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OSHA Safety Hazard Information Bulletin on
Misuse and Improper Maintenance of Double Acting Hydraulic Cylinders
March 23, 1993
The Directorate of Technical Support issues Hazard Information Bulletins (HIBs) in accordance with OSHA Instruction CPL 2.65 to provide relevant information regarding unrecognized or misunderstood health hazards, inadequacies of materials, devices, techniques, and safety engineering controls. HIBs are initiated based on information provided by the field staff, studies, reports and concerns expressed by safety and health professionals, employers, and the public. Information is compiled based on a thorough evaluation of available facts, literature and in coordination with appropriate parties.
The Eau Claire District Office investigated a fatality involving a double acting hydraulic cylinder which was improperly set up for use.
The double acting cylinder involved in the incident was a hydraulic jack that extended or retracted using hydraulic pressure and was used to squeeze materials into proper position for welding. Such cylinders require that two hydraulic hoses be connected, one below and one above the piston in the cylinder. It is a routine matter to connect and disconnect the hoses using quick disconnect couplings. The cylinder manufacturer's literature clearly warns against attaching only one of the two hoses to a double acting hydraulic cylinder. The construction, inspection, testing, maintenance, and operation of these cylinders should comply with the American National Standards Institute (ANSI) Safety Standards for Jacks, ANSI B30.1.
Investigation of the incident revealed that only one of the two hydraulic hoses was properly attached between the hydraulic pump and the cylinder. When pressure was applied to the cylinder by a hydraulic pump, the shutoff ball of the top quick disconnect coupling attached to the cylinder was forcefully expelled and fatally injured a worker.
The hydraulic cylinder was equipped with a pressure relief valve in the ram. Accordingly to the manufacturer of the cylinder, the relief valve was set at approximately 12,000 psi (82,700 kPa). The relief valve, if it was properly functioning, should have prevented damage to the ram when the top hose was inadvertently left disconnected or improperly connected. However, the relief valve did not open at 12,000 psi (82,700 kPa).
Following the incident, the manufacturer of the cylinder tested identical couplings to failure. The shutoff balls were found to fail at pressures over 27,000 psi (186,000 kPa). In view of its test report, the manufacturer believed that the relief valve of the cylinder involved in the incident had been improperly tampered with, and therefore did not function at the preset pressure.
Based on the information available, it appears that the accident occurred because the top hose was not properly connected as required by the manufacturer. Additionally, the relief valve may have been inappropriately adjusted and did not function at the preset pressure.
Compliance and consultation personnel should be aware that improper maintenance, replacement or adjustment of relief valves on double acting cylinders could create the potential for overpressurizing the cylinder system which could result in equipment failure and harm to employees. ANSI B30.1 and the manufacturer's literature should be used to determine compliance with the proper procedure for maintenance and use of double acting hydraulic cylinders.
Please distribute this bulletin to all Area Offices, State Plan States, Consultation Projects and appropriate local labor and industry associations.