Abstract: At 1:40 p.m. on June 14, 2021, Employee #1, a maintenance worker at a large dairy farm, was modifying and constructing a truck rack to install a new welder. While using a 4.5 inch Makita vertical portable grinder (model 9557PB, serial number 1300706) equipped with a worn 6.5 inch cutting wheel, the fractured wheel separated from the grinder and struck the employee's left hand. The grinder was operated without the side handle, forcing the employee to hold the grinder closer to the rotating wheel, and was not equipped with a safety guard. The grinder is rated for 4.5 inch wheels but was used with a larger worn wheel. Employee #1 suffered serious injuries to the left hand, requiring hospitalization for over 24 hours and surgical treatment. The employee was transported to Petaluma Valley Hospital. Regulatory actions cited serious violations for failure to maintain the grinder per manufacturer's recommendations, lack of safety guard, damaged flexible cord, and inadequate injury and illness prevention program related to grinder safety and employee training.