This incident is a PERFECT example of what can happen when STORED ENERGY is overlooked. For energy sources like hydraulics and pneumatic (e.g., gases), merely closing a valve and locking it closed or locking out a pump is NOT full energy control. Procedures MUST include the means to dissipate the stored energy to the Zero Energy State (ZES). Keeping in mind that sometimes the dissipation of this stored energy in and of itself can be a hazardous task and may require special PPE and procedures so as not to cause injury or create a hazard.
While carrying out weekend maintenance activities on an excavator in October, three workers were exposed to a high-pressure fluid release ending in two people being taken to hospital by ambulance. A working group of five people carried out maintenance activities on the excavator on 31 October 2015. These workers were a leading hand, a tradesperson, and three apprentices. The leading hand had to leave the worksite, giving the apprentices certain tasks to carry out in his absence. Maintenance activities continued under the guidance of the tradesman. The excavator was isolated using the main single-point isolation valve. One task was the replacement of a check valve in the excavator track tensioning circuit. The workers assumed that the hydraulic circuit was isolated and all energy dissipated. Upon unscrewing the fitting on the check valve, high-pressure hydraulic fluid was released. The release of high-pressure hydraulic fluid injured three people, with two being taken to hospital for exploratory surgery.
INVESTIGATION
The investigation identified the following:
- The check valve was on the hydraulic track adjuster circuit. The main isolation valve isolated the circuit; however, the stored energy was NOT dissipated. The circuit has three accumulators with up to 60 liters of total capacity of pressurized fluid.
- The excavator’s manufacturer procedure REQUIRED the accumulators to be drained. They were not drained.
- The task of changing the check valve was given to two apprentices.
- There was no hydraulic circuit diagram available on the job.
- The leading hand was not on the site then, and the tradesperson was unaware of the jobs given to the two apprentices, even though he was close to them.
RECOMMENDATIONS
Mine operators are reminded that effective isolation and energy dissipation is a critical risk control when working on high-pressure fluid systems. It requires all of the following steps before working on fluid systems:
- Isolation of energy
- Locking of the isolation point
- Energy dissipation of all circuits on the downside of the isolation valve
- Verification (test for dead) that there is no residual pressure in the circuit.
Mine operators should:
- Remind tradespeople of the potential for residual stored energy from accumulators and valves. Tradespeople should always dissipate the energy and verify that the circuit is not pressurized before attempting to work on fluid systems.
- Installing pressure gauges in all hydraulic circuits to verify that all stored hydraulic energy is dissipated.
- Always review the manufacturer’s information regarding the safe repair or maintenance method.
- Ensure that tradespeople fully understand the procedure for the task and have schematics/piping diagrams readily at hand.
- Verify competencies for the task.
- At all times, provide adequate mechanical supervision of apprentices when carrying out maintenance activities.
Further Information:
SB13-01 Fluid injections result in surgery
SB12-02 Fluid power isolation failures
SA16-06 Fatal high pressure hydraulic injection
SA06-04 Hydraulic injection near miss
MDG 41, Fluid power system safety
MDG 40, Hazardous energy control
NOTE: Please ensure all relevant people in your organization receive a copy of this Safety Alert and are informed of its content and recommendations. This Safety Alert should be processed systematically through the mine’s information and communication process. It should also be placed on the mine’s notice board.
Issued by:
Gary Parker, Chief Inspector of Mines – Appointed pursuant to Work Health & Safety (Mines) Act 2013
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Disclaimer
The information contained in this publication is based on knowledge and understanding at the time of writing. However, because of advances in knowledge, users are reminded of the need to ensure that information on which they rely is up to date and to check the currency of the information with the appropriate officer of NSW Department of Industry or the user’s independent advisor.
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