Final answer:
In an IDLH environment, a Self-Contained Breathing Apparatus (SCBA) must be used to provide clean air and protect from harmful substances.
Step-by-step explanation:
When an atmosphere contains flammable or toxic gases or has an imbalance in oxygen levels creating an IDLH (immediately dangerous to life and health) condition, the necessary protective equipment to use is a Self-Contained Breathing Apparatus (SCBA). This apparatus provides clean air to the wearer and ensures they can breathe safely in hazardous environments.
SCBAs are commonly used by firefighters and in industrial settings where there's a risk of air contamination. They include a mask that covers the nose and mouth, a tank of compressed air, and a regulator. Proper use of SCBAs is critical to prevent inhalation of harmful substances and to provide emergency respiratory protection in life-threatening situations.