Abstract: On August 15, 2018, at least thirteen employees were working for a manufacturer of fluid power valve and hose fittings. One employee was operating a Toyota model number 5FGC25 forklift, with serial number 12326, to arrange stock for production. It was in use in the shipping and receiving area of the main production floor for performing normal operational duties during the morning hours. Employees on the main production floor began to have significant headache symptoms, prompting employers to contact the natural gas supplier for the worksite. First responders arrived on the scene at approximately 12:45 (either a.m. or p.m.). Twelve employees were treated for elevated carboxyhemoglobin levels. Eight employees were transported to Waukesha Memorial Hospital by ambulance due to significantly elevated carboxyhemoglobin levels caused by carbon monoxide emitted from the forklift. Four other employees went to the hospital for monitoring due to slightly elevated carboxyhemoglobin levels. Treated employees included men and women, aged 21 to 58 years old. All employees recovered fully from the carbon monoxide exposure with treatment. In all, twelve employees were hospitalized. A thirteenth employee was not hospitalized. The faulty forklift was later repaired and returned to service.