HEPA/ULPA Validation and Replacement Procedures: When to Replace?

A HEPA H14 or ULPA U17 on a cleanroom ceiling costs from several million to several tens of millions of VND. In a plant with thousands of FFUs, scheduling validation and replacement at the right time saves billions while keeping the cleanroom in compliance. This article rounds up the validation procedure, the signs of replacement, and how to swap HEPA/ULPA safely.

1. Why is periodic validation necessary?

HEPAs and ULPAs are the final filter between the outside environment and the product/cleanroom. If there is:

• A pinhole in the media — contaminated air slips through unfiltered.
• A gasket leak — air bypasses around the frame.
• Efficiency decay over time — the media ages.

…the entire cleanroom drops out of class. A GMP-WHO/EU audit will catch it immediately and demand remediation.

Periodic validation:

• Detects leaks early before product contamination.
• Demonstrates compliance in internal and external audits.
• Enables accurate budgeting for filter replacement.

2. Common tests

a. DOP Test (Dioctyl Phthalate)

• Traditional test using DOP aerosol at 100 µg/L.
• Detects leaks and measures overall efficiency.
• Now rarely used because DOP is a suspected carcinogen — classified by the US EPA.

b. PAO Test (Poly Alpha Olefin)

• The most common test today — replacing DOP.
• PAO aerosol (a non-toxic synthetic oil) generated by a cold generator.
• Applied from HEPA H13 upwards.

c. PSL Test (Polystyrene Latex Sphere)

• Uses calibrated PSL particles at 0.1, 0.3, and 0.5 µm.
• Applied to ULPA U15 and above — for greater precision.

d. Particle Count Test

• Counts particles by size in the cleanroom using a particle counter.
• Measured at rest and in operation per ISO 14644-1.

3. On-site PAO test procedure for HEPA

Step 1: Preparation

• Shut down the cleanroom (or one zone) for safe access.
• Install the PAO generator in the supply duct upstream of the HEPA.
• Set up the sampling probe connected to an aerosol photometer (Tsi, Topas, Air Techniques, etc.).
• Measure the upstream aerosol concentration (before the HEPA) — typically 20-80 µg/L.

Step 2: Scan the HEPA surface

• Pass the probe over the downstream HEPA surface at 5 cm/sec.
• Cover the entire area + gasket region + frame clamping zone.
• Probe 2-3 cm above the surface.

Step 3: Analyse results

• Leaking areas: photometer shows aerosol > 0.01% of upstream concentration for HEPA H14, or 0.005% for ULPA U15.
• Mark leak points with a marker.

Step 4: Remediate

• Small gasket leak: adjust the gasket, re-tighten the frame.
• Media leak: patch with specialised silicone (HEPA only, not ULPA).
• Large or multiple leaks: replace the HEPA.

Step 5: Re-test after remediation

• Repeat the scan to confirm the fix.
• Issue a test report with photos and the technician's signature.

4. Recommended validation frequency

By cleanroom class

Cleanroom class	HEPA/ULPA scan-test frequency
GMP A (LAF, vaccine filling)	Every 3-6 months
GMP B	Every 6 months
GMP C	Every 6-12 months
GMP D	Every 12 months
Semiconductor fab Class 1-10	Every 6 months (ULPA U17)
Electronics cleanroom Class 1,000-10,000	Every 12 months
Ultra-clean OR	Every 6 months
Negative-pressure isolation room	Every 6 months (critical)

By event

• After installing a new HEPA: 100% scan test.
• After AHU/HVAC repairs: scan the affected HEPAs.
• After incidents (water leak, impact): scan the affected zone.

5. Signs a HEPA/ULPA needs replacement

Four main indicators:

a. ΔP across the HEPA exceeds 2× initial

• New HEPA H14: initial ΔP ~200-250 Pa.
• Replace once ΔP > 500 Pa.

b. Scan test detects unrepairable leaks

• Large holes or multiple holes — cannot be fully patched.

c. Particle count exceeds the limit

• Measured in the cleanroom per ISO 14644-1.
• Grade C room reading > Class 10,000 → HEPA issue.

d. Past design life

• Typical HEPA H13/H14: 3-5 years.
• ULPA U15-U17: 5-10 years (used in already-clean environments).
• HEPA for negative-pressure isolation rooms: 1-2 years (high microbial load).

