Opinion by Judge POLITZ; Partial Concurrence and Partial Dissent by Judge FISHER.

Lashawn Lowell Banks appeals his guilty plea conviction for possession of a controlled substance with intent to distribute, and for being a drug user in possession of a firearm. His plea followed the district court’s denial of his motion to suppress certain evidence. Banks reserved his right to appeal. A close review of the record, counsel’s arguments, and guiding principles, persuades us that a reversal and remand is in order.

BACKGROUND

The present action concerns the execution of a search warrant on Banks’ apartment by North Las Vegas Police Department officers and FBI agents. The officers positioned themselves at the front and rear of the apartment and followed the statutory “knock and announce” procedure by knocking loudly on the apartment door and announcing “police search warrant.” See 18 U.S.C. § 3109 . After fifteen to twenty seconds without a response, armed SWAT officers made a forced entry into Banks’ apartment.

Once inside, the officers found Banks in the hallway outside his bathroom. Banks, who obviously had just emerged from his shower, was forced to the floor and handcuffed. He then was seated at his kitchen table for questioning and shortly thereafter was provided underwear with which to cover himself. Two agents questioned Banks while other officers searched his apartment. Banks maintains that he was under the influence of drugs and alcohol during the interrogation. Both agents, however, testified that they perceived no indications that Banks was under the influence. Banks also asserts that he was nervous and intimidated by a “good-cop versus bad-cop” routine utilized by the interrogating agents and the hooded SWAT officers searching the apartment. The interrogating agents maintain that Banks appeared calm and was able to reason throughout the interview.

The agents questioned Banks for approximately forty-five minutes, and about midway thereof asked Banks to reveal his suppliers. Banks stated that he would not reveal his suppliers before talking to an attorney. The agents continued the questioning.

*703 Prior to trial Banks moved to suppress the statements he made during the interrogation. He contends that the statements should have been suppressed on the grounds that they were obtained: (a) in violation of 18 U.S.C. § 3109 because the officers failed to wait a reasonable period of time before forcefully entering his residence when executing the search warrant; (b) in violation of the fifth amendment because he did not make a knowing and voluntary waiver of his rights during the interrogation; and (c) in violation of the fifth amendment because the interrogation continued after he made an unequivocal request for an attorney. The district court denied the suppression motion. Following this denial, Banks pled guilty to possession of a controlled substance with intent to distribute and to being a drug user in possession of a firearm.

Banks expressly reserved his right to appeal the court’s denial of his Motion to Suppress. This appeal followed.

ANALYSIS

I. 18 U.S.C. § 3109

We review a trial court’s legal conclusions de novo, reviewing findings of fact underlying those conclusions for clear error. 1

Title 18 U.S.C. § 3109 , commonly referred to as the “knock and announce” statute, establishes guidelines for federal law enforcement officers when executing a search warrant. The statute directs that:

18 U.S.C. § 3109 .

Under the facts at bar this statute raises two critical issues: (a) whether the officers provided notice of their authority and purpose; and (b) whether they were refused admittance. There is no dispute that proper notice of authority and purpose was given herein. Before us is the second issue, refusal of admittance.

Banks contends that the officers executing the search war rant entered his apartment illegally because they failed to wait a reasonable time, after receiving no response, before forcefully entering his quarters. Banks further contends that because the entry was in violation of his fourth amendment rights and 18 U.S.C. § 3109 , all evidence, including his statements, constitute fruits of an illegal search and should be suppressed. We find this contention persuasive.

A literal application of the statute would allow entry only after both announcement and specific denial of admittance. Our precedents, however, dictate that an affirmative refusal of entry is not required by the statute, and that refusal may be implied in some instances. See, e.g., United States v. Allende, 486 F.2d 1351, 1353 (9th Cir.1973). “A failure to answer a knock and announcement has long been equated with a refusal to admit the search party and a justification for forcible entry.” United States v. Ramos, 923 F.2d 1346, 1356 (9th Cir.1991) overruled on other grounds by United States v. Ruiz, 257 F.3d 1030 (9th Cir.2001) (citations omitted). Furthermore, “[t]here are no set rules as to the time an officer must wait before using force to enter a house; *704 the answer will depend on the circumstances of each case.” 2

Section 3109 serves the following interests: (a) reducing the risk of harm to both the officer and the occupants of the house to be entered; (b) helping to prevent the unnecessary destruction of private property; and (c) symbolizing respect for individual privacy summarized in the adage that “a man’s house is his castle.” United States v. Bustamante-Gamez, 488 F.2d 4, 9 (9th Cir.1973) (quoting Miller v. United States, 357 U.S. 301, 307 , 78 S.Ct. 1190 , 2 L.Ed.2d 1332 (1958)).

