Ohio Rev. Code § 4113.04
If the employee of any employer referred to in section 4113.03 of the Revised Code receives any personal injury by reason of any defect or unsafe condition in any ways, works, boats, wharves, plant, machinery, appliances, or tools, except simple tools, in any way connected with or in any way used in the business of the employer, such employer is deemed to have had knowledge of such defect before and at the time such injury was so sustained, and when the fact of such defect is made to appear upon trial of an action brought by such employee or his personal or legal representatives against any such employer for damages on account of such injuries so received, the defect is prima-facie evidence of neglect on the part of such employer. The employer may show by way of defense that such defect was not discoverable in the exercise of ordinary care.
R.C. §4113.04