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Exhaust ventilation design and occupational exposure to respirable crystalline silica during ready-mix concrete truck drum cleaning.

Almaguer-D; Echt-A; Shulman-S
American Industrial Hygiene Conference and Exposition, June 2-7, 2001, New Orleans, Louisiana. Fairfax, VA: American Industrial Hygiene Association, 2001 Jun; :3
A study was conducted to evaluate worker exposures to respirable crystalline silica during interior cleaning of ready-mix concrete truck drums. This study was conducted at a ready-mix concrete plant with a fleet of 27 ready-mix trucks. Ready-mix drum cleaning operations are conducted once per calendar year, during the winter slowdown. The cleaning of ready-mix drums becomes necessary as the drum interior becomes caked with cured concrete requiring worker entry to the drum, a confined space. The worker utilizes a jackhammer to break the concrete layer and remove the cured concrete from the drum interior. Two control systems were designed to reduce employee exposures during drum cleaning operations. One, a local exhaust ventilation (LEV) system was designed to be attached to the jackhammer being used for breaking cured concrete lining the drum interior. The second, a general exhaust ventilation (GEV) system was designed to remove dust from the drum interior. To determine the effectiveness of the designed controls, personal breathing zone air samples were collected on employees required to enter the drum interior to remove cured concrete. Respirable particulate samples were collected at a flow rate of 1.7 liters per minute using a 10-mm nylon cyclone and a pre-weighed, 37-mm diameter, 5-um pore-size polyvinyl chloride filter, in accordance with NIOSH Method 7500. Samples from four control combinations (no controls, LEV, GEV, and LEV/GEV combined) were collected in randomized blocks to determine the effectiveness of the control designs in reducing worker exposures during concrete removal operations. Statistical analyses of the sampling results indicate that the use of LEV alone was the most effective control, reducing airborne silica concentrations by about 48 percent (p<0.05). No statistically significant reduction (relative to no control) was determined from use of GEV.
Workers; Work-environment; Work-areas; Humans; Men; Women; Exposure-levels; Silica-dusts; Silicosis; Silicates; Concretes; Confined-spaces; Exhaust-systems; Ventilation-systems; Ventilation; Jack-hammers; Dusts; Air-samples; Respirable-dust; Particulates; Statistical-analysis; Airborne-dusts
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American Industrial Hygiene Conference and Exposition, June 2-7, 2001, New Orleans, Louisiana