The primary form of protection from overexposure by inhalation in Witenberg science laboratories is fume
hoods. Laboratories are generally equipped with at least one negative pressure fume hood that pulls vapors of
hazardous chemicals away from the user. If the laboratory does not have a hood, then a negative pressure
glove box should be used or an appropriate respirator.

The CHP states that whenever exposure by inhalation is likely to exceed the threshold limits described in
the MSDS for that particular chemical, a fume hood should be used. Therefore, before using a compound
check the MSDS for that compound to determine whether it should be used exclusively in a fume hood. The
CHP also provides guidelines for threshold limit value (TLV) or permissible exposure level (PEL). If the
TLV or PEL is less than 50 ppm or 100 mg/m3 then the chemical should be used only in a fume hood.

Before using a fume hood, check to see that it is working properly. This can be accomplished by closing the
sash to within one inch of being completely closed and taking a small strip of tissue or Kimwipes and placing
it near the one inch opening. If the hood is working, the strip of tissue should be drawn into the hood
demonstrating negative pressure. If the strip does not show negative pressure, then inform the lab
supervisor to see if the room ventilation is turned on. The hoods do not work if the
room ventilation is not working. If the room ventilation is working and the hood is not, call physical plant
so a maintenance worker can check to see if a fan belt is broken or a circuit breaker has been tripped.

The hood performance can be greatly affected also by these factors:

1.  Objects obstructing the return ducts. In particular, often people store chemical in hood. This cluttering
     of the hood interferes with the air being pull from the back bottom portion for the hood. Remove
     unnecessary chemical and equipment and return them to their proper location.
2.  The position of the equipment or apparatus should be at least 6 inches back from the front sash. This
     can improve the capture rate by 1000 times.
3.  Positioning the sash in the down position greatly increases the flow rate through the aperture. It is
     strongly recommended that the hood sash be kept down whenever possible.
4.  Secondary currents created by portable fans, traffic in front of the hood, and wind conditions outside
     the building can push fumes into the room.
5.  Positioning of the baffle at the rear wall of the hood determines whether the air will be drawn form the
     top or bottom of the hood. This baffle plate should be in the down position for fumes lighter than air
     and when using a burner in the hood. The position of the baffle should be up for fumes that are
     heavier than air. Most hoods are set at the median position to draw moderately from both points.
     Only the Building Supervisor and laboratory supervisors are authorized to change the baffle position.

After you have checked the MSDS and find that you are not required to use a hood, the reagent may be
used in the open laboratory provided the room ventilation is working.