The University of Iowa

Local Exhaust Ventilation (LEV)

LEV is a ventilation system designed to capture and remove contaminants at the point of generation. Some of the most common types of LEVs on campus covered by this program are snorkels, down draft tables, ductless fume hoods, and paint booths.  Fume hoods and biosafety cabinets are also types of LEV but their use and testing are covered by their own separate programs.

For questions about LEVs contact the EHS Industrial Hygienist or the Occupational Safety Coordinator in charge of LEV testing. Contact information can be found on the contact us page.

Because there are many types of LEV systems, it is not possible to provide guidance on how to best use all of them.  Below are some general instructions on using LEV and specific information for the most common types used on campus.

General Tips

  • For self-contained units that use a filter (i.e. ductless fume hoods and down draft tables) ensure it has the correct filter for the chemical you are working with.  A HEPA filter will only provide protection for particles, vapors and gases will pass right through.
  • Ensure there is air flow before starting work. Clogged duct work and filters can drastically reduce the amount of air flow in a system.
  • Read any manuals that come with the system so that you are aware of its intended use and any limitations it has.

Ductless Fume Hoods/ Enclosures

  • Follow all the guidelines for ducted fume hoods. These can be found in the  ICON training course, Chemical Fume Hoods - W485CM, and in the UI Chemical Hygiene Plan, Section 9.0 Facility and Equipment Safety.
  • Do not use Bunsen burners or hot plates in the units unless the manual states that is acceptable. The heat from these instruments can damage the filters if the hood is not designed for it.
  • If you are using one that has carbon filters for controlling exposures to fume and vapors, consult this Ductless Fume Hood Use Guide


  • For procedures where the chemicals are being heated, the snorkel can be placed above the operation like a mini canopy hood.
  • For low velocity contaminant release (i.e. general chemical mixing and welding), position the snorkel at 30-45 degrees off horizontal in front of the employee to maximize the capture zone.  The capture distance listed on the LEV test sticker is how far the snorkel should be placed from the source.
  • For higher velocity contaminants (i.e. sanding and grinding), place the snorkel so the particles are thrown into the snorkel. The snorkel may need to be moved closer than the listed capture distance.

Canopy Hoods

  • Canopy Hoods should only be used with hot processes as they depend on the lift from the hot air to carry the contaminates into the hood.
  • Canopy hoods should not be used if the employee needs to lean over the work area.
  • Adding sides to the canopy hood can help increase its efficiency and reduce the impact of cross drafts.

Downdraft Table

  • Downdraft tables are best for processes that generate larger particles and can be ineffective at capturing contaminants from hot processes.
  • Keep the surface as free of other tools and materials as possible as this can restrict the airflow making the table ineffective.
  • Work as close to the bench top as possible to maximize the collection effectiveness.

Paint Booth

  • Always spray straight into the fume hood. If multiple sides of a piece need to be painted rotate the piece so the paint can continue to be sprayed straight in.

Annual Testing

Environmental Health & Safety (EHS) checks airflow performance of most LEV systems on an annual basis. For various reasons EHS is unable to test all systems on campus.

Passing Airflow Values

EHS reviews each LEV and sets a passing airflow value for each piece. The following is the sources EHS uses in setting this value:

  1. OSHA regulations
  2. Manufactures’ documentation
  3. Initial testing and balancing reports for a building.
  4. Recognized design criteria from non-regulatory sources such as ACGIH and ASHRAE.
  5. Exposure monitoring to determine if the LEV is working to control exposures.


If the LEV is connected to the building ventilation, submit a repair request through the Green button on the FM@YourService portal.  Certain repairs may require FM to secure outside contractor resources. 

If the LEV is not attached to the building ventilation system, it is the department’s responsibility to fix the issue. If the department is unsure who to contact for a repair, they may submit a request through FM@YourService for help in finding a 3rd party to complete the repair.