To determine whether an HEPA filter needs to be replaced, it’s quite simple. I’ll present you with a straightforward method that can be applied directly on-site without the need for complex instruments. Line workers will understand it easily.
1. The most intuitive and quickest method (without instruments)
– The wind speed has significantly decreased
– Turn on the fan and place your hand at the outlet. You’ll feel very weak and soft wind
– Before it was strong, but now it’s noticeably weaker → It’s likely clogged
– The dust in the operation area has increased
– More dust is falling on the tabletop and samples
– The colony count and contamination rate have risen → First suspect that the HEPA filter has failed
– The usage time has exceeded the limit
– In a regular laboratory: ≥ 2 years
– In a workshop with excessive dust and poor environmental conditions: ≥ 1 year requires a focused check
– The primary filter is already very clean, but the wind speed is still low
– The primary filter has been washed or replaced, but the wind speed still cannot increase
→ The blockage is in the HEPA filter, not the primary filter
2. Precise determination using instruments (the most standard)
1. Wind speed detection (most commonly used)
– Normal outlet wind speed for horizontal laminar flow cleanroom:
0.3 – 0.6 m/s
Judgment:
Continuous multiple readings < 0.25 m/s → Must replace the HEPA filter
2. PAO/DOP leak detection (most authoritative)
Leakage on the filter surface / frame
Filter efficiency is lower than 99.97% @ 0.3 μm
→ Replace immediately
3. Check for the following situations, replace immediately without hesitation
– The HEPA filter is deformed, damp, moldy, or damaged
– The filter paper is cracked, de-laminated, or leaking air
The cleanliness test has been continuously unqualified
– After replacing the primary filter and cleaning the duct， the wind speed still does not meet the standard
– The usage time exceeds 3 years and has never been replaced