The laboratory chemical fume hood is the most common local exhaust ventilation system used in laboratories and is the primary method used to control inhalation exposures to hazardous substances. When used properly, fume hoods offer a significant degree of protection for the user. Understanding the limitations, the appropriate maintenance techniques, and overall design of the fume hood will ensure your safety while using hazardous materials. The purpose of a chemical fume hood is to prevent the release of hazardous substances into the general laboratory space by controlling and then exhausting hazardous and/or odorous chemicals. In the event of an accidental spill, the fume hood will contain the spilled chemicals and exhaust the fumes away from the user and laboratory zone.
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Labconco Corporation Fume hoods Photograph Courtesy of Labconco CorporationTo determine if a chemical is required to be used inside of a chemical fume hood, first check the Safety Data Sheet (SDS). Statements found in Section 2 on a SDS such as “Do not breathe dust, fumes, or vapors” or “Toxic by inhalation” indicate the need for a fume hood. As a best practice, always use a chemical fume hood for all work involving the handling of open chemicals (e.g., preparing solutions) whenever possible. For more information about hazardous chemicals visit the Chemical Hygiene Plan (CHP) webpage.
A chemical fume hood is a ventilated enclosure used to trap and exhaust vapors, gases, and nanoparticles. The exhaust fan is typically stationed at the top of the building and pulls air through the duct work connected to the hood and exhausts it into the atmosphere.
Typical Fume Hood DesignVertical: The sash rises up and down and is optimal for shielding the user from contaminants with a large glass window pane. The vertical sash is framed, moves along tracks mounted inside of the hood’s wall, and is pulled up and down by a cable and pulley or chain and sprocket system. When using a hood with a vertical opening, raise the sash to the designated working height, generally 18” above the work surface, indicated by the black arrow on EHS’s inspection sticker. When not in use, close the vertical fume hood sash for the greatest level of safety and containment. This practice will improve air quality in laboratories and reduce energy use.
Horizontal: The sash moves side to side and is comprised of multiple window panes. This gives the user more freedom to work in a certain area of the fume hood while reducing costs because the sash is never completely open. EHS will post an approval sticker specific to the horizontal sash openings, affirming the horizontal sash opening in inches. When not in use, close the horizontal fume hood panels for the greatest level of safety and containment. This practice will improve air quality in laboratories and reduce energy use.
Combination: This is a sash designed with a horizontal pane system built into the vertical sash. EHS will measure the air velocities of each sash position and post the working height along with the horizontal sash sticker to the fume hood. Only use sash in one direction at a time. When not in use, close both the sash and horizontal panels for the greatest level of safety and containment. This practice will improve air quality in laboratories and reduce energy use.
Fume Hoods & Sash Enclosures Vertical Sliding Sash Horizontal Sliding sash Combination Sliding Sash Images courtesy of Labconco CorporationConstant Air Volume (CAV): This type of fume hood exhausts the same amount of air at all times, regardless of the horizontal or vertical sash position. As the sash is opened and closed, the air velocity at the face of the hood will change.
Variable Air Volume (VAV): This type of fume hood contains a face velocity control, which controls the fan speed to maintain a constant air velocity at the face of the hood. This type of exhaust allows for optimal hood performance regardless of the sash position, and provides significant energy savings by reducing the air flow rate when the sash is closed. When you are not working in the VAV fume hood, CLOSE THE SASH, turn off the lights, and conserve energy.
Think SAFE. Think GREEN.
You may notice this sticker placed on your fume hood; indicating that it operates as a VAV hood.
Any fume hood not currently in use may be evaluated to determine whether it may be temporarily turned off (hibernated) by contacting Physical Facilities Engineering at . Calling PF engineering to have your fume hood shut off can reduce the electricity used to power the fan, thus conserving energy, reducing greenhouse gas emissions, and saving your University thousands of dollars per year.
General Lab Use: Conventional hoods found on Purdue’s campus and are approved for general chemistry, radioisotopes, and carcinogen or toxic chemical work.
