ASHRAE Journal - October 2023 - 43

TECHNICAL FEATURE
classic conceptual metaphor for such a hierarchy with
an emphasis on engineering controls.
The U.S. OSHA Respiratory Protection Standard
(29 CFR 1910.134(a)) also stipulates that engineering
controls, instead of respirators, must be implemented
when pertinent control solutions are feasible.
Nevertheless, fi nalization of an engineering control
solution can be time-consuming (weeks, months or even
longer depending on its complexity). In the interim,
especially for high-risk operations, effective application
of administrative controls, together with personal
protective equipment, should be pursued.
Engineering controls generally are directed at
retrofi tting process, equipment or environment to
prevent overexposure to various risk factors. The book
Prudent Practices in the Laboratory defi nes engineering
controls as " measures that eliminate, isolate or reduce
exposure to chemical or physical hazards through
the use of various devices. " Similar descriptions are
documented in other literary references.1 - 3 Typical
examples include but are not limited to industrial
TABLE 2 Typical types of ventilation with their features and applications.
TYPE OF VENTILATION
General Exhaust Ventilator
Environmental Rooms
Chemical Fume Hoods
Ventilated Storage Cabinets
Biosafety Cabinets
Glove Box
Downdraft Table
Elephant Trunk
Slot Hood
Ductless Chemical Fume Hood
Ventilated Balance Enclosure
Benchtop Ventilated Enclosures
FEATURES (AIR CHANGE RATEa OR FACE VELOCITY)
6 - 12 air changes/hour, depending on room design and
system operation
0 air changes
10 - 15 air changes/minute
or 60 fpm - 100 fpm, depending on hood type
1 - 2 air changes/minute
A1: 75 fpm; A2/B1/B2: 100 fpm
Varies from no change to very high rate of change,
depending on the glove box and the application
150 fpm - 250 fpm,
depending on design
150 fpm - 200 fpm at opening
Varies with application
10 - 15 air changes/minute
5 - 10 air changes/minute
Variable per the needs of the materials
ventilation systems (e.g., biosafety cabinets, chemical
fume hoods and other ventilation devices) for (bio)
chemical hazards4,5 and machine guarding systems
(e.g., enclosures, shields, barricades and safety
interlocks) for physical hazards.6,7
Industrial Ventilation for (Bio)Chemical
Exposure Risk Control
Ventilation, as a method of occupational exposure
control, has a long history, having possibly fi rst been
articulated by Agricola (1561) and emphasized in his
publication.1,8 Industrial ventilation systems are
TABLE 1 Rule of ten.
LEVEL OF VENTILATION CONTROLS
Confi ned Space - Virtually No Ventilation
Poor - Limited Circulation
Good - General ~6 ach
Capture
Containment
FRACTION OF SATURATION
VAPOR CONCENTRATION (SVC)
1/10th of Saturation
1/100th of Saturation
1/1,000th of Saturation
1/10,000th of Saturation
1/100,000th of Saturation
EXAMPLES OF APPLICATION
Less volatile or hazardous chemicals
Special environmental controls
Nonhazardous amounts of fl ammable, toxic or reactive chemicals
No wood pulp-based products
Flammable, toxic or reactive materials
Materials with uncharacterized or unknown hazards
Highly toxic, hazardous or odiferous chemicals
(if equipped with fl ame arrestors)
Biological materials
Nanoparticles, as of the date of publication
Minute amounts of volatile chemicals
Positive pressure for specialty environments
Negative pressure for highly toxic materials
Perfusions with paraformaldehyde, work with volatile, low to moderately
hazardous materials with higher vapor density where access from more than
one side is necessary
Local ventilation of a tabletop
Discharge from equipment such as a gas chromatograph
Local ventilation of higher density materials at the source,
such as an acid bath
Materials that are compatible with the fi ltration system, in controlled
quantities and under controlled conditions
Not suitable for particularly hazardous substances
Weighing and initial dissolution of highly toxic or potent materials
Benchtop equipment, such as rotovaps
aAir change per hour (ach) or air change per minute (acm) should not be a sole criterion for ventilation effectiveness as suggested by ACGIH.9
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