Note: Fume hoods are also called laboratory hoods. However, biological safety cabinets are often mistakenly called “hoods,” they are cabinets.
What is the difference between a laboratory and any other room at Tufts?
There are three primary differences: containment, decontamination and ventilation. Containment is defined as a room designed to prevent the spread or release of hazardous airborne materials outside the room by special walls, floors, ceilings and doors under normal and emergency conditions such as fire. Decontamination is the ability to remove hazardous materials from the surfaces of the room, supplies and equipment including chairs and desks. Ventilation is the planned supply and removal of air from a space or room. Laboratory ventilation accomplishes four objectives:
The laboratory operates such that air flows into the laboratory from adjoining areas such as the hallway. More air is removed from the room than is supplied.
All of the air that enters the laboratory is exhausted and is not recycled or allowed to reenter the building also called 100% exhaust.
The amount of air exhausted results in 4 to 12 complete air changes per hour which dilutes any air contaminants produced during experiments on the open bench or from equipment and other operations outside the fume hood.
Much if not all of the air is exhausted through fume hoods which are designed to contain hazardous air contaminants under normal and emergency conditions.
What experiments can be conducted on the open bench and what needs to be moved into the fume hood?
The simple answer is that any procedure that results in the production of air contaminants that are toxic, flammable, corrosive, irritating or have a nauseating odor should be conducted in a fume hood.
A more detailed answer is written in the section Guidelines for Fume Hood Use on page 24 of the Tufts Research and Laboratory Safety Guide and provides more specific guidelines for toxic, corrosive and irritating chemicals:
Use a fume for handling any amount of powder, liquid or gas with a TLV or PEL (concentration in air that is safe) of less than 5 ppm or 0.2mg/M3.
Also if the chemical has an Oral Lethal Dose (50%) (oral LD50)in rodents of 10 mg/kg ( this would be a poison).
This information is located on the Safety Data Sheet which each chemical user should review before handling any chemical.
Use a fume hood when handling more than 500 mL of any liquid or gas with a TLV or PEL between 5 and 50 ppm or powders between 0.2 and 2 mg/M3. A chemical will evaporate or become airborne if it has a vapor pressure of 25mmHg at room temperature (20C) or if it is heated or sprayed as a mist.
This information is located on the Safety Data Sheet.
In addition the following rules should be followed when using fume hoods:
Do not store chemicals or chemical wastes in a fume hood. Move chemicals in and out as they are used. (TU Chemical Hygiene Plan).
Do not store equipment in a fume hood; the larger the equipment the more air turbulence and chance for air to be pushed out the sash into the laboratory.
Perform operations at least 6 inches in from the sash. A tape will remind the user of where 6” is.
The user should check to make sure the fume hood has been tested within 12 months.
The user should work with the sash at the safe height where the airflow is 100 feet per minute +/- 10% (90-110). Excessive face velocity creates turbulence and leakage into the laboratory.
The user should watch the flow indicator at all times to ensure that air is being sucked into the fume hood-this could be a mechanical, electrical or simple piece of Kimwipe (thin paper) hanging from the sash!
All equipment is raised at least 1 -2” above the work area of the fume hood to allow airflow under the piece of equipment.
Never install shelves in a fume hood. If ventilated chemical storage is needed, use a ventilated storage cabinet.
Perform operations while viewing through the glass sash. This provides secondary eye and face protection and maintains correct airflow through the opening.
Never place your head into the fume hood unless it is empty of ALL equipment and chemicals.
Prevent liquid spills into the cup sink in the fume hood if one is present. Seal drain with temporary cap to prevent release of chemicals into drain system.
Biological Safety Cabinets are NOT fume hoods and should not be called “hoods” (it causes much confusion). The TU Biological Safety Manual discusses the selection and use of Biological Safety Cabinets.