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The Parallel Intake Mine Ventilation System

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Gases

Air

Air is a mixture of gases. At sea level, clean, dry air is comprised of 78.09% Nitrogen, 20.94% Oxygen, 0.03% Carbon Dioxide and 0.94% inert gases, mainly Argon with some Hydrogen and Helium. Mine air can be contaminated by gases such as Carbon Monoxide, Sulphur Dioxide, Hydrogen Sulphide, Nitrous Oxides, high levels of Carbon Dioxide or high humidity. Contaminants are normally removed by the mine's ventilation, but in a disaster situation the ventilation can be disrupted.

Contamination to mine air can be caused by:

  1. Blasting or other explosions;
  2. Fire;
  3. Exudation from rock;
  4. Decay of timber;
  5. Absorption of oxygen by water, or oxidation of timber or rock;
  6. Diesel motors;
  7. Battery charging;
  8. Gases released by ground water; or
  9. Contaminated compressed air or ventilation intake.


Oxygen (O2)

Oxygen is necessary for life and combustion. A concentration of 21% in air is ideal for man, with diminished levels having various effects depending on the degree. At 17%, people working will breathe a little faster and more deeply. A 15% level will cause dizziness, buzzing in the ears, rapid heartbeat and often headache. 9% causes unconsciousness and 6% is almost always fatal. A candle will be extinguished when the level falls to about 16%. Mine air should have an Oxygen concentration of at least 20%.

As Oxygen is more soluble in water than Nitrogen (N2), air in a confined area in the presence of water will usually have a reduced Oxygen level. Air from a hydraulic compressed air plant has an Oxygen level of about 17.7%. The presence of impurities in air dilutes the air and so reduces the Oxygen level. Other causes of reduced Oxygen levels in mines are absorption into rock, heat, combustion and the breathing of men in confined spaces (there is sufficient oxygen in 1m3 of air for an average man at rest to survive for one hour).

High Oxygen levels breathed at atmospheric pressure are not harmful and reduce fatigue during work, however breathing 80% Oxygen will cause irritation after 48 hours.

Breathing pure Oxygen under pressure greater than 1.5 bar for any length of time can lead to Oxygen poisoning which results in irreparable damage to the nervous system. The signs and symptoms of Oxygen poisoning are excess salivation, disorientation, headache, muscle twitching and possible death.


Carbon Dioxide (CO2)

Carbon Dioxide is an almost inert gas and is produced by the combustion or decomposition of organic matter. Breathing more than 5% CO2 can cause poisoning with identical effects to Oxygen poisoning. Mine air should not be more than 0.5% CO2.

The following table shows the effects that various concentrations of CO2 in air with a normal Oxygen level have on a person at rest (exertion worsens the effect):

	%CO2	Increase in respiration

	0.5	Slight
	2.0	50%
	3.0	100%
	5.0	300% and laborious
	10.0	Unbearable


Carbon Monoxide (CO)

Carbon Monoxide is one of the most dangerous gases that can be encountered in mines. It cannot be seen or smelled and is highly poisonous and explosive. Carbon Monoxide is produced when organic matter burns in a low Oxygen environment (incomplete combustion). It is produced in mines by diesel motors and blasting, which proper ventilation caters for, and by fires in confined areas and uncontrolled explosions, which the ventilation may not cope with. Mine air should not contain more than 30 ppm of Carbon Monoxide, ie TLV CO = 30 ppm.

Carbon Monoxide is poisonous because the substance in blood that carries oxygen to the cells of the body (haemoglobin) absorbs Carbon Monoxide 300 times easier than Oxygen, with the effect that the cells of the body progressively become starved of Oxygen. The higher the concentration of Carbon Monoxide breathed, the faster the rate that Oxygen is excluded from the blood, and the fewer early symptoms of poisoning experienced.

When haemoglobin has absorbed Oxygen or Carbon Monoxide it becomes red, but Carbon Monoxide is not absorbed by the cells and so blood vessels that normally carry dark de-oxygenated blood carry bright coloured blood, with the effect that a person suffering from Carbon Monoxide poisoning looks a very healthy colour, with pink lips, even for some time after death.

