Blasting stumps

[RPM]

Whoops - missed one point. The old electric dets or 'hot wire' dets did have a fair reputation for being unreliable. They used very dodgy primary explosives like azides and styphnates that go off with exposure to heat or percussion.

If anyone does go this route you want to use the more modern, much safer, exploding bridge-wire (EBW) type. These use a much safer secondary explosive like PETN. The vaporizing bridge-wire initiates the shock that causes detonation in the PETN.

You can also get them with a little toroid core that means they can only be fired at a specific frequency of current - lowers risk due to electrical noise (but not capacitive discharge). I think the brand name is Magnadet or something like that.

Always have an experience explosives engineer on hand when tackling anything like this etc. etc. etc.

 

[DrDan]

RPM

Yes, I'm also one of those who like anything that goes "bang"! As soon as I turned 21 I went and got a blasters licence in IL. Now since I'm in a wheelchair I can't get back as fast so I've mellowed out a little. I have a friend that teaches blasting for the coal miners. Real "milktoast" guy. You'd never place his face with that of an expert explosives person. I do have a lot of respect for those who really know how to use explosives to get a job done. My expertise was limited to stumps, however when we finished we had about a half case of 2 X 16 sticks and proceded to hollow out a 30' crater in the bottom of a gravel pit. Great fun!!!

Regarding the dangers, I guess I've always looked at it like I'd rather go via a quick accident then living to 90 in a nursing home with some nurse wiping my rear. I am pretty careful though.

Refresh my memory on what the percentages of dynamite mean. I think the higher percentage the faster the explosive burn. Right?

Boom!

Dr Dan

 

[RPM]

We always joked about that too. Since the blast wave would be traveling supersonically, you wouldn't know anything about it. It would be just like turning the lights off.

As far as the percentage - my hands on experience is all plastic explosives work. If I remember rightly though, it is the proportion of nitroglycerin to total mass of the charge.

Alfred Nobel made all his money by discovering kieselguhr - which acts as a stabilizer for nitroglycerin - and his combination of the two as dynamite. I believe that kieselguhr was long ago replaced by other inert ingredients, but couldn't tell you their names.

There's a good reference at the US Army Corps of Engineers site - it's a sizable Adobe Acrobat document. All public domain stuff although pretty dated.

By the way, some more detail on modern detonators such as I was referring to can be found here.

 

[skent]

My Uncle worked as a welder for the Army, one of his jobs was to modify/weld Japanese/German bombs to be used by the Allies. He was wounded in action and sent home early. His 'buddies' packed his footlocker and included some souvenirs, several (40mm I think) anti-aircraft rounds. . They didn't have powder in them, but had live primers. When he unpacked his footlocker in the states, he was afraid of getting into trouble so he stashed them upstairs in the hog pen.

Fast Forward 40 years. . . .

When we moved out to the farm, my kids were quick to locate the three anti-aircraft rounds and told me
about them. State Police advised me to contact the State Fire Marshal who in turn contacted the Ft
Indiantown Gap Bomb Squad who showed up the next day. They determined that two of the rounds were
tracers and asked if they could 'detonate' them in an open field. I asked if I could videotape the process and they said sure.

They coordinated with the fire marshal and he in turn contacted the State Police, 911 operator, Fire
Departments and county governments to notify them of the boom. They took the rounds to the middle of an open field about 500 yards from my house and mixed a 'quantity' of plastic explosive. I didn't realize that the plastic explosive came in two parts and had to be mixed just prior to use, and was safe for several minutes after mixing. They then used a radio controlled detonator (had a 4 digit code that was set) and the receiver was 10' from the rounds with a twin lead going to the cap.

My 5 year old was home from school that day and when the Lt. yelled "fire in the hole" three times, let Paula
push the button. All of us jumped when it went off. Got it all on videotape, including the Sargent saying "I
think I used a little too much"

There wasn't much left of the rounds, just some scrap metal and a hole in the field 4 feet round and 18 inches deep.

Seems the Army has had quite a problem with this very thing over the years. The in flux of souvenirs from
soldiers have caused quite a problem and many people are afraid of charges from the Army. According to the two men from Ft Indiantown Gap, the Army has adopted a policy of "No Questions Asked" for those people who have this very situation. Seems many munitions were ending up buried in back yards or discarded in landfills. Quite a problem.

All this occurred months after we moved in and just after the Oklahoma City Bombing, and neighbors seeing
the State Fire Marshal going in and out of out driveway several times, and the Bomb Squad show up, and the explosion. . . . . what would you think????? We still enjoy the videotape from time to time. . . . .




Steve

 

[RPM]

Skent,

You don't have to mix plastic explosives - what you saw was probably a binary explosive. These usually have a couple of liquid components which are mixed prior to use. I'm very surprised they used this approach - it's primitive and I would argue less safe than plastic explosives. A plastic explosive is normally a powdered high explosive mixed with a plasticizer in bulk or sheet form. No further preparation required.

You can burn several pounds of plastic explosives and even discharge a rifle into them and they won't detonate. You have to initiate the detonation with a shockwave - it's fundamentally different physics from burning (deflagration).

You were right to be careful around the primers on those old shells though. They become very unstable over time - stay well away and let the guys in the padded suits deal with them!

 

[dmccarty]

Dr. Dan,

When you used the auger on stumps, did the stumps have tap roots like some pine trees or where they wide stumps like oaks? Did you have to tamp material into the auger hole after placing in the BoomBoom stuff?

Most of the stumps I have to remove are pines and from the trees that have been blown down they have 2-3 feet long tap roots. I could never figure out how I was going to get under the stump to blow it out of the ground. Oaks would be easy but the pines with tap roots I could not see doing. Now there are some pines without tap roots and I have some on the property. I just can't tell which has a tap root from looking at the cut stump.

This problem and the money side pushed the idea of blowing the stumps out of the ground.

Later...
Dan McCarty