Mine gases and testing, maintenance of fire seals

Mine gases and testing, maintenance of fire seals

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2. Mine gases and testing. & Maintenance of fire seals.

3. A.Mines gases and testing: Dry air at sea level will be composed of: Oxygen - 20.90 Nitrogen including Argon - 79.07 Carbon dioxide - 0.03

4. Mine gases continues:- Atmospheric air entering the mine undergoes changes and Gets contaminated with noxious gases given by the strata and from other sources. Five chief harmful (i.e. Poisonous n Toxic) gases, met within the mines, are CO 2 , CH 4 , CO, NO 2 and H 2 S.

5. OXYGEN (O 2 ) Physical properties:- Colourless, tasteless and odourless gas. Slightly soluble in water 5% by vol at 0 C at 1 bar. Molecular weight = 32 Sp. Weight – 1.33 kgf /m 3 Specific gravity = 1.106 Boiling temperature = (-) 183 C at 1bar. Freezing temperature = (-) 219 C at 1bar Present in air = 21% (by volume)

6. Physiological effects : Safe Limit: 20% - Normal Breathing Warning limits: 17% - Heavy breathing, palpitation 15% - Losses the desire to make any effort. Danger Limits: 12% - Feeling of airlessness 10% - Serious headache, bluish lips 9% - Unconsciousness in 1 hour and death due to oxygen starvation 7% - Instant loss of sense – death Detection: Percentage of O 2 is detected by Flame Safety Lamp, Oxor, Oxymeter and Multi gas detector.

7. NITROGEN (N 2 ) properties :- Colourless, tasteless, odourless and inert gas. Slightly soluble in water 2% by volume at 0 C at 1 bar. Molecular weight = 28 Sp. Weight – 1.17 kgf /m 3 Specific gravity = 0.97 Boiling temperature = (-) 195.5 C at 1bar. Freezing temperature = (-) 237.8 C at 1bar Present in air = 79.07% (by volume) Source of N 2 inside mine includes: Source Explosive ( 1kgf of nitroglycerine release 135 liters of N 2 at STP) Decomposition of organic substances.  

8. Physical properties of CO 2  Colourless, odourless, slightly acidic taste . Soluble in water 180% by volume at 0 C at 1 bar . Molecular weight = 44, Sp. Weight – 1.96 kgf /m 3 Specific gravity = 1.106 Boiling temperature = (-) 183 C at 1bar. Freezing temperature = (-) 219 C at 1bar Present in air = 21% (by volume)  

9. Physiological effects:- Safe Limit: 0.03% - Normal 0.50% -Ventilation increase by 5% Warning limit: 1% - Noticeably deep breathing 2% - 50% increased amount of air breathed at rest 3% - Breathing doubled even at rest, fatigue (flame safety lamp will extinguishes) Danger Limit: 5%- Breathing tripled, extremely heavy breathing 6% - Suffocation and desire to sit down, Violent panting and exhaustion 10% - Loss of sense, can not be endured for more than a few minutes 20-25% - Fatal, cause death after some hours Detection: Percentage of CO 2 is detected by Flame Safety Lamp and Multi gas detector.  

10.  Colourless, tasteless and odourless gas. Slightly soluble in water 3.3% by volume at 0 C at 1 bar. Molecular weight = 28, Sp. Weight – 1.17 kgf /m 3 Specific gravity = 0.97 (air=1) Boiling temperature = (-) 190 C Melting temperature = (-)207º C Harmless concentration = 0.0016% Allowable concentration = 0.005% Temperature of ignition = 630- 810º C Reaction, 2CO +O 2 = 2CO 2 CO forms due to incomplete combustion. So detection of CO in mine air is usually an indication of fire or spontaneous combustion.   CARBON MONOXIDE(CO) Physical Properties:

11. Toxic effect of CO on persons : CO % in volume PPM Working time Effects Safe Limit: 0.005 50 Full shift No effects 0.01 – 0.02 100 – 200 1 hour No effects Warning Limit: 0.02 200 2 hours Slight headache 0.04 400 45 min Severe headache Danger Limit: 0.12 1200 1 hour Collapse 0.20 2000 10 min Death possible 0.30 3000 5 min Death possible 1.00 10000 1 min Death possible Detection: Percentage of CO is detected by CO detector, Toximeter, Multi gas detector, Continuous Environmental Monitoring System and Chip Measurement System (digital).

