Planning a Pass-Through Chamber - Which Type Fits?
A pass-through chamber (pass box) moves material into the cleanroom without a person crossing the barrier. This guide explains the three types - passive, active with interlock and HEPA-purged - along with sizing, interlock logic and cleaning as a compact alternative to a walk-in material airlock.
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What does a pass-through chamber do?
A pass-through chamber is a transfer hatch with two opposing doors that moves material between two clean zones without anyone crossing the cleanroom barrier. It cuts personnel traffic - the largest particle source in any cleanroom - and takes far less floor space than a walk-in material airlock.
The core principle is the interlock: only one of the two doors can open at a time. This preserves the pressure gradient between zones and prevents a direct air short-circuit from the dirty side to the clean side.
Passive, active or HEPA-purged?
There are three basic designs that differ in airflow and interlocking. The choice depends on the cleanroom class, the contamination risk of the material and the required throughput.
The passive box has no own air supply and simply transfers goods between two zones of equal cleanliness. The active version adds electrical locking with a traffic-light indicator and an optional dwell timer. The HEPA-purged box floods the item with filtered air to shed adhering particles before the inner door is released.
- Passive: low cost, low maintenance, ideal for consumables in lower ISO classes.
- Active interlocked: safe door logic, status light and logging for regulated processes.
- HEPA-purged: active particle reduction, required when entering ISO 6 or cleaner.
- Stainless steel 1.4301/1.4404 (304/316L) as the standard for pharma and microelectronics.
What matters when planning and installing?
Three figures are fixed before ordering: the clear chamber opening, the wall thickness and the interlock logic. The opening must fit the largest item transferred regularly - typical inside dimensions run from 400 x 400 x 400 mm to 600 x 600 x 600 mm.
- Check pressure cascade: the chamber must not short-circuit the pressure gradient between zones.
- Provide an emergency release in case of power failure (personnel and material safety).
- For HEPA purge, add the purge lead time into the process cycle.
How is the pass box cleaned and tested?
Smooth stainless surfaces with rounded internal corners wipe-disinfect without residue. Clean from the clean side toward the less clean side using cleanroom wipes and approved disinfectants.
- Test the interlock regularly: both doors must never open at the same time.
- Inspect seals and door catches for wear.
- Leak-test the HEPA filter per ISO 14644 and document the result.
Frequently asked questions
When do I need a HEPA-purged rather than a passive box?
As soon as material moves from a less clean into a cleaner zone (say ISO 6 or cleaner), an active HEPA purge makes sense because it sheds adhering particles before release. If both sides share the same cleanliness, a passive box is usually enough.
Why can only one door open at a time?
The interlock keeps the pressure gradient between zones and prevents a direct air short-circuit. If both doors opened together, unfiltered air could flow into the cleanroom.
Which inside size should I choose?
Size the clear opening to the largest item transferred regularly and add 20 to 30 % reserve for handling. Common sizes range from 400 x 400 x 400 mm to 600 x 600 x 600 mm.
Passive or active interlocked?
Passive boxes with a mechanical interlock are cheap and low maintenance. Active, electrically interlocked models with a status light and logging suit higher throughput and regulated, documented processes.
Looking for a pass-through chamber?
We supply passive, active interlocked and HEPA-purged stainless pass boxes - sized to your wall thickness, cleanroom class and throughput.
Safe door logic
Mechanical or electrical interlock with emergency release.
HEPA H14
Optional purge at 99.995 % capture efficiency.
Standard-based
Designed to ISO 14644-1.
Expert advice
Cleanroom specialists help with size and type.