Anteroom
A small room between a controlled room and the rest of the building that people pass through to enter, used for gowning, hand hygiene, and pressure separation. Its pressure is set so opening one door never connects the controlled room directly to uncontrolled space.
Also called ante-room, airlock, gowning room
What is an anteroom in a cleanroom or isolation suite?
An anteroom is the entry room between a cleanroom or isolation room and the corridor, where people gown and where the door sequence keeps the controlled room from opening straight onto uncontrolled space. USP 797 requires an ISO 8 or cleaner anteroom at least 0.020 inches of water column above unclassified space.
Anteroom: how it works
An anteroom works through its doors and its pressure. With interlocked or alarmed doors only one door is open at a time, so the controlled room only ever opens onto the anteroom. The anteroom's pressure decides where air goes when a door opens: in a cascade it sits between its neighbors, as a bubble it sits above both and pushes air out each way, and as a sink it sits below both and exhausts the air it draws from each.
Where you meet the term
- At the entrance to a USP 797 cleanroom suite, where compounding staff gown before entering the buffer room.
- Between a USP 800 negative buffer room and the corridor, where the anteroom is the highest-pressure space in the suite.
- At the entry to an aseptic processing area, where the FDA guidance calls for airlocks and interlocking doors.
How to check it
- Try both doors. With interlocks, the second door should not open while the first is open, or an alarm should sound when both are open together. Owner check
- Measure the pressure step on each side. A technician measures the differential across each anteroom door with both doors closed and compares the direction and size with the design. Technician
Anteroom: what it is not
- An anteroom is not just a corridor with a door. Without pressure control and door management it does not separate the rooms on either side.
- An anteroom does not run at the same pressure as its cleanroom. USP 797 requires a step of at least 0.020 inches of water column between them.
Anteroom questions
What is the difference between a bubble and a sink airlock?
A bubble airlock is held above both neighboring spaces, so air flows out of it in both directions and neither side's air reaches the other. A sink airlock is held below both, drawing air from each side into its own exhaust, which suits containment where that exhaust is filtered.
Does an anteroom need its own air changes?
Where it is classified, yes. USP 797 applies the ISO 8 rate of at least 20 air changes per hour or the ISO 7 rate of at least 30 to an anteroom of that class, and USP 800 requires at least 30 for the ISO 7 anteroom of a sterile hazardous drug suite.
Why should both anteroom doors never open together?
With both doors open the controlled room connects to the corridor through an opening no airflow can hold a pressure difference across. Interlocks or alarms prevent it and keep the anteroom working as a buffer.
Where this definition comes from
Written from standards body publication, government guidance material held in the HVAC Bench evidence record. Where a document limits a definition to certain models, that limit is repeated here rather than generalised across a brand.
- General Chapter 797, Pharmaceutical Compounding, Sterile Preparations2023 revision, official 1 November 2023, for sterile compounding: at least 30 air changes per hour of HEPA-filtered supply in ISO 7 buffer rooms and anterooms and at least 20 in ISO 8 rooms, with at least 15 of them supplied by the HVAC system through HEPA filters; a minimum positive pressure differential of 0.020 inches of water column between the buffer room and anteroom and between the anteroom and unclassified space, monitored continuously; rooms maintained at 20 degrees Celsius or cooler and 60 percent relative humidity or below; and certification of primary and secondary engineering controls every six months.
- General Chapter 800, Hazardous Drugs, Handling in Healthcare SettingsEngineering controls for hazardous drugs: storage rooms and nonsterile containment secondary engineering controls externally vented, at least 12 air changes per hour, and negative between 0.01 and 0.03 inches of water column relative to adjacent areas; sterile hazardous drug buffer rooms of ISO 7 air quality with HEPA-filtered supply, externally vented, at least 30 air changes per hour, and negative between 0.01 and 0.03 inches of water column; an ISO 7 anteroom with at least 30 air changes per hour and at least 0.02 inches of water column positive to adjacent unclassified areas; and a containment segregated compounding area externally vented with at least 12 air changes per hour at the same negative pressure range.
- Guidance for Industry: Sterile Drug Products Produced by Aseptic Processing, Current Good Manufacturing PracticeFDA guidance recommending a positive pressure differential of at least 10 to 15 pascals between adjacent rooms of differing classification with doors closed, outward airflow sufficient to minimize ingress when doors open with door-open time strictly controlled, at least 12.5 pascals from an aseptic processing room to adjacent unclassified space, airflow for at least 20 air changes per hour as acceptable for ISO 8 supporting rooms, a critical area velocity of 0.45 meters per second (90 feet per minute) plus or minus 20 percent, and HEPA filter leak testing at installation and at intervals such as twice a year for the aseptic processing room.