Fume Hoods/Laboratory Ventilation

Updated April 05, 2011


Exhaust ventilation is the primary means of preventing exposure to hazardous substances in laboratories and other workplaces. A basic exhaust system consists of an enclosure(s) and/or drops exhausted through duct work that runs to a fan and stack on the building roof. The appropriate type of exhaust system will depend on the processes and materials used in your research. Several types of laboratory ventilation are described below.

Types of Exhaust Ventilation

  • Chemical Fume Hoods — Chemical fume hoods are the standard enclosures in chemical laboratories that when properly used and maintained minimize exposure to hazardous gases, dusts, mists, and vapors that may be encountered in laboratory research. Instructions on proper fume hood use are contained in your Department's Chemical Hygiene Plan. Special purpose fume hoods include:
    1. Perchloric acid hoods – equipped with a water wash down for use with heated perchloric acid
    2. Plastic hoods for work highly corrosive materials
    3. HEPA filtered laminar flow hoods for particle free chemical work
  • Specialty Local Exhaust Ventilation — Specialty local exhaust ventilation (SLEV) includes gas cabinets, drops for vacuum pumps, adjustable snorkels and certain equipment that requires connection to a exhaust system. EHS works with researchers and Facilities in the design and installation of SLEVs.
  • Biosafety Cabinets — Most biosafety cabinets (BSCs) on the campus are Class II A2. While this type of BSC is designed to provide personnel and environmental protection against biological materials it is not suitable for volatile chemical use. Check with your EHS Biosafety Safety Officer if questions arise as to the safe use of biosafety cabinets.
  • General Ventilation — In some cases a lab may not require a fume hood or SLEVS. General exhaust ventilation not associated with specific equipment may then be required to maintain a minimum air change rate in the lab. Areas that contain compressed or liquefied gases may also require general exhaust.


Ventilation Survey Program

Chemical Fume Hoods — Each fume hood  is surveyed yearly by the EHS office. This survey includes a check of the airflow, physical integrity and alarm functionality. Before using a fume hood check to be sure the survey sticker is up to date. 


Specialty Local Exhaust Ventilation —Airflows at high priority SLEVs are also checked yearly, less critical SLEVs are checked at a longer interval.


Biosafety Cabinet Certification —Yearly biosafety cabinet certification is required and  is each lab's responsibility.


Problems with Fume Hoods and Other Ventilation

If your fume hood monitor alarm sounds or you feel that the exhaust ventilation is not functioning correctly, you need to take immediate action. Shut off any experiments or processes in the hood, post a “do not use” sign. Both the EHS Office and Facilities department will respond as quickly as possible to any problems involving laboratory ventilation. If submitting a work order online, be sure to cc: environment@mit.edu and mark the work order “URGENT.” An alternative method to report an urgent problem to Facilities is by calling FIXIT (3-4948) which is monitored 24/7. If you have questions about whether your monitor is operating correctly or more general questions regarding the safe operation of your fume hood, please contact the EHS Office at (617) 452-3477 (2-EHSS).






 Fume Hoods and Energy Conservation

Because they move conditioned air out of the lab continuously, fume hoods are highly energy-intensive. An older constant volume fume hood in US climates can use more than 3 times as much energy annually as a single family home. This type of hood fume hood, with a sash opening six feet wide and two to three feet high, can circulate more than a 1000 cubic feet of air (cfm) through the sash opening at a face velocity about 100 feet per minute (fpm). The energy to filter, move, cool or heat, and in some cases clean this air is one of the largest demands in most lab facilities.

Innovations in fume hood technology and design are reducing airflow thru fume hoods while maintaining or increasing safety and performance. High performance hoods have baffles, sashes and other hood features that improve containment at a lower face velocity. Newer hoods are also designed for use with a maximum sash height of 18" except for equipment setup.   In variable air volume (VAV) fume hoods, as the sash is lowered, the air volume passing through the hood is reduced while maintaining a minimum velocity resulting in energy savings from not having to filter, move, cool or heat, and clean that additional air.  So, please keep your sash as closed as possible when working in your fume hood, and closed completely when you are away from the equipment. Help MIT save energy and the environment: Shut Your Sash!

Stickers were developed and placed on fume hoods in several labs on campus to promote safer and more energy efficient use of fume hoods. To request fume hood stickers for your VAV fume hoods, please contact the EHS Office.

Read more about MIT’s novel efforts to save energy by promoting better sash management at http://web.mit.edu/newsoffice/2007/fumehoods-0601.html.

 Exhaust Ventilation and Nanomaterials

The majority of the fume hoods on campus are constant velocity by-pass or variable air volume (VAV) fume hoods that researchers may use for nanomaterial work. The sash height should be kept at 18" or below and the hood must have a current inspection sticker. If you have  questions as to whether your hood is suitable contact EHS. 

If researchers are using very light, fluffy nanomaterials that may be disturbed by airflow in fume hoods, EHS is recommending enclosures that have been developed for sensitive balances; certain vendors have tested their balance enclosure and they work well in containing nanoparticles. Also the airflow from these enclosures is HEPA filtered.  Contact EHS for more information.

In some applications biosafety cabinets may be used provided the nanomaterial work does not include volatile chemicals.  Depending on the procedures used, it can be difficult to manipulate materials in a biosafety cabinet due to the low sash height.

For additional EHS information on working safely with nanomaterials click here.