12. HYDROGEN SULPHIDE (H 2 S) Physical properties : Colourless, Sweetish taste with characteristic odor of rotten egg.. Soluble in water – 440% by Vol. at 0ºC and bar. Molecular weight = 34 Sp. Weight – 1.43 kgf /m 3 Specific gravity = 1.2 (air = 1) Melting Temperature = (-)83ºC Boiling temperature = (-) 60.2 C at 1bar. Allowable concentration = 0.00066% Odour concentration 0.0001% to 0.0002% and at 0.02% irritates the eyes and throat in 5 – 10 min. Highly poisonous gas. Allowable concentration = 0.00066%  

13. Physiological effects : 0.01% - Slight poisoning after 1 hour 0.02% - Poisoning after one hour without serious consequence. 0.05% - Serious poisoning after 30-45 min. 0.10% - Cessation of respiration and death quickly occurs within 10 min. Detection: Percentage of H 2 S is detected by rotten egg smell and Multi gas detector.  

14. Physical and Physiological properties of SO2: Colourless, acidic taste and strong pungent smell. Soluble in water 4000% at 0 C and 1 bar. Molecular wt. = 64, Specific wt. = 2.72 kgf /m 3 Specific.gr = 2.22 (air =1). Melting temperature = (-)72.7ºC Boiling temperature = (-) 10ºC Extremely poisonous gas, concentration of 0.05 is dangerous to life. SO 2 is detected at a concentration of 0.0005% by its Characteristic smell – burning sulpher. It is formed in underground from explosives and burning of coal. Detection: Percentage of SO 2 is detected by Multi gas detector  

15. Physical and Physiological properties NITROGEN OXIDES (NO 2 , N 2 O 4 , N 2 O 5 ): Red brown colour, acidic taste and pungent smell. Molecular wt. (NO 2 ) = 46, N 2 O 4 = 92 Specific wt.= (NO 2 ) 1.96 kgf /m 3 Specific gr. = 1.59 (air = 1) Highly soluble in water. Harmless concentration = 0.00025% Fumes extremely poisonous and its poisonous effect starts after 3-4 hours. 0.025% may be fatal to man and effect human lungs. Formed inside the mine due to heavy blasting operation, fumes of diesel exhaust gas etc. Detection: Percentage of Oxides of Nitrogen (NO 2 , N 2 O 4 , N 2 O 5 ) are detected by Multi gas detector

16. Physical properties of Methane : Colourless, odourless, tasteless gas. Molecular weight = 16, sp.weight = 0.716 Kgf/ m 3 Specific Gravity = 0.554 (air = 1) Slightly soluble water – 3.5% by vol.at 1 bar. Diffuses 1.6 times as fast as air. Although odourless; in some mines it is emitted with impurities and has characteristic odour. Methane gas is explosive and practically all mines emit methane more or less. Methane is responsible for several explosions inside mine through out the world. Methane is lighter than air, so it accumulates at the roof or roof cavity and in rise workings, the chances of methane concentration is very pronounced. Death due to methane suffocation in dead end faces of steeply rising workings are not uncommon. Methane is flammable and forms explosive mixture. CH 4 + 2O 2 = CO 2 + 2H 2 O 1 Vol +2 Vol = 1 Vol +2 Vol (condensed) (Reaction starts even at 300º C)  

