One of the primary safety devices in laboratories where chemicals are used is the laboratory fume hood. A well-designed fume hood, when properly installed and maintained, can provide a substantial degree of protection for the researcher, provided its proper use and limitations are understood.
Laboratory fume hoods are designed to protect workers by containing and exhausting harmful or toxic fumes, gases, or vapors emitted by chemicals used in the hood. A typical fume hood has an exhaust blower mounted so that air from the room is pulled into and through the hood, creating directional airflow. The “pull” at the hood opening is termed “face velocity” and is usually measured in feet per minute (fpm).
Proper face velocity of the hood is critical to the protection of the worker. Too little flow allows currents or disturbances in the laboratory air to overpower the hood and draw contaminants into the room. Too much flow can result in turbulence and eddies that also can lead to contaminants escaping the hood. Baffles and other aerodynamically designed components determine how air moves into and through the hood. Contaminants inside the hood are diluted with room air and exhausted to the outside via the hood’s duct system, where they are dispersed.
The volume of air exhausted by the hood depends on a number of factors, the most important of which are hood size and design. With the average chemical fume hood exhausting around 750 to 1,000 cubic feet per minute of conditioned air, you can see how hoods put a large load on the laboratory’s heating, ventilating and air-conditioning (HVAC) system, thus impacting operational costs.
Chemical fume hoods are inspected annually by the Office of Environmental Health and Safety. Labels that indicate the sash height for adequate containment are affixed to the fume hood. All fume hoods are equipped with a magnehelic gauge or other continuous monitoring device to monitor the flow of air. Proper readings of the monitoring device can also be found on the inspection label.
What is the frequency of the inspections of your fume hood?
| Monthly | 12% |
| Quarterly | 12% |
| Every 6 months | 13% |
| Annually | 52% |
| Every two years or more | 5% |
| Not applicable | 1% |
| Don’t know | 5% |
It would be difficult to imagine a chemistry laboratory without at least one fume hood. Eighty-nine percent of respondents have a fume hood in their lab.
| Yes | 89% |
| No, but planning to purchase | 5% |
| No, and no plans to purchase | 6% |
Fume hoods are notorious for consuming expensive resources, particularly electricity and conditioned air that is vented to the environment along with volatile chemicals and other toxins.
A decade ago, low-flow hoods revolutionized the industry by reducing air throughput and related energy costs by 40 percent. More recently, ductless hoods changed the equation in favor of greater energy efficiency and cost savings.
Ductless fume hoods use activated carbon filters to remove toxins from the airstream. Unlike traditional hoods, which vent tens of thousands of cubic feet of heated or conditioned workspace air per day, ductless fume hoods return conditioned air to the lab. This translates to a significant drop in energy use and operating costs while protecting the environment. A ductless fume hood requires no ductwork, arrives fully assembled, and may be installed in locations where, barring a significant and expensive renovation process, a traditional fume hood could not.
| Conventional ducted fume hood | 60% |
| Benchtop ductless fume hood | 10% |
| Canopy ducted fume hood | 10% |
| Variable air volume ducted fume hood | 8% |
| Down flow workstation | 6% |
| Portable ductless fume hood | 5% |
A great deal of innovation has occurred in fume hoods during the last decade. Fume hood manufacturers have incorporated interesting innovations. Today’s hoods have expanded viewing areas and improved counterbalance systems that assist in raising and lowering the glass window. Fume hood vendors have also addressed ergonomics, an important consideration, since many organic chemists practically “live” inside their hoods. Hood entrances are now slanted back, rather than outward, which makes them easier to work in for long periods. Sash designs have also improved, and some units now feature horizontal sliding panels.
Another interesting development is the “intelligent sash,” which closes when a motion sensor detects no movement in front of the hood for a specified time period, for example, when the operator walks away. This feature alone can reduce energy consumption by 70 percent.
Hood baffle designs have also undergone significant improvements, Baffles are cleverly angled, and even perforated, to allow for best airflow navigation to the exit point; that is, to reduce airflow residence time in the hood as much as possible. Today’s baffles are also easily removed for cleaning, which prolongs the service lifetime of the hood.
Most new fume hood purchases are for new laboratories, according to Environmental Health and Safety.
| Setting up a new lab/developing a brand new method | 38% |
| Replacement of aging fume hood | 32% |
| Addition to existing systems; increase capacity | 22% |
| Changing from the current type of fume hood | 4% |
| Other | 4% |
Fume hoods are installed in laboratories to protect workers from hazardous vapors generated by laboratory experiments. However, simply conducting these experiments in the fume hood does not guarantee adequate protection. What labs are doing when it comes to their fume hood specification and maintenance programs:
|
| Agree | Disagree |
| All fume hoods have been tested within the past year (see the next question for frequency of tests). | 90% | 10% |
| Test labels are properly affixed to the fume hoods tested. | 86% | 14% |
| Storage in fume hoods is kept to a minimum and care is taken to not impede proper airflow (According to EH&S - Minimize the number of objects stored in the hood – keep at least 50% of the working surface clear, if possible). | 92% | 8% |
| To maximize hood effectiveness and minimize personal exposure to toxic vapors or gases, our lab uses fume hoods in accordance with the operational guidelines (According to EH&S - The efficiency of a fume hood is very dependent on its functional status and on how it is used. Users must ensure proper operation of fume hoods by performing the proper maintenance checks before each use). | 97% | 3% |
Users should be aware of problems that may arise during fume hood specification and installation. Traditionally, laboratory furniture suppliers provide fume hoods as well. Although a few manufacture hoods that are standards-compliant, many still construct fume hoods as though they were simple boxes. Fume hood prices are often bundled with furniture prices, and that makes it difficult for the end user to make informed decisions.
Environmental Health and Safety provides the following wish list for potential fume hood buyers:
- Local installation and support for ducting, controller and exhaust blower
- Appropriate safety certifications
- Construction materials for specific application: for example, polymer inner liners for corrosive acids, ceramic work tops for high temperatures
- Local references for the supplier/installer
- Aesthetics and cost
Factors/features important to lab research respondents in their decision-making processes:
| Durability of product | 98% |
| Low maintenance/easy to clean | 98% |
| Performance of product | 97% |
| Safety and health features | 96% |
| Ease of use: ergonomic operation | 95% |
| Low operating costs | 90% |
| Total cost of ownership | 86% |
| Value for price paid | 85% |
| Warranties | 85% |
| Service and support | 79% |
| Availability of supplies and accessories | 74% |
| Vendor reputation | 68% |
| Past experience with product | 41% |
| Currently using vendor’s product | 21% |
Completed surveys: 354
