Job Controls for Silica Exposure End when Work Area and Associated Equipment Are Dust Free

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Type:  Lessons Learned

Publisher:  Babcock & Wilcox, Pantex-B&W

Published As:  Public


Topics:  Respiratory Protection, Occupational Safety and Health

Lesson ID: 2013-PTX-LL-1001
Date: April 5, 2013

Lesson Statement: Visible dust should never be used as an assessment for silica exposure. The respirable sized particles that you cannot see pose the greatest exposure hazard. A HEPA vacuum should never be breached post job except for cleaning under proper silica controlled conditions. Any vacuum and associated equipment used for capturing of silica, including the equipment's exteriors, should be wet cleaned post job while using proper PPE (HEPA Respirator/ disposable clothing etc.).

Discussion: Background: Silica, also called quartz, is found naturally in the earth's crust. Silica is the basic component of sand and rock. Concrete and masonry products also contain silica. Construction and maintenance workers may be exposed to silica when working with stone, concrete, brick, or masonry.

Activities that can lead to possible silica exposure include chipping, hammering, drilling, saw cutting, grinding, crushing, loading, dumping rock and concrete, abrasive blasting using sand, abrasive blasting on concrete or stone surfaces, and dry sweeping. One activity that is not typically considered as a concern is the clean-up of equipment which is designed to capture and contain silica. Concrete floor grinders, drills, hand held grinders, etc., can be used for construction and maintenance operations and could utilize HEPA filters to capture and contain silica. Improper handling of HEPA filters, HEPA vacuums, and associated support equipment during set-up, during the actual operation, and post-task/clean-up activities could result in an exposure or a possible overexposure.

Discussion of Events: B&W Plant Maintenance Department Personnel were using a concrete floor grinder to grind a portion of flooring. The supervisor, involved employees, and representatives from the Safety & Industrial Hygiene (S&IH) Department conducted a pre-job briefing at the work site. There were a total of three employees assigned to the job; all were to take turns using the floor grinder. S&IH technicians equipped two of the workers with Breathing Zone (BZ) pumps and one with a noise dosimeter. In addition, an area sampling pump was placed near the actual work locations.

This particular concrete floor grinder, Hum-B Surface Grinder Model #SG-30, and the associated HEPA vacuum/dust collector, Pulse-Bac Extender 55/40 Model #103556HD, had been used on previous occasions and monitoring results had been less than detectable for silica.

Operations commenced at approximately 0830 and lasted until approximately 1430. One of the two workers, who had been wearing a BZ, left the area during lunch and did not return to the work site. That left one worker wearing a BZ and the other wearing a noise dosimeter. S&IH technicians were still in the area.

When work concluded at approximately 1430 the two workers began the process of breaking down the equipment and placing the equipment into an enclosed transport trailer. This involved removing the HEPA vacuum from the top of the dust collector and disconnecting associated vacuum hoses connecting the grinder to the HEPA vacuum. The workers mentioned the vacuum and dust collector were outside the facility and that they saw a swirl of dust when they raised the HEPA vacuum from the collector. The workers lowered the HEPA vacuum onto the collector and resumed other clean-up operations. The worker who was wearing the BZ was still wearing the BZ when the HEPA vacuum was raised. After a period of time, the HEPA vacuum was raised, no swirling dust was noticed, and all site equipment was transported to the appropriate storage area.

The BZ was removed when the material was loaded. S&IH personnel did not view the loading operations. The filters associated with the two BZ pumps and the one area sampling filter were taken to an on-site lab for analysis. The filters were weighed, and it was determined that one BZ filter, the one worn by the worker that loaded the equipment, weighed more than the pre-use weight.

The lab notified an S&IH Industrial Hygienist that the filter could have contaminants. The filter was sent to an off-site lab and results were received confirming the filter had 0.041 mg/m3 crystalline silica. This is more than the 0.025 mg/m3 allowed by the 2012 edition of the ACGIH sampling booklet. The results of the second BZ filter and the area sample filter were both non-detect.

Analysis: Yard personnel have performed approximately five concrete floor grinding operations per the supervisor, and the floor grinders are equipped with an engineering control in the form of a shroud covering the grinder that exhausts into a HEPA vacuum dust collector. Previous monitoring results for the actual grinding operations have been less than detectable for crystalline silica.

Grinding operations have been controlled, but the subsequent clean-up and breaking down of equipment, which is always exterior to the facility, has not been adequately analyzed or controlled. The emphasis was on the actual operation as the higher perceived hazard and not on the set-up, post-task, and clean-up processes.

1. Stopped concrete grinding work until the JSHA has been revised.
2. Perform a Training Needs Analysis on the Surface Grinder.
3. Revise the JSHA associated with floor grinding operations & Train applicable Yard workers on approved Surface Grinding Operations JSHA.
4. Brief S&IH personnel on reviewing Maintenance work packages as addressed in WI, Execute Maintenance Work and Provide Feedback.
5. Develop a PM process to identify, handle, and clean any vacuum cleaners and power tools that are associated with Silica Dust.

References: PER-2012-0641

Contact: Lauri Minton/806-477-3556

Reviewer: Lou Ann Cox

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