VENTILATION FOR SINKING VERTICAL, SUB-VERTICAL AND DECLINE SHAFTS Derek Walters Turgis Consulting

Virtually every shaft or decline sunk is unique in some way

Major differences being: Location Size and Depth Capacity Infrastructure Amount of development required from shaft or decline

Regulatory requirements No longer prescribed (formerly 0.15 m³/s/m² face area). Based on risk assessment and occupational exposure limits.

Occupational Exposure Limits (OEL) OEL = Time weighted average 8 hour day 40 hours a week. OEL – C = Instantaneous value which must never be exceeded. OEL-STEL = Maximum exposure for 15 minute TWA and not more than 4 times per day.

OEL AND STEL AFTER BLASTING SubstanceOELOEL-C / STEL ppmmg/m³ppmmg/m³ Carbon Monoxide (CO) Carbon Dioxide (CO 2 ) Nitric Oxide Nitrous Oxide Nitrogen Monoxide Nitrogen Dioxide3559 Silica dust (respirable) Coal dust (respirable)-2-- Particles not otherwise classified Inhalable particulates-10-- Respirable particulates-3--

Operating outside South Africa: Comply with local regulations. Or In the absence of local regulations use South African regulations. These comply with internationally accepted norms and are thus defensible.

The purpose of ventilation is to dilute and remove pollutants. Always assume that flammable gas may occur. SA Limit 1.4 % flammable gas in atmosphere. Define “Atmosphere” as 150 mm away from the source in any direction. Design must be robust enough to cater for abnormal but reasonably anticipated events.

Vertical shafts Determine requirement for ventilating the shaft barrel. Determine work that is to be done concurrently or in conjunction with sinking. Including: Station and other development Raise Boring Holing with other excavations

Determining basic air requirements Ordinary sinking: Air volume providing minimum of 0.5 m/s in shaft is good practice. Example: An 8.0 m shaft would require 50.3 m² x 0.5 = 25.2 m³/s

Determining re-entry times Shaft diameter: 8 m diameter (50.3 m²) Required re-entry time: 15 minutes Number of air changes: 8 between face & stage Distance from the face to the stage when raised for blasting: 50 m Air quantity (Q) = (Air changes x Volume) / Time Q = ( 8 x 50.3 x 50) / 15 x 60 = 22.3 m³/s In this case the minimum air quantity required is 22.3 m³/s

Force system

Exhaust – overlap system

Force – exhaust system

Airflow reversal

Ventilation of development from the shaft Unique design for each shaft. Designed as an integral part of the sinking shaft

Common problems Inadequate air for development activities. Column leakage due to improper installation and damage.

Recommended 2 or 3 mm thick “Corten” columns They are: Robust Can easily be refurbished and re-used

Decline development Single decline using conventional force system with flexible ducting (world norm). Twin declines.

Occupational exposure limits - Diesel Equipment Carbon dioxideCO ppm Carbon monoxideCO30 ppm Nitric oxideNO25 ppm Nitrogen dioxideNO 2 3 ppm Sulphur dioxideSO 2 2 ppm Diesel particulate matterDPMNot specified Suggested 400 µg/m³

Determining air requirements Currently no legislated minimum air quantity in SA Many other countries have regulations in place. These minimum air quantities vary considerably from country to country. Suggested volume is 0.075m³/s/kW rated power A 150 kW LHD would require (150 x 0.075) = 11.3 m³/s

Multiple vehicles used in series EquipmentkWm³/s/kWFactorm³/s 20 t Truck LHD Utility vehicle Drill rig Total air required32.9

Sizing of ventilation columns Identical 1.0 m Ø columns, 1500 m long, 15% leakage. Air quantity15 m³/s20 m³/s Fan Pressure4147 Pa7295 Pa Face quantity12.9 m³/s17.2 m³/s Fan input 75% efficiency 82.9 kW194.5 kW

Heat loads These are site specific and are affected by: Ambient conditions Depth Rock geothermal gradient Rock thermal characteristics Area of rock exposed Diesel equipment Other mechanical and electrical heat loads Ground water inflow rate

To determine the need for cooling a heat balance must be done. There are a number of computer programs to calculate this and to predict The working conditions in the decline being sunk.

Conclusions The ventilation system should be uniquely designed to cater for sinking and any additional development that may be required. Avoid the “one size fits all” approach.