HighDrill strings comprise multiple sections of steel pipe connected by threaded joints, transmitting rotation torque and pull/push forces from the drill rig to the drill head potentially hundreds of metres underground. These pipes operate under extreme stresses including rotation torque up to 50,000 Nm, tensile loads during reaming and product pullback up to 500 tonnes, compressive loads during pilot hole drilling, and bending stresses when steering through curves. If connections fail from inadequate makeup torque, corrosion, or fatigue, or if the drill head becomes stuck and string suddenly releases, the stored elastic energy causes violent whipping of the failed section. Workers positioned near the failure point can be struck by whipping pipe sections weighing hundreds of kilograms moving at high velocity, or become entangled in rotating components. Drill string failures have caused traumatic amputations when workers' limbs contacted rotating or whipping pipe, crush injuries from pipe sections striking bodies or heads, and fatalities when workers became entangled in rotating equipment. The hazard is highest during reaming and pullback operations when tensile loads approach equipment limits.
Consequence: Traumatic amputation of limbs from contact with whipping pipe, fatal crush injuries from being struck by failed drill string sections, entanglement causing severe injuries or death, or ejection of drilling fluid under pressure through failed connections.
MediumHDD operations expose workers to diesel exhaust emissions from drill rig engines operating continuously throughout boring operations, which may last days or weeks for long bores. Operators positioned at drill rig controls work in close proximity to exhaust outlets for extended periods. Diesel exhaust contains numerous hazardous substances including nitrogen oxides, carbon monoxide, particulate matter, and diesel particulate matter classified as a Group 1 carcinogen. Drilling fluid systems also create aerosols when pressurised fluid escapes from connections or when fluid-contaminated equipment is handled. Bentonite drilling fluids contain additives including polymers, surfactants, and in some cases biocides that can cause respiratory irritation when inhaled as aerosols. Workers conducting drill pipe connections or cleaning equipment are exposed to drilling fluid mist and spray. Chronic exposure over career duration may contribute to respiratory disease development, while acute exposure causes eye and respiratory tract irritation affecting worker comfort and performance.
Consequence: Chronic respiratory disease from long-term diesel exhaust exposure, acute respiratory irritation affecting work performance, eye irritation from drilling fluid aerosols, or exacerbation of pre-existing respiratory conditions including asthma.
HighDrilling fluid circulation systems operate at pressures of 50-200 bar (750-3000 psi) pumping bentonite slurry through the drill string to provide borehole stability and remove cuttings. High-pressure hoses, connections, and pump components store substantial energy that can cause severe injuries if failures occur. Workers connecting or disconnecting drill pipe sections must handle fluid hoses under pressure, with risk of unexpected releases if connections are loosened while pressure remains in the system. Hydraulic systems powering drill rig functions also operate at high pressure (200-350 bar), creating injection injury risks if seals fail or hoses rupture. Pressure releases can cause high-pressure fluid injection injuries where fluid penetrates skin and spreads through tissue causing severe internal damage requiring amputation. Whipping hoses from sudden pressure release can strike workers causing lacerations and blunt trauma. Drilling fluid discharge from failed connections creates extremely slippery surfaces leading to slip injuries particularly on elevated work platforms.
Consequence: High-pressure fluid injection injuries requiring amputation, lacerations and blunt trauma from whipping hoses, severe slip injuries on fluid-contaminated surfaces, or hydraulic fluid fires if pressurised fluid contacts hot engine components.
HighHorizontal directional boring inherently involves working in close proximity to existing underground utilities, with risk of inadvertent contact particularly with electrical cables that may not be accurately located or may have deviated from recorded positions. If the drill string contacts an energised electrical cable, the metallic pipe becomes a conductor transmitting electric current to surface equipment and creating electrocution hazards for ground crews handling pipes or operating equipment. High-voltage electrical cables (11kV and above) can arc to drill strings that pass within close proximity without physical contact, with arc flash causing severe burns and pressure waves causing trauma. Drill rig operators positioned at controls can be electrocuted if the rig frame becomes energised from drill string contact with electricity infrastructure. Even low-voltage services can cause fatal electrocution in certain circumstances, particularly if workers are grounded through wet conditions or metal structures. The drilling process makes contact detection difficult because operators cannot visually observe the drill head underground and may not receive immediate indication that electrical contact has occurred until someone is injured.
Consequence: Fatal electrocution of equipment operators or ground crews, severe burn injuries from electrical arc flash, cardiac arrest from electric shock, or extensive electrical burns requiring long-term medical treatment and rehabilitation.
MediumDrilling fluid frac-out occurs when pressurised bentonite slurry escapes from the borehole to surface through fractures in the formation or inadequate cover over the bore alignment. This typically happens when drilling through fractured rock, loose granular soils, or areas with inadequate soil cover over the bore. Fluid pressure in the borehole (typically 0.5-2 bar above groundwater pressure) forces slurry into fractures until it reaches surface, creating environmental contamination. Frac-outs on land surfaces create cleanup requirements and potential contamination of soil and vegetation, while releases into waterways cause significant environmental harm from bentonite suspending sediments, reducing light penetration, and affecting aquatic life through gill irritation. Large frac-out volumes can exceed site fluid storage capacity making containment difficult. Ground heave from excessive drilling fluid pressure can lift pavements or damage underground services. Environmental authorities may issue notices requiring immediate cessation of works and can prosecute companies for environmental harm, with penalties and remediation costs potentially exceeding project values.
Consequence: Environmental prosecution and penalties for waterway contamination, costly remediation of frac-out materials, project delays from regulatory stop-work orders, damage to site reputation, or ground instability affecting surface structures.
