A senior millwright with over 32 years of experience was killed, and 2 other millwrights were injured, while trying to disassemble a hydraulic accumulator to rebuild it. The victim had previously rebuilt, at least one other accumulator salvaged from another part of the mill. He was viewed by everyone, including managers, as the expert in this task. Warning labels on the accumulator and in the rebuild kit instructions stated that all gas pressure must be released prior to disassembly. However, this step was skipped in the disassembly process and pressurized nitrogen gas remained in the accumulator. While the victim was slowly removing an 8-inch diameter cap from the end of the accumulator, the cap violently exploded off the cylinder and hit the victim in the abdomen and pelvis. The flying cap killed the victim. His co-workers were injured by the cap and related debris.
Hydraulic accumulators are used in equipment and processing systems throughout general industry, construction, and agriculture to provide a separate reservoir of pressurized fluid which supplements pump flow, provides stored energy, dampens shock loads and pulsations, and they can also act as an auxiliary power source. In operation, pressurized hydraulic fluid enters the accumulator chamber where, depending upon the type of accumulator, it either compresses a gas or compresses a spring. A pressure drop at the accumulator oil port allows the spring or compressed gas to discharge the fluid back into the system. The accumulator in this incident was a gas-type accumulator, using a piston to separate the fluid from the gas. The manufacturer’s maintenance procedures are to release the pressure from both the hydraulic fluid chamber and the nitrogen gas chamber of the accumulator prior to disassembly. Releasing both hydraulic and gas pressure involves two separate steps, each performed at opposite ends of the accumulator.
Here are some tips to help ensure safe use of accumulators:
- Be sure to follow manufacturer’s recommendations and confirm all pressure is released prior to performing any maintenance work on pressurized systems and components. To see how to test pre-charge on an accumulator, click here.
- Install a “dump valve” in hydraulic systems to ensure hydraulic energy is released from the system when the equipment is shut down.
- Be sure you are properly trained to recognize the potential hazard of stored energy and how to eliminate or control it.
- Be empowered to stop work and re-evaluate a situation whenever potentially hazardous or unusual methods are being used to accomplish a task.
- Consider altering the placement of warning labels, or applying additional labels or tamper-proof seals, on the cap area of accumulators to ensure they remain visible to maintenance personnel.
- Place warning labels on the side of the hydraulic accumulator stating that contents are under pressure and should be released by opening and removing the gas valve prior to disassembly.