High Performance: These fume hoods have containment-enhancing features allowing them to operate at lower face velocities while protecting the operator. Since less room air is exhausted, energy is conserved. EHS will tag high performance hoods with a special standard operating procedure sticker, informing users of the appropriate air velocity range determined by the University.
Perchloric Acid: Special hoods equipped with a stainless steel or PVC duct and properly timed water wash down system. The wash down system must be used following each use of the acid hood. Using perchloric acid in a general lab fume hood may cause the acid vapors to settle onto the ductwork and create explosive perchlorate crystals. Serious injury or fatality may result to hood users or maintenance staff if the acid crystals are exposed to vibration and detonate.
Polypropylene (Acid Resistant): Dilute acids may be used at room temperature in most fume hoods, but if you are performing acid digestion, heating, or working with concentrated acids such as: HF, Aqua Regia, Nitric Acid, Piranha Solutions, etc., acid resistant hood and ductwork is required. Strong acids are corrosive to the duct work found in general lab fume hoods. Fume hoods constructed from polypropylene material are long-lasting and designed to resist harsh chemicals for years.
Walk-In: Equipped with a floor-mounted design, walk-in hoods specialize in exhausting chemicals that are used alongside large laboratory equipment. When using a walk-in hood, close the bottom sash to the floor and only raise the top sash to EHS’s designated working height. Do not obstruct the area at the face of the hood.
Ductless Filtered: Designed to remove potential hazardous fumes and vapors from the work area as the exhausted air passes through absorbent material, such as activated charcoal. Occasionally, the EHS department is asked to approve purchases of ductless, filtered fume hoods for use in research labs. We do not recommend ductless fume hoods. We do not believe ductless fume hoods provide reliable protection against chemical exposure, and think they may, in fact, give workers a false sense of security.
The ductless hood's appeal is largely economic because it does not require the expensive ductwork that traditional hoods need to exhaust fumes to the outside. However, in practice these hoods require constant attention and, if not carefully selected, don’t provide adequate protection. In many cases, the filter is designed for specific chemicals and will not protect against the variety of current and future chemicals used in a typical research university lab. The problems associated with breakthrough and with desorption of vapors from the absorbent material plague ductless fume hoods. Departments would also face expenses to change charcoal filters and to dispose of the old/used filters, which would be classified as hazardous waste. Therefore, depending upon the amount of use, annual maintenance costs to the owner could exceed several hundred dollars. Internal blowers for ductless hoods have also been known to be loud and prevent effective communication within the lab. Fume hoods, ducted or filtered, should only be installed in fully exhausted labs with minimum dilution ventilation rate of 6 to 8 air changes per hour. Ventilation codes do not allow general return or exhaust air from a laboratory space with a fume hood to be recirculated to classrooms or offices.
If a department is purchasing or owns a ductless fume hood, they must develop written laboratory standard operating procedures (SOPs) that must include the following:
Performance indicators are important safety devices that must be monitored regularly and are necessary for every chemical fume hood on Purdue’s campus. Each hood should be equipped with a monitoring device used to continuously measure air flow, and provide a visible reading to the hood user. The most common types of visual performance indicators found in Purdue’s laboratories are differential pressure manometers or gauges, and digital monitoring devices. It is important to the health and safety of the laboratory occupants to pay close attention to the digital or posted reading. A broken or missing performance indicator may result in lab occupants being unaware of air flow changes, and increasing the risk of chemical exposure. If you believe that your hood is missing a performance indicator, your current device has been damaged, or is out of range; please contact EHS immediately to have one installed.
Inclined Manometer: Detection system mounted in a slightly inclined position; capable of measuring pressure above and below atmospheric. EHS supplies the red gauge oil used to quantify the velocity pressure measured by a change in differential pressure from total atmospheric. Manometers found on Purdue’s campus will be one of the two types shown below. EHS will calibrate the device when air velocity measurements are inspected annually and record the reading on a sticker along with the date. A difference in ± 0.05 inches of water column of the recorded reading may indicate air velocity changes to your fume hood. Continuing to use a fume hood with high or low flow poses a risk to the user and lab occupants if the chemicals are not adequately contained and exhausted.
