How to maintain steady barometric pressure in a mine

Keeping an eye on the barometer is critical during mining operations because situations in which the barometric pressure either rises too high or drops too low can create serious safety risks. The Mine Safety and Health Administration outlines the dangers of both situations, as well as steps that can be taken to mitigate them.

Hazards associated with a rising barometer

Higher atmospheric pressure reduces methane liberation from the coal seam into the active mine atmosphere. As atmospheric pressure rises, air from active areas of the mine will tend to migrate toward sealed areas and into gobs, introducing oxygen into those areas of the mine. A zone with an explosive methane/air mixture could exist behind seals or on the fringes of the gob. Mines with coal that is prone to spontaneous combustion could experience elevated carbon monoxide levels.

To prevent dangerous rises in pressure, MSHA recommends:

• Sample the atmosphere behind seals and check for explosive mixtures when they are in-gassing because of a rising barometer.
• Have a plan for inerting the atmosphere behind seals if explosive mixtures are present.
• Monitor the atmospheric monitoring system for signs of elevated CO concentrations indicating possible heating in the gob.
• Maintain a recording barometer at the mine and check the trending of barometric pressure each shift.
• Increase monitoring of gobs when the barometer rises.
• Establish the mine’s action levels for gases resulting from heating in gob areas.
• Obtain a regional barometric forecast that will indicate expected changes to alert miners of the potential hazards associated with the changing barometric pressure.

Hazards associated with a falling barometer

Falling atmospheric pressure can liberate methane from the coal seam into the mine atmosphere at a greater rate, and also may appear in areas of the mine not normally prone to methane accumulation. Explosive methane/air mixtures may be present in the areas of the seals. Atmosphere from the gob areas with methane and low oxygen concentrations will migrate toward active areas of the mine.

MSHA-recommended best practices to prevent a drop in barometric pressure include:

• Make frequent checks for methane in work areas when the barometer is falling.
• Maintain adequate ventilation in the face area to prevent methane gas accumulations.
• Ensure areas in front of seals are ventilated so gases liberated from the sealed area are swept away.
• Apply adequate rock dust in all areas of the mine.
• Take extra precautions when travelling in areas near seals or gobs when the barometer is falling, as methane and low oxygen levels may be present.
• Maintain a recoding barometer at the mine and check the trending of barometric pressure each shift.