Carbon Monoxide is slowly released from the blood through the lungs, and low level poisoning can be recovered from with no permanent damage, but in sustained or high level poisoning, there will be damage to the organs from Oxygen starvation.

Protection against Carbon Monoxide poisoning is the purpose of filter type self rescuers. They contain a catalyst called Hopcalite which causes Carbon Monoxide to bond with oxygen to form Carbon Dioxide. These self rescuers are not effective in oxygen deficient atmospheres. Being a catalyst, the Hopcalite is not consumed by the conversion process, but its life is determined by the amount of moisture it is contacted by. The conversion process produces heat, so when used in a high concentration of Carbon Monoxide, a Hopcalite self rescuer can become unbearably hot. Oxygen generating self rescuers also become fairly hot, but can be used in any atmosphere.

The following table shows the effects of breathing various concentrations of Carbon Monoxide (1000ppm = 0.1%):

PPM	EXPOSURE TIME		SYMPTOMS

50	long			slight
200	several hours		slight
400	2 - 3 hours		headache
1200	30 min (with exercise)	palpitations
1200	90 min			weakness in legs
1200	2 hours			confusion, headache,
				nausea
2000	30 min			unconsciousness

The following table shows the symptoms caused by various levels of blood saturation by Carbon Monoxide:

% SATURATION	SYMPTOMS

0 - 10		None
10 - 20		Tightness across forehead, possible
		headache.
20 - 30		Headache, throbbing in temples.
30 - 40		Severe headache, weakness, dizziness,
		dimness of vision, nausea, vomiting,
		collapse.
40 - 50		As for 30 - 40 with increased pulse
		and respiration and more possibility
		of fainting and collapse.
50 - 60		Fainting, increased pulse and
		respiration, coma with intermittent
		convulsions.
60 - 70		Coma with intermittent convulsions,
		depressed heart action and respiration,
		possible death.
70 - 80		Weak pulse and respiration, death.


Hydrogen Sulphide (H2S)

Hydrogen Sulphide is one of the most poisonous gases known. It can be produced by blasting in sulphide orebodies or, along with methane (CH4), by the decay of organic matter, mainly in stagnant water.

In low concentrations, a rotten egg smell is noticeable, but in high concentrations the sense of smell is paralysed. Long exposure to concentrations as low as 50 ppm (chronic poisoning) can cause inflammation of the eyes and respiratory tract and lead to bronchitis, pneumonia and oedema (swelling) of the lungs. Acute poisoning can occur from breathing concentrations above 600 ppm and results in serious damage to the respiratory tract and lungs within a few minutes. Breathing 1000 ppm will cause almost instantaneous death. TLV 10 ppm.


Oxides of Nitrogen (NO, NO2, N2O4 = NOx)

Oxides of Nitrogen are produced in mines by the burning or incomplete detonation of explosives, and by diesel engines. They are corrosive to the respiratory tract and can result in death even the day after the casualty has apparently recovered.

Nitrogen Dioxide (NO2) is the most commonly encountered of the Oxides of Nitrogen, and it is also the most toxic as it combines with water in the respiratory tract to form Nitric Acid. Several hours after exposure, oedema of the respiratory tract occurs, which can be followed by bronchitis, pneumonia or death. Breathing 200 ppm for a few minutes can cause serious illness and breathing 700 ppm for about half an hour will be fatal. Nitric Oxide (NO) is rarely encountered as it readily combines with oxygen to form Nitrogen Dioxide. TLV NO2 = 3 ppm.


Sulphur Dioxide (SO2)

Sulphur Dioxide is a suffocating, irritating gas that can be produced in mines by fires or blasting in sulphide orebodies, and can be given off by explosives. It is very poisonous and highly irritating to the eyes and respiratory tract. Breathing 100 ppm will cause great discomfort and breathing 500 ppm for any length of time will be fatal. TLV 2 ppm.


Hydrogen (H2)

Hydrogen is normally produced in mines by battery charging. It can also be produced when water or foam are used on a fire, or given off by rock that is made red hot by a fire.


