Final answer:
When breathalyzer results show 0.00%, a urine drug test is necessary to check for non-alcoholic substances that may cause impairment, as a breathalyzer is designed to measure only ethanol concentration in breath.
Step-by-step explanation:
If breathalyzer results are 0.00%, a urine drug test should be secured to determine the cause of impairment. This is because other substances aside from alcohol can cause impairment, and these substances may not be detected through breathalyzer tests designed specifically to measure blood alcohol content (BAC). Since the breathalyzer would only measure the ethanol concentration in a person's breath, it would not detect the presence of other drugs or controlled substances which could also impair an individual's ability to operate a vehicle safely. While breathalyzer tests are commonly used to detect alcohol impairment, if the results are 0.00%, it suggests that there may be another cause for the impairment, such as drugs or other medical conditions.