Examples of Inclined Manometers Dwyer KingMagnehelic Differential Pressure Gauge: Monitoring device that measures the difference in differential pressure across an orifice in the duct or between the laboratory and the fume hood exhaust duct. They are mounted on the outside of the hood and detect pressure differences from atmospheric, operating with an aneroid pressure gauge. EHS will calibrate the Magnehelic at the annual inspection of the fume hood and record the location of the pointer for the official reading along with the date. A difference in ± 0.05 inches of water column of the recorded reading may indicate air velocity changes to your fume hood. Continuing to use a fume hood with high or low flow poses a risk to the user and lab occupants if the chemicals are not adequately contained and exhausted.
Magnehelic Differential Pressure Gauge
Digital Monitoring Device: This device measures air velocity with a sensor and either has a display in feet per minute (fpm) and/or an alarm system, alerting users if the air flow is out of range. Electronic fume hood monitors/controllers measure either the air velocity or the sash position. Sash position is correlated to the air velocity at that sash opening area to determine face velocity. Digital monitors will display velocity on a screen, while some only contain an alarm system and is color coded accordingly:
Digital Monitoring Device Color Codes Red Yellow Green ALARMIf your fume hood control device is going into alarm mode please contact EHS so we can assess the air velocity of the fume hood. A EHS representative will determine if the air flow is within the recommended range and either submit a work order for repair or suggest that the digital monitoring device be calibrated. If a monitoring device is not reading accurately and needs serviced, it may alarm even if the air velocity is within the safe zone. Calibration of digital monitors is serviced by the designated Zone Maintenance to your area by submitting a Request for Services, 18A work order.
Examples of Digital Monitoring Devices Fisher Scientific Phoenix Controls Labconco KewauneeEvery chemical fume hood on Purdue’s campus is routinely inspected once per year by EHS’s Industrial Hygiene Technician as a protocol to the University’s health and safety program. Upon completion of the hood inspection, EHS will record:
This information will be labeled on a yellow sticker and placed at the indicated approved working height related to that face velocity measurement. Users should raise the sash to the working height indicated by the black arrow on the label when operating the hood. Hood operators may raise the sash above this point for equipment set-up only. Do not manipulate chemicals or run experiments with the sash open above the designated working height. This sash height is specifically determined to contain and exhaust chemicals, and is necessary for your overall safety. Additionally, a horizontal sash sticker will be placed on the front of the hood if horizontal panels are utilized. All chemical fume hoods should also be labeled with a yellow lab hood operating procedures sticker specific to general and high performance fume hoods.
Standard Fume Hood Operating Procedures
General Use: 80 fpm ≤ FV ≤125 fpm
Storage Only: FV < 80 fpm or FV > 125 fpm
High Performance Fume Hood Procedures
General Use: 70 fpm ≤ FV ≤100 fpm
Storage Only: FV < 70 fpm or FV > 100 fpm
Defined by the American Society of Heating, Refrigerating and Air-Conditioning Engineers; this published standard specifies a quantitative test procedure for evaluation of a laboratory fume hood.
EHS or a third party independent fume hood professional will conduct ASHRAE 110 testing to determine adequate containment As Installed (AI) or As Used (AU) methods in accordance with the published ASHRAE 110 Standard 110-. This practice is generally conducted at EHS’s discretion; typically for fume hoods at maximum capacity, complex/special cases, or newly installed or relocated fume hoods. This procedure consists of extensive smoke tests, face velocity and cross draft measurements, tracer gas containment using sulfur hexafluoride (SF6), computer graphing of measurable SF6 inhaled by a positioned mannequin in parts per million (ppm), and a general performance report. If you have safety concerns regarding the containment of chemicals or air flow patterns of your fume hood, please contact the Industrial Hygiene section of EHS to discuss if your hood would be a good candidate for further testing.
Before using a fume hood: Verify it has been inspected within the last 12 months, airflow is sufficient, the lights are working, side panels are intact, and the hood performance indicator is in good standing.
Personal Protective Equipment (PPE): Must be worn in accordance to your lab’s hazard assessments including: lab coat, safety glasses/goggles, gloves, aprons, and the minimum lab PPE required in the CHP (Chemical Hygiene Plan).
