The following is from April 20, 1995 Federal Register that established procedures for using Alcohol Screening Devices.  

 

When the Dept. of Transportation proposed rules for using Alcohol Screening Devices they requested comments regarding extending the time to complete the confirmation test.  The original rule required the confirmation test be conducted 15 – 20 minutes after the screening test.  Various commenters suggested increasing the interval to 30 minutes, to one hour, and to two hours to remove barriers to using Alcohol Screening Devices. 

 

DOT created the following chart to demonstrate the impact of increasing the interval between screening and confirmation tests.  The chart assumes that an individual metabolizes alcohol to lower alcohol concentration by 0.01 to 0.02 an hour. 

 

 

Screening Test Alcohol Concentration

 

	Screening Test Result
	.06	.05	.04	.03
Interval1	Predicted Confirmation Result after Interval
20 minutes	.053 – .056	.043 – .046	.033 – .036	.023 – .026
30 minutes	.050 – .055	.040 – .045	.030 – .035	.020 – .025
40 minutes	.046 – .053	.036 – .043	.026 – .033	<.02 – .023
60 minutes	.040 – .050	.030 – .040	.020 – .030	<.02 –  .020
120 minutes	.020 – .040	<.02 – .030	<.02 – .020	<.02

1. 1.      Interval is the time between screening test and confirmation test

 

 

The chart shows that a low screening test result will not confirm positive after an interval of 40 minutes, and that moderate screening results will not confirm positive with an interval of two hours.  Therefore, in the final rule DOT decided to require confirmation tests be conducted within 30 minutes of the screening test. 

 

If it takes longer than 30 minutes from screening test to confirmation test, the test is still valid, but the rule requires the BAT to document the reason for the delay on the Alcohol Test Form.