Survey report: evaluation of an air shower for reducing exposure to carbon monoxide at United States Port of Entry, Calexico, California, report no. CT-171-33a.
From July through December 2002, an engineering control evaluation was conducted to assess the effectiveness of a redesigned external air supply installed in two lanes at the Calexico West Port of Entry. Air diffusers, known as air showers, delivered roof top air to primary inspection lanes 5 and 7 at a height of 10 feet above ground. This improved delivery system was expected to provide cleaner, rooftop air closer to the inspectors breathing zone resulting in reduced exposure to carbon monoxide. In the initial in-depth survey, carbon monoxide (CO) concentrations measured on the inspectors and in the lane area for those lanes outfitted with the air shower (primary lanes 5 and 7) were compared to those with existing ventilation (primary lanes 4, 6, and 8). Following the initial survey, fixed area CO monitors were installed in primary inspection lanes 4 through 8 to provide long-term measurement of area CO concentrations . The long-term data was collected over several months to assess seasonal environmental variations and the effect of variable traffic flow among the primary inspection lanes. The results of the in-depth and long-term surveys showed that the air showers, as installed, did not result in lower personal or area CO concentrations. During the in-depth survey, shift average area CO concentrations, in the lanes with the air shower installed, ranged from 8.4 ppm-17.3 ppm (Lane 5) and from 5.8 -13.6 ppm (Lane 7). In the lanes without the air shower, shift average CO concentrations ranged from 6.1-10.9 ppm (Lane 4), 5.6-10.9 ppm (Lane 6) and 4.8-9.0 ppm (Lane 8). The shift average CO concentrations measured on the inspectors during the in-depth survey, in the lanes with the air shower installed, ranged from 6.2-13.9 ppm (Lane 5) and from 5.9 -11.3 ppm (Lane 7). In the lanes without the air shower, shift average personal CO concentrations ranged from 7.6-10.8 ppm (Lane 4), 4.8-10.7 ppm (Lane 6) and 6.1-7.3 ppm (Lane 8). While these average personal CO concentrations do not exceed applicable occupational exposure limits, some instantaneous peak CO concentrations exceeded the NIOSH ceiling limit of 200 ppm with a small number approaching the level considered Immediately Dangerous to Life and Health (IDLH), 1200 ppm. It is important to note that although these peaks exceeded the NIOSH recommended ceiling, they were very brief in duration (1 minute or less), thus resulting in low shift-average concentrations. Long-term average CO measurements also showed no substantial difference in primary area CO concentrations between those lanes outfitted with the air shower compared to those with existing ventilation systems. The ability to achieve significant reductions in shift average CO concentrations will likely be difficult due to a variety of factors affecting exposure, including: multiple CO sources (significant car congestion); environmental factors (poor ambient wind dilution due to blockages surrounding the primary inspection area), required work activities (inspection requires workers to walk around the vehicle removing them from the ventilated booth and placing them closer to the tailpipe) and current work practices (car on vs. off, proximity of idling cars). Based on the CO concentrations measured during this evaluation, major changes at the Calexico Port of Entry may not be warranted. However, further worker monitoring should be continued to help understand and mitigate the peak exposures and to assess changes in exposures based on traffic volume, operational procedures and work practices, as well as facility changes and ventilation system changes. Additionally, the use of real-time personal CO monitors (with audible alarms) and possibly video exposure monitoring should be considered to investigate factors, including work practices, which may be leading to exposure to instantaneous CO concentrations above the NIOSH ceiling.
Engineering-controls; Environmental-control-equipment; Control-technology; Region-9; Air-contamination; Air-quality-control; Air-sampling; Air-treatment-equipment; Gases; Air-flow; Automotive-exhausts; Equipment-design; Exposure-assessment; Ventilation; Exposure-levels; Exposure-limits; Breathing-atmospheres; Breathing-zone
National Institute for Occupational Safety and Health, Division of Applied Research and Technology, 4676 Columbia Parkway, Mailstop R-5, Cincinnati, OH 45226