17. Continues: Ignition temperature 650º C to 750ºC – This temperature may be higher or lower than these limits depending on the type of igniter. The product of explosion temperature reaches 2150- 2650ºC, if it takes place in confined space (volume constant); and 1850ºC if the product of explosion can expand freely (P=constant). One volume of CH 4 needs 2 volumes of air, i.e , two volumes O 2 for complete combustion. So most powerful explosion is given by a mixture containing 1/11 by volumes of CH 4 ( ie 9.5% CH 4 ) Methane air mixture ignites at 510º C when adiabatically compressed to 60-70 atmospheres. In a confined space, the explosion pressure can reach up to 7-10 atmosphere. CH 4 is not explosive below 5% and above 16%. From 5 up to 15% CH 4 is explosive . 7-8% CH 4 mixture is easily ignited. The hot surface ignites CH 4 at a temperature higher than flame temperature. Flame safety gauge temperature must be about 1200º C. to ignite the gas. CH 4 coming in contact with hot source ignites with a delay. Thus, at 650ºC the delay is 10 sec. and at 1000ºC it is 1 sec. Delay time diminishes with the increase of pressure. Velocity of flame propagation depends on many factors. At 10-12% CH 4 velocity of propagation is about 0.6m/sec. In still air but in a fluctuating mixture it may in crease upto hundreds of meters per sec. CH 4 explosions are accompanied by two shocks. Forward shock travels from the source of ignition and the reverse wave results from the pressure drop due to cooling of gas. The mechanical damage by reverse wave is higher than the direct explosion wave. The explosion area is generally filled with hot gases such as CO 2 , N 2 and some CO. The area may be devoid of O 2 , if coal dust takes part in explosion considerable amount of CO is formed which makes the atmosphere poisonous.   Detection: % of CH 4 is detected by Flame Safety Lamp, Methane Meter, Riken Methane Indicator, Multi gas detector, Continuous Environmental Monitoring System and Digital PX Methanometers.

18. DIFFERENT FIRE RATIOS FOR ASSESSING STATUS OF UNDERGROUND FIRE OR HEATING Interpretation of the data collected by sampling is a powerful tool known as fire indices Some of these are as follows. Graham’s ratio - [CO]/ O 2 Young’s ratio -[CO2]/ O 2 Willett’s ratio - CO/[excess N 2 + CO 2 = combustibles] Oxides of carbon ratio -[CO]/[CO 2 } Jones and Trickett ratio -{[CO 2 ]+0.75[CO]-0.25[H 2 ]} / O 2 A feature of several of the ratios is the oxygen deficiency (O 2 ). This is a measure of the oxygen that has been consumed.  

19. Graham Ratio: This ratio (CO/O 2 DEFICIENCY RATIO) generally expressed as a percentage, represents the fraction of the oxygen absorbed as a result of heating of fire which appears as carbon monoxide. The formula for the calculation is:   CO ratio = 100 CO = 100 CO O2 def. 20.93/79.04 N 2 -O 2 0.265 N 2 -O 2   Example: Suppose an air sample drawn from sealed off area have the following composition: CO 2 = 6.79% O 2 = 5.19% CO = 0.059% N2 = 87.96% Oxygen deficiency in this case = (20.93/79.04)x 87.96 - 5.19=18.11 Then CO/O 2 deficiency ratio = (0.059/18.11) x 100 = 0.32% As a thumb rule, it can be taken that 0.4% or less indicates normal value 0.5% indicates necessity for a thorough a check-up 1% indicates existence of heating 2% indicates serious heating approaches active fire 3% and above indicates active fire with certainly

20. Fire indices Continues: CO 2 /O 2 DEFICIENCY RATIO or YOUNG’S RATIO: Carbon dioxide produced as a percentage of oxygen absorbed considered to be direct guide of heating. The rise in the CO 2 /O 2 and simultaneous fall in CO/O 2 indicates further development of the fire. [CO 2 ]/O 2 deficiency ratio, rising trend above 40% is warning level. [CO 2 ]/O 2 deficiency ratio, above 50% indicates dangerous condition. WILLETT’S RATIO : This ratio carbon monoxide produced divided by sum of black damp and combustible gases present. This ratio can be used as a criterion of progress towards the extinction of fire behind the seals under circumstances where the Graham’s index does not apply. Willett ratio below 5% indicates active fire. As it increases to 12.5 and above indicates fire become extinct.  

21. Fire indices continues: OXIDES OF CARBON RATIO : This ratio, [CO]/ [CO 2 ] indicates the completeness of the combustion or oxidation. It is a powerful tool to determine the progress of the fire, rising during the early stages and tending to remain constant during flaming combustion. It rises rapidly as the fire become fuel rich. If the value of this ratio is more than 2% it indicates native fire in the adjacent zone.     JONES AND TRICKETT RATIO: This ratio {[CO 2 ]+0.75[CO]-0.25[H 2 ]}/ O 2 serves as an indicator of the type of fuel involved in any fire or explosion. It is also used as measure of reliability of sample analysis. This ratio was developed by Jones and Tricked for determining whether methane or coal dust has been involved in a mine explosion. Typical values of this ratio are given below. Methane - 0.4 to 0.5 Coal, oil, conveyor belting - 0.5 to 1 Timber - 0.9 to 1.6   A ratio noticeably less than 0.5 in a coal mine fire could be indicative of extinguishment or greatly reduced coal temperatures.

