The word "fast" is pronounced /fɑːst/ in British English and /fæst/ in American English. The initial sound /f/ is a voiceless labiodental fricative. In British English, the vowel /ɑː/ is a long open back unrounded sound, while in American English, /æ/ is a short near-open front unrounded vowel. The final consonant cluster /st/ consists of a voiceless alveolar fricative /s/ followed by a voiceless alveolar plosive /t/. The pronunciation may vary slightly depending on regional accents, but these are the standard IPA transcriptions for "fast."