OSHA Hazard Information Bulletins
Hydraulic Systems Modifications

July 11, 1991




  • Director
  • Office of Field Programs


  • Director
  • Directorate of Technical Support


  • Hazard Information Bulletin - Hydraulic Systems Modifications

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. HIBs do not necessarily reflect OSHA policy.

The Dallas Regional Office has brought to our attention a hazard associated with the improper modification of hydraulic systems.

According to information received from the Lubbock Area Office, an auxiliary pump was installed on a hydraulic cotton baler to increase the working pressure from 3000 to 5000 p.s.i. The hydraulic flexible fluid hoses, designed for 3000 p.s.i. maximum, were not replaced by ones appropriate for 5000 p.s.i. When the pump was placed in operation, the hydraulic hose coupling failed. The failed coupling caused hydraulic fluid to be discharged creating a short in a 440 V electrical power line resulting in a fatal fire ball. An employee was killed and others were injured as a result of the flash fire.

It is our understanding that many cotton gins in the United States are modifying presses in order to reduce bale pressing time. Modifications to a higher pressure should always be approved by a competent engineer or the manufacturer of the equipment. An appropriate system safety analysis should be applied to assure that the subsystem modification will not adversely affect the safe performance of the operation.

Petroleum based hydraulic fluids are widely used. Hydraulic oil becomes hot during operations. A heated petroleum based hydraulic fluid presents a considerable fire hazard, particularly in those processes where ignition sources are usually present. A typical petroleum based hydraulic fluid has flash point that range from 300 to 600 degrees fahrenheit and an auto ignition temperature of 500 to 750 degrees fahrenheit. However, when hydraulic fluid is accidentally discharged under high pressure an easily ignited fine oil mist is sprayed over the surrounding area. When the mist reaches an ignition source the result can be a torch-like ball of fire.[1] If the oil mist is confined, a violent explosion can occur.

All hydraulic hoses, tube lines and fittings should be periodically inspected. Any deterioration must be carefully examined to determine whether further use of the component would constitute a hazard. Conditions such as the following should be sufficient for consideration of replacement:

  1. Any evidence of hydraulic oil leakage at the surface of a flexible hose or its junction with the metal and couplings;
  2. Any blistering or abnormal deformation to the outer covering of a hydraulic hose;
  3. Hydraulic oil leakage at any threaded or clamped joint that cannot be eliminated by normal tightening or recommended procedures; and/or
  4. Evidence of excessive abrasion or scrubbing on the outer surface of a hose, rigid tube, or hydraulic fitting. Modification must be made to eliminate the interference of the elements in contact, or otherwise protect the components.[2]

Please distribute this bulletin to all Area Offices, State Plan States and Consultation Project Officers.


  1. Ryan, Kenneth E., Fire hazards of hydraulic fluids, Professional Safety, June, 1984, pages 34 to 36.
  2. OSHA Requirement Guide Corporation, Equipment Guide Book, 1977, pages 12 and 13.