Lesson Learned Statement:Change control processes should ensure that a hazard assessment is conducted any time the work process changes.
Hazard controls should include personal protective equipment that protects workers against the highest potential air concentrations reasonably expected until air monitoring verifies that engineering controls are adequate.
Indicators should be visible to workers so they can tell when ventilation equipment malfunctions.
Discussion:Abrasive blasting operations to decontaminate structural steel were moved from a building being demolished to an adjacent building in order to continue decontamination operations during the demolition. The operation was conducted in a single enclosure with one sponge blast unit used to remove radiological contaminated lead based paint from structural steel.
The blast unit was changed to a steel shot unit just prior to the move. Engineering controls, work practice techniques, and personal protective equipment had been established based on both previous work at the site and the subcontractors' experience at other work locations. Air monitoring conducted prior to the move indicated air concentrations for lead were well below the maximum use concentration for the air-purifying respirators in use.
A hazard assessment was conducted to evaluate moving the operation to the new building, adding a second enclosure, and adding a second blast unit to each enclosure. The assessment concluded that the existing engineering controls, work practice techniques and personal protective equipment were adequate for the new operation. These controls consisted of an 18,000 cfm ventilation unit for each enclosure; use of a magnet to separate the steel shot from the lead paint dust; a vacuum system to collect the dust from the table and floor; a classifier to further separate dust from the shot before being recycled to the hoppers supplying the blast units; and use of a full-face powered air purifying respirator.
Air monitoring following the move and after the switch to steel shot indicated an increase in air-borne dust levels, but they were still below the maximum use concentration for the respirator. Soon after the addition of the second blast unit to each enclosure, dust was observed coming from the south enclosure and work was suspended in that enclosure. The following day, air monitoring results were received indicating that four of the ten air samples exceeded the maximum use concentration for the powered air-purifying respirators being worn. All work was then suspended.
Analysis:One of the nine hoses on the south enclosure's ventilation machine connecting it to the HEPA filter manifold located inside the building was disconnected. Loss of a hose on the manifold at this point would have severely reduced the ventilation and account for the three high sample results from the south enclosure. However, one of the air samples taken on a blaster working in the north enclosure was also high. Subsequent monitoring confirmed that some workers operating the blasting equipment intermittently exceeded the maximum use concentration of the respirators being worn.
The investigation also revealed that lead paint dust was not being adequately removed by the classifier and lead paint dust was in fact being entrained with the steel shot when it was recycled. It was also determined that with the addition of a second blast unit in each enclosure the volume of steel shot and lead paint dust exceeded the capability of the operators to recover the shot using the magnet and the vacuum system. Workers had begun using brooms and shovels to collect the shot and load it in the classifier since the magnet was too slow and the vacuum system clogged frequently. This in effect eliminated the initial cleaning step of the process. As work proceeded dust levels increased as more and more lead paint dust was being entrained with the recycled shot since the classifier which worked well for sponge blast material was unable to adequately separate the dust from the steel shot.
While the subcontractor had experience with abrasive blasting operations for similar work, there was no data to estimate the impact of adding a second blast unit to each of the enclosures or that the classifier could separate lead dust from the steel shot under these conditions. This resulted in an inadequate evaluation of the process change since the new process had not been adequately characterized by monitoring and the equipment selected for separating lead paint dust from the steel shot had not been proven to be adequate. As a result, improper protective equipment was prescribed, i.e. air-purifying respirators instead of airline respirators.
Workers in the south enclosure failed to recognize that the ventilation system had malfunctioned since streamers used to indicate the machine was working had been placed only on the exhaust of each machine which was located outside the building. These streamers indicated that the machine was running but would not show that a hose had come off the manifold inside the building. There were no streamers inside the enclosure, which would have alerted the workers to the malfunction. Due to the timing of the ventilation failure, i.e. just after a second blast unit was added, workers assumed that the increase in dust levels in the enclosure were the result of adding the second blast unit.
To determine the extent of potential personnel exposure, blood samples of the workers were taken and analyzed for lead. Analysis of the samples indicated workers blood lead levels were well below the action level of 40 ug/dl.
Recommended Actions:workers were required to wear airline respirators, the ventilation system was repaired, the two enclosures were combined and a third 18,000 cfm ventilation machine added, streamers were added to the inside of the enclosure, a complete inspection of the ventilation system was conducted daily, and a supervisor was required to be present in the enclosures during blasting operations. In addition workers were retrained in work practice techniques, informed that sweeping of lead paint dust is strictly prohibited, and that supervision was to be contacted if unexpected conditions occur.
Originator:Bechtel Jacobs Company, LLC; L. E. May, (423) 576, Environmental, Safety & Health-4018;
Validator:C. J. Witherspoon
Contact:Joanne E. Schutt, (423) 574-1248
Name Of Authorized Derivative Classifier:J. S. Paris
Name Of Reviewing Official:J. F. Preston
Priority Descriptor:Yellow / Caution
Keywords:shot blasting, abrasive blasting, lead, airborne dust, ventilation
References:Occurrence Report: ORO-BJC-K25GENLAN-1999-0009
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DOE Function / Work Categories:Management
Occupational Safety & Health - General
Hazard:Personal Injury / Exposure - Airborne Materials
Personal Injury / Exposure - Hazardous Material (General)
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