6. Safe HEPA replacement procedure

Standard HEPA replacement (terminal box)

1. Shut down the relevant FFU/fan.
2. Open the terminal-box cover.
3. Wearing nitrile gloves, remove the old HEPA and seal it in a PE bag.
4. Clean the frame and gasket.
5. Install the new HEPA, tighten the bolts evenly (opposite pairs first).
6. Restart the FFU, measure ΔP to verify it matches the rated value.
7. Scan-test to confirm no leaks.
8. Record the replacement.

Replacing HEPA in a negative-pressure isolation room — Bag-in/Bag-out

The HEPA in an isolation room contains dangerous pathogens (TB, viruses, bacteria). You must never remove it directly:

1. Bag-in/Bag-out housings have an integrated PE bag wrapping the filter.
2. The technician puts their arms into the outer PE bag and removes the old HEPA into the bag.
3. Knot the PE bag and cut off the sealed section.
4. Install the new HEPA through a second pre-loaded PE bag.
5. Dispose of the bagged old HEPA as hazardous waste (incineration at 1,000°C+).

ULPA replacement at a semiconductor fab

• Same as standard HEPA, but stricter:
• Wear a dry bunny suit, double gloves, safety goggles.
• The new ULPA must come with a scan-test certificate.
• After install: measure particle count in the room to confirm class before resuming production.

7. Cost and budget management

Indicative HEPA/ULPA cost

• HEPA H13 575×1175: 2-4 million VND.
• HEPA H14 575×1175: 3-6 million VND.
• ULPA U15 575×1175: 6-10 million VND.
• ULPA U17 575×1175: 12-20 million VND.

Scan-test cost

• 1-3 million VND per HEPA (depending on quantity and access difficulty).
• Often bundled: 10 HEPAs = 15-25 million VND.

Budget management

• Keep a HEPA register by batch with install dates.
• Plan replacement in batches (pool HEPAs of the same zone and grade) to cut logistics cost.
• Budget 3-8% of initial capex per year for filter replacement.

8. Choosing a new HEPA/ULPA supplier

• Full certificates: EN 1822-1:2009 + PAO/PSL scan test on each unit.
• Correct dimensions: re-measure the terminal-box frame before ordering — a few mm off and it will not fit.
• Frame material: aluminium, powder-coated steel, or stainless depending on environment.
• Gasket: PU (standard environments) or neoprene/chloroprene (chemical decontamination).
• Specialised packaging: shock-protected, do not flip.
• Warranty 12-24 months.

9. Management software and tools

Large plants should invest in:

• CMMS (Computerized Maintenance Management System) — track schedules, tests, and records.
• Integrated BMS — read ΔP from every FFU/AHU sensor with threshold alerts.
• Online particle counting — integrated with BMS, alerts on class drift.

Conclusion

HEPA/ULPA validation and replacement are the highest-economic-value maintenance activities in cleanroom operations — ensuring product quality while avoiding wasteful early replacements. Running a periodic PAO test programme, monitoring ΔP via BMS, and having a bag-in/bag-out procedure for high-risk rooms are the foundation for every GMP plant, hospital, and electronics fab.

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About Green Filter

Green Filter supplies HEPA H13/H14 and ULPA U15/U16/U17 with full PAO/PSL scan testing, specialised packaging, and long-term warranty. We also provide on-site scan-testing services with professional photometers and trained technicians.

📞 Contact Green Filter for HEPA/ULPA replacement and scan testing: [insert hotline / email / website]

See also: What is a HEPA Filter? · ULPA Filters U15/U16/U17 · Operating rooms and negative-pressure isolation rooms.