In the postgraduate fire safety engineering programme, students come from diverse educational backgrounds, leading to varying levels of familiarity with the fundamental principles essential for understanding fire engineering concepts. As a result, a significant amount of new knowledge must be delivered, which often increases the cognitive load on students. To address this, instructional design should focus on minimising unnecessary cognitive load on students' working memory. This paper applies specific methodologies derived from Cognitive Load Theory to reduce cognitive load in an intensive teaching mode implemented across two fire safety engineering courses. To enhance student learning, constructivist principles were also applied by reinforcing student involvement during lectures through active learning strategies. The learning performance of forty students was assessed through pre- and post-lecture tests, including multiple-choice and discussion-type questions, and the results were compared to evaluate their retention of key concepts taught in class. The findings show that nearly all students demonstrated improvement in the post-lecture tests, retaining new knowledge in both their short-term and long-term memory. The performance of different student groups--categorised by enrolment status, work experience, and academic background--was also analysed and compared. The findings indicated that students with professional experience in the fire industry performed slightly better than those without such experience. Student scores increased significantly, with notable improvements in both multiple-choice and discussion-type questions. In interviews, students highlighted that techniques used during lectures, such as interactive breaks and rehearsal sessions after each segment, were instrumental in helping them absorb content and enhance long-term knowledge retention.