Abstract: At approximately 7:45 a.m. on December 26, 1990, at Spoto Nursery, the employer and Employees #1, #2, #3, and #4 were preparing to dig up four rows of small walnut trees that were being raised for resale. The employer was operating a power take-off winch on a D-4 Cat on the south side of the trees. A 3/8 in. by 400 ft airplane cable was pulling the tree digger from the north side to the south side. The winch on the Cat pulls the tree digger under a row of trees. The digger enters the ground approximately 2 ft and cuts off the tree roots. The four employees were helping to start the digger into the ground; it had entered the ground approximately 1 ft. The winch was pulling the tree digger when, because of the frozen ground, the 5/8 in. by 2 in. bolts broke away from the runners on the tree digger, causing it to fly up and hit the employees. Employees #1, #2, #3, and #4 were taken to Rideout Hospital in Marysville for treatment. Employees #1 and #3 were hospitalized. The employees had been given safety instructions by the employer. All the employees were experienced in this particular job. The temperatures had been at a record low for about a week. The ground was frozen and presented a condition the employer did not anticipate; the digger normally cuts right through the loam soil. This digger has been used by the owner, his father, and grandfather without presenting any problem.