Laboratory Ventilation

2 Types of Laboratory Hoods  Constant Volume  Conventional  By-Pass  Auxiliary-Air  Reduced Air Volume  Variable Volume  Special Application  Perchloric Acid  Radioisotope  Distillation and Walk-In

Laboratory Ventilation3 Constant Volume Hoods Conventional Hoods: This is a basic enclosure with an interior baffle and movable front sash. Closing the sash increases the face velocity of the air through the sash opening. By-Pass Hoods: These are designed with by-pass openings above and below the sash that allow a constant face velocity when the sash is closed. By- pass hoods comprise the majority of hoods on the market today.

Laboratory Ventilation4 Constant Volume Hoods (Contd.) Auxiliary-Air Hoods (AKA: Induced-air, Balanced-air, Make-up air). This is a variation of the By-pass hood which can provide up to 50% of the exhaust air from the outdoors through a separate intake. Reduced Air Volume Hoods: Another variation of the By-pass hood, this enclosure uses a by-pass block to partially obstruct the by-pass opening above the sash. This results in less air volume than other same-sized hoods, which means they can use smaller blowers.

Laboratory Ventilation5 Variable Volume Hoods Variable volume hoods vary the amount of room air exhausted while maintaining the required face velocity using two methods. The methods are:  utilizing a movable damper that opens and closed based on airflow and sash position.  varying blower speed to meet air volume demands.

Laboratory Ventilation6 Special Application Hoods Perchloric Acid Hoods: These hoods are dedicated for use with perchloric acid only, due to the possibility of an explosion if contact with organic matter occurs. Can be made of SS 316, Type-I PVC, or ceramic-coated material. A washdown system is required to prevent the accumulation of highly reactive perchloric salts. Radioisotope Hoods: Liner materials, such as SS 304 or lead, need to be impervious to radioactive particles. These hoods should have HEPA or charcoal filters incorporated in the ductwork to trap radioactive particles in the exhaust air. Distillation and Walk-In Hoods: These hoods are designed to accommodate large lab equipment that can be permanently installed in the hood or mounted on wheels to allow it to be rolled in the hood for use.

Laboratory Ventilation7 Other Laboratory Enclosures  Canopy Hoods  designed to remove steam, heat or odors from bulky apparatus such as ovens or steam baths. Not for hazardous substances.  Downdraft Hoods  blower mounted below the work area. Used for gases with a greater density than air and particulates.  Biological Safety Cabinets  designed to contain viruses and other microbes. Used with HEPA filters to trap particles.

Laboratory Ventilation8 Other Laboratory Enclosures (Contd.)  Clean Benches  force room air through a HEPA filter and over a work surface. Designed for product protection only.  Glove Boxes  provide a physical barrier from contaminant.

Laboratory Ventilation9 Hood Comparison Chart