Which of the following are two common signs that a lab filter or HEPA system might be underperforming?

• A. Rising background contamination in samples and increased pressure drop or reduced airflow through the filter
• B. Lower room temperature and reduced humidity
• C. Increase in fan noise but stable readings
• D. Decreased filtration efficiency but no change in pressure

Answer: (A)

The question is testing how to recognize when a lab filter or HEPA system is not performing by looking for practical, real‑world symptoms. Two common signs to watch for are rising background contamination in samples and an increased pressure drop or reduced airflow through the filter. When a filter collects particles, its pores get blocked, which raises the resistance to air passing through. That shows up as a higher pressure drop and often less overall airflow. At the same time, a filter that is loading up or has worn seals can become less effective at trapping particles, so more contaminants slip into the room and end up in samples. Together, these two indicators point to a filter that's both choking the airflow and failing to clean the air as well as it should.

The other options don’t align as reliably with filtration performance. Environmental changes like room temperature and humidity don’t directly reveal how well the filter is working. A louder fan with stable readings could mean a mechanical issue elsewhere rather than a filtration problem. And a decrease in filtration efficiency without a change in pressure is less typical, since reduced efficiency usually accompanies some change in airflow resistance or other symptoms that would be detectable in system measurements.