At what frequency must the air flow rate in the return airway of a main upcast fan be measured and recorded?

• A. Weekly
• B. At least once each month
• C. Daily
• D. On shift

Answer: (B)

The main idea is to regularly verify that the return path of the upcast fan is delivering the intended airflow and to keep a documented record for trend analysis and compliance. The return airway can be affected by fan performance, ducting changes, or blockages, and if you don’t monitor it regularly you might miss a drift in airflow that could impact gas dilution in occupied areas. Measuring and recording at least once each month provides a practical cadence: it’s frequent enough to catch gradual declines or shifts, yet not so burdensome that it disrupts operations. Daily or per-shift checks would create excessive workload and might reflect short-term fluctuations rather than meaningful, trackable trends, while weekly checks could miss slower changes. Monthly recording gives ongoing visibility into ventilation performance and supports safe, compliant operation.