36 CFR § 3.11 - When is testing for alcohol or drugs required?
(a) At the request or direction of an authorized person who has probable cause to believe that an operator of a vessel has violated provisions of § 3.10, the operator must submit to one or more testing procedures of the blood, breath, saliva or urine for the purpose of determining blood alcohol and/or drug content.
(1) Refusal by an operator to submit to a test is prohibited and proof of refusal may be admissible in any related judicial proceeding.
(2) Any test or tests for the presence of alcohol and drugs must be determined by and administered at the direction of an authorized person.
(3) Any test must be conducted by using accepted scientific methods and equipment of proven accuracy and reliability operated by personnel certified in its use.
(b) The results of chemical or other quantitative tests are intended to supplement the elements of probable cause used as the basis for the arrest of an operator charged with a violation of § 3.10. If the alcohol concentration in the operator's blood or breath at the time of testing is less than alcohol concentrations specified in § 3.10(a)(2), this fact does not give rise to any presumption that the operator is or is not under the influence of alcohol.
(c) The provisions of paragraph (b) of this section are not intended to limit the introduction of any other competent evidence bearing upon the question of whether the operator, at the time of the alleged violation, was under the influence of alcohol, or a drug, or drugs, or any combination thereof.