What “HEPA” really means
The term HEPA (High Efficiency Particulate Air) has become common language, but its technical application in archival contexts requires precision. Not all HEPA filters are equal: the European standard EN 1822 distinguishes several subclasses with significantly different performance.
In cultural heritage conservation, this distinction is not academic. A historical archive hosts microorganisms, fungal spores, bacteria and biologically active dust that no lower-class filter can reliably capture. Choosing the correct filter class is an integral part of a professional dust-removal protocol.
Reference standard: EN 1822-1:2019 classifies EPA, HEPA and ULPA filters based on filtration efficiency at the Most Penetrating Particle Size (MPPS) — the hardest particle size to capture, typically 0.1–0.3 μm.
- 99.95% — H13 efficiency (particles ≥ 0.3 μm captured by the HEPA 13 class)
- 99.995% — H14 efficiency (particles ≥ 0.3 μm captured by the HEPA 14 class)
- 0.1–0.3 μm — MPPS, critical range for fungal spores and viral fragments
Technical comparison: H13 versus H14
The table below summarizes the operational differences relevant to dust removal in historical archives, according to the EN 1822 standard and ICROM guidelines (International Centre for the Study of the Preservation and Restoration of Cultural Property).
| Parameter | HEPA H13 | HEPA H14 |
|---|---|---|
| Overall efficiency | ≥ 99.95% | ≥ 99.995% |
| Local efficiency (MPPS) | ≥ 99.75% | ≥ 99.975% |
| Particles ≥ 0.3 μm | Effective | Very effective |
| Aspergillus spores (2–3 μm) | Reliable capture | Total capture |
| Stachybotrys spores (3–5 μm) | Reliable capture | Total capture |
| Bacterial fragments (< 1 μm) | Partially effective | Reliable capture |
| Acidic particles from inks (0.1–0.2 μm) | Reduced efficiency | Partially effective |
| Suitability for ISO 5–6 classified environments | ISO 6 only | ISO 5 and above |
| Differential pressure resistance | High | Very high |
| Relative equipment cost | Base | +25–40% versus H13 |
| Recommended standard for historical archives | Minimum acceptable | Recommended standard |
Porcacchia Egidio uses exclusively vacuum units with certified HEPA H14 filtration for all interventions on historical document collections.
Efficiency by hazardous particle type
Filtration efficiency is not uniform across all particle sizes. Fungal spores, bacteria, binding fragments and dust mites vary greatly in size. Understanding where H13 and H14 really differ helps explain why choosing the correct class is decisive for archives.
| Biological category | Size | H13 | H14 |
|---|---|---|---|
| Fungal spores | 2–5 μm | 99.5% | 99.99% |
| Bacteria | 0.5–2 μm | 97% | 99.9% |
| Acidic particles | 0.05–0.2 μm | 78% | 95% |
| Dust mites | 200–500 μm | ~100% | ~100% |
Critical particle sizes in archives
Not all archival materials deteriorate the same way. Medieval manuscripts on parchment, notarial registers on nineteenth-century machine-made paper, historical photographs on silver bromide gelatin: each type has a specific vulnerability. Understanding which biological contaminant attacks which medium helps in selecting the correct treatment.
| Biological contaminant | Size / Risk | H13 | H14 |
|---|---|---|---|
| Aspergillus niger | Spores: 2.5–3.5 μm | ✓ | ✓✓ |
| Stachybotrys chartarum | Spores: 3–5 μm · High toxicity | ✓ | ✓✓ |
| Bacillus subtilis | Spore-forming bacteria: 0.8–1.2 μm | ~ | ✓ |
| Chitinous mite fragments | Particles: 0.5–1.5 μm · Allergenic | ~ | ✓ |
| Organic VOCs from inks | Particles: 0.05–0.15 μm | ✗ | ~ |
| Inorganic degradation dust | Particles: 1–10 μm | ✓ | ✓✓ |
✓✓ Total capture (>99.99%) · ✓ Effective capture (>99.75%) · ~ Partial effectiveness · ✗ Not significant
When H13 is not enough
The question archive managers ask us most often is: “The previous operator used H13, can we keep doing that?” The answer depends on the type of document collection and its conservation conditions.
