The Calexico Port of Entry (P.O.E.) serves as the gateway between Mexicali, Mexico and the United States. Over 20,000 vehicles enter the U.S. through the Calexico Port of Entry every 24 hours. The border vehicle inspection area consists of 11 primary inspection lanes and a vehicle secondary inspection area. All traffic enters the Calexico Port of Entry through one of the primary inspection lanes. If a more thorough inspection is necessary, cars are directed to the secondary inspection area and the engines are shutdown during vehicle searches. Each primary inspection lane has one agent which may be employed by the U.S. Customs Service or the U.S. Immigration and Naturalization Service (INS). Each federal agency typically provides half of the inspectors during each shift. Inspectors for both agencies are rotated among primary inspection lanes, vehicle secondary, pedestrian lane, pedestrian secondary, and operations. The 9 hour work shift is divided into 30 minute intervals. Inspectors do not stay in the primary inspection lane for more than two 30 minute periods before they are assigned to another location which is either inside of the office building or out of the lane area. They have to spend at least one hour away from the lanes before starting another assignment in the primary inspection area. Each inspector can spend a maximum time of 3.5 hours in primary inspection lanes per shift. Data was collected to evaluate worker exposures to CO and to assess the performance of the ventilation systems for controlling the CO exposures. Personal air samples for CO exposure were collected in the breathing zone of the workers using ToxiUltra atmospheric monitors (Biosystems, Inc) with CO sensors. PHD Ultra multi-gas monitors (Biosystems, Inc) were used to collect area samples from the roof over the main building. Air sampling was performed for CO and used as a surrogate for the many other air contaminants generated by automobile exhaust such as nitric oxides, hydrocarbons, and particulates. Table 2 lists all CO measurements taken during the two day survey. Personal and area samples were collected. Personal samples on the agents in the primary inspection area were collected with matching samples collected inside of the respective inspection booth. These samples were collected to give an indication of the protective nature of the booth and to provide data for video exposure monitoring. Roof top samples were collected to provide information on the level of CO contamination in the supply air for the inside and outside of the booths. There were three area samples and 4 matched area/personal samples taken on November 15. There were 3 area samples and 3 matched area/personal samples taken on November 16. Roof top CO levels are also included in the table. During the monitoring period, there were three peaks above the NIOSH ceiling of 200 ppm with one peak exceeding the upper limit of the instrument (1000 ppm). Although this concentration was transient, it should not be encountered within the occupational environment. All of these high readings were measured inside the booth at primary inspection lane 8 (see Figure 9). The matched area/personal samples were collected for two primary reasons: 1) to evaluate the protective nature of the booth ventilation and 2) to provide data for video exposure monitoring. The key findings were that the booths seemed to provide good protection when the ventilation systems were operating properly. Figures 14, 15 and 16 show the effectiveness of the booth in controlling CO concentrations in lanes 4 and 1. The average CO concentrations in Lane 4 during the time period from 2:46 p.m.-3:01 p.m. (see Table 2 and Figure 15) was 15 ppm for the personal sample on the agent while the average inside the booth was 1 ppm showing a reduction of 93% over a 15 minute time period. Also the peak exposure was 95 ppm on the agent versus 11 ppm inside the booth resulting in a reduction of greater than 88%. In Figure 14, the peak CO concentration reaches 35 ppm while the corresponding peak in the booth is approximately 3 ppm. These examples indicate the exposure reduction potential of adequate ventilation. Based upon the findings of this study, several recommendations can be made to reduce CO exposures to customs and INS agents at the Calexico, California Port of Entry (POE). Our recommendations are primarily based upon the need to reduce carbon monoxide exposures for officers performing inspections. In that regard, the NIOSH recommendations should be evaluated by experts within the Customs and Immigration departments for their potential impact upon officer safety. They should also be evaluated by each agency for operational and cost feasibility prior to implementation. The recommendations are based on data and observations gathered during the NIOSH visit.