Poorly placed materials on the work surface of the fume hood increases the risk for chemical exposure because hazards are not efficiently exhausted out of the hood. The first photo indicates the user does not have material at least 6” inside the hood and the hazardous chemicals are near the breathing zone. The second photo is an improvement of the first, but half-way inside is still not the optimal position for exhausting fumes. The best placement of material displayed in the third photo is approximately 3/4 inside of the hood, where chemicals can immediately be exhausted out the back and through the top duct work. Keep in mind that placing materials more than ¾ inside the hood can block air flow to the back baffles.
Never use a fume hood while in alarm mode. By muting the hood alarm you may be ignoring a possible malfunction with either the air flow or unsafe sash height. When a hood is alarming, lower the sash, and allow the fume hood to properly contain and balance the air velocity. Report continuing malfunctions or power failures to your designated Zone Maintenance crew or the Industrial Hygiene section of EHS.
Do NOT use “Storage Only” hoods for chemical use. Fume hoods posted with a Storage Only sign indicate the air flow is insufficient for toxic chemical work and may only be used for storing materials or closed waste containers.
Post-pone all experiments and close open containers while hood repairs are being made. Once a work order is placed to Zone Maintenance by either your building deputy or EHS’s Industrial Hygiene section, a sign will be posted on the fume hood stating the hood is not safe to use and repairs are in process. Failure to relocate or end experiments while repairs are in process poses a health and safety risk to the lab as well as maintenance workers. During the repair process, fume hoods do not provide adequate ventilation for open chemicals.
Do NOT lean into the fume hood. It is unsafe for lab users to insert their body or head inside the hood, beyond the front sash. Leaning inside the hood positions contaminants in the breathing zone of the user ad disrupts air flow. This also increases the risk for chemicals spills and accidents. Only extend properly protected hands and arms into the hood and keep sash heights as low as possible, or even completely closed, always making sure the sash is between you and your work.
Do NOT use a fume hood for:
If you have any questions or comments about your chemical fume hood, contact someone from Radiological and Environmental Management's Industrial Hygiene section.
To improve safety in the science classroom, educational facilities should utilize Fume Hoods and Air Cleaners. Fume Hoods, such as Ductless Fume Hoods or Exhaust Hoods, provide the first layer of defense against harmful fumes and particulate created from experiments, demonstrations, or studies. Chemistry Fume Hoods can also help protect from other hazards such as chemical or thermal burns and chemical adsorption. Air Cleaners provide a secondary safety control in the science classroom by filtering airborne pollutants and microorganisms overall improving the classroom or lab air quality.
Fume Hoods provide a vital safety control for a variety of purposes in the science classroom and higher education laboratories including:
• Chemistry demonstrations
• Observing students performing chemistry experiments
• Evaporating solvents or using solvents/adhesives
• Biological applications and studies
• Microscopy
• Slide preparation
Fume Hoods used in an educational setting must follow regulations set by the government and educational associations including OSHA, the university or school safety board, and the National Science Teaching Association (NSTA). Adhering to strict safety guidelines helps optimize fume hood performance in order to help improve safety in the science classroom.
Occupational Safety and Health Association, OSHA, regulates workplace exposure of harmful substances but these standards also apply to schools for faculty and student safety. For all chemical labs, OSHA has Standard 29 CFR 1.910. offering guidance on proper chemical handling and safety (OSHA, ). This standard suggests creating a chemical safety plan, ensuring proper ventilation, installing proper engineering controls or fume hoods, and utilizing PPE (OSHA, ). Also, certain chemical fumes pose more serious health risks and require lower thresholds of exposure to reduce potential harm. Lab safety managers need to be aware of the chemicals in use, association exposure limits, and methods of reducing exposure. Refer to OSHA’s Permissible Exposure Limits – Annotated Tables for the legal exposure limit for each chemical (OSHA, n.d.).
Universities set their own fume hood safety requirements and certification process. For example, Stanford requires all fume hoods to have an average face velocity of 100 FPM and a minimum of 70 FPM at any time (Stanford, n.d.). Also, Stanford has a clearly defined Laboratory Fume Hoods Performance Criteria and Certification Protocol (Stanford, ). This extensive document details the certification process and requires annual fume hood certification. Contact your University’s safety officer for institution-specific guidelines on fume hoods.
