Gas Exam - Part 5 Flashcards
In terms of taking a bag sample from a goaf seal, Explain positive and negative pressures
Pressure flows from high to low. If positive pressure on seal from the mine atmosphere side ( or rising barometer) no leakage from the goaf will occur and air may be drawn into sealed area, bag sample maybe influenced by mine atmosphere and not be true sample . If a negative pressure acting on a seal from the mine atmosphere (or falling barometer) the goaf will be breathing out and a true goaf bag sample may be sampled.
- What instrument can be used to accurately determine the pressure which a seal is breathing in or breathing out?
Watergauage
Manometer
Name 2 hazards when taking a bag sample
Trip hazards- uneven ground, floor heave behind LW
Irrespirable atmosphere- damaged seal breathing out, low ventilation in C/T
Strata Hazards- C/T behind LW taking weight, roof/ rib failure
How can a seal change from a negative pressure to a positive pressure. Give 2 examples?
As the barometer rises and falls- falling barometer results in negative pressure and seal breath out, rising barometer results in positive pressure and seals breath in.
Ventilation changes- pressure balance chambers can be constructed to change seal from negative pressure to positive. Additional seal constructed, pressure in created chamber maybe increased by using ducting from AUX fan or intake air roadway
Name the specific location and time to take a bag sample from an open goaf
From the goafstream in the T/G located between the rib and last chock. Take on the low barometer between 2-4pm/am
How do you detect a goaf stream?
Warmest stream of air discharging from the goaf between the last chock and the T/G rib. Feel it with your hands and confirm with the hand held gas detector.
Name six bits of information required for a bag sample tag
Name of person Location Time Date Readings from ITX Temperature
What gas ratio is used for determining the source of fuel in a fire/heating?
Trickett’s Ratio- derived from the consideration of the products of oxidation of CH4 and coal and the conc relative to the depletion of 02. (<0.5 CH4 explosion, >0.87 coal dust explosion)
What does the CO/CO2 ratio indicate
Temperature of the coal
What is the formula for CO Make?
CO (L/min) = ppm X Quantity X 0.06
What is the benefit of analysing a CO Make compared to that of a raw CO concentration
Small increases in CO concentration can be disguised in high air flows, where they cannot with CO Make
Calculation of a CO Make Question eg: Calculate the CO Make of 8ppm in 30m3/sec
CO Make = 8 x 30 x 0.06
= 14.4 l/min
Calculate CO concentration (ppm) eg: A goaf is making 20l/min. What is the CO concentration in 45m3/sec?
ppm= CO make / Q * 0.06
= 7.4ppm
What is the purpose of a dry air free calculation?
Calculates out the atmospheric air in the sample, allowing samples to be properly compared after the dilution effect from air leakage has been removed
According to the regs, a mine gas monitoring system must provide for the calculation of which ratio?
Grahams Ratio
