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
Chapter 7–Room Ventilation, Makeup Air, and Pressurization Control Systems
Laboratory Room Pressurization
In addition to providing the minimum required air changes per hour (ACH) for each
laboratory room, a properly designed laboratory ventilation system will maintain the
laboratories (as well as any rooms having potentially hazardous or pungent fumes) at
a negative static pressure with respect to the non-laboratory areas of the facility.
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A room at a negative static pressure means that the room will be at a slight vacuum
with respect to an adjacent area that is not also negatively pressurized. With
negative room pressurization, a slight air movement into the laboratory from adjacent
non-laboratory areas will always take place especially through a doorway, under and
around closed doors, and through various other openings that typically exist. This
intentional air movement towards the laboratory interior provides added assurance
that fumes or hazardous airborne substances will not migrate out from a laboratory or
similar type of room where fumes or unpleasant odors may be present. Without room
negative pressurization, the potential for such an undesirable air exchange exists,
especially whenever a laboratory door is opened.
Pressurization Concept
Prior to addressing how to ensure a laboratory room is maintained under a negative
static pressure, the next few paragraphs briefly discuss the concept of static
pressure. If you are not already familiar with the concept of static pressure as it
applies to heating, ventilation, and air conditioning (HVAC), you may find this
discussion helpful.
Most everyone is familiar with the general concept of air pressure. Everyone knows
that the air in an automobile tire is at some air pressure. However, what is not always
realized is that all pressure measurements are really a measurement of a pressure
difference. For example, if an automobile tire pressure is measured as 35 psi with a
tire gauge, it really means that the difference between the pressure within the tire
and the air surrounding the outside of the tire is 35 psi. One input of the pressure
gauge connects to the inside of the tire while the other input (not obvious to the user)
must be open to the outside.
It’s also commonly understood that given the opportunity, air will flow from where the
pressure is higher to where the pressure is lower. Thus, if an automobile tire
develops a puncture, we know air will flow out and eventually result in a flat tire. This
airflow continues until the pressure is the same inside and outside of the tire. The
direction of airflow is always from where the pressure is higher (which is considered
to be positive) to where the pressure is lower (which is considered to be negative).
Thus, the inside of an inflated tire is at a positive pressure with respect to the outside
air surrounding it.
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Many rooms such as animal holding areas, cage cleaning, etc., routinely generate odors that must not be allowed to
migrate to other areas of the facility. In addition, chemical storage rooms may also pose a potential hazard from a spill
or leak. These types of rooms along with regular laboratory rooms must be included in the requirements for negative
room pressurization.
62 Siemens Building Technologies, Inc.