Lab Manager Magazine's Independent Guide to Purchasing a Fume Hood

Purchasing the correct fume hood for your laboratory is a very important, long-term decision and your choice in lab ventilation systems will affect future lab planning, flexibility and safety. This guide will introduce the four main fume hood types available. Read about each one and then proceed to LabWrench.com to check out all the latest models.

Ducted Fume Hoods

In the past, were the only option available to labs and account for only one component of a total lab ventilation system, which includes a series of ducts, blowers and filters running through the entire building. However, choosing the right fume hood enclosure for inside your lab space is very important.

Conventional Ducted Fume Hoods often describes the traditional, less elaborate fume hoods that have a constant air volume. Face velocity is inversely proportional to the sash height unless a by-pass is in place. The by-pass helps direct airflow and reduces the increase in face velocity as the sash closes. The by-pass enables the hood to have a more constant volume of exhaust air. This provides general protection to the lab worker.

Variable Air Volume Ducted Fume Hoods maintain a constant face velocity regardless of the sash position by employing a closed loop system that is constantly measuring and adjusting the amount of air being exhausted. In many hoods, inaccurate face velocities will sound audible and visual alarms, which in addition to the constant face velocity, greatly increase the protection of the lab worker. This also reduces the total volume of supply and exhaust air needed, which in turn lowers total energy costs.

Canopy Ducted Fume Hoods are typically used when the area that needs ventilation is too large to fit inside a regular hood. They are suspended above the work area. The lab worker is not protected well, as the fumes are often drawn right across the user’s breathing zone.

Ductless Fume Hoods

Ductless Fume Hoods are single enclosed units that require no duct work or fixed installation. They remove fumes, vapors and particles from both the experiment and the lab worker by filtering them through a combination of HEPA and carbon filters and exhausting them safely back into the lab air.

Benchtop Ductless Fume Hoods offer a very convenient alternative to traditional ducted fume hoods as they can be placed on rolling carts and moved around the lab as required, or permanently mounted to a bench. The lab worker is protected as the fumes are drawn back, up and away while clean air is recirculated back into the lab after being filtered.

Down Flow Workstations direct air in the opposite direction as most other hoods; they push it down. The air containing powders or chemicals with high molecular weights are swept into the base of the workstation, protecting the lab worker by removing it away from their breathing zone.

Portable Ductless Fume Hoods are designed to go anywhere science takes you in the field or for temporary hood needs in the lab. The lab worker is protected as the fumes are drawn back, up and away while clean air is recirculated back into the environment after being filtered.

Biological Safety Cabinets

Biological Safety Cabinets provide effective containment for lab workers working with human pathogens. There are three separate classes of BSC’s available: Class I, II and III; some with additional sub-class levels. These classes are designated by the National Sanitation Foundation.

Class I Biological Safety Cabinets have an un-recirculated airflow away from the lab worker that, after going through a HEPA filter, is vented into the atmosphere. They provide the lab worker adequate protection but do not protect the samples in the cabinet from contamination.

Class II Biological Safety Cabinets are used when working with microorganisms in containment levels 2, 3 and 4 labs. They are divided into two types, A and B, determined by their construction, airflow velocities, patterns and exhaust systems. They protect the lab worker, samples and the external environment.

Class III Biological Safety Cabinets have both HEPA-filtered supply and exhaust air and are totally enclosed and gas tight while work is performed using long-sleeved gloves. The cabinet is kept under negative pressure of at least 120 Pa while an exterior exhaust system maintains airflow. This protects the lab worker, the samples and the external environment.

Laminar Flow Hoods

Laminar Flow Hoods provide clean air via a HEPA filter to the lab bench space and a constant air flow out of the work area, which prevents surrounding room air from entering. The air flowing out of the hood also suspends and removes contaminants and particles creating clean air spaces.

Horizontal Laminar Flow Hoods bring in external air through a pre-filter, and HEPA filter then push it in horizontal lines outward from the back of the hood workspace. While this protects the samples from particle contamination, these hoods are not intended to protect the lab worker.

Vertical Laminar Flow Hoods move air down from the top of the unit in a vertical line through a HEPA filter to the bottom intake. A blower then pushes the air back up to a HEPA filter exhaust. While this protects the samples from particle contamination, these hoods are not intended to protect the lab worker.

PCR Enclosures

PCR Enclosures are designed specifically to provide a Class 5 work space for PCR experiments by moving HEPA filtered air downward. What makes them unique is a UV light that eliminates DNA and RNA contaminants.

Fume Hood Sponsors: