Abstract: At midmorning on July 27, 2011, two rig helpers were involved in the installation of a deep well turbine pump in rural Madera, CA. Employee #1 was a contractor employee leased through Clover Resource Solutions, Inc. Employee #2 was an employee of Anderson Pump Company of Chowchilla, CA, the company installing the pump. An elevator clamp failed, allowing a 20-foot section of 8-inch well case to fall and strike the two employees. Employee #1 suffered a concussion. He was not hospitalized. This incident was reported on the same day to Cal/OSHA Division by the Human Resources and Safety Director for Anderson Pump Company. Investigation determined that a dual employer relationship was created by contract between the primary employer, Clover Resource Solutions, Inc., and the secondary employer, Anderson Pump and Machine, in accordance with the Division's P&P C-1D. As reported, an elevator clamp failed, allowing a 20- foot section of 8-inch well case to fall and strike the two employees. The elevator clamp was a forged ferrous metal clamping device for lifting 8- to 10-inch well casing. In this device, a chain would allow for adjustment of the clamp in diameter to accommodate different diameters and terminated in a two-fingered flange attached to a threaded rod with nut. The fingered flange would fit into a saddle provided on the clamps housing. Tightening the nut causes the device to clamp around the pipe, securing it for hoisting. Results of the visual inspection of the clamp revealed a clean break of the fingers without an indication of cracking or other indication of fatigue and failure. The threads on the adjustment rod and nut did not show signs of deformation or galling. According to industry sources, these clamps are common in the well drilling and service industry although not currently in production. No requirement current or historical was found to cause users to inspect or test these clamps for structural integrity. Several other clamps were inspected with same results, that is, no defect was observed. Several sources in the industry asserted they had never heard of an elevator clamp failing. Although not conclusive, a possible explanation for the clamp's failure was the fingers were not fully seated in the saddle, causing excessive load on the tips. Root cause of the injury event was determined to be unforeseeable catastrophic failure of the elevator clamp. The employer was found to have a well devised health and safety program with an effective Injury and Illness Prevention Program, including employee training and equipment maintenance.