Special Testing for Possible Carry Over Effects Using the Intoximeters, Inc. Alco-Sensor IV at 10 Degrees Celsius

Conde, Edward · 2002 · ROSA P / United States. National Highway Traffic Safety Administration

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Summary

This study investigates the potential for alcohol carry-over effects in hand-held breath alcohol testers during low-temperature operations. The research was motivated by concerns that moisture and ethanol from a subject’s breath could condense onto the cool internal surfaces of unheated devices, potentially causing residual alcohol to contaminate subsequent tests and produce false-positive results. The study specifically examined the Intoximeters, Inc. Alco-Sensor IV, a widely used device that lacks a built-in heater or flushing pump, to determine if this phenomenon occurs and how it can be mitigated. The experimental design involved laboratory testing conducted in a walk-in environmental chamber maintained at 10°C. Researchers used two versions of the Alco-Sensor IV: a screening version (Version 58.12) and an evidential/screening version (Version 1.10). Simulated breath samples with a concentration of 0.170 grams of ethanol per 210 liters were administered using wet bath simulators. The study compared results under various conditions, including standard screening protocols, the use of the optional Cell Enhancement Module (CEM) heated flushing accessory, and the device’s evidential mode, which requires an air blank check before testing. Results demonstrated that carry-over effects did occur in the unheated screening mode when proper protocols were not followed. After repeated testing with high-concentration samples, residual alcohol condensed in the instrument’s airway. When a breathless sample or an alcohol-free breath was taken immediately after, the device registered false positive readings, such as 0.084 BrAC. However, no carry-over was observed when the device was operated in evidential mode, which automatically checks for residual alcohol, or when the CEM heating accessory was used to flush the airway with warm air. Additionally, allowing sufficient time for evaporation or performing an air blank test prior to the subject’s breath eliminated the carry-over effect. The study concludes that while alcohol carry-over is a valid concern for unheated breath testers in cold environments, it can be effectively prevented through procedural controls or hardware modifications. The authors recommend using air blanks, testing two separate breath samples, or employing warm air flushing to ensure accuracy. The report includes a table assessing various NHTSA-approved breath testers for features like heaters and flushing pumps, noting that NHTSA will consider these findings in future model specifications for both screening and evidential devices.

Key finding

Unheated Alco-Sensor IV screener devices produced false positive results due to alcohol carry-over at 10 degrees Celsius, whereas evidential mode operation and heated flushing accessories prevented contamination.

Methodology

lab_experiment

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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• alcohol detection systems