Smoke

Smoke consists of fine particles of solid and liquid matter suspended in the atmosphere. These particles are mostly Carbon and hydrocarbons. These hydrocarbons, along with other gases that can be produced in a fire, can make smoke explosive, particularly when more Oxygen is allowed to reach a fire.


Gas Detection

Gases can be detected and their concentrations measured either with electronic devices or detector tubes. Gas levels can also be monitored by devices such as the Flame Safety Lamp or by watching a canary.

Electronic samplers are available for a variety of gases, some will test for more than one, and give a constant indication of the current gas level, usually with an alarm to indicate that a dangerous level is reached.

Gas detector tubes are used with a special pump that draws a measured amount of air through a chemical in the tube. The chemical in the tube changes colour when contacted by the gas that it is designed to test for. The higher the concentration of the gas, the more of the chemical that changes colour. Scales on the tube give the concentration of the gas from the amount of the chemical that has changed colour.

There is more than one brand of tube available, and the correct pump must be used with the correct tube. Also, there are over 130 different types of tube available, each with a specific use. Detector tubes should be stored in their box, in a cool place.

Prior to testing for a gas with a detector tube, the pump should be tested for leaks. This is done by inserting an unbroken tube in the pump, depressing the pump and observing that the pump stays depressed.

The procedure for using a detector tube is:

  1. Check the 'use by' date on the box of tubes;
  2. Check that the tube is of the correct type;
  3. Test the pump;
  4. Break the ends of the tube;
  5. Insert the tube in the pump in the direction of the arrow;
  6. Read the scales on the tube for the lower of the number of pumps required (shown as n=);
  7. Hold the pump in the appropriate place for the test being performed;
  8. Depress the pump and allow it to fully inflate (repeat this the appropriate number of times);
  9. Read the appropriate scale (if no reading, use the higher number of pumps);
  10. Record the results.

When testing for gases, it is important to be aware of the properties of the gas, there is little point in testing near the backs of a still area for SO2 which has a high specific gravity (air has a S.G. of 1, a gas with an S.G. greater than 1 is heavier than air). There are two main methods of gas testing, point and traverse.

Point testing is done by holding the apparatus at a specific height (usually three quarters of drive height) for the duration of the test.

A traverse test is performed by moving the apparatus from side to side and top to bottom of the drive during the test.

When gas testing is performed, the plan of the area should be labelled to show the location of the test. A record should be kept with the following information:

  1. The position;
  2. The date and time;
  3. The method used;
  4. The number of pumps used;
  5. The result.

Location

Gas

Reading

N=

Method

Time

Date

Plan

Label

Tube

Label

                 
                 
                 
                 
                 
                 
                 
                 
                 
                 
                 
               

TOTAL

RESCUE

 

 

GAS DATA

Gas

S.G.

Explosive

Range

(%)

TLV &

STEL

Soluble

in Water

Colour

Odour

Taste

O2

1.11

-

-

Moderately

-

-

-

N2

0.97

-

-

Slightly

-

-

-

CO2

1.53

-

0.5%

3%

Highly

-

Acrid

Soda

Water

CO

0.97

12.5 - 74

30ppm

400ppm

Lightly

-

-

-

H2S

1.19

4.5 - 45

10ppm

15ppm

Highly

-

Rotten

Eggs

Sweet

SO2

2.26

-

2ppm

5ppm

Highly

-

Sulphur

Acid

NO2

1.59

-

3ppm

5ppm

Highly

Reddish

Brown

Acrid

Acrid

H2

0.07

4 - 74

-

-

-

-

-

CH4

0.55

5 - 15

-

Slightly

-

-

-

Emergency Response Considerations

Self-Contained Breathing Apparatus

Drager PA93

Hazardous Chemicals

Drager BG174

Drager BG4

Fire

Fire Fighting

First Aid

Rope Rescue

Case Study - Pasminco Fire

Major Disaster Case Studies

Glossary

Summary of the Principles of Rescue Work

Guidelines for the Frequency of Practice Sessions


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