--- title: "USP 797 Pressure, ISO Class, and Humidity Limits | Aethair" description: "USP <797> limits for sterile compounding: buffer room pressure, ISO Class 5 and 7 particle counts, and humidity, plus a recommended configuration." url: https://aethair.io/standards/usp_797/ --- Compliance · United States Pharmacopeia # USP General Chapter <797>: pharmaceutical compounding, sterile preparations Indoor: sterile compounding pharmacies (USA) **USP General Chapter <797>**, Pharmaceutical Compounding — Sterile Preparations, sets the standards for compounding sterile medications, in a revision that became official on November 1, 2023. Its facility requirements are built on the ISO 14644-1 cleanliness classes. The primary engineering control where compounding happens operates at **ISO Class 5 (3,520 particles/m³ at ≥0.5 µm)**. It sits inside an **ISO Class 7 buffer room (352,000 particles/m³)** with at least 30 air changes per hour, held at a **positive pressure of at least 0.020 inches of water column (about 5 Pa)** relative to adjacent, less clean areas. Relative humidity in compounding areas is held at **60 % or below**. [Schedule a call](https://calendly.com/d/ctdd-mkr-v9v/aethair-demo-website) [Configure USP 797 Monitoring](https://aethair.io/build/?params=differential_pressure,particle_count,humidity) At a glance **United States Pharmacopeia** Indoor: sterile compounding pharmacies (USA) 3 parameters · 4 limit values [Differential Pressure](https://aethair.io/parameters/differential_pressure/) [Particle Count (by size)](https://aethair.io/parameters/particle_count/) [Relative Humidity](https://aethair.io/parameters/humidity/) 1 device measures them all - **Aethair PRO** Aethair Diff. Pressure [Official text from United States Pharmacopeia](https://www.usp.org/compounding/general-chapter-797) Limit values ## USP 797 Limit Values Every value United States Pharmacopeia publishes for the 3 parameters below, with its averaging period, as the standard states it. [**Differential Pressure** Meteorology](https://aethair.io/parameters/differential_pressure/) **5 Pa** *Minimum, buffer room (positive)* 0.020 in. w\.c. relative to adjacent less clean areas [**Particle Count (by size)** Particulate Matter](https://aethair.io/parameters/particle_count/) **3520 particles/m³** *ISO Class 5 primary engineering control, ≥0.5 µm* **352000 particles/m³** *ISO Class 7 buffer room, ≥0.5 µm* [**Relative Humidity** Meteorology](https://aethair.io/parameters/humidity/) **60 %** *Maximum, compounding areas* Who it applies to ## Who Must Comply Pharmacies, hospitals, outsourcing facilities, and clinics that compound sterile preparations in the United States, as enforced by state boards of pharmacy and accreditors. Hazardous drugs add the requirements of USP <800>. Monitoring ## How Monitoring Demonstrates Compliance Classification and certification are periodic: certified particle counts and airflow tests at set intervals, following ISO 14644. What has to be shown continuously is the pressure relationship, which the chapter expresses as a number, with temperature and humidity recorded alongside. A continuous record with alarms shows the cascade held between certifications and flags a door, filter, or fan problem when it happens. [Customize this configuration](https://aethair.io/build/?params=differential_pressure,particle_count,humidity) ### Who measures each parameter | Parameter | Aethair PRO | Aethair IAQ | External | | - | - | - | - | | [Differential Pressure](https://aethair.io/parameters/differential_pressure/) | Diff. Pressure cartridge | — | — | | [Particle Count (by size)](https://aethair.io/parameters/particle_count/) | Built in | Built in | [1 instrument](https://aethair.io/parameters/particle_count/) via Thiamis | | [Relative Humidity](https://aethair.io/parameters/humidity/) | Built in | Built in | [12 instruments](https://aethair.io/parameters/humidity/) via Thiamis | Devices ## Devices That Cover USP 797 How much of this standard one Aethair monitor covers, followed by the third-party instruments in the sensor catalog that measure its parameters. Each connects to Environet through a Thiamis gateway, which adds whatever the monitor leaves out. Aethair monitors [**Aethair PRO** Built in + Aethair Diff. Pressure Covers all 3](https://aethair.io/products/pro/) [**Aethair IAQ** Built-in sensors 2 of 3: Particle Count, Relative Humidity](https://aethair.io/products/iaq/) Covers part of it (combine on one Thiamis) [**Particles Plus** Particulate & Dust Monitors 2 of 3: Relative Humidity, Particle Count](https://aethair.io/sensors/particles-plus-particulate-dust-monitors/) [**Fluke Calibration 1620A DewK** Heat Stress & Comfort 1 of 3: Relative Humidity](https://aethair.io/sensors/fluke-calibration-heat-stress-comfort/) Solutions ## Solutions Judged Against USP 797 ### [Healthcare Air Monitoring](https://aethair.io/solutions/healthcare/) Clinical air quality, pressurization, and patient safety [All solutions](https://aethair.io/solutions/) Article Library ## Articles on USP 797 ### [Hospital Air Quality Monitoring: Standards by Space](https://aethair.io/resources/healthcare-air-quality-monitoring/) Hospital air quality standards from ASHRAE 170 and The Joint Commission explained, plus what to measure in operating rooms, isolation rooms, and labs. ### [ASHRAE 170 Requirements and Which Edition Applies to You](https://aethair.io/resources/ashrae-170-requirements/) ASHRAE 170 requirements explained: what the standard sets, which edition your facility is held to, what changed in 2025, and how each value gets verified. [All articles](https://aethair.io/resources/) Questions ## USP 797 FAQ What pressure differential does USP 797 require? At least 0.020 inches of water column (about 5 Pa) positive pressure in the buffer room relative to adjacent, less clean areas. What ISO classes does USP 797 use? ISO Class 5 for the primary engineering control where compounding takes place, inside an ISO Class 7 buffer room, as defined by [ISO 14644-1](https://aethair.io/standards/iso_14644_1/). What humidity does USP 797 call for? Relative humidity in compounding areas held at 60 % or below.