Did it just knock the bullet off course?
December 6, 2014 5:58 PM   Subscribe

Detcord burns extremely quickly. One of the finest applications of high speed photography I've ever seen. Merry Christmas! posted by butterstick (23 comments total) 16 users marked this as a favorite
I've been on a few cave digs where we've used detcord to make small rocks out of big ones. You drill a series of 6-inch deep holes about a foot apart from each other, then cut pieces of detcord long enough to daisy-chain them from one hole to the next & 1 blasting cap at the end. We were shaving off a 10 inch by 6 inch by 10 foot length of rock with each blast, widening up a narrow crevice. The small mushroom clouds were pretty impressive.

9/11 & the would-be shoe bomber made cave digging considerably more difficult as you have to have permits & licenses to get ahold of the stuff any more.
posted by Devils Rancher at 6:23 PM on December 6, 2014 [5 favorites]

ok devils rancher you have to tell us all about cave digging now please
posted by thug unicorn at 6:29 PM on December 6, 2014 [12 favorites]

Nice. Very cool.
posted by asavage at 7:07 PM on December 6, 2014 [14 favorites]

> Nice. Very cool.

"I mean, it's no cement mixer or hot water heater, but cool"
posted by mrzarquon at 7:32 PM on December 6, 2014 [5 favorites]

How do I get a job like this guy's?
posted by InsertNiftyNameHere at 7:35 PM on December 6, 2014

He hates these kegs!
posted by TedW at 7:38 PM on December 6, 2014 [14 favorites]

Detonating cord (also called detonation cord, detacord, det. cord, detcord, primer cord or sun cord) is a thin, flexible plastic tube filled with PETN (pentaerythritol tetranitrate). With the PETN exploding at a rate of approximately 4 miles per second, any common length of det cord appears to explode instantaneously.

That's 14,000 mph; 80% the speed of the International Space Station. That's really, really fast.
posted by leotrotsky at 7:43 PM on December 6, 2014 [4 favorites]

The Christmas tree is awesome at all speeds--thanks!
posted by Monsieur Caution at 8:09 PM on December 6, 2014

Waste of good beer.

(Where's my "skip this ad" button? Jeeze!)
posted by Chocolate Pickle at 8:31 PM on December 6, 2014

Trashcan man is quivering in a corner somewhere

bumpity bumpity bump
posted by h00py at 8:36 PM on December 6, 2014 [4 favorites]

> (Where's my "skip this ad" button? Jeeze!)





sometimes works. (That's the embedding URL.)
posted by benito.strauss at 8:53 PM on December 6, 2014 [3 favorites]

That's 14,000 mph; 80% the speed of the International Space Station. That's really, really fast.


Okay, that's fast. Not quite orbital speed, but it's fast. Not arguing that.


Detcord is not primacord.

Primacord is a high explosive -- PETN or RDX -- wrapped around a cotton string. The amazing thing about primacord is that to make a connection, you tie a knot -- which beat the hell out of every other way to make a connection between an initiator and a primary explosive that we had in WWII.

Primacord, being a high explosive, is not something you just leave laying around, The US Army Corps of Engineers taught a trick for cutting down a tree. Three wraps of primacord, and *boom*, tree falls down.

But that's not detcord.

Detcord is completely different. Detcord is a very thin layer of PETN or RDX inside a plastic tube.

Putting something explosive inside a tube isn't new. Fireworks operators are very familiar with quick match. Black match is simple -- black powder on a cotton string. Black match burns about three feet a minute. If you wrap black match in a paper tube, you get quick match. Quick match burns many feet per second. This is the trick detcord uses.

For detcord, you line a thin plastic tube with PETN or RDX. It's one of the safest fuses made -- I've seen detcord used in a hotel conference room. If you watch Mythbusters, in the high speed shots, you'll see this bit of light crawl towards the thing they're blowing up. When that bit of light reaches the thing they're blowing up, it blows up.

That's Detcord.

Primacord is much easier to work with. It's faster, connection are literally as easy as tying a know, but it's a high explosive, and there's enough high explosive involved that you have to be careful with it.

Detcord? You can hold it as it fires. It's the perfect fuse. It's fast, it's reliable, and it won't hurt you by itself. Originally, the hard part about detcord was figuring out which detcord was fired and which wasn't, until they dyed the exposive so that we knew the white detcord was already fired, and the pink or green detcord (depending on who made it) was ready to fire.
posted by eriko at 10:26 PM on December 6, 2014 [13 favorites]

20K ft/sec? I thought it burned a bit faster, but I guess the memory plays faster and looser than I'd like it to--I keep remembering some staff sergeant with three fingers on his left hand telling us that it burned about 50k feet per second. I also remember him telling us not to crimp the blasting caps with teeth.

We used det cord to cut down smallish trees, to make a clearing for the dustoff. Sometimes we laid a few feet of along each side the trail, to collect anyone the claymores missed.

I love slo-mo stuff.
posted by mule98J at 10:39 PM on December 6, 2014 [1 favorite]

In the last video the action starts at 2:40, you can skip all the beginning.
posted by marienbad at 12:58 AM on December 7, 2014

Bah! I did the beer keg fountain in college with a screwdriver.
posted by KingEdRa at 8:19 AM on December 7, 2014

There are only three senior pyrotechnicians in Canada who have the det cord authorization.

One of the three, not to name names, can be very vocal about his experiences with it. "You know those scenes in movies where they blow up an entire ship in the water? That's det cord."

