When particles aren't the problem, microbes are
VHP Pass Box
Ask anyone who runs a sterile suite what really worries them about a transfer hatch. It is rarely the dust. It is what is alive on the surface of the material going in. Sweeping particles off a surface does not kill anything. Killing takes a chemical cycle, not just clean air.
- vH₂O₂ cycle
- ISO Class 5 chamber
- HEPA H13 / H14
- EU-GMP Annex 1
- IQ/OQ/PQ
FIG. 01One VHP cycle: the vapour concentration rises, holds, then is purged back below the safe residual limit before the inner door will release.
What a VHP pass box is
A VHP pass box is a dynamic transfer chamber with a vaporized hydrogen-peroxide (VHP) decontamination cycle added to it. The box removes the airborne particles and the micro-organisms (bioburden) sitting on the material's surface, before that material enters an aseptic or sterile area.
That is the job this box does. It holds the material, floods it with hydrogen-peroxide vapour, then clears the vapour away before the inner door will open. Fabtech has built more than 2,000 controlled environments across every industry that needs controlled air since 2004. We make our VHP pass boxes in-house. So the box and the aseptic room it serves are sized and validated by one accountable team, not bought off a shelf.
A dynamic box blows clean air across the material and carries the particles away. A VHP box goes a step further. It bio-decontaminates the surface chemically, to a validated sporicidal kill. This is the box you reach for when the material has to enter the cleanest environments there are, a sterile suite or an isolator. A low particle count on its own is simply not enough there.
How a VHP pass box works (the cycle)
The box will not let anything through until it has finished a full decontamination cycle. Six steps, in a fixed order. The inner door stays locked for all of them.
| Step | What happens inside the chamber |
|---|---|
| 1. Load and close | Material goes in. The outer door closes and the electromagnetic interlock locks the inner door. |
| 2. Conditioning | The chamber is prepared, typically dehumidified and brought to temperature. Relative humidity and temperature govern how the peroxide distributes across surfaces, and that is what drives the kill. |
| 3. Gassing / injection | Vapourised hydrogen peroxide is introduced until the chamber reaches the target concentration. Fabtech's box is built to dock to an external / room VHP unit, so the generator serving the suite supplies the vapour rather than a generator built into the hatch. |
| 4. Dwell / exposure | The H₂O₂ vapour is held for a validated time, so it contacts every surface and achieves the required microbial kill. |
| 5. Aeration | The chamber is purged with HEPA-filtered air. The peroxide is catalytically broken down to water vapour and oxygen, until residual peroxide sits below the safe limit. |
| 6. Release | Only when aeration is complete does the interlock release the inner door, so the material can be taken into the aseptic area. |
FIG. 02The six steps in their fixed order. The interlock holds the inner door through all of them.
The cycle as it actually runs
A list of steps hides the thing that decides everything else: time. Drawn as a curve, the cycle shows why the humidity has to fall before the vapour can rise, where the minutes actually go, and why the inner door will not release until the concentration has come back down.
FIG. 03One bio-decontamination cycle against elapsed time. The concentration axis carries no scale on purpose: the residual limit at release is validated per installation and confirmed on request. The time axis carries the two figures that matter: a typical total cycle of 30 to 55 minutes, with 15 to 30 minutes of it spent in aeration.
Aeration, not the kill, sets the throughput.
Here is the part most specifications get wrong. The dwell achieves the kill fairly quickly. Purging the peroxide back down to a safe residual is the slow, rate-limiting step.
In practice a typical total cycle runs about 30 to 55 minutes. Aeration alone accounts for 15 to 30 minutes of that. So aeration time, more than the kill, is what decides how many transfers an hour this box can really do.
- 30 to 55min
- Typical total cycle
- 15 to 30min
- Of that is aeration alone
The proof that separates a VHP box from a dynamic one
A dynamic box can show you it cleared the particles. A VHP box has to prove something harder. It has to prove it killed what was on the surface. And that proof is a measured number, not a claim.
