ASHRAE Journal - September 2023 - 13

COLUMN ENGINEER'S NOTEBOOK
upon the design professionals to understand the hazards
and design engineering controls to mitigate potential
exposure-science teachers and professors may not have
the background needed to do so.
The NFPA Diamond (Figure 5) is a useful tool for
identifying and categorizing hazards. It identifi es four
categories of hazard by color and uses a numerical rating
system to indicate the level of hazard. The numeric
category ranges from 0 to 4, with 0 representing no
hazard and 4 representing the highest hazard. Health
hazards are identifi ed with a blue diamond, fi re hazards
are identifi ed with a red diamond and reactivity hazards
are identifi ed with a yellow diamond. A white diamond
is used to identify specifi c hazards, such as acids,
corrosives, radioactive, etc.
When designing science labs, it is important to obtain
a list of all chemicals that will be used and review the
material safety data sheets (MSDS) for each. These data
sheets normally list the hazards and identify the NFPA
rating for each hazard category. Designers should also
understand how the chemicals will be used. Will they
be used on an open bench? In the fume hood? Only in
the prep room by the instructor? This understanding
will then guide the design of engineering controls to
minimize exposure risk.
Containment
Understanding the principle of containment is key
to designing safe laboratories. Primary containment
is the fi rst line of defense against exposure and is
typically the fume hood for hazardous chemicals and the
biological safