A Bad Case Of Gas

(from the Gerdau MRM Newsletter)

During the recent shutdown, the water ball was removed from service to permit the completion of the mechanical and structural work which started in April. Prior to the shutdown, a detailed schedule was developed to ensure the waterball could be returned to service when required to support plant operations. An integral part of the schedule was to develop a procedure to work safely within a confined space. With the assistance of a very timely seminar held at the Learning Center and consultation with a contractor (TMIF) experienced in work of this type, the criteria required to work safely and provide emergency evacuation was assessed.

Based on this assessment the contractor documented a procedure to ensure the safety of the workers while work was in progress. This included the use of a full time watchman at the ground level entrance, who signs in and out all personnel entering and leaving the ball. This watchman was in radio contact with a second attendant in charge of an emergency evacuation hoist positioned on top of the ball. Other procedures included forced air intake and exhaust and the use of body harnesses by all personnel accessing the ball. Interior gas levels were measured and determined to be safe by the work crew each time the ball was entered or at four hour intervals. All typical confined space work requirements were satisfied at this point, however, just before the shutdown began, it was suggested by the contractor (TMIF) to go one step further and continuously monitor the ball environment after the pre-entry checks were completed. This suggestion was incorporated into the daily work procedure.

Work started and continued for five days without incident. On the second last day, the work crew returned from their lunch break, completed their pre-entry check and resumed work. Approximately on half hour later, the gas monitor alarm sounded. The work crew evacuated the ball. Levels for carbon monoxide (CO) exceeded the alarm level (35ppm). Within a short period of time the CO levels dropped to a safe level and the crew returned to work. One hour later the alarm sounded again. After evacuating the ball again levels were checked and levels in excess of 500 ppm were indicated. Second and third detectors were used to confirm that the very high levels being indicated were valid. Work only resumed after the levels returned to an acceptable level.

The source of the CO was traced to the portable gas generators and welding machines being used during the scheduled power outage. A test using a smoke bomb confirmed that air currents rising from the base of the waterball carried the exhaust fumes up to a small open hatch approximately 120 feet above the ground. Opening or closing the hatch could in fact control CO levels.

This incident could easily had fatal consequences for the five boilermakers working inside the ball. The use of a procedure that exceeded the basic requirements for work of this type contributed to the detection of a situation created by unlikely and unforeseen circumstances. More importantly it was the disciplined and consistent application of the procedure by the work crew over the entire time the job was in progress that prevented a tragedy. In spite of delays created by these incidents and significant extra work discovered after the ball was drained, the crew from TMIF was able to return the waterball for service on schedule.

In 2001, the ball will be repainted inside and out. With the knowledge gained from this experience, we plan to further improve and refine our safety procedure before next year's shutdown.

- Glenn Yablecki & Wayne James

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