Gas Exam - Part 3 Flashcards
What is the ignition temperature of CH4?
595 degrees
What is the minimum amount of O2 required for methane explosion?
12.2 % O2
What are the legal limits for CH4?
AUX FAN POWER TRIP 2% DIESEL VEHICLE WITHDRAW 1% DIESEL VEHICLE SHUT DOWN 1.25% NERZ/ ERZ1 INTERFACE TRIP 0.5% NERZ/ ERZ1 INTERFACE ALARM 0.25% SHEARER POWER TRIP 2% (CUTTERS @1.25%) MEN WITHDRAW 2.5%
What is the legal limit for CH4 in regards to the main fan?
Not stated in the Regs, but must be done by risk assessment to determine % and the time period that this can occur for. All headings into the main fan shaft must be monitored by CH4 sensor
Is CH4 poisonous?
No, but becomes slightly narcotic at high concentrations
What are the physical/ chemical properties of CH4?
COT
Slightly soluble in water
What is the explosive range of CH4?
5-15 %
At what percentage is CH4 most easily ignited on a heated surface?
5-6%
What is meant by the term lag of ignition?
The time it takes for a gas to ignite after it has come in contact with the ignition source
What is the lag time for 5-6% CH4?
2 seconds
How is CH4 produced and where about is it found?
Methane is a seam gas and is liberated from the coal during the winning of coal during production. Also released from cracks, stress panes, slips and faults
Due to it being lighter than air, it is found on the roof and accumulate in high spots and cavities
What is the effect of suspended coaldust on the LEL of CH4?
Can lower it from 5% to 0, depending on the coal dust concentration and the coals volatility
At what percentage is CH4 most explosive?
9.46%
What effect does temperature have on the upper and lower explosive limits of flammable gas/ air mixture?
As the temperature increases, the LEL decreases and the UEL increases
What are the physical/ chemical properties of H2?
Colourless Odourless Tasteless
Not readily soluble in water
Is H2 poisonous?
No
Is H2 flammable?
Yes, flammable range between 4-75%
Why is H2 most dangerous (X5) ?
Wide flammable range
Almost absence on the lag of ignition
Instantaneous build up to maximum pressure
Half initiation energy required for CH4
Low ignition temperature
Where can H2 be found (X3) ?
Mine fires, Spontaneous combustion, advanced heatings, battery charging stations
Where can H2S be found in a mine?
Seam gas where sulphides present in the coal
Stagnant water
What is the highest concentration of H2S without causing death?
500ppm – Breathed without causing death. Within half an hour produces serious inflammation of the eyes, palpitations, fainting
What are the physical/ chemical properties of H2S?
Colourless, Rotten Egg Smell, Sweetish Taste
Highly water soluble
What are the effects that H2S has on humans?
Irritates the eyes & respiratory tract as well as the CNS. In high quantities death comes about through respiratory arrest
Is H2S flammable?
Yes 4.3 - 45%
