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flintgreasewood

Anfo Usage And Regulations

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Flint - I don't know much about the Regs. but I have used ANFO for many years Underground. Given that my Shaft-Sinking and Drifting has been mostly with either Hand-held Drills and / or Electric Hydraulic Jumbos and in mostly hard rock, I will try and limit my thoughts to your application in the Gravels you are working.

 

Before I talk about the usage, just a quick word on Regs. If you are storing any quantity I would expect that some sort of small-scale Magazine would have to be established and Licensed. Detonators, whether Electric or Non-El and Cordtex ( Blasting Cord ) will also have to be stored separately. You can actually buy small ready-made Explosives Magazines / Containers for use on small Mining Operations and I would expect that the storage / handling regulations should be something that MSHA could advise on. Perhaps a look at their Website or a phone call might turn up some useful info.

 

The other thought about storage is that rather than buy it ready mixed as an Explosive, you can buy the prilled AN which is basically a Fertilizer until it is mixed with Diesel so perhaps it may not be subject to as many restrictions as a ready-made Explosive would be. We mixed our own in a Cement mixer as and when we needed it. The other application which comes in handy if you were say down in sunny Arizona for example on a hot day and needed to cool your Beer is to throw the Beer in a 5 Gallon Bucket, cover it with ANFO then add water. Instant Fridge. It's a crude fix but when you're thirsty, hot Beer doesn't quite cut if for me. 

 

Moving on to usage. In the Shaft ? Probably not. As you know ANFO is basically useless once it's wet so unless you have some type of sleeve to keep your holes dry or use a Sump at a lower level and you pump the water out then ANFO will be no good. If it were me, I would use a Cartridge / Packaged Explosive obviously sized according to the Diameter of the Holes you are Drilling. If the ground is not that hard and consolidated then perhaps one or even two Cartridges might suffice depending of course on the depth of the Hole and the size of the Cartridges themselves as they are available in various sizes ( Diameter ) and lengths. Don't forget to tamp them. Tamping is simply " popping " the Cartridge skin by splitting it with some gentle compression downwards with a round wooden stick / rod with a flat end. Remembering of course to be gentle with the Primer as one of the Cartridges will have to have a Detonator inserted. Experimentation will be required with both the Drilling Pattern and Hole Depth and then the quantity of the chosen Explosive to figure out the optimum process. As you have seen first-hand, shovelling out at the bottom of a Shaft is not the easiest Job in the world. For example, in harder ground, I found it even more back-breaking when I kept hitting larger pieces of Rock or clumps of dirt mixed in with the smaller size fragments, all of which seemed to want to weave themselves together  after the Blast. Eventually, I managed to close up the Hole spacing to produce smaller sized fragments of ground which was a lot faster and easier to shovel. I liked to call it " Rice ".

 

More later.      

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Moving on - The use of ANFO in Drifting.  

 

In hard rock and dry holes, no problem. Cheap and easy. Bring in wet holes or Unconsolidated ground conditions such as your Gravels then issues quickly develop. Apart from the moisture, I foresee partial collapse of the holes as you withdraw your Drill Steel. Not completely, but enough to frustrate proper charging. This will come from the percussion of the drill combined with the rotation of the drill steel. If you get to that stage of drilling, you will need to make up a " scraper " which is simply a length of heavy gauge wire about 4ft. or 5ft. long ( depending on the length of your hole ) with one end bent at right angles ( 90 degrees ) for about 5/8". The other end is bent back 8" at 90 degrees then bend that piece in half again at 90 degrees towards the other end to form a handle. Make sure both bends are made in the same direction. i.e. If the handle points down, then the end of scraper will also be pointing down. The idea being to insert the scraper to the back of the hole and clean out any obstructions which may have fallen in. The question now is, how much moisture or water is present in the drilled holes ? Is there enough to neutralize the effectiveness of the ANFO, or perhaps even bad enough to wash it out ? I had to charge a wet Drift with ANFO many times, day in, day out, on a particularly nasty job and the only way it could be done was to drill " relief " holes which were basically drains for de-watering. This kept the good holes dry enough to keep ANFO in them long enough to Blast the round / heading / face / drift / tunnel etc. When it became too wet, we had to switch to Cartridges.

 

Charging with ANFO generally requires Air Pressure. That means a Compressor topside. You'll need a Compressor anyway to run the hand-held drill. There are lots of small, portable pneumatic ANFO loaders available which would be suitable for your application. Just google " ANFO Loader ". Bear in mind ANFO needs to be Primed. That means a Detonator on its own or preferably a Detonator inserted in to a single Cartridge ( PowerGel ) which is placed at the back of the hole. The ANFO is then blown in to the hole, via the loader and under sufficient pressure to help it pack tight. Loose ANFO as a rule will generally not propogate ( i.e. carry the initial detonation from the primer ) so if it isn't packed tight enough in the hole then the primer will simply blow the ANFO back out of the hole like a big dose of Buckshot.

