A 30-year-old man with known asthma presents to the Emergency Department with acute shortness of breath, wheeze, and difficulty speaking in full sentences. His peak expiratory flow rate (PEFR) is 45% of his predicted best. Oxygen saturation is 93% on air. Respiratory rate is 28/min, heart rate is 115/min. What feature classifies this asthma attack as severe according to BTS/SIGN guidelines?