Someone else spoke about using det cord in a military exercise. They levelled a concrete street post as thick as an old tree trunk, apparently. Powerful stuff.
posted by quiet earth at 9:49 AM on December 7, 2014

So, bro, why does he blow up that perfectly good suburban?
posted by chavenet at 11:14 AM on December 7, 2014 [1 favorite]

ok devils rancher you have to tell us all about cave digging now please

Essentially, most of the caves around the US with reasonably large entrances have been found, (though not all -- I have walked up to perfectly large entrances hitherto unknown to ranch owners on a couple of occasions) so the majority of discoveries in the past 20 years or so have been dug into. There are two kinds of digging -- digging at the surface at a small expression that indicates a larger void beneath, or in-cave digging to continue past constrictions. I've done a fair amount of both.

On the surface, you might find a tiny crack in the rock with huge amounts of air blowing out of it, or a slight depression that takes water but doesn't pool, or maybe a couple of boulders that look like there's not much underneath them because of the way they slump. Digging into a cave from the surface can be as easy as moving a couple of rocks by hand, or perhaps involve years-worth of blasting many feet underground, following a tiny hole. Or maybe a bulldozer. Or a shallow pit with rubble at the bottom, & a tripod & pulley system to haul buckets.

So a lot of the surface digs I've done have just been with gloves, buckets, a good rock hammer, a couple of pry bars and a whole lot of sweat. However, when you get into bedrock, and you've got a fissure or a little hole that's too small for a body but is blowing lots of air, explosives are a much more expeditious way forward. A long time ago, in the 90's & before, kinepack was commonly used, but it was difficult to get a lot done with, because you had to drill large holes for it, or somehow adhere it to the wall you wanted to remove so that the explosive force wouldn't just be wasted outwards. This is where detcord is really useful because of its size. You can carry a hammer drill & a masonry bit with enough battery power to drill quite a few holes just large enough for detcord. & you can move a large amount of rock in an afternoon. This is a photo I managed to snap of about 30 feet of detcord that we set off right at the surface, trying to enlarge a crevice back in 2000 or so. The scrub cedars in the picture, are all 8-10 feet tall, for reference.

In-cave digging is of course, considerably more delicate. It mostly involves moving rocks or mud by hand. It happens frequently that you find yourself at a constriction & you can see obvious larger passage just beyond, so of course there's incentive to enlarge the constriction enough to fit a body through. Every one dreams of making some major miles-long discovery in this fashion, & occasionally, it happens. Once in a while, you need chemical persuasion underground as well, but we go with much smaller things. In the 90's, some folks developed a technique called rock shaving. You drill a hole just large enough to tightly hold a .22 or .25 caliber blank cartridge 6 or 8 inches deep & 3 or 4 inches from the edge of the rock that you wish to remove or make into smaller rocks. You carefully tamp a cartridge down to the bottom of the hole, cover the hole with a large blanket of some sort (I used a 3x3' piece of rubber roofing material) with a small hole in the middle, then you insert a steel rod behind the cartridge, which is cut at a slight angle, so that when you hit the rod with a hammer, it sets off the rimfire cartridge. Sometimes it works great, but it's kinda dangerous. The rod can blow back, shrapnel can escape the blanket, & sometimes the damn thing just won't fire. I had to leave a bent rod stuck in a hole with a live cartridge under it one time, because it would neither fire nor come out after it bent from me hitting it wrong with the hammer. I felt really bad about this, but knew not what else to do. There it probably sits, 12 years, later, rusted & a dud by now, i'm sure. People have largely stopped rock shaving lately, because it is dangerous, and have started instead filling straws with black powder & setting them off from a distance with wires & a battery. I've watched once, but don't really know this technique, except that it similarly involves drilling holes just large enough for the charges.

The most famous examples of cave digging that have led to significant discoveries that I can think of off the top of my head include Lechugilla in New Mexico & Natural Bridge Caverns just north of San Antonio. The guy first through into natural bridge is a friend & neighbor, & if you're ever there (a fine tourist cave, seriously) you will see his amazingly detailed map just inside the ticket office entrance.
posted by Devils Rancher at 2:32 PM on December 7, 2014 [8 favorites]

I predict that the detcord in slo-mo will inspire a sfx shot in a Hollywood action film in 3... 2... 1...
posted by anonymisc at 5:11 PM on December 7, 2014

Guys, wear seatbelts. You could be dancing. Now watch my SUV explode.
posted by oceanjesse at 6:44 PM on December 7, 2014

Devils Rancher: "you insert a steel rod behind the cartridge, which is cut at a slight angle, so that when you hit the rod with a hammer, it sets off the rimfire cartridge. Sometimes it works great, but it's kinda dangerous. The rod can blow back ..."

That sounds familiar.
posted by exogenous at 9:48 AM on December 8, 2014

Well, 2 things -- yes, it does sound familiar, so you never, ever have a body part in line with the potential exit path of the tamping rod, should it blow back. I would always reach in as much from the side as possible with my hammer held at arm's length. Usually, the pin just bounced back on the hammer head a little bit, as most of the force was absorbed by the rock you shaved off. Also, the rods are pretty small -- about the size of an un-sharpened #2 pencil, not some 8-foot long, 50 lb. monstrosity. Gage's accident is truly fascinating, though.
posted by Devils Rancher at 4:37 PM on December 8, 2014

« Older Oslo gets a long winter, a decent summer, and a...   |   Good restrooms, merry gentlemen! Newer »

This thread has been archived and is closed to new comments