an aid to keep you from cutting the cap instead of crimping it, you then look through the open hole of the crimper, while intoning the words, “Romper, Stomper, Bomper, Boo!” just like that lady on Romper Room. (This may sound silly, but it’s very important: cutting the cap could lead to an explosion.)
Once your sure you know which part is the crimper, you slip that part of the crimpers around the cap, about 1/8th to ¼ of an inch below the top of the hollow end of the blasting cap. After the crimpers are firmly seated, but before you crimp down, you rotate your arms to bring the cap-fuse-crimper assembly out to your side, down low, but as far away from your body as possible, while turning your face in the opposite direction. Then you squeeze the crimpers, crimping the cap onto the fuse. You do all the turning away, etc. to protect your eyes and upper organs from possible shrapnel, should the blasting cap explode when you crimp it. (Now you see why I don’t recommend crimping with your teeth. Right?)
A Final Note of Caution For Writers, Concerning Primer Cord Confusion
In some films you watch, you may hear characters refer to the fuse they’re going to light as: “primer cord” or “Prima Cord.” Please DO NOT make the same mistake in your writing!
“Primer cord” is Detonating Cord, which is NOT a fuse. And, “Prima Cord” is just a manufacturer’s brand name for a type of detonating cord. Detonating cord (often called Det Cord) is filled with PETN or RDX, which burns at 22,000 feet per second if you’re using military grade stuff.
With that burn rate, Det Cord doesn’t really just burn. It EXPLODES!
I mean it. It really does explode. For example: I have personally used Det Cord to cut down small trees in order to create emergency helicopter landing zones (LZ’s). I have also used it to cut through wooden doors (Use it on the hinge side, and it cuts the door off its hinges, for instance.), and to make fairly clean, linear cuts in thin metal.
For those wondering how to use it to open an area for an LZ here’s how it works: If you have a fairly large field with a few too many small trees growing in it to make a good LZ, you just run a line of Det Cord over to the base of a small tree and wrap it three to six times around the trunk (depending on diameter), then keep running the Det Cord over to another tree and wrap it around that one three to six times, etc., until you’ve got the bases of all the trees that are in your way wrapped with Det Cord. After that, you hook up a couple of blasting caps and tape them to one end of the Det Cord. Then, just back off and fire the caps. When the caps go off, the whole line of Det Cord goes BANG! and the trees all fall down. Then you and your buddies move in and drag off the trees, so they won’t get blown up by the rotor wash and knock down the chopper with flying branches when it tries to come in for a landing.
To illustrate the difference between Det Cord and Time Fuse, let me explain that if you run Time Fuse through trees in a similar manner, all you’ll wind up with is Time Fuse that’s melted to the base of the trees and all along the ground. Time Fuse absolutely does NOT explode. That’s why it makes such a good fuse.
Now, let me also warn you that you may run into somebody, someday, who says: “I once lit Det Cord (or Primer Cord) with my trusty Bic lighter, and all it did was burn. It doesn’t explode!” My suggestion is that you simply nod and remain silent, and hopefully that idiot will go away. Because, he’s probably telling you the truth.
If you set Det Cord on fire with a match or lighter (For God’s sake DON’T EVER use a mechanical match, or you might kill yourself!) the stuff will burn and smoke, and stink to high heaven (I know because I’ve done it). But, it won’t explode — because RDX and PETN (Det Cord is usually filled with one or the other) doesn’t go off from heat alone. It requires heat AND shock or compression. (That’s why you don’t want to set it off with a mechanical match; that shotgun primer will give it both heat and shock/compression — and the result will be an explosion.)
In this context, Det Cord is a little like C-4, because — as I’m sure R.T. and most of our other Viet Nam vets will attest — if you light C-4 with a lighter, it also burns without blowing up. In fact, you can even use C-4, that way, as a sort of heat tab, to cook on it. But . . . if a person tries to put out the flame by stomping it with a boot heel, that person is likely to be called “Stumpy” for the rest of his/her life. Because stomping on the burning C-4 usually provides all the shock/compression it needs to explode. And the resulting explosion is probably going to blow that stomping boot (along with the foot inside it) right off the end of the stomper’s leg.
And, just so we’re clear: slowly pushing down with that boot heel, to sort of grind out the flame without stomping it, can also sometimes provide just enough compression to accomplish the same thing (i.e.: earning a new, undesirable, nickname).
Det Cord works the same way. If that idiot who set it on fire had then hit it with a hammer, you’d probably have been spared his odious visit!
So, as I’ve hopefully convinced you, no matter what you’ve seen or heard on TV or in the movies, Primer Cord (or Prima Cord – remember, that’s just a brand name) is not a fuse; it’s an explosive.