 

In summary, it may not even be practical, for a number of reasons, to use ANFO at all. In which case, have you considered ditching the use of a Compressor and instead of Drilling and Blasting, perhaps stick with toys that run off a generator. Compressors can be very tricky at times. From memory, didn't you say you had an Electric Jack-Hammer up there ? I've seen them used in the Opal Mines and although the ground is probably much softer, they seem quite effective in that application where very selective ( and instant ) ground breaking is required. They are unfortunately quite heavy so you will have to come up with a clever way of supporting it on some type of mount so you don't have to support the weight yourself. Anyway, it sounds like the big issue to consider first and foremost is whether or not to actually Drill & Blast ?  

 

Your thoughts ?

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Flintgreasewood - I've also used ANFO underground. Its a big topic, perhaps you could give us an idea of just what kind of info you are looking for.

 

As Steve says,

You need compressed air to fill the holes.

You need a detonator to touch it off.

Its water soluble, so while slightly damp conditions are OK, really wet, water out of the drill holes conditions are not.

As a small operator you don't want to do the mixing yourself, buy premixed, bagged material.

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Thanks Steve, for that good info on anfo.  I sure am not committed to using anfo but want to explore it as a possible option.

It would be used in permafrost drifts, so wet conditions shouldn't be a concern.  Since I don't know the first thing about what size holes...diameter and length and hole patterns I can only say that I am thinking of using my electric hammer drill to put in 1" x 3' holes.  If that won't cut it, let me know.

Since I will be mucking by hand, I don't need to blast too much at one time.  It would seem to me that with such small holes that packing the anfo would be do-able with simple tools...yes?  Wondering if I could make pre packed tubes of anfo that I could push into the hole.  Just a thought.

    Of course I'll be in compliance with all MSHA regs for anfo...which could be very difficult.  A friend was using anfo in his permafrost mine and eventually gave up on it.

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One inch diameter holes seem awful small. To fit you would need a dynamite maybe 3/4 inch in diameter - not sure that is a product generally available. Tiny holes might be a detonation propagation problem, especially if you use some tube set up. Probably would lead to more duds. 

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I've done a bit more research and now know that the minimum hole diameter for anfo to detonate is 1 1/2".  However this does not assure a complete detonation of the charge.  2" is considered sufficient diameter to allow for complete detonation.  I'm thinking that since typical blast holes are in the range of 20' to 30', a 1 3/4" diameter hole between 3 and 4 feet would be sure to completely detonate.  I've found a pretty slick new electric hammer drill made by Hilti specifically for mining.  It uses various diameter button bits screwed to a shaft.  I'd probably use a 1050mm shaft.  Tomorrow I'll find out how much that cool tool costs.  Lots more to learn.

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Flint - Now you're talking. That's in line with what I would probably do. Try and manage without Compressed Air if you possibly can. 

 

Hilti is a good reliable brand. You might even be able to lease one for a few weeks or so just to try it out before you buy one. The dealer or yourself will have to come up with a solution to support the Unit in the Drift to take the weight while you drill with it otherwise it's another back-breaking exercise like shovelling in the Shaft.      

 

Getting back to the earlier post above -

 

To Drill & Blast or not to Drill & Blast ? - That is the question !

 

Once you have that question answered, everything else like Drilling Tools, Hole Size and Spacing / Patterns, Explosives, Ventilation, etc. will follow suit. Don't be too concerned though about Hole Diameter or Hole depth just yet as the combinations are extensive. It will simply be a matter of finding what works best in your situation. For example, on hole depth, we used to drill 14ft. holes by hand ( using a rock drill of course ) but we start off drilling using a 6ft. Drill Steel. The trick is the Diameter of the Button Bit or Tungsten Tip on the 6ft. Drill Steel has to be larger than the following Drill Steel, which in this particular case was 10ft. Then it follows on that the smallest Diameter Drill Steels we had were the 14ft. which had to follow inside the 10ft.

 

For example, in your own case you can start with your 1050 mm Shaft ( Drill Steel ) and look at the results. If you decided later that you wanted to try a 5ft. round for example then it simply becomes a matter of " sizing " your button bits accordingly if you want to deepen a hole. Bearing in mind that the more Gravel you Blast, the longer you will toil on that shovel unless you come up with something mechanical to move your pay dirt topside.         

 

I worked in an Exploration Shaft once which was about 10ft. in Diameter and about 300ft. Deep. We hardly ever picked up a Shovel to remove broken ground. As part of your ongoing research, check out Vacuum Ore Lifters. The Ore Lifters are designed to move dirt Vertically. As you advance your Drift, you will have to come up with a solution to move your gravel Horizontally.

 

More later.         

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