December 11, 2019 by Dulce Lienau
The hoods are a type of ventilation system with the primary function of protecting the user from exposure to chemical vapors, gases, dust and aerosols. Fume hood also function as physical barriers between reagents and the laboratory, offering protection against inhalations, spills of hazardous substances, reactions and fire.
A typical Fumehood bell has a box-shaped structure with a mobile window. Experiments are carried out inside the hood that is constantly and safely ventilated, usually by fans and ducts. Chemical vapors are extracted and diluted many times in the atmosphere making them harmless to human health. If there are environmental concerns, a treated extraction system can be installed to remove most of the vapors from the external air stream.
The Low hood works by maintaining negative air pressures inside the cabin and thus preventing the escape of any air particle outwards. The speed at which the air enters the hood is very important to ensure the safety and effective operation of the equipment, since this is how the protective barrier is created that will not let any of the contaminated air inside. High speeds can generate turbulence that will allow indoor air to escape, but low speeds may not be enough containment.
In Lowhood, a frontal flow rate between 0.3m / s (60 feet per minute) and 0.5m / s (100 feet per minute) is recommended, however, it is important to review the safety regulations applicable in your area.
Types of extraction hoods
Table extraction hoods, for general uses.
Distillation hoods: It is characterized by having a very low base, which translates into a large workspace, which allows large distillation equipment to be installed inside the cabin. Its other characteristics are very similar to standard bells.
Bells for perchloric acid: Perchloric acid reacts violently with organic materials, so these bells require incorporating a washing system in order to prevent perchlorate residues. The inner liners are made of acid resistant materials such as stainless steel and the corners are rounded for easy cleaning. All procedures that use this acid must be carried out in a hood of this type to avoid dangerous reactions when coming into contact with other substances.
Radioisotope hood: It is used to protect users from radioactive material. It has a special base to support the cabin made from lead. The interior is stainless steel and rounded corners.
Bells for acid digestion: They have special coatings made of highly acid resistant materials for example non-plasticized PVC; for complete acid digestion applications that need high temperatures, materials for example PVDF should be used. The front panel can be made of polycarbonate to resist scratches of hydrofluoric acid.
Floor bells: Used for applications that requires large devices. As the name implies, these bells are mounted on the ground and do not have a work surface, which makes it easier for cabin equipment to enter and exit.
Bells for demonstration: it has 4 glass sides and is commonly used for teaching, as it allows students to see the teacher's maneuvers from any angle.