Final answer:
A respirator with an independent air supply used by firefighters is known as an SCBA, or Self-Contained Breathing Apparatus, essential for breathing in hazardous environments.
Step-by-step explanation:
A respirator with an independent air supply used by firefighters to enter toxic or otherwise dangerous atmospheres is known as an SCBA, which stands for Self-Contained Breathing Apparatus. This device not only allows firefighters to breathe in smoke-filled or hazardous environments but also protects them from inhaling harmful particulates. Drawing from aerospace technology, which has led to the development of lightweight and durable breathing systems, SCBAs are a critical component of a firefighter's personal protective equipment. These devices ensure a constant supply of clean air, vital when dealing with fires or chemical hazards, similar to the protective suits used in BSL-4 laboratories that come with their own air supply to maintain positive pressure.