Clean Room Monitoring: What Temperature, Humidity and Pressure Should Your Clean Room Hold?

Most clean room problems aren’t dramatic failures. They’re slow drifts: a door that doesn’t close fully, an AHU filter loading up, humidity creeping up through the monsoon. This guide covers what to monitor, the limits most facilities work to, and the small practical mistakes that cause trouble during audits.

What Should a Clean Room Monitor?

At minimum, three things: temperature, relative humidity (RH) and differential pressure against the adjacent area. Particle counts and air changes matter too, but they’re usually checked periodically during qualification. Temperature, humidity and pressure can change within minutes, so they need watching continuously.

What Temperature and Humidity Should a Clean Room Be Kept At?

There’s no single number. It depends on the product and the process. As a working reference, these are the ranges most facilities use:

Application	Typical Temperature	Typical RH	Why
Pharma oral solids (tablets, capsules)	20–25 °C	30–55%	Many powders and gelatin capsules absorb moisture; tablets stick, capsules soften or turn brittle
Pharma sterile / injectables	18–22 °C	45–55%	Operator comfort in full gowning, which reduces shedding and sweating
Electronics / PCB assembly	20–24 °C	40–60%	Below ~30–35% RH, static discharge risk rises sharply
Hospital operation theatre	20–24 °C	40–60%	Patient and staff comfort, infection control

Your own limits should come from your product’s stability data and your validated HVAC design. Treat the table as a starting point, not a specification.

What Differential Pressure Should Be Maintained Between Clean Rooms?

Most GMP guidelines, including EU GMP Annex 1 and WHO guidance, suggest a pressure differential of around 10–15 Pa between adjacent rooms of different cleanliness grades. The cleaner room is kept at the higher pressure, so air always flows out of the clean area, never in.

There’s one important exception. Rooms that handle potent drugs, hormones, cytotoxics or biohazards are often kept at negative pressure relative to the corridor. That keeps the product inside rather than keeping dust out. In these rooms, a reversed pressure reading is a safety issue, not just a quality one.

Why Does Clean Room Humidity Keep Rising During the Monsoon?

Outside air in much of India can stay above 80% RH for weeks. If the AHU’s cooling coil isn’t removing enough moisture, or the dehumidifier is undersized, room RH climbs. The temperature can look perfectly normal while this happens. Watching temperature alone hides the problem, which is why humidity needs its own reading and alarm.

Where Should Clean Room Sensors Be Placed?

• Not directly in front of supply air diffusers. You’ll read the conditioned air, not the room.
• At working height (about 1–1.5 m), near where product is actually exposed.
• Away from heat sources like ovens, sealers and lights near the sensor.
• Pressure ports on the wall between the two rooms being compared, kept clear of door swing.
• A display at the entry door, so staff see the room status before they enter, not after.

Should a Clean Room Alarm Trigger Instantly?

Not quite. Opening a door causes a pressure dip lasting a few seconds. If the alarm fires on every door opening, staff learn to ignore it. A common practice is to allow a short delay, often 30–60 seconds, before alarming on pressure, while keeping temperature and humidity alarms on their normal response. The goal is an alarm people take seriously.

Common Clean Room Monitoring Mistakes

1. Three separate gauges, read at three different times. No one gets a single picture of whether the room is in spec.
2. Magnehelic pressure gauges that are never zero-checked. Needles stick and tubes crack over the years.
3. No alarm outside working hours. AHUs trip at night, and the room is out of spec before the morning shift arrives.
4. Sensors never calibrated. Humidity sensors in particular drift over time. Most facilities recalibrate at least once a year.
5. Manual logbook entries. Readings get written from memory or “rounded off”, which auditors are trained to spot.

How Often Should Readings Be Recorded?

For GMP areas, continuous monitoring with automatic recording is now the expectation. Where manual records are still used, readings are typically logged at fixed times each shift. Any out-of-limit value needs a documented reason and corrective action, not just a tick.

Quick Checklist for Your Clean Room

• Limits for temperature, RH and ΔP defined from product needs and HVAC design
• Pressure direction confirmed for each door (positive or negative)
• Sensors at working height, away from diffusers
• One combined display at each room entry
• Alarms with sensible delays, covering nights and holidays
• Annual calibration of all sensors, with certificates on file