22. Continues: CONCLUSION: To assess the status of fire none of the above methods, taken singly, can give a precise and definite picture of progress of heating. It is therefore needed that the information as may be available from all the indices taken together along with temperature measurement data should be considered carefully to draw any inference regarding the status of fire. The history of fire, the mining condition are to be kept in the perspective for making necessary interpretation.  

23. Continues: INTERPRETATION OF FIRE CONSTITUENTS   In relation to mine fire, the mining Engineer is called upon to interpret the results of samples of mine air, which have been taken for one of the following purposes: to detect the occurrence of a fire or heating. To determine the inflammability of the atmosphere on return side of a fire which is being attacked by direct methods of fire fighting. To keep a check on the inflammability of atmosphere inside a fire area being sealed off. To keep watch on the trend of development or dying of fire inside a sealed off area. To find out condition of fire and inflammability of atmosphere inside a sealed off area before it is reopened.    

24. Continues: The main products of combustion of coal area carbon monoxide, carbon dioxide and water vapour oxidation of sulphur in coal may give rise to some sulphur dioxide and hydrogen sulphide. Distillation of coal may result in production of methane and hydrogen and in very small percentages of ethane, ethylene, and acetylene etc. also.     Soon after sealing, the atmosphere in the sealed off area will be found to contain a relatively high percentage of carbon dioxide, a small percentage of carbon monoxide. The percentage of methane depending on the gassiness of the seam, the remained being nitrogen.

25. Continues: If the fire is active, the percentage of oxygen falls quickly and the percentages of carbon monoxide and carbon dioxide rise sharply. A continuing fall in the percentage of oxygen and a continuing rise in the percentages of carbon monoxide and carbon dioxide indicate continuance of fire. The percentage of carbon monoxide may rise to as much as 0.3 to 0.4% and the percentage of carbon dioxide to as much as 5%.   As the fire dies out, the percentages of carbon monoxide and carbon dioxide fall, their being a corresponding rise in the percentage of nitrogen. Should there be a leakage of air, there will be instantaneous rise in the percentage of oxygen and a fall in the percentage of carbon monoxide and carbon dioxide because of dilution by extraneous air.

26. Continues: In the application of gas analysis to the detection of heating the important thing to ascertain the CO/O2 ratio normal to the district concerned. This may vary from about 0.1% to about 0.05% in the main returns and about 1.0% in the working place. Any increase in the ratio indicates the development of heating. Broadly a ratio exceeding 1% demands careful watching when heating is taking place, the CO/O2 ratio increases, 2% indicates serious heating and 3% indicates active fire.   The CO produced/O2 absorbed (CO Index) is a ratio that is not affected by dilution and is found to be widely accepted over the years as criteria of the state of heating and fires in their early as well as in their later stages of development.   Co 100 x CO Co Index. ------------------------ = -------------------------------- O2 0.265 x N2 – O2

27. Continues: When Co N2 and O2 are the percentages of Carbon monoxide, Nitrogen and Oxygen in the air sample.   The following analysis was taken in a seam when dangerous heating was taking place. Percent Carbon dioxide 0.40 Methane 1.03 Oxygen 19.90 Nitrogen 78.67 Carbon monoxide 00.03   Co 100 x 0.03 Co Index.------------------------ = -------------------------------- =3.16% O2 0.265 x 78.67 – 19.90 The panel in which the sample was taken was immediately sealed off. Attention is specially drawn to the low value of CO percentage as compared with relatively high value of the CO/O2 RATIO.

28. Continues:   INFLAMMABILITY OF MIXTURES OF GASES :   METHOD- I   The lower, upper and nose limit of inflammable gases like methane, carbon-monoxide, hydrogen and unsaturated hydrocarbons is given below: Flammability limits vol % age Combustible Gas ------------------------------------------------------ Lower Higher Nose limit Methane 5.0 14.0 5.93   Carbon Monoxide 13.0 72.0 13.78   Hydrogen 4.0 72.0 4.30   Unsaturated Hydrocarbon 3.0 14.7 3.10   Emission of firedamp from the strata and production of combustibles such as CO, H2 and other saturated hydrocarbons may render the atmosphere explosive. CH4, H2 and other hydrocarbons may be found as product of combustion/distillation even in a non-gassy mine.   For interpretation of inflammability of mixture of gases a number of methods have been developed. Given below is one method which is found to be easy, speedy practicable and reliable.    