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The National Science Teaching Association (NSTA) offers science educators and professionals best practices and safety guidelines for teaching science. For fume hoods, NSTA suggests using equipment that has been inspected following the National Fire Protection Association (NFPA) 45 Standard (Roy, ). The NFPA 45 Standard requires fume hoods to provide continuous ventilation, be constructed of a material that meets chemical and application requirements, and use an airflow device to ensure proper ventilation (NFPA, ).
Safety recommendations and guidelines vary by the educational institution but mainly educators can improve safety in the science classroom and proper fume hood operation by following these 10 tips.
1. Always test that the fume hood is working properly before use (Wright State University, ).
2. Notify the safety or lab manager if airflow suddenly changes or if the fume hood is not working properly (Wright State University, ).
3. Always use appropriate personal protection equipment (PPE) such as goggles, gloves, and lab coats (Wright State University, ).
4. Never stand inside the fume hood or place your head inside (Wright State University, ).
5. Clean up spills right away (Lab Manager, ).
6. Review a chemical’s Material Safety Data Sheet (MSDS) to ensure you are using the proper filter and fume hood type for the application (Wright State University, ).
7. Never use the fume hood for storage of chemicals (Wright State University, ).
8. Keep objects at least 6 inches inside the fume hood to optimize proper fume extraction (EHS UC Berkeley, ).
9. Use the proper sash placement and keep the sash closed when not in use (Wright State University, ).
10. Test fume hoods periodically for proper airflow and operation (Wright State University, ).
Improving the overall classroom air quality can provide many benefits to the students and staff. Not only does it help reduce exposure to harmful substances but, studies have shown that with increased air changes and ventilation, students have improved test scores, concentration, and overall academic success (Gout et al.,). Also, improved indoor environmental quality (IEQ) helps reduce disease transmission in turn reducing healthcare costs, absenteeism, and illness (Gout et al.,). Similarly, school staff and faculty will feel reassured with extra respiratory protection leading to improved morale and reduced absences.
Science class safety can be vastly improved by utilizing proper engineering controls that help improve air quality. Fume Hoods provide the vital first layer of defense against exposure to harmful fumes and particulate. Depending on the application and chemicals used, fume hoods are available as a ductless design that filters out contaminants and recirculates the air, or as an exhaust design that externally ducts fumes and particulate. Air Cleaners offer a secondary control for airborne particles, germs, and other microorganisms.
Ductless Fume Hoods provide fume containment and extraction by removing most of them from the airflow and releasing the filtered air back into the surrounding room. The ductless design removes the need for ductwork and make-up air in turn reducing installation cost and time.
Best Use: Science experiments and demonstrations that emit particulate and/or fumes. Best for use with chemicals that are easy to filter.
Benefits:
• Compact and portable
• Easy to install
• Long-lasting filters
• Reliable operation
• Clear construction options available ideal for classroom demonstrations
Widths: 12”, 18”, 24”, 30”, 40”, 50”, 60”, and 70” (Custom widths available)
Filters Available: HEPA Filter [up to 99.97% efficiency on particles 0.3 microns and larger], ASHRAE Filter [up to 95% efficiency on particles 0.5 microns and larger], Activated Carbon, and specialty-blended filtration [i.e. acid gas, mercury, aldehyde, and ammonia]. (Dual filter set-up available for applications that emit both fumes and particulate)
Approximate Airflow & Inlet Velocities by Model
Model Airflow* Inlet Velocity (CPF + HEPA)** Inlet Velocity (CPF + Activated Carbon)** 12” & 18”* Up to figure, airflow may vary depending on filter media, **CPF = Carbon Pre-Filter
Exhaust or Ducted Fume Hoods provide fume control by directing fumes into the ductwork and releasing the air outside of the building. Exhaust fume hoods offer the best protection for volatile chemicals with noxious fumes. Please note: The safety manager or end user must refer to local, state, and federal guidelines for external ducting to ensure compliance.
