Industrial hygiene – Maximum safe working concentration of carbon dioxide: What is the maximum allowable concentration of CO2 for safe working conditions, expressed in ppm?

Introduction / Context:
Carbon dioxide (CO2) is a normal constituent of air and a marker of ventilation adequacy in occupied spaces. At elevated concentrations it can cause headaches, drowsiness, and impaired cognitive function; very high levels can be dangerous.

Given Data / Assumptions:

• The question asks for a standard, widely taught safe working limit.
• Traditional engineering exams cite 5000 ppm (0.5% by volume) as an 8-hour time-weighted average for occupational exposure.

Concept / Approach:
Different organizations publish guidance, but 5000 ppm is the conventional classroom value for maximum allowable workplace concentration over a full shift. Lower thresholds (e.g., 1000 ppm) are comfort/ventilation targets, not occupational exposure limits.

Step-by-Step Solution:
Eliminate very low values used for indoor air quality comfort (50–1000 ppm).Recognize 5000 ppm as the widely referenced occupational limit.Exclude 10,000 ppm as a short-term/upper bound value not used as the primary safe working limit.

Verification / Alternative check:
Occupational hygiene texts commonly list 0.5% CO2 as the accepted full-shift limit; values beyond that are used for short-duration exposure guidelines only.

Why Other Options Are Wrong:

• 50/1000/2000 ppm: indicate good ventilation benchmarks, not legal exposure maxima.
• 10,000 ppm: too high for an 8-hour general limit.

Common Pitfalls:
Confusing indoor air comfort targets with occupational exposure limits; mixing up ppm and percent units.

Final Answer:
5000 ppm