29. Continues: GRAPHICAL METHOD BASED ON EFFECTIVE COMBUSTIBLES AND EFFECTIVE INERT GASES : This method takes into account three features of mixture of fire gases:- Effective inert component, which is defined as (Excess N2 + 1.5 CO2) volume percent, Effective combustible component which is defined as (CH4 + 1.25 H2 + 0.4 CO) volume percent, and Methane The ratio R of ------------------------- Total combustibles For various mixtures of methane, carbon monoxide

30. B. Maintenance of fire seals: Reg. 118A. Further precautions against sp.heating. (1): (c)Except permitted by DGMS , no extraction of pillars in any seam or section shall be commenced until fire dams or stoppings have been provided in all entrances to the panel, except entrances kept open for ventilation and haulage, suitable doors or openings may be left and bricks and other suitable material shall be kept readily available in their vicinity. Shale or other carbonaceous material shall not be used in the construction of fire dams or stoppings. (d) A panel shall be isolated by adequate stoppings as soon as it has been goaved out.

31. Inspection of fire seals: Reg.118A (3)(c)The isolation stoppings built around goaved out area shall be inspected once at least in every seven days. A report of inspection shall be recorded in BPB and shall be signed and dated by the person making the inspection. Reg.122 (3) In every fiery seam or gassy seam of the second or third degree , arrangements shall be made once at least in every 30 days to ascertain the atmospheric condition behind the stopping built to seal off the area of old workings, or such goaf, or a fire or sp. Heating, unless stoppings are explosion proof.

32. Continues…. (4)(a) every stopping erected to isolate or control a fire or sp. Heating BG or to seal off goaf or an area of old workings shall be numbered , and shall be of adequate strength and so maintained as to prevent any leakage of air or gas through it where water is likely to accumulate behind any such stopping, there shall be provided in the stopping a suitable pipe or other device to drain away the water with out permitting any leakage of air or gas. (5) A CP shall once at least in every 7 days , inspect all stoppings erected to isolate or control a fire or sp. Heating BG. During every such inspection, he shall ascertain the general condition of the stopping, and ascertain the temp. and humidity of the atmosphere out side the stopping. For every stopping , he shall place his signature, with date , on the check board provided for the purpose at suitable position on the stopping and this record shall be maintained for a period of not less than 3 months. A report of every such inspection shall also be recorded in BPB and shall be signed and dated by the person making the inspection. Further DMS may require above inspections to be made at shorter intervals as he may specify.

33. DGMS circulars CMR 100(4)118A(1)(a)/118A(4),119 & 122 Selection of site and design, standard and manner of construction of isolation and preparatory stoppings under Reg.10094)/118A as also build under Reg 119/122 to isolate or control a fire or sp. Heating or to seal off/ sectionalise disused workings shall be as follows: 1.Selection of site: be free from cracks and geological disturbances 2. 3 mtrs away from pillar corner 3. Sufficient space is still available on the out bye side to enable to re- inforced

34. Continues 4 . Converted into explosion proof subsequently. Design of construction Bricks in lime/cement motor Minimum thickness of stopping Gassiness of seam caving stowing 3 rd degree Two stoppings each 1 M 1 mtr thick n 4.5m apart filled incombustible material 1 n 2 nd degree 1 M to be reinforced 0.5 M CH4 exceeds 2% Explosion proof

35. Continues: Minimum depth of locking of both brick and RCC stoppings into roof, floor and sides In coal one metre 50 cms In shale 30 cms 30 cms In sand stone roof/floor 15 cms 15 cms Plastering: at least 1 M in all sides with sufficient thickness of lime or cement to prevent leakage Water seal: Sampling pipe: 25 mm or 50 mm dia fitted with suitable sluice valve/cap. S.P. should be extended up to a distance of at least 3 M in bye of the stopping and placed with in 30 cms of the roof. White washing: to detect fine cracks and serial numbered Up to stopping roof shall be well supported, properly ventilated and kept clear of obstruction The pillars containing IS stopping should not be extracted or reduced.