Best Use: For chemical use especially ones that have a low odor threshold, are hard to filter, or produce noxious fumes
Benefits:
• Includes a powerful in-line fan with variable speed control
• Made of all chemical resistant materials
• Continuous fume removal
• Reliable operation
Widths: 24”, 30”, 40”, 50”, 60”, and 70” (Custom widths available)
Air Volume: 240 – 700 CFM (approximately)
Ambient Air Cleaners provide a secondary engineering control that helps remove airborne contaminants and particles from the air flow. These systems can be mounted on the ceiling, the wall, a table, or on a fume extractor stand (not included). Sentry Air offers two variations depending on the airflow needed and the size of the room.
Best Use: General room air filtration
Benefits:
• Low maintenance
• Easy-to-install
• Powerful airflow
Main filters available: HEPA Filter [up to 99.97% efficiency on particles 0.3 microns and larger], ASHRAE Filter [up to 95% efficiency on particles 0.5 microns and larger], Activated Carbon, and specialty-blended filtration [i.e. acid gas, mercury, aldehyde, and ammonia].
Dual-Stage: MERV 8 pre-filter and MERV 15 bag filter
For added protection against diseases and microorganisms, the GermKiller UV Air Sanitizer helps cleanse the air of contaminants using powerful UV-C lights. This system works by drawing ambient air into the system, filters out large particles with a pre-filter, and processes the air with two UV-C bulbs. The UV-C light deactivates microorganisms and releases the cleansed air back into the surrounding room.
Best Use: Help prevent disease or microorganism’s transmission
Benefits:
• Easy-to-install – no ductwork required
• Adjustable fan speed
• Deactivates DNA in microorganisms
• Four-way louvre helps direct outgoing airflow
Air Volume: 300, 375, or 450 CFM
• Laboratory Fume Hoods
• Rotary Evaporator Fume Control
• COVID-19 Air Filtration Solutions for Schools
• 5 Air Quality Tips to Improve Work Efficiency
EHS UC Berkeley. (, October). Proper Use of a Fume Hood Video. Video retrieved from https://youtu.be/A4AHxLnByts
EPA. (, July). What is a MERV rating? Indoor Air Quality (IAQ). Retrieved from https://www.epa.gov/indoor-air-quality-iaq/what-merv-rating
Gout, Elise; Modaffari, Jamil; Rosenthal, Jill; Snover, Tara. (, August). School Air Filtration and Ventilation Strategies To Improve Health, Education, Equity, and Environmental Outcomes. Center for American Progress. Retrieved from https://www.americanprogress.org/article/school-air-filtration-and-ventilation-strategies-to-improve-health-education-equity-and-environmental-outcomes/
Lab Manager. (, September). 5 Steps to Using a Fume Hood. Lab Health and Safety. Retrieved from https://www.labmanager.com/lab-health-and-safety/5-steps-to-using-a-fume-hood-
NFPA. (). NFPA 45 Standard on Fire Protection for Laboratories Using Chemicals. Retrieved from https://link.nfpa.org/free-access/publications/45/
OSHA. (, May). . Occupational exposure to hazardous chemicals in laboratories. Code of Federal Regulations. Retrieved from https://www.ecfr.gov/current/title-29/subtitle-B/chapter-XVII/part-/subpart-Z/section-.
OSHA. (n.d.). Permissible Exposure Limits – Annotated Tables. United States Department of Labor. Retrieved from https://www.osha.gov/annotated-pels/table-z-1
Roy, Ken. (, November). Lab Safety and the ‘Dirty Dozen’. National Science Teaching Association. [Web log post]. Retrieved from https://www.nsta.org/blog/lab-safety-and-dirty-dozen
Stanford. (, November). Laboratory Ventilation Management Program Appendix 10.2.1. Stanford Environmental Health & Safety. Retrieved from https://ehs.stanford.edu/manual/fume-hood-testing-and-performance-standards
Stanford. (n.d.) 3.10 Fume Hood Construction, Installation & Performance. Stanford Environmental Health & Safety. Retrieved from https://ehs.stanford.edu/manual/laboratory-standard-design-guidelines/fume-hood-construction-installation-performance