A hood or hood in laboratories are an effective means of capturing flammable, irritant, corrosive, carcinogenic vapors, etc. to prevent personnel exposures and avoid their dissemination in the laboratory atmosphere. When the hatch is down, the cab is also a physical barrier that protects the operator from hazards such as splashes, aerosols, fires, and minor explosions.
Fume hoods are a type of ventilation system with the primary function of protecting the user against exposure to chemical vapors, gases, dust, and aerosols. They function as physical barriers between reagents and the laboratory, offering protection against inhalations, spills of hazardous substances and fire.
A typical hood has a box-shaped structure with a movable window. The experiments are carried out inside the hood that is ventilated constantly and safely, usually by means of ducts. Chemical vapors are extracted and diluted many times in the atmosphere rendering them harmless to human health. If there are environmental concerns, a treated exhaust system can be installed to remove most of the vapors from the outside air stream.
It works by maintaining negative air pressures inside the cabin and preventing any air particles from escaping to the outside. The speed at which the air enters the hood is very important to guarantee the safety of the equipment. High speeds can create turbulence that will allow the air inside to escape, but low speeds may not be enough containment.
What should you keep in mind when using a fume hood?
- Place the work area more than 20 cm. behind the plane of the bell mouth. This practice helps reduce vapor concentrations by up to 90% at the cabin inlet.
- Do not put the head inside the cabin when pollutants are generated.
- Do not make sudden maneuvers during operations, as the internal flow of the cabin is destroyed.
- Remove the materials that are in the hoods and that will not be used in the process. Do not store chemicals or appliances in the hood. Chemicals must be in a safe and approved location.
- If you use heat generating equipment, place it at the bottom of the hood, in order to minimize convective currents in the interior flow.
- In the case of using devices or large volume containers, during an experiment, they should be placed on a secure platform with 5 to 7 cm legs. high that do not obstruct the air flow.
What should the environment of the hood be like when in use?
- Minimize the passage of people in front of the cabin.
- Keep the doors and windows closed, in case the laboratory has openings for air renewal.
- Do not block exhaust and / or ventilation openings.
- Fans or air conditioning should not directly affect the front of the hood. These equipments will not turn on when working in the booths.