In a laboratory, a fume hood is often the most important piece of safety equipment. It’s the primary line of defense that stands between a researcher and a cloud of hazardous, toxic, or volatile fumes.
But how do you know it’s actually working?
You can’t see the airflow. You can’t smell a problem until it’s too late. The “safety” of a fume hood is not a guarantee—it’s a variable that must be continuously measured. This is the critical job of the air velocity sensor.
What is Fume Hood “Face Velocity”?
“Face velocity” is the speed of the air being pulled into the fume hood, measured at the opening (the “face”). This measurement is everything.
- Too Slow: If the velocity is too low, dangerous fumes can escape the hood and enter the lab, exposing personnel.
- Too Fast: If the velocity is too high (a common issue when a system “overcompensates”), it creates turbulence. This turbulence can also cause fumes to spill out of the hood.
There is a precise “sweet spot”—typically 80-120 feet per minute (FPM) or 0.4-0.6 m/s—that ensures fumes are safely captured and exhausted.
The Job of the Air Velocity Sensor: Your 24/7 Watchdog
An air velocity sensor (also called an air velocity transmitter) is the “speedometer” for your fume hood. It is mounted in the exhaust duct or on the hood itself to provide a precise, real-time measurement of the airflow.
Its job is simple but non-negotiable: to provide the data that confirms containment.
This data feeds two critical systems:
- The Alarm System: If the face velocity drops below the safe limit (e.g., the sash is opened too wide, or the exhaust fan falters), the sensor triggers an immediate audible and visual alarm, telling the user to stop work and close the sash.
- The Building Control System: In modern labs (VAV, or Variable Air Volume systems), the air velocity sensor tells the system how to adjust the fan speed in real-time to maintain the perfect face velocity, saving massive amounts of energy.
What Happens When an Air Velocity Sensor Fails?
A failed sensor is a silent failure—and the most dangerous kind.
If the air velocity sensor becomes clogged with dust or “drifts” out of calibration, it can “lie” to the control system.
It might report a safe 100 FPM, when the actual airflow has dropped to a dangerous 60 FPM. The system sees no problem, the alarm never sounds, and the lab technician is left completely unprotected.
Why “Good Enough” Isn’t Good Enough for Labs
You cannot use a standard commercial-grade HVAC sensor in a fume hood. You must use a precision air velocity sensor designed for the job.
Key features to demand:
- High Accuracy at Low Airflows: It must be precise within the narrow band of safe operation.
- Chemical Resistance: It must be built to survive potential exposure to corrosive chemical fumes.
- Long-Term Stability: It must resist “drift” to ensure the readings are as accurate in three years as they are on day one.
Your First Line of Defense
The fume hood is your safety barrier. The sensor is its lock. Don’t compromise on a component this critical.
Precision is required for laboratory and critical environments. Our technical experts can help you select the right air velocity sensors to ensure your fume hoods are safe, compliant, and efficient.
Need to verify your lab’s safety?
Contact our technical specialists for a complimentary consultation or explore our comprehensive range of Air Velocity Sensors.
