Safety Alert

Tensioner Bolt Failure

On July 17, 2025, a miner at a surface limestone operation sustained serious injuries
while performing repairs on a belt drive motor. During the repair process, the motor’s
tensioning system was being adjusted when a ¾-inch diameter all-thread tensioner bolt
failed, causing the bolt to break loose and strike the miner in the face. Spring-integrated
designs with constant pressure and continuous vibrations pose potential safety concerns.

Best Practices

• Ensure all miners receive thorough training to identify workplace hazards and perform tasks safely.
• Maintain all equipment and safety devices in proper working condition to ensure safe operation by reviewing manufacturer manuals prior to service; replace worn or damaged components; and use tightening sequences and tighten as recommended.
• Check component quality by examining bolts, washers, springs, and nuts for visible defects like rust, cracks, corrosion, thread damage or deformation.
• Conduct a risk assessment before starting work to identify and control all forms of stored energy, including mechanical, electrical, hydraulic, gravitational hazards, and unintended motion of equipment.
• Alignment matters: Ensure all components are properly aligned before bolt installation. Misalignment can lead to uneven stress distribution within the system, possibly leading to their premature failure. 

Miners and mine operators can find safety and health information on MSHA.gov.