Entries may be classified into four basic categories, consistent with the interests served by 18 U.S.C. § 3109 :(1) entries in which exigent circumstances exist and non-forcible entry is possible, permitting entry to be made simultaneously with or shortly after announcement; (2) entries in which exigent circumstances exist and forced entry by destruction of property is required, necessitating more specific inferences of exigency; (3) entries in which no exigent circumstances exist and non-forcible entry is possible, requiring an explicit refusal of admittance or a lapse of a significant amount of time; and (4) entries in which no exigent circumstances exist and forced entry by destruction of property is required, mandating an explicit refusal of admittance or a lapse of an even more substantial amount of time. Id. at 12 . The action at bar falls into the final category because no exigent circumstances existed 3 and the entry required destruction of property — i.e., the door to Banks’ apartment.

Consideration of the foregoing categories aids in the resolution of the essential question whether the entry made herein was reasonable under the circumstances. In addressing that inquiry, we categorize entries as either forced or non-forced. The reasonableness must then be determined in light of the totality of the circumstances surrounding the execution of the warrant, particularly considering the duration of the officers’ pause before making a forced entry after the required knock and announcement.

Our task is to determine what constitutes a reasonable waiting period before officers may infer that they have been denied admittance. In assessing the reasonableness of the duration of the officers’ wait, we review all factors that an officer reasonably should consider in making the decision to enter without an affirmative denial. Those factors include, but are not limited to: (a) size of the residence; (b) location of the residence; (c) location of the officers in relation to the main living or sleeping areas of the residence; (d) time of day; (e) nature of the suspected offense; (f) evidence demonstrating the suspect’s guilt; (g) suspect’s prior convictions and, if any, the type of offense for which he was convicted; and (h) any other observations triggering the senses of the officers that reasonably would lead one to believe that immediate entry was necessary.

In the case before us, the officers knocked once and announced their purpose. The officers heard no sound coming from the small apartment that suggested *705 that an occupant was moving away from the door, or doing anything else that would suggest a refusal of admittance. We know from the record that sounds were transmitted relatively easily, for Officer Tomas-so, waiting outside at the rear of the apartment, heard Officer Crespo’s knock at the front door. Yet none of the officers testified that they heard any sound coming from within the apartment. There was nothing else that triggered the officers’ senses, and there were no exigent circumstances warranting a waiver of the reasonable delay. The officers had no specific knowledge of any facts or reasonable expectations from which they could reasonably have believed that entry into Banks’ residence would pose any risk greater than the ordinary danger of executing a search warrant on a private residence.

Because the officers were not affirmatively granted or denied permission, they were required to delay acting for a sufficient period of time before they could reasonably conclude that they impliedly had been denied admittance. After pausing a maximum of fifteen to twenty seconds, the officers forced entry. Banks came out of his shower upon hearing the sound of his door being forced open, and stumbled into the hallway concerned that his apartment was being invaded. Upon entering, the officers found Banks naked, wet, and soapy from his shower. Under these circumstances, we are not prepared to conclude that the delay of fifteen to twenty seconds after a single knock and announcement before forced entry was, without an affirmative denial of admission or other exigent circumstances, sufficient in duration to satisfy the constitutional safeguards.

II. Banks’ Fifth and Sixth Amendment Claims

As noted above, we review a trial court’s legal conclusions de novo, and our review of findings of fact underlying those conclusions is for clear error. However, “[w]e review the district court’s determination that the defendant knowingly and voluntarily waived his Miranda rights under the clearly erroneous standard.” United States v. Fouche, 833 F.2d 1284, 1286 (9th Cir.1987).

1. The Voluntariness of Banks’ Statements

The fifth amendment states that no person “shall be compelled in any criminal case to be a witness against himself.” 4 Under the teachings of Miranda v. Arizona, 5 to assure the meaningful protection of this fifth amendment right, a defendant subject to custodial interrogation must be advised of his “right to remain silent, that any statement he does make may be used ... against him, and that he has a right to the presence of an attorney, either retained or appointed.” Id. at 444, 86 S.Ct. 1602 . A knowing and voluntary waiver of these rights is permissible. Such a waiver, however, must be established by a preponderance of the evidence. Colorado v. Connelly, 479 U.S. 157, 168-69 , 107 S.Ct. 515 , 93 L.Ed.2d 473 (1986).

