Equipment		Mine Development
Natural Forced Air Conditioning     Return to Systems Menu Return to Main Menu		Ventilation air is moved through pipes or ducts underground so it can be directed as needed. Large ventilation ducts with fans provide forced ventilation. Ventilation requirements are increasing in mines because of the increased use of diesel equipment so the size of ducts and fans are also increasing. Long, small-diameter ducts offer even more flexibility. Ventilation doors are sometimes used to block the flow of air.

Forced Ventilation		Mine Development
Natural Air Conditioning Equipment     Return to Systems Menu Return to Main Menu		As mining operations develop, it is necessary to use forced ventilation. A fan is used to blow through a duct or tubing. The inlet of the fan is located in fresh air and blows into the face of the work heading. The fan can also suck air from the heading. The advantage of the exhaust fan is that blasting gases can be removed quickly from the face. Both systems have certain advantages depending on conditions. Deep mines have ventilation systems. A large fan or a series of fans moves air through the mine. It is necessary to control of air on various levels so it can be directed to where it is needed. This is done using regulator doors or door locks.

Composition of Air

Pure, dry, normal air has the following composition:

			Respiratory
	Accurate	Analysis	Effects	Mine	Ventilation
	By Vol.	By Wt.	By Vol	By Vol	By Wt
Oxygen	20.93	23.02	20.93	21	23
CO2	0.03	0.04	0.03	-	-
Nitrogen	78.10	75.50	79.04	79	77
Argon	0.94	1.44	-	-	-
Total	100.00	100.00	100.00	100.00	100.00

These percentages are lowered by water vapour present in the air. In most calculations concerning ventilation of mines, air is considered to be composed of 2 gases only.

Ventilation

Underground mining operations require sufficient clean air for personnel to breathe and for equipment to operate.

Air exchange is required for the removal of contaminants from :

• Explosive gases

• Dust

• Poisonous gases

• Radioactive Emissions

• Objectionable fumes

The best method for controlling these contaminants is to prevent their formation or dilute the contaminants so they are no longer dangerous.

Air-Conditioning

Workers are most productive if they can work in comfortable temperature ranges.

Both extremes of temperature cause worker inefficiency. Some mines are very cold in winter so the intake air is often heated by specially designed heaters.

As mining gets deeper, the temperature usually increases. The air brought in from the surface is not adequate to cool the mine enough to maintain a work efficient temperature at the working headings. When this occurs, it is necessary to introduce some some of air conditioning to allow the air flow to the heading to be cooled.

Methods include: cooling water which is sprayed through the warm mine air or mechanical refrigeration units can be used.

 

Natural Ventilation

Natural ventilation is still used whenever possible. As air warms it becomes lighter and tends to rise. Cold air gets heavier and tends to sink. Shallow mines can often take advantage of these air properties.

Levels can be ventilated naturally if proper conditions exist. Warmed air tends to rise and flow along the back. The longer the level becomes, the less effective the natural ventilation because the air will short circuit and not flow into the face.

Raises are difficult to ventilate naturally. As the raise is blasted, hot gases form and tend to stay in the back of the raise. Eventually the gases may cool and settle out of the raise. A shaft will usually ventilate well if coll air is brought to the collar. The cool air will flow down to the bottom and the warm air rises causing relatively good ventilation.

 

Ventilation Testing

Measuring the flow of Air

A) Velometer

This is a small portable device with a hinged vane attached to a pointer which moves over a scale . The instrument is connected by a short length of tubing to one of several different jets, which are held where the velocity or pressure of the air is to be measured. The pressure of the air against the vane moves the vane and its pointer.

B) Anemometer

This device is like a little windmill. The revolutions of the wheel are indicated by a pointer on a dial. By noting the revolutions made per minute, the spped of the air can be determined.

C) Other devices include : Pitot tube, Inclined Gauges, and Micromanometers.

 

Mine Gases

Oxygen	- no colour, taste, or smell -@ 21% all kinds of lamps burn -@ 15% breathing becomes laboured -@ 10% life is in danger
Carbon Dioxide	- colourless, odourless - product of complete combustion - causes death by suffocation -@ 3% breathing is difficult -@10% death can occur
Carbon Monoxide	- colourless, odourless - incomplete combustion -@0.05% is dangerous
Methane	- colourless, odorless, burns - explosive when mixed with air
Hydrogen Sulfide	- offensive odour - @.15% is fatal
Hydrogen	- explosive when mixed with air
Nitrogen Dioxide	- reddish brown colour - incomplete combustion

 

Shaft-Sinking

Shafts are of various sizes and shapes. They can be square, rectangular, circular, elliptical, or any special shape. The shaft may be inclined or vertical depending on the orientation of the orebody.

Shafts are the vertical or inclined openings through which men, supplies, ore and waste are transported. They are the chief service openings during the development and operation of a mine, and a space for compressed-air pipes or electric cables.

