Which two atmospheres require monitoring before entry?

• A. Normal breathable air and vacuum
• B. Oxygen-deficient and toxic/hazardous atmospheres
• C. High humidity and heat
• D. Cold and dry air

Answer: (B)

The main idea is that entry into a space is only safe if the air inside is not hazardous. You must check for two specific conditions: oxygen-deficient atmospheres and toxic/hazardous atmospheres. If the oxygen level is too low, a person can lose consciousness quickly, which makes entry deadly without proper breathing apparatus or ventilation. If toxic or hazardous gases or vapors are present, they can cause poisoning, irritation, or other serious harm even when oxygen seems adequate. A space may have normal air in terms of oxygen, yet still contain dangerous contaminants, so monitoring for both oxygen levels and toxic/hazardous substances is essential. That’s why these two atmospheres require monitoring before entry. The other options describe environmental conditions like humidity and temperature or non-attainable states like vacuum, which don’t define the immediate atmospheric hazards that mandate entry monitoring.