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Chemical Fume Hoods

I. The Issue:

Many of the experiments and demonstrations routinely conducted as part of the standard high school science curriculum often involve volatile substances, the heating of materials, or reactions which may result in the evolution of gases or odors. As a result, these activities may release materials that could adversely impact indoor air quality and create a health hazard for the occupants. In addition, it may not be possible to totally eliminate and replace all the activities and materials which generate nuisance or hazardous emissions with totally benign replacements, consequently there exists a need to provide enhanced mechanical ventilation in these classrooms in order to properly evacuate these contaminants. Failure to adequately ventilate these classrooms may enable contaminants to build up to hazardous concentrations in these areas. Furthermore, improper ventilation of these rooms could cause these contaminants to enter the building heating and ventilation system and place the entire school population at risk as the materials are distributed throughout the building. Therefore, it is imperative that each chemical procedure be reviewed for potential impacts on indoor air quality. Where possible alternatives should be sought which do not generate hazardous emissions or which generate fewer or less toxic emissions. For those circumstances where no alternatives exist, safe and proper mechanical ventilation must be provided to remove the contaminants from the building as a means to maintain the health and safety of the occupants.

II. The approach taken:

An initial component of our survey was to review the activities occurring in each of the high school science classrooms as a means to evaluate whether these activities could adversely impact indoor air quality. During this effort, we determined that potentially hazardous activities requiring additional mechanical ventilation were occurring in most of the classrooms utilized by the science department. Please note that additional mechanical ventilation may also be needed in middle school science areas as well as secondary level art studios.

Next, a survey of the classrooms used by the high school science staff indicated that less than 40% of these rooms were equipped with chemical fume hoods. In addition, we found that none of the middle school science rooms or the secondary level art studios had been equipped with chemical fume hoods to provide additional mechanical exhaust. As a result, the construction of the individual classrooms limited what activities or materials could be safely used by the occupants without jeopardizing indoor air quality.

Our next step was to have the existing hoods inspected and re-calibrated to ensure that the units functioned properly. The initial use and reliance on inexperienced and unqualified repair personnel caused this task to be time consuming and difficult to resolve. We utilized three contractors over a period of more than four years before we were able to fully assess, repair, and re-calibrate our hoods. The problems we encountered highlight the need to utilize experienced and knowledgeable ventilation specialists from the start.

Once all the fume hoods have been repaired and re-calibrated, we intend to provide the staff with additional training which outlines how the units should be used in order to promote the safe and proper operation of the hood. Furthermore, a preventative maintenance and re-calibration schedule will be established for each unit. As part of this routine, each hood will be tested and re-calibrated at least once annually by a trained professional. All hoods found to be malfunctioning or out of calibration will be immediately removed from service until the unit has been repaired.

III. Observations made:

During this evaluation, we noted that the existing chemical fume hoods were not routinely used for their intended purpose but were instead used for the storage of equipment or chemicals. In addition, almost all activities involving the use of volatile materials or resulting in the generation of fumes, vapors or odors were conducted at bench top without the aid of additional mechanical ventilation. As a result, these activities may have adversely impacted the indoor air quality in the effected areas.

We also observed that the staff used the hoods to evaporate unwanted reagents or experimental byproducts as a means to reduce or consolidate laboratory waste. State and federal hazardous waste management regulation consider this improper and illegal waste treatment. Therefore, you should not copy this practice because you would be promoting the introduction of contaminants into the atmosphere and the local environment.

Our survey also found that neither the staff nor the students had been provided with guidance in terms of how to safely operate the hoods or what activities and uses were considered appropriate and acceptable. As a result, the hoods were rarely operated in a manner to maximize the effectiveness of the unit and the safety of the operator.

During our inspection, we noted that most of the fume hoods were in a state of serious disrepair. We found units that were missing interior panels and covers and as a result leaked contaminants. We found hoods with malfunctioning or inoperative ventilation fans. We also observed hoods vented through duct work that was perforated. Finally, we also found that all the hoods serving the science area were constructed so that the hood exhaust was located adjacent to the hood intake. As a result materials evacuated by the hood could be re-entrained by the intake and brought back into the classroom.

IV. Problems or concerns noted:

V. Actions taken:

During my survey, I noted that the staff rarely used the chemical fume hoods in the science area. Upon closer examination, it became obvious that many of the units were in a state of disrepair. Our efforts to investigate and repair the fume hoods provides evidence of the need to hire a trained and competent professional to evaluate and maintain these units. During this review, we initially found that the exhaust fan had been removed from the majority of the units, presumably for energy savings. The remaining units were found to be equipped with improperly sized and balanced intake and exhaust fans. In addition, when tested with smoke, approximately half the units or associated ductwork were found to leak contaminants into the building. A final and fatal flaw was also detected for all chemical fume hoods. All hoods were found to be constructed with the exhaust located adjacent to the intake for each unit, consequently even if functional, the hoods could not remove contaminants from the classrooms and laboratories without reintroducing the materials to the building.

We have worked with an architect and a certified industrial hygienist to correct and resolve these deficiencies. We have also provided the staff with additional training regarding the safe and proper use of the hoods. In addition, each hood has been labeled to indicate the safe work area within the hood as well as the proper sash height for safe operation.

