Final answer:
The first way of informing personnel of a NBC hazard or attack is through the use of alarm systems and sirens.
Step-by-step explanation:
The first way of informing personnel of a NBC (Nuclear, Biological, and Chemical) hazard or attack is through the use of alarm systems and sirens. These warning systems are designed to alert individuals in a specific area of the presence of a hazardous situation.
For example, during the Cold War, air raid sirens were used to alert people of a potential nuclear attack. The sound of the sirens would indicate that individuals needed to seek shelter immediately.
This method of informing personnel is effective because it provides an immediate and noticeable warning that allows individuals to take appropriate action to protect themselves.