Monitoring Airflow in Local Exhaust Ventilation (LEV) Systems

May 31, 2021 | Posted By: John Callanan

Local exhaust ventilation (LEV) is an engineering control measure to reduce employee exposure to airborne contaminants in the workplace. LEV systems capture or contain process emissions and carry them away, minimizing the risk of workers breathing in contaminated air. Although LEV systems vary considerably, common elements include:

  • A hood to capture contaminants (dust, fumes, gas, vapor) generated at the source
  • Ducting to carry contaminated air away
  • An air cleaner
  • A fan that moves air from the point of contaminant generation to a safe point of discharge
Local exhaust ventilation system performance monitored with airflow switches and monitors.
LEV (local exhaust ventilation) system being monitored with airflow switches to optimize performance.

LEV system performance should always be monitored to ensure that the system is working as designed and effective in protecting employees. This is not new. Environmental and process engineers are continually upgrading engineering controls as well as implementing new measures to control potential hazards in the workplace. (OSHA standard 1910.94 addresses ventilation for general industry.)

One auto parts manufacturer is currently installing Degree Controls air velocity and temperature switches to monitor ventilation systems for their welding and grinding workcells. Specifically:

  • An S-Series airflow switch is installed in the ducting of LEV systems to monitor air velocity at the hood.
  • If air velocity drops below a given trip point, the switch provides an alarm signal to the PLC.

Depending on the process and design of the particular LEV system, the client installs additional S-Series switches to help identify the cause of a potential drop in airflow rate. For example, in some systems, airflow switches are being used to monitor air velocity just after air cleaners and at the output of fans.

Know the Air Flow Rate for Safe Workspaces
Knowing and monitoring airflow rates within LEV systems provides assurance that systems are working effectively and helps keep employees safe by immediately alerting users to potential problems. Monitor local exhaust ventilation using DegreeC probe style air velocity and temperature switches mounted in duct. Trip point, alarm delay, and recovery point are configurable, and choice of open drain or relay output signals to your PLC or controller.

LEV monitoring using airflow switches and monitors that alarm at a set threshold.
The switch is installed inside the duct of an LEV system and the monitor is mounted to the face of the capture hood. The combination of airflow switch and monitor allows for alarming based on a user-defined threshold to maintain a safe work environment.

Alternatively, use DegreeC’s Rooster™ Monitor100 with probe style sensor for a flexible airflow monitoring solution with advanced capabilities. The Monitor100 is typically mounted to the face of the capture hood with the sensor installed in the exhaust duct. Air velocity and temperature are measured and displayed simultaneously, and the Monitor100 alarms visually and audibly when airflow drops below a user-defined level. Alarm behaviors are fully configurable, and Rooster™ is convenient and easy to use with a glove-friendly, touch-panel display. 

As you work to design and develop your LEV hoods and systems, incorporate airflow sensing, monitoring, and control products from Degree Controls to ensure that exhaust air velocity is sufficient to gather and remove process emissions for effective exposure control.

About the Author

John Callanan
John Callanan

As a Technical Sales Engineer John works with clients to provide airflow monitoring solutions tailored to their needs. He holds a Bachelor of Science Degree in Technical Management.