High production from deep mines usually sink vertical shafts. As a rule, the shafts have a big cross sectional areas so large quantities of air can be moved underground, as well as providing a cage with enough area to carry large equipment into and out of the mine. The ore skips are usually large and travel at high speeds in the shaft. To provide this capacity, these shafts are often circular in shape and up to 25 - 30 feet in diameter.

 

Drifts

Drift Cycle

In a freshly blasted heading, the first thing that is done is to scale or bar down loose rocks, then water the walls and muck pile to control dust.

Mucking out the blasted material comes next. Usually a mucking machine is used to fill ore cars.

After all of the muck is removed, the heading is rock bolted or timbered.

If no ground support is needed, then drilling of the next round is started. A jackleg drill is usually used but jumbo drills are becoming popular.

Jackleg  Drill

 

A burn-cut round is used to break the advancing heading.

Loading the round comes next. The first stick of explosive that goes into the hole is called the detonator stick, which contains the cap and fuse. The rest of the hole is then filled with explosive.

 

Once the opening has been blasted the cycle starts again.

 

Raises

Raise Cycle

a) Timbered Raises

A stoper drill is commonly used for drilling in a raise. The V-cut type of round is popular. Before blasting down the round, the timber below must be protected and the blasted rock must be directed into an orepass or chute. A common procedure is to direct the ore into a slide, which keeps the broken ore from dropping down the manway. The timbers that are directly exposed to the blast are covered with lagging. The round is then loaded and blasted.

After the blast, the loose rock needs to be cleaned away and water is used to control the dust. The loose rock on the back and sides must be scaled down. After the raise has been made safe, the manway slide is removed, a floor is built on top of the timber set, and the timber for the next set is hoisted and set in place where it is aligned and blocked tightly into position. The cycle is then ready to start again.

b) Raise Machines

A recent development in driving raises is the mechanical raise-climbing machine, which runs on a track fastened to the sides of the raise. It includes a drilling platform and a means of hauling supplies up the raise.

When the climber gets to the top of the raise, the miners climb onto the deck, scale down the loose rock, and are ready to drill. When drilling is complete, another section of track is added and the climber is moved down to a protected position.

On this track is a row of teeth, which meshes with the gear on the raise climber. Turning the gear directs the climber up or down the raise. The climber is driven by compressed air.

c) Raise Bore Machines

Hard rock can now be cut with various types of rotary bits so drilling or boring large diameter openings has become practical. A raise boring machine drills a pilot hole to the level below. A drill rod or shaft is extended through the hole to the level below where a large diameter bit is fastened on.

The raise bore machine lifts the bit and creates a high force or thrust of the bit against the face while rotating the bit. The finished section is smooth and often support is not required.

 

Blasting

In underground mining the physical properties of the rock to be blasted, the particular function of each shot hole, the kind of explosive used, and the way the holes are loaded and fired must be studied to ensure optimumal breaking of rock.

 

Historical Background

Many of the great engineering feats of the world were accomplished at a time when there were no explosives known.

During the building of King Solomon's temple, some 80,000 men laboured in subterranean quarries breaking out blocks of stone with wooden wedges driven into grooves in the rock and then wet with water.

 

King Hiram of Tyre is thought to have secured 3 tons of silver per year from the Rio Tinto mine using 40,000 men.

 

The Roman Emperor Claudius completed the aqueduct from Rome to Lake Fucinus some 50 miles away. Over 30,000 men laboured for 11 years, using the primitive method of breaking rock by wooden wedges and also by fire-setting.

Dynamite didi not come into use until 1867.

 

Blasting Theory

1) Strength of the explosive should be proportional to the resistance of the rock.

2) The burden should be properly proportioned to the strength of the explosive and the resistance of the rock.

3) Blasting of the rock to leave 2 or more faces will require a smaller quantity of explosives than if only 1 free face is left by preceeding blast.

4) It is more economical to break to a system of regular faces and benches than to blast in an irregular manner

5) Where possible, the simultaneous firing of several shots grouped closely together often requires less powder than if shots are fired singly.

6) No more explosive should be used than is required to break rock to the proper size and leave it in the best position for handling.

In most mining operations, explosives are placed in drill holes. If explosives are placed in a drill hole and detonated, the result is usually a crater of varying size.

The bottom of the cone is formed at the free face. If the rock is resistant to breaking, sometimes hardly any cone is formed. If the rock is easily broken, the cone may start at the bottom of the hole.

Wherever possible, 2 free faces are provided for an explosive. It is always best to have the hole filled with explosives parallel to one free face.

A free face sometimes has broken rock lying next to it and this is called a burdened face. It has been found that explosives usually break well against a burdened face. The force of the explosive must compress it slightly so the solid rock can expand and break.

 

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