Many incidents that occur when working on mobile hydraulic machinery are careless accidents, such as slips and falls. "Fortunately, you don't hear a lot about the hydraulic injuries," says Scott Kane, global platform manager - mobile, Parker Hannifin Corp. "But when they do occur, they are very severe."

Hydraulic injuries occur mainly due to the failure to relieve pressure prior to working on a hydraulic system. "It is guys disconnecting a hose or cracking a seal... while there is still pressure in the system. Then they end up getting sprayed," says Kane.

A lot of potential energy is stored in the hydraulic system. According to Dennis Kemper, account application engineer, Gates Corp., hydrostatic systems can produce pressures as high as 8,000 psi and temperatures up to 250° F. Work groups can generate pressures up to 4,000 psi and temperatures up to 212° F. Drain or return line hoses don't have much pressure, but still have temperatures up to 275° F.

A ruptured hose releases this energy. "Unless you have ever seen a hydraulic hose rupture under 5,000 psi, you have no idea what kind of potential energy is there," says Kane. "People take it for granted."

There is also the possibility for serious burns. "Allow the system to cool to ambient temperature before performing any work on it," advises Raymond Wilkins, chief engineer, fluid conveyance, Eaton's Hydraulics Operations.