There are three scenarios in which H13 is not sufficient and H14 becomes the only technically defensible choice:
01. Archives with confirmed active mold presence
When preliminary mycological analysis detects colonies of Aspergillus, Penicillium or Stachybotrys, airborne spores during dust removal reach concentrations high enough that the extra safety margin offered by H14 becomes essential to protect operators and prevent recontamination of the collection.
02. Photographic collections and film reels
Emulsions on cellulose acetate and nitrate bases are especially sensitive to sub-micron fragments. Gram-negative bacteria release endotoxins in particles often smaller than 1 μm — below the efficiency threshold guaranteed by H13.
03. Destination environments classified ISO 5 or above
If the treated material must be transferred to certified environmentally controlled storage (ISO 5-level facilities for exceptionally valuable collections), dust removal with H14 is a prerequisite for maintaining the destination room’s environmental classification.
Beware of H13 vacuum units with uncertified ULPA filters: some operators claim H14 performance by swapping in an ULPA product not certified to EN 1822. Always verify the presence of CE marking and the individual filter test certificate (not just the type certificate), as required by EN 1822-4.
A HEPA H14 filter captures 10 times more harmful particles than an H13 in the critical 0.1–0.3 μm range. For an archive that has existed for centuries, this margin is not optional.
Porcacchia Egidio technical guidelines, 2024 revision
The Porcacchia operational protocol
Selecting the filter class is only one element of a professional dust-removal protocol. Overall effectiveness depends on the integration of four components:
A. Preliminary mycological and bacteriological analysis
Before any mechanical intervention, environmental and surface sampling identifies the contaminants present, quantifies their biological load, and determines the correct PPE for operators. The results also determine the required filter class.
B. Laminar-flow vacuum units with EN 1822-4 certified H14
Porcacchia’s equipment uses vacuum units with low-vibration brushless motors, antistatic nozzles, and a HEPA H14 filter with an individual test certificate (not just a type certificate). Every filter is replaced according to a documented preventive maintenance plan.
C. Category III PPE and containment zones
Operators work in a delimited negative-pressure zone (differential ≥ 8 Pa), wearing FFP3 masks, Tyvek suits and nitrile gloves. Treated material is immediately sealed in dedicated containers before being repositioned.
D. Technical documentation and intervention report
At the end of every intervention, a report is produced including: regulatory reference, serial number and installation date of the H14 filter, biological concentration measured pre/post intervention, and the signature of the technical lead. The document becomes part of the collection’s conservation file.
Case study 2024 · Viterbo Chapter Archive
Intervention on a medieval parchment collection. The “Instrumenta Capitularia” collection (13th–16th c., approx. 840 parchments) showed a significant Aspergillus glaucus infestation detected during the preliminary site visit. Dust removal with H14, preceded by full classification of the collection, reduced the fungal load by 89% compared to initial levels, with residual concentrations below the ICROM risk threshold. The entire operation took place over three 6-hour sessions without interrupting partial access to the collection.
- 840 parchments treated
- –89% fungal load reduction
- 18h total intervention time
What to ask a dust-removal operator
Before entrusting a historical document collection to an operator, here are the technical requirements that should be documentable:
- EN 1822-4 certificate for the installed HEPA filter (not just the type, but the serial number)
- Installation date and operating hours of the filter (typical service life: 800–1200h)
- Preliminary mycological analysis report signed by a certified biologist
- Containment plan and differential pressure management during the intervention
- Spent filter disposal protocol (special waste, CER code 15 02 02)
- Professional liability insurance specific to cultural heritage activities (category G)
- Intervention report delivered to the client with a timestamp
All the documents listed above are a standard part of the technical documentation that Porcacchia Egidio delivers to every client at the end of every dust-removal intervention.