Types of Fume Hoods in Laboratory-Accumax India

Fri Sep 17, 2021

Types of Fume Hoods

This is the most fundamental classification.

Ducted Fume Hoods: These are the traditional workhorses of the lab. They are connected to a ventilation system that pulls air from the hood and exhausts it outside the building. This is the safest and most versatile option for handling a wide range of hazardous, toxic, or odorous chemicals, as the contaminants are completely removed from the building's internal air.
- Pros: Highly effective for containing all types of chemicals, including highly volatile and corrosive ones. No need to monitor or replace filters.
- Cons: High energy consumption (expelling conditioned air from the lab), costly to install, and not portable.
Ductless Fume Hoods: Also known as recirculating fume hoods, these are self-contained units that do not vent air outside. Instead, they use a series of filters (typically activated carbon and/or HEPA filters) to remove contaminants before returning the "clean" air to the lab.
- Pros: Energy-efficient (doesn't exhaust conditioned air), lower installation cost, and portable.
- Cons: Limited in application. They are only safe for use with a specific range of chemicals that their filters are designed to handle. Filters must be regularly monitored and replaced, which adds to operational costs and can become a hazardous waste disposal issue. They are generally not recommended for highly toxic or unknown chemicals.

Within the category of ducted fume hoods, there are different designs based on how airflow is managed.

Constant Air Volume (CAV) Fume Hoods: The most common type of ducted fume hood. They maintain a constant volume of air being exhausted, regardless of the sash position. This means the face velocity (the speed of air at the hood's opening) changes as the sash moves.
- Conventional: The most basic CAV design. The face velocity increases as the sash is lowered, which can cause turbulence and interfere with experiments if the velocity gets too high.
- Bypass: An improved CAV design with an opening above the sash. As the sash is lowered, this "bypass" opens up, allowing air to enter through both the sash opening and the bypass. This helps maintain a more consistent face velocity, reducing turbulence.
Variable Air Volume (VAV) Fume Hoods: These are more sophisticated and energy-efficient. They use sensors to adjust the exhaust fan's speed based on the sash position.
- How it works: When the sash is lowered, the hood reduces the volume of air being exhausted, keeping the face velocity constant.
- Pros: Significantly reduces energy costs, as less conditioned air is removed from the lab.
- Cons: More complex and expensive to install and maintain.

These are designed for specific, high-risk applications.

Perchloric Acid Fume Hoods: Used exclusively for work with hot concentrated perchloric acid. They are constructed with a special non-porous material (like stainless steel with seamless welds) and have an integrated water wash-down system to prevent the buildup of explosive perchlorate salts.
Radioisotope Fume Hoods: Built for handling radioactive materials. They are often constructed with stainless steel to allow for easy decontamination and are designed to hold heavy lead shielding.
Acid Digestion Fume Hoods: Built with corrosion-resistant materials (like polypropylene) to withstand harsh acids, such as nitric, sulfuric, or hydrochloric acid.
Canopy Hoods: These are not for hazardous chemicals. They are designed to vent heat, steam, or non-toxic fumes from equipment like ovens or autoclaves. They lack a front sash and do not provide a containment barrier.