What factor has resulted in fewer opportunities for personnel to experience live-fire situations?

The correct answer focuses on the increase of internal hazards in fires involving lightweight and/or synthetic materials. This is crucial as modern construction materials, such as lightweight components and synthetic substances, can burn faster and emit more toxic gases than traditional materials. Consequently, these changes increase the dangers present during live-fire training scenarios. The heightened risk profile associated with these materials necessitates stricter safety protocols and often leads to limited opportunities for personnel to engage in live-fire training. Consequently, training programs may find it necessary to reduce or modify live-fire practices to ensure the safety of trainees.

While the other factors listed may influence training dynamics in some way, they do not directly address the specific hazards created by modern materials used in fire situations. For instance, the decrease in entry-level personnel assignments to EMS duties doesn't inherently relate to live-fire training opportunities but rather to broader staffing and operational procedures. Likewise, while the increase in training hours and the decrease of internal hazards might impact training effectiveness and settings, they do not encapsulate the very immediate risks posed by the evolving nature of fire incidents.