What are Fume Hoods?

A fume hood is a ventilated enclosure in which harmful volatile chemicals can be used. Fume hoods are a primary means of safety from hazardous fumes, vapours and powders. They are not storage cabinets. Operators should be trained on the proper use of the fume hood or vented enclosure and encouraged to use it properly.

When purchasing a fume hood, there are several questions you need to ask:

• What size fume hood do I need? How much space do I have?
• Am I putting the fumehood on an existing countertop?
• What chemicals will I be working with in the fume hood?
• Is personnel protection or sample protection more important?
• What is the face velocity needed for the experiment?
• Will you be heating anything in the fume hood?

NOTE: Look for fume hoods that meet both SEFA and ASHRAE standards.

4 MAIN TYPES:

DUCTED FUME HOODS: a total ventilation system that includes a series of ducts, blowers and filters running through the entire building.

• Conventional Ducted Fume Hood: have a constant air volume. Face velocity is inversely proportional to the sash height.
• Variable Air Volume Ducted Fume Hood: maintains 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.

DUCTLESS FUME HOODS: a single enclosed unit that requires no duct work or fixed installation. Removes fumes, vapors and particles from both samples and personnel by filtering air through a combination of HEPA and carbon filters and exhausting them safely back into the lab air.

• Benchtop Ductless Fume Hood: can be placed on rolling carts and moved around the lab, or permanently mounted to a bench. Personnel are protected as the fumes are drawn back, up and away while clean air is recirculated back into the lab.
• Downflow Workstations: pushes air down. Air containing powders or chemicals with high molecular weights are swept into the base of the workstation, protecting personnel by removing it away from their breathing zone.

BIOLOGICAL SAFETY CABINETS: provides effective containment for personnel working with human pathogens. There are 3 Classes:

• Class I: pulls air away from personnel and after going through a HEPA filter, is vented into the atmosphere. Protects only personnel, not samples.
• Class II: used when working with microorganisms in containment levels 2, 3, and 4 labs. They are divided into 2 types: A and B, determined by their construction, airflow velocities, patterns and exhaust systems. Protects personnel, samples and the external environment.
• Class III: have both HEPA-filtered supply and exhaust air and are totally enclosed and gas tight. Work is performed using long sleeved gloves. Cabinet is kept under negative pressure of at least 120Pa while an exterior exhaust system maintains airflow. Protects personnel, samples and the external environment.

LAMINAR FLOW HOODS: provides 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.

• Horizontal Laminar Flow Hoods: brings in external air through a pre-filter and HEPA filter, then pushes it in horizontal lines outward from the back of the hood workspace protecting samples. Not intended to protect personnel.
• Vertical Laminar Flow Hoods: moves 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. Protects samples, not intended to protect personnel.
• PCR enclosures: designed specifically to provide a Class 5 work space for PCR experiments by moving HEPA filtered air downward. UV light eliminates DNA and RNA contaminants.