An operator began preparations for a cleaning run, and was unaware that a maintenance task to calibrate a pressure transducer was scheduled to also take place that morning. The calibration required a break on a hydrogen line in order to install a Measuring and Test Equipment (M&TE) gage, which was used in the calibration. At the time the operator was informed of the calibration, the cleaning run procedure had been initiated but the actual cleaning had not yet begun. A discussion between his supervisor and the facility maintenance coordinator resulted in a decision to proceed with the maintenance task and suspend the cleaning run until afterwards.
The operator evacuated the hydrogen line and the hydrogen cylinder was valved out. The maintenance work package procedure had been revised at an earlier date to allow the maintenance task to be performed without employing Hazardous Energy Control (HEC), which would have involved a single point worker lockout for isolation of the hydrogen cylinder. Although employment of HEC alone would not have prevented the incident, the lack of this control was identified during the incident review as an adverse impact to overall worker safety. Corrective actions pertinent to HEC documentation are also being tracked but are separate from the corrective actions identified under this occurrence report.
After the hydrogen cylinder was valved out, the maintenance workers made the line break at the M&TE test port on the hydrogen line, and installed the M&TE. This introduced room atmosphere air into the line and volume vessel. The hydrogen bottle was then valved in to perform the necessary calibration in incremental steps. After the calibration was completed, the M&TE was removed from the test port, allowing the line and volume gas to backfill with room atmosphere air again. The test port plug was reinstalled and the operator evacuated the contents from the hydrogen line, but not the volume vessel. The maintenance work package did not specify the correct Post Maintenance Test (PMT) which would have included system restoration using a specific operations procedure. This procedure directs the evacuation of the volume and sampling of the system prior to resuming a cleaning run, neither of which were performed.
The cleaning run resumed, and the operator did not receive the expected response on some of the process parameters during the run. He then asked for assistance from technical support personnel in evaluating the abnormalities. Technical personnel recommended sampling of the system contents. The initial sample came back with the oxygen level being above our procedural limit for a flammable mix. Second and third samples showed that a flammable mix did not exist. An initial critique was held to address the potential flammable mix issues. During this critique, evaluation of the events indicated that the work control process was not adequate prior to and after the maintenance task, and Conduct of Operations practices were weak. Due to this additional information, a second critique was held. Additional corrective actions were identified.
- Safety Systems
- Measurement / Sensing Device
When performing maintenance evolutions, proper work control processes must be in place to insure that process systems are adequately prepared, remain in a safe energy state during the maintenance evolution, and are properly restored afterwards.