Fume hoods are enclosures that ventilate toxic gases, vapors, and fumes away from the working area. The fume hood's ventilation system is separated from the area or central HVAC system, with separate opening and piping infrastructure.
Due to its separate installation and working design, the vented toxic gases are not re-used with the HVAC ventilation system.
They maintain negative pressure air inside the hood by drawing air from outside the hood to into it. It effectively prevents air escape into the area, and instead, air escapes through the ventilation ducts into the environment.
The main aim of a fume hood is to protect its user from the gases used during the process. It is only designed to pull air away from the air or environment, and do not contain any temperature-affecting components or mechanisms, so inside environmental condition is not effected or changed.
In most designs, the enclosure has a working bench where the process occurs at an average person's working height, where they sit and perform the required process. On the upper side of the fume hood, a blower is installed to blow air away from the person's working area.
The air enters into the hood from the person's face side, flowing through the working area and exits from the upper side. Upon exiting, the air carry away any chemicals, fumes, and vapors in the working area.
Exhaust air flows through filters to prevent hazardous and toxic components from entering the environment. The airflow can be controlled according to the requirements by adjusting the blower speed.
A physical barrier between personnel and the processing
The use of toxic, reactive, and potent chemicals in pharma is common, and becomes more critical during the R&D and testing phase. Because these chemicals change their states and very often increase their reactive ability.
Additionally, chemicals in vapor and fumes states are more dangerous because they can be inhaled without being noticed.
Fume hoods provide a physical barrier between the process and humans, providing a safe environment for operators to deal with the chemicals.
The sash in the fume hood is a physical barrier between the work area and the operator. It is a transparent glass that moves vertically or horizontally, depending on the equipment design. The operator can adjust its position following safety while providing a clear view of the occurring process.
Some advantages of fume hood, include but are not limited
Prevents inhalation of chemicals
Spilling of chemicals in the laboratory or area of installation
Face velocity in pharmaceutical fume hoods
The main factor of the fume head's performance depends on the face velocity, which is the air drawn into the fume hood. Its velocity must be optimally selected for adequate ventilation and hood operation.
The recommended face velocity of the fume hood must lie in the range of 80 fpm and 120 fpm. However, these values can also differ from application to application. If face velocities of fume hoods deviate from these recommended values, it will disturb the airflow pattern and ventilation capability of hood, and must be rectified for optimum hood performance.
If the face velocity is too much, it can cause turbulence around personnel in the working area, drawing contaminants through the sash.
Meanwhile, lower face velocity cannot capture the required contaminants from the working area, and result in compromised performance. Operator movement and door opening/closing ( in the hood's area) will further worsen the fume hood's performance under too low face velocity.
To prevent effects from the outside world, face velocity must not deviate from standard values, by
· Carefully selecting the fume hood’s location
· It must be installed as far as possible from the source of airflow and disturbances, such as windows and doors.
Components of pharmaceutical fume hoods
Some standard components of fume hoods are mentioned below
Main Body
It is the main structure on which all the components are installed. Examples...
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