Open doors, open windows, or portable fans
may compromise an efficiently designed ventilation system, according to McGriffen
(1985:39), creating drafts and wind currents that hamper the primary system. In
the case of inefficient ventilation however, alternative remedies should be implemented.
A well-designed exhaust hood effectively removes gases, vapors and fumes from
the workplace. Exhaust systems may include permanently installed or portable equipment.
In either case, air contaminants are contained at their source (i.e., local exhaust)
and are exhausted away from the worker and out of the work area. A well-designed,
well-maintained, and properly installed local exhaust ventilation system gives substantial
protection to workers, provided workers are aware of the unit's capabilities and
limitations ("Laboratory Fume Hoods," National Safety Council Data Sheet I-687-80).
If not correctly planned however, some exhaust hood installations create more
problems than they solve. The major oversight in many installations is providing
for adequate make-up air to replace that exhausted. The exhaust capacity and capture
velocity of a hood must be carefully considered. The hood's exhaust capacity, which
is measured in cubic feet per minute (CFM) units is the total amount of air that
is drawn through the open face of the hood (Koenigsberg, 1982). A four-foot wide
fume hood operating at a face velocity of 100 linear feet per minute removes 800
CFM. Unless the existing air supply system to your workstations can be adjusted
to make up this difference, the room will be a strong negative pressure, restricting
needed air and creating drafts through cracks and windows, as well am making doors
difficult to open.
The selection of an appropriate exhaust hood for a work area, if planned carefully,
can be the "cadillac" of solutions to ventilation problems. Careful consideration
must first be give n to actual workspace design and activities however, before adding
this control measure.