Normal Air is made up of :
Nitrogen 78%
Oxygen 21%
Trace Gases 1%
Specific Gravity :
The weight of a gas compared to an equal volume of normal air at the same temperature and pressure.
Normal air has a specific gravity of 1
This determines where in mine atmospheres, or within a confined space, we will find concentrations of particular gases
Examples:
Carbon Dioxide 1.529 floor to mid drift
Hydrogen 0.0695 against back or roof
Oxygen 1.105 evenly distributed
Hydrogen Sulfide 1.2 floor to mid drift
Carbon Monoxide 0.967 evenly distributed
Sulfur Dioxide 2.264 floor
Gases can and do pool
Gases tend to flow as fluids in quantity
These effects can displace Oxygen.
Ventilation:
Heavier gases are harder to ventilate than lighter gases.
WHY ?
What are we ventilating with ?
Normal Air specific gravity of 1.0
THE EXPLOSIVES!
Methane 5-15 %
Carbon Monoxide 12.5-75 %
Hydrogen 4-74 %
Hydrogen Sulfide 4.3-45 %
Hazards of ventilating concentrations of any of these are:
IGNITION SOURCES!
MOVING IRRESPIRABLE GAS!
In a mine or within a confined space, what is the minimum percentage of Oxygen necessary?
19.5%
Anything less means VENTILATE!
Most digital Oxygen detectors are set to alarm at 19.5%