Banks contends that his statements were obtained involuntarily and through coercion in violation of his fifth amendment rights. He complains that because he was under the influence of alcohol and narcotics at the time of the interrogation, he was unable to make a knowing and voluntary waiver of his rights. He further asserts that his statements were coerced because he was terrorized by the entry of the *706 police into his home, intimidated by officers employing the “good-cop versus bad-cop” routine, and in fear of being paraded naked around the neighborhood. Our review of the record, however, persuades us that the district court did not err in its determination that he made a knowing and voluntary waiver of these rights.

A confession made in a drug or alcohol induced state, or one that is the product of physical or psychological pressure, may be deemed voluntary if it remains “the product of a rational intellect and a free will.... ” Medeiros v. Shimoda, 889 F.2d 819, 823 (9th Cir.1989) (citations omitted). The interrogating agents testified about Banks’ demeanor during the interrogation. Neither detected any indication that Banks was under the claimed adverse influence, and both described him as calm and able to reason. Similarly, the record demonstrates that Banks was able to understand the circumstances, follow instructions, and answer questions. From the record, Banks does not appear to have been “incapacitated” by his use of drugs and alcohol. During the interrogation, he answered some of the agent’s questions while refusing to answer those regarding his suppliers and was able to provide officers with the combination to his safe. Pri- or to being taken to the police station, he requested that his girlfriend be contacted so she could secure his apartment. Because the evidence supports the district court’s conclusion that Banks’ statements were the product of rational intellect and a free will, we hold that the district court did not err in finding a knowing and voluntary waiver.

2. Banks’ Right to Counsel Under Miranda

Banks also contends that his statements were obtained in violation of his right to counsel under Miranda. No further questioning of a suspect may occur after he expresses the desire to consult with counsel, and police must clarify an ambiguous or equivocal request for an attorney. Miranda, 384 U.S. at 474 , 86 S.Ct. 1602 ; see also United States v. Fouche, 833 F.2d 1284, 1287 (9th Cir.1985), cert. denied, 486 U.S. 1017 , 108 S.Ct. 1756 , 100 L.Ed.2d 218 (1988). Notwithstanding, “a defendant may selectively waive his Miranda rights, deciding to respond to some questions but not others.” Bruni v. Lewis, 847 F.2d 561, 563 (9th Cir.1988) (citations omitted).

In support of his claim that his right to counsel under Miranda was violated, Banks asserts that during the latter part of his questioning he told the agents that he wanted to consult with a lawyer about the possibility of making a “deal” in exchange for divulging information about his suppliers. The record reflects that when the agents asked Banks a question regarding his suppliers, he responded that he wanted to speak to an attorney before revealing his suppliers to see if he could secure some consideration, what one might deem a quid pro quo, for his cooperation with the officers. The agents reasonably understood Banks’ statement to mean he was willing to answer some questions but not others. That conclusion is fully supported by the record. 6

The judgment is AFFIRMED in part, REVERSED in part and the matter is REMANDED for further proceedings consistent herewith.

. United States v. Granville, 222 F.3d 1214, 1217 (9th Cir.2000) (noting that legal conclusion that “knock and announce” statute was violated is reviewed de novo, while findings regarding facts underlying the conclusion are reviewed for clear error).

. McClure v. United States, 332 F.2d 19, 22 (9th Cir.1964), cert. denied, 380 U.S. 945 , 85 S.Ct. 1027 , 13 L.Ed.2d 963 (1965).

. This court reviews the mixed question of law and fact as to whether exigent circumstances exist de novo. United States v. McConney, 728 F.2d 1195, 1204-05 (9th Cir.1984) (on banc). Exigent circumstances exist when "there [is] a likelihood that the occupants [will] attempt to escape, resist, destroy evidence, or harm someone within....” Id. at 1205. No such evidence was presented in this case.

. U.S. Const., amend. V.

. 384 U.S. 436 , 86 S.Ct. 1602 , 16 L.Ed.2d 694 (1966).

. Fouche, 833 F.2d at 1287 ("[I]f [a suspect] is indecisive in his request for counsel, there may be some question on whether he did or did not waive counsel ... Situations of this kind must necessarily be left to the judgment of the interviewing Agent.”) (quoting Miranda, 384 U.S. at 436 , 86 S.Ct. 1602 ).