Basic Documentation
Table Of Contents
- About this Application Guide
- Chapter 1–Introduction
- Chapter 2–Goals of the Laboratory Environment
- Chapter 3–Unique Ventilation Needs of a Laboratory Facility
- Chapter 4–Ventilation Systems Classification
- Chapter 5–Laboratory Facility Exhaust Systems
- Chapter 6–Laboratory Containment Units - Ventilation
- Chapter 7–Room Ventilation, Makeup Air, and Pressurization Control Systems
- Chapter 8–Laboratory Temperature and Humidity Control Systems
- Chapter 9–Laboratory Emergencies - Ventilation System Response
- Chapter 10–Laboratory Ventilation System - Validation
- Chapter 11–Laboratory Ventilation System - Commissioning
- Glossary
- Index
Laboratory Room Pressurization
However, a more complex situation arises when a room that requires protection from
contamination from adjacent areas could itself also be a source of potentially
hazardous airborne fumes to the adjacent areas. In such circumstances, an
arrangement that maintains the room at a slight positive pressure to prevent the
influx of contaminated air along with a provision that still prevents outward airflow to
the adjacent areas is necessary. Figure 14 shows how this can be achieved by
utilizing a dual pressurization arrangement for a laboratory room that has chemical
fume hoods, although the same arrangement can be applied to rooms that have
biological safety cabinets.
The difference between Figure 14 and the preceding figures is the addition of a
vestibule or airlock at the entry to the laboratory room. In operation, the laboratory
room with the fume hoods (or vented biosafety cabinets) is maintained at a slight
positive static pressure by the airflow tracking method. In other words, somewhat
more supply air is always provided to the laboratory room than the total amount of air
that is exhausted from the room. However, the vestibule is exhausted at a rate that
not only removes the excess laboratory supply air but also an additional amount of
air that is sufficient to make the combination of the two rooms (laboratory and
vestibule) at a negative static pressure with respect to the adjacent area.
For example, in Figure 14, the laboratory might have 200 cfm more supply airflow
than its total exhaust. The vestibule might then be exhausted at approximately 300 to
400 cfm. This results in a net excess exhaust of 100 to 200 cfm for the combination
of laboratory and vestibule. The combination of these two rooms are thus negative
with respect to the adjacent area. This not only keeps air from the adjacent area from
entering the laboratory room but also ensures against any laboratory air migrating
out into the adjacent area.
When implementing a dual pressurization type of room pressurization arrangement, it
is advised that the laboratory itself (walls and ceiling construction) is tightly sealed,
so there is no opportunity for air to pass directly to the adjacent area. Depending on
the individual situation, it may be desirable to utilize an airlock type of entry
arrangement whereby only one door (the door between the adjacent area and
vestibule, or the door between the laboratory and vestibule) may be opened at a
time.
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