Basic Documentation

Laboratory Ventilation Codes and Standards
Siemens Industry, Inc. 106
Topic Requirement(s) Commentary
Room and Duct
Pressurization
(Continued)
American National Standard for Laboratory Ventilation, ANSI/AIHA Z9.5-2003
5.1.1
As a general rule, airflow shall be from areas of low hazard to higher hazard
unless the laboratory is used as a Clean Room (such as Class 10,000 or better),
or an isolation or sterile laboratory, or other special-type laboratories. When flow
from one area to another is critical to emission exposure control, airflow
monitoring devices shall be installed to signal or alarm that there is a malfunction.
Air shall be allowed to flow from laboratory spaces to adjoining spaces only if
• There are no extremely dangerous or life-threatening materials used in the
laboratory.
• The concentration of air contaminants generated by the maximum credible
accident will be lower than the exposure limits required by 2.1.1. (Note that
2.1.1 references OSHA PELs, NIOSH RELs, ACGIH TLVs, AIHA WEELs and
the German MAKs.)
AIHA Commentary to 5.1.1 In many laboratories, momentary door opening to
allow the movement of materials and personnel in and out of the laboratory will
not cause a significant safety condition because of the short duration of time for
any contaminants to escape from the laboratory to the corridor.
5.1.1.1 Airlocks shall be utilized to prevent undesirable airflow from one area to
another in high hazardous applications, or to minimize volume of supply air
required by Section 5.1.1
Scientific Equipment & Furniture Association
SEFA 1–2006 Recommended Practices for Laboratory Fume Hoods
7.2 Room Pressurization
The standards and guidelines stress the importance of room
pressurization
for
laboratory spaces. Laboratories that use laboratory fume hoods should be
maintained at a relative negative pressure to corridors and other adjacent
spaces
in the building (such as the exception of clean room laboratories
that may operate under positive pressure).
7.0 In order to maintain the negative pressure requirement, the total exhaust
volume for a lab must always exceed
the supply air volume by a specific
volumetric offset or the flows must be controlled by a pressure differential
control system. The volumetric offset method is the most common. If the total of
all hood exhaust is less than the maximum possible supply flow, an
additional exhaust device, normally
referred to as the general exhaust valve, is
required.
7.2 Laboratories that use laboratory fume hoods should be maintained at a
relative negative pressure to corridors and other adjacent spaces in the building
(such as the exception of clean room laboratories that may operate under
positive pressure).
(Continued on Next Page)
In (2), NFPA 45 recognizes the dynamics
involved in maintaining negative room
pressurization, particularly with VAV laboratory
ventilation systems. For instance, changes in
the total room exhaust can occur whenever a
VAV fume hood sash is repositioned. This
creates a need to make a corresponding
change in the room supply makeup airflow
which requires a finite amount of time. This
time period (albeit perhaps only a few
seconds) will nevertheless result in an
unavoidable short term room pressure
variation. Accepting this fact can greatly
simplify acceptance testing
AIHA similarly acknowledges the short term
pressure changes and downplays their effect
on safety.
Airlocks are not necessary for the majority of
laboratories. They are only applied when very
unique and highly toxic chemicals and
substances are routinely present (that is;
highly poisonous gasses). In such situations
consideration should be given to conducting
the experiments in gloveboxes in lieu of fume
hoods (Also refer to Airlock definition.)