# Engineering Controls Database

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## Control of Crystalline Silica Dust When Grinding Concrete

| Problem:                                        | Construction workers may be exposed to hazardous dust containing crystalline silica when using handheld electric grinders to smooth poured concrete surfaces                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
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| What this means to you:                         | Breathing dust that contains crystalline silica can lead to the development of silicosis, a deadly lung disease.  No effective treatment exists for silicosis, but it can be prevented by controlling workers’ exposure to dust containing crystalline silica. Exposure to crystalline silica has also been linked to lung cancer, kidney disease, reduced lung function, and other disorders.  A NIOSH study found that workers grinding concrete to smooth poured concrete surfaces after forms were stripped were exposed from 35 to 55 times the NIOSH recommended exposure limit (REL) for airborne dust containing crystalline silica.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
| Description of control:                         | NIOSH found that dust exposures could be reduced if a local exhaust ventilation (LEV) shroud was attached to the grinder.  The LEV system consistedof a grinder that was equipped with a ventilation shroud, a length of flexible corrugated hose, and a portable electric vacuum cleaner that acted as the fan and dust collector for the ventilation system.  Four commercially available shrouds were used in the NIOSH study.The shroud can be purchased with the grinder, separately, or as a unit with the vacuum cleaner and hose.  The commercially available grinder/shroud pairs should be connected with a 1.5- or 2-inch hose with a relatively smooth interior and a length of no more than 15 feet to provide adequate air flow.  The choice of a vacuum cleaner depends on the task.  It should draw at least 10 amps and have sufficient flow rate to capture dust and transport it to the vacuum source.  The vacuum should also (1) use a high-efficiency particulate air (HEPA) filter to reduce the chance of releasing dust containing crystalline silica from the vacuum into the worksite (2) use a pre-filter or cyclone to increase the length of service of the HEPA filter (3) use a filter replacement indicator and (4) allow filters to be cleaned and replaced or full collection bowls or bags replaced without exposing the operators to dust**Grinder in use with the control in place****Diagram of grinder showing main parts** |
| Engineering and Physical Hazard Report Numbers: | 247-11; 247-15-A; 247-15C; 247-21;                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| NAICS Codes:                                    | 2357;23571;4213                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
| Keywords:                                       | concrete finishersconstruction workerselectric grindersgrinderssmoothing concrete                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
| How well does this control work?                | The NIOSH study found that all grinder/shroud combinations reduced dust exposure by at least 90%.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |

November 16, 2018
National Institute for Occupational Safety and Health