Under which condition can a person be exposed to an atmosphere containing a concentration of Carbon Dioxide not more than 30,000 ppm?

• A. A continual personal monitoring method is used to calculate the time-weighted average (Gas detector); The TWA is not more than 12,500 ppm for not more than 8 hour day or 40 hour week; or The TWA is not more than the adjusted value having regard to a recognised standard for adjusting exposure limits for extended working hours.
• B. The TWA must be 30,000 ppm with no monitoring.
• C. Only in emergencies with PPE.
• D. Never allowed.

Answer: (A)

The key idea is that exposure limits are defined as a time-weighted average (TWA) and must be controlled through ongoing monitoring. To allow exposure to an atmosphere up to 30,000 ppm of CO2, you need continual personal monitoring to calculate the TWA over the work period. The TWA must not exceed 12,500 ppm for a standard 8-hour day or 40-hour week, or it must not exceed the adjusted value allowed by a recognized standard for extended working hours. This framework lets higher short-term concentrations occur only if the overall average remains within the permitted limit, which is why continual monitoring and the appropriate TWA adjustments are the correct condition.

The other options are not appropriate because they either remove the essential monitoring requirement, rely on PPE for general conditions, or state an absolute prohibition.