An inexpensive tip for screening the function of a chemical fume hood is to test the unit using a 60 to 90 second colored smoke bomb. If the unit is functioning properly it should easily evacuate the smoke to the outdoors. Common problems you may observe would be the failure of the smoke to exit the unit, smoke leaking from the hood or ductwork, and smoke reentering the intake or the building ventilation system. One word of caution would be to coordinate all smoke tests with your fire department to ensure that all area smoke detectors have been disabled prior to testing. This graphic and inexpensive demonstration can be a useful indicator of whether a serious problem may exist. This test does not replace the need to have the units tested and re-calibrated on annual basis by a competent professional. Also, all units found to display improper air flow should be removed from service until inspected and repaired.

Lessons learned:

1. You must test and re-calibrate your hoods annually in order to ensure that they function properly. Be sure to use a qualified personnel when completing this task.

2. Provide your staff and students with training and guidance in terms of the safe and effective operation of chemical fume hoods. Many individuals fail to realize that the Plexiglas sash provided on most units is designed to function as a safety shield in the event of a minor explosion or that proper air flow can only be achieved when the sash is set at a specific height. You need to inform the user of each feature associated with your hoods.

Tips and suggestions:

1. Use a smoke bomb to test mechanical ventilation: This simple and inexpensive test can provide you with a quick and easy qualitative assessment of the function of a chemical fume hood or kiln exhaust. The use of brightly colored smoke will enable you to easily determine if exhaust may be escaping from the test unit, the ductwork associated with the unit, or if the exhaust is reentering other portions of your ventilation system. This is only a quick and dirty analysis designed to check for major problems. This approach does not replace the need to have a trained professional inspect, maintain and calibrate these units.

2. Seek assistance from local resources: We are all in this together. Tap into the assistance that is available from federal, state and local environmental, and health and safety agencies. Do not overlook local residents, corporations, and medical facilities. These groups have a vested interest as parents and tax payers, and are frequently willing to provide technical expertise and assistance.

3. Rotate classroom activities or utilize centrally located hoods when conducting potentially hazardous procedures: Due to the cost of constructing and maintaining chemical fume hoods and the amount of use the units frequently receive, it is rarely justifiable that each science classroom or art studio should be equipped with a hood. A more cost effective solution would be to rotate classroom activities and to utilize centrally located hoods when potentially hazardous procedures are to be conducted.

4. Adopt a microscale curriculum: The microscale concept is to alter your experimental procedures so that you use approximately 1/10th of the amounts originally planned for by the author. Conversion to microscale may require the purchase of new glassware, however the benefits include the development of better techniques by the staff and students, decreased chemical usage, lowered exposure to hazardous materials, and a reduction in hazardous waste generated. For more information describing microscale contact: Dr. Mono M. Singh, Director, The National Microscale Chemistry Center, 315 Turnpike Street, Merrimack College, North Andover, Massachusetts 01845, Telephone: (978)837-5137, Fax: (978)837-5017, or via e-mail at 'msingh@merrimack.edu'

5. Adopt a less toxic curriculum: As previously suggested, you must review the curriculum to determine if safer, less toxic alternatives can be implemented. I have found that frequently many options exist for providing the same educational experience, however some motivation must be provided to prompt the search for a safer alternative. I recommend that you consult your state pollution prevention agencies for assistance. In Massachusetts, we are fortunate to have the Office of Technical Assistance and Surface Cleaning Laboratory. These agencies provide free, non-regulatory pollution prevention assistance to the public. In Burlington, we have also adopted a number of procedures presented in "40 Low-waste, Low Risk Chemistry Labs", by David Dugan, published by J. Weston Walch of Portland, Maine (207-772-2846). We have found this text to provide a more detailed discussion of EHS issues associated with the procedure combined with the use of less toxic alternatives than normally found in most chemistry text books.


1. Internet resources: The following is a compilation of useful Internet addresses that may assist you when researching EHS or regulatory issues.

Site Description
http://www.osha.gov Exit EPA Click for Disclaimer OSHA regulations & guidance
http://www.acs.org Exit EPA Click for Disclaimer American Chemical Society
http://www.aiha.org Exit EPA Click for Disclaimer American Industrial Hygiene Association
http://www.nyfa.org/ Exit EPA Click for Disclaimer Center for Safety in the Arts
http://www.ABIH.org Exit EPA Click for Disclaimer American Board of Industrial Hygiene

2. Potential sources for written guidance describing school EHS issues:

The Maryland Department of Education has published a number of helpful technical bulletins describing potential EHS issues in schools as well as potential corrective action.

Maryland Department of Education
Office of Administration and Finance
Office of School Facilities
200 West Baltimore Street
Baltimore, Maryland 21201

The Center for Safety in the Arts monitors and evaluates a broad range of health and safety concerns involving the arts and theater. This group has also published a large volume of health and safety guidance.

Center for Safety in the Arts
5 Beekman Street, Suite 820
New York, New York 10038

The National Microscale Center at Merrimack College has prepared guidance describing the benefits as well as how to initiate a microscale curriculum. The center also conducts training for those wishing to develop a microscale program.

Dr. Mono M. Singh, Director
The National Microscale Chemistry Center
315 Turnpike Street
Merrimack College
North Andover, Massachusetts 01845
Telephone: (978)837-5137
Fax: (978)837-5017
e-mail at msingh@merrimack.edu.

prepared by Todd H. Dresser, Environmental Engineer (formerly of)
Burlington Board of Health, 29 Center Street, Burlington, MA 01803

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