When choosing a fume hood, it is important to pick the right unit for the intended application. While some devices appear similar in construction, not all of them protect workers from chemical threats. Fume hood buyers must also make sure that the unit they choose meets their required space, size and material specifications. Most importantly, buyers must understand their ventilation needs and how a fume hood unit meets that demand. Before committing to a system, it is critical that buyers consult with a professional to verify that a unit can perform adequately. Ten important tips can help fume hood buyers choose the right unit for their laboratory or work environment. The following information is taken from RDM.
1. Understand How Fume Hoods Work
Laboratory fume hoods provide ventilation in areas where workers handle harmful, airborne chemical emitting substances. The laboratory hood captures and filters the airborne contaminants, preventing workers from inhaling dangerous toxins. The units draw airborne particles away from operators, minimizing contaminant contact. A blower pulls air out of the room and through exhaust ductwork creating pressure, which ventilation specialist measure in velocity. Special components allow operators to control the airflow. The laboratory hood also combines the contaminants with air to mitigate environmental damage as the toxins disperse.
2. Decide on the Hood Type
Most fume hoods are conventional or bypass models and provide fixed or dynamic air volume. Conventional hoods come equipped with an interior baffle and moving front sash and are the most cost-effective option. By-pass hoods maintain a constant velocity, even when operators adjust the sash. The units allow lab personnel to work without affecting their procedures and represent most available units on the market.
3. Determine Special Applications
Some laboratory work requires special hood components. Perchloric acid hoods contain chloric acid and incorporate a system to wash the toxins off the laboratory hood. Operators use radioisotope hoods that conform to radioactive material handling laws by supporting radioactive shielding and incorporating special charcoal filters. To work with oversized projects, laboratory workers use distillation or walk-in hoods, making sure not to stand inside the unit while toxins are released into the air.
4. Beware of Fume Hood Look-alikes
Air-moving units can protect things other than humans but appear physically similar to laboratory fume hoods. Canopy hoods remove steam from large areas. For environments that produce gases and floating materials that are heavier than air, operators use downdraft hoods. Ductless carbon-filtered enclosures use special filters to absorb potentially lethal airborne compounds and introduce fresh air into the laboratory or work area. Biological safety cabinets contain dangerous airborne particles and sometimes introduce fresh air into the work area. Clean benches – often used by electronics and pharmaceutical manufacturers - blow air over a flat area to prevent damage to merchandise but do not protect users from hazardous materials.
5. Figure out the Specifications
It is important to choose a hood proportionate to the intended work area; the required workspace dictates the interior fume hood width. Yet, manufacturers often provide the external width in their data sheets. Fume hood buyers must also consider the compounds that they will ventilate and choose the corresponding liner. The material used to construct the hood housing must also stand up to the chemicals that will pass through. Some work applications require transparent splash sashes, while others require an explosion proof hood. The National Electric Code provides details about how certain components prevent sparks that lead to explosions.
6. Determine the Lighting and Accessibility Needs
When an application requires lighting, power supply lines should run on the hood if possible, or on the attached work area. Hood lighting should have vapor-proof or explosion-proof characteristics. If the service valves rest inside the unit, they should resist corrosion and offer easy access, and electrical wiring should not contact vapors.
The Americans with Disabilities Act requires employers to provide equipment with accessible features. Hood dimensions must facilitate wheelchair use, and alert systems must produce enough sound so that partially deaf individuals can hear the alarm.
7. Estimate the Desired Performance
When choosing a fume hood, buyers must consider how much contaminants will pass through the system. The units should reduce user containment contact considerably, using the correct air velocity suited for specific compounds. Regulatory agencies require employers to limit contact with these materials and designate how much exposure workers can safely endure. It is important not to produce too much velocity, as this can prevent the hood from properly filtering air. “Industrial Ventilation, A Manual of Recommended Practice” clarifies this principle.
8. Evaluate Air Movement Specifications
The most important part of the fume hood is the blower. Many enterprises prefer centrifugal blowers due to their efficiency and quiet operation. More cost-effective, but less efficient, units house the blower in the hood. When choosing blower size, buyers must determine how much air the unit will move after connecting it to the ductwork. The required air volume is equal to the sash opening size times the average required velocity. The American National Standards Institute (ANSI) mandates that fume hoods alert operators when the unit does not meet this requirement. For toxic materials, fume hood systems may also filter the air that releases into the environment.
9. Consider the Unit Features
Buyers must choose a base cabinet and work surface, which the fume hood rests on, that serves the desired application. Local building codes regulate the materials used for hood ductwork. By-pass locks and sash stops can limit exhaust demand and conserve internal temperatures. Sash alarms encourage users to keep the sash at a designated setting. Some fume hoods incorporate fire-extinguishing systems. Each time that operators make a change or addition to a fume hood they should retest the entire system.
10. Decide Where to Place the Unit
Fume hoods change the airflow in a room. While buyers make some choices, it is imperative to consult with a ventilation expert to confirm all decisions. Details such as the equipment that will reside in the room with the fume hood changes how air will move through the room. The hood must also rest where foot traffic, other hoods and ventilation systems will not disturb airflow. If possible, the fume hood should also rest one foot away from any wall in the work area to allow room for servicing.
There are many factors to consider when purchasing a fume hood. The unit must suit the intended purpose and provide protection from dangerous substances. To do this, buyers must consider the work that users will complete using the units and make sure that the fume hood has the power to provide the required ventilation. Understanding these criteria helps buyers make better decisions, and prepares them to discuss their needs with qualified ventilation professionals.