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 and/or drops exhausted through duct work that runs to a fan 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 minimize exposure to hazardous gases, vapors, and dusts that may be encountered in laboratory processes. Instructions on proper fume hood use are contained in your Department's Chemical Hygiene Plan. Special purpose fume hoods include:
- Perchloric acid hoods – equipped with a water wash down for use with heated perchloric acid
- Plastic hoods for work highly corrosive materials
- 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 working correctly, you need to take immediate action. Shut off any experiments or processes in the hood and 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.
Submit a work order to Facilities, mark it "URGENT", and cc: firstname.lastname@example.org. An alternative method to report an urgent problem to Facilities is by calling FIXIT (253-4948) which is answered 24/7. If you have questions about whether your hood monitor is working correctly or general questions about the safe operation of your hood, please contact the EHS Office at 617-452-3477.
Fume Hoods and Energy Conservation
Because they move conditioned air out of the lab continuously, fume hoods are highly energy-intensive. An older fume hood in an MIT lab can use more than 3 times as much energy annually as a single family home. The energy to filter, move, cool and heat air is one of the largest energy demands in most lab facilities.
Innovations in fume hood technology and design are reducing airflow thru fume hoods while maintaining safety. In one type of new hood (variable air volume), as the sash is lowered, the air volume passing through the hood is reduced while maintaining a minimum velocity. This results in energy savings from not having to filter, move, cool and heat, the additional air.
So keep your sash as low 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! "Shut Your Sash" Stickers are available to remind researchers to lower the fume hood sashes. To request them please contact the EHS Office.
Exhaust Ventilation and Nanomaterials
Light, fluffy nanomaterials may be disturbed by airflow in fume hoods. EHS recommends enclosures that have been developed for sensitive balances to handle these types of nanomaterials. Vendors have tested the balance enclosures and they work well to contain nanoparticles. The airflow from these enclosures can be HEPA filtered. Contact EHS for more information about working safely with nanomaterials