- 01
A sporicidal log reduction
The kill is commonly specified as a 6-log reduction of resistant bacterial spores. That is a million-fold reduction. Fabtech confirms the validated log-reduction target for your cycle on request.
- 02
Biological indicators
That kill is proven with biological indicators carrying resistant spores, typically Geobacillus stearothermophilus. They are placed at the chamber's hardest-to-reach points, then incubated after the cycle.
That biological evidence is the line between a VHP box and a box that merely blows clean air. It is why a VHP box gets specified for transfers where sterility, and not just a low particle count, is the requirement.
FIG. 04A 6-log reduction, six steps of ten: from a million resistant spores down to one. Commonly specified for VHP cycles and proven with biological indicators at the chamber's hardest-to-reach points.
VHP, dynamic or static: the short answer
All three share interlocked doors. A static box only isolates one room from the other. A dynamic box adds HEPA airflow and removes particles. A VHP box adds a hydrogen-peroxide cycle and removes micro-organisms as well. You step up from static to dynamic to VHP as the cleanliness rises, and as the consequence of getting it wrong rises with it. The full side-by-side detail sits in the static vs dynamic vs VHP comparison .
Where VHP pass boxes are used
A VHP box belongs wherever surface bioburden, and not just particles, has to be eliminated before a transfer.
The isolator question
Isolators and RABS
This is where the "what is VHP in an isolator?" question lands. VHP is the standard way to bio-decontaminate the inside of an isolator. A VHP pass box applies the same chemistry to the material being transferred into it, so the transfer does not break the isolator's sterility.
Sterile & aseptic pharmaceutical manufacturing
Components and tools are transferred into Grade A/B filling areas.
Cell & gene therapy and biologics
Contamination risk is high here and aseptic assurance is critical.
Containment and potent-compound handling
A validated surface kill is required before the material moves.
What you can't put through a VHP cycle
Hydrogen-peroxide vapour is a strong oxidiser. Over repeated cycles it degrades some materials. So a VHP box is not a universal steriliser, and that is worth knowing early rather than late.
| Material or load | What repeated VHP cycles do to it |
|---|---|
| Certain elastomers | Absorb peroxide, then discolour or weaken |
| Nylon | Same pattern: absorbs peroxide, can discolour or weaken |
| Uncoated paper / cellulose | Absorbs peroxide readily |
| Packaging that traps vapour | Lengthens aeration, so it slows the whole cycle |
FIG. 05Absorption is the common failure mode. Trapped vapour is what lengthens the cycle.
Fabtech provides the validation protocols for the unit, covering IQ/OQ/PQ. Sensitive items still need cycle-specific material-compatibility testing, so the user confirms each material against repeated cycles before routine use. Load patterns are validated with the cycle rather than assumed.
It is a real constraint, and one worth designing around early. It is also one more reason this box gets specified with the process, rather than bought to fit a process that already exists.
Standards and validation
Of the three pass-box types, the VHP box is the one that gets validated most heavily. It is not enough that it works. You have to be able to show, on paper, that it works every time.
Two rulebooks set the bar. EU-GMP Annex 1 governs the aseptic transfer the box enables, at Grade A/B, and VHP transfer is a recognised way to bring material into a Grade A environment. ISO 14644-1 still applies to the chamber's own clean zone, which is verified by particle count on top of the bio-decontamination. India's Schedule M and WHO-GMP put the same expectations on Indian sterile manufacture.
Design
Design qualification
The unit, its cycle scope and the destination grade agreed on paper before anything is built.
Installation
Installation qualification
The installed box verified as built: chamber, HEPA filters, interlock and the docking to the suite's VHP unit.
Operation
Operational qualification
The cycle proven to run as specified: interlock logic, gassing, dwell and aeration all exercised.
Performance
Performance qualification
Performance proven in use, with biological indicators across the chamber's hardest-to-reach points.
FIG. 06Qualification runs in order, and each stage is signed off before the next begins.
Cleanroom validation and qualification
| What gets qualified or tested | What that involves |
|---|---|
| The unit itself | DQ/IQ/OQ/PQ |
| Chamber cleanliness | Particle count to ISO Class 5, matched to the destination grade |
| Filter integrity | HEPA integrity testing (PAO/DOP) |
| The VHP cycle | A validated VHP cycle, proven with biological indicators across the chamber's hardest-to-reach points |
| Residual peroxide | Confirmation that aeration brings residual H₂O₂ below the safe limit before the door releases |
FIG. 07The qualification file for a VHP pass box, stage by stage.
Equipment validation and AMC are available for the unit. One point often confuses people. A pass box is a transfer hatch inside a classified room, and it discharges nothing to atmosphere. So fume-hood exhaust rules and CPCB rules do not apply to it.
How Fabtech approaches sterile transfer
Fabtech Cleanrooms is a cleanroom equipment manufacturer. It designs, builds and validates controlled environments across India, including the sterile and containment suites a VHP transfer point serves.
VHP pass boxes are manufactured in-house. They are supplied as standalone products and integrated into turnkey aseptic projects, and they are built to dock to the suite's external / room VHP unit. The cycle, the aeration and the interlock logic are set to match the Grade A/B environment and the isolators the box feeds.
Proof of capability
Fabtech has delivered HEPA-filtered, classified and containment cleanrooms for pharma and research clients across India. That is the aseptic and bio-containment engineering a VHP transfer point sits within.
Turnkey cleanroom solutions Talk to an engineer about your aseptic transfer points
Named work
- Ajanta PharmaPharma
- DesanoPharma
- PGICH NoidaBSL-3
- ASMC ShahjahanpurBSL-3
Would you like a named VHP-pass-box reference to review before you commit? Just ask, and we will walk you through a comparable transfer point.
The release interlock
The clean-side door is not opened by an operator. It is released by the cycle.
Aeration has to bring the residual peroxide below the safe limit before the electromagnetic interlock will release the inner door. The interlock discipline is shared with every pass box Fabtech builds. The chemistry above it is what makes this one different.
- Typical total cycle
- 30 to 55 min
- Of that is aeration
- 15 to 30 min
Frequently asked questions
It is the pass box you use when clean air alone will not do. It is a dynamic transfer chamber that runs a vapourised hydrogen-peroxide (VHP) decontamination cycle on the material, removing surface micro-organisms and not just particles. That is what lets material enter a sterile suite or an isolator.
Vaporized hydrogen peroxide, H₂O₂ in vapour form (also written "vapourised", and known generically as vapour-phase hydrogen peroxide). It is a vapour-phase sporicide used to bio-decontaminate surfaces.
VHP is the standard method of bio-decontaminating the inside of a pharmaceutical isolator. A VHP pass box applies the same hydrogen-peroxide chemistry to the material being transferred in. So the transfer does not break the isolator's sterility.
Surface bio-decontamination. It sporicidally treats the outside of components, tools and containers before they enter a sterile or aseptic area, an isolator or a RABS. The treatment is taken to a measured sporicidal log reduction.
A dynamic box uses HEPA airflow to remove particles. A VHP box adds a hydrogen-peroxide cycle, so it also kills micro-organisms. VHP is what you use for transfers into the cleanest, sterility-critical areas.
A typical total cycle runs about 30 to 55 minutes. Aeration accounts for 15 to 30 minutes of that. Purging the peroxide back to a safe residual level is the slow step, so aeration sets the throughput more than the kill does.
A VHP pass box is qualified in stages. DQ/IQ/OQ/PQ. That is design, installation, operational and performance qualification. HEPA filter integrity is tested. The aerosol is PAO/DOP. The cycle is proven with biological indicators carrying resistant spores across the chamber. Aeration must bring residual peroxide to a safe level before release.
Tell us about the aseptic side
Share the grade on each side of the wall, what the material is and how many transfers an hour you need. Our engineers come back with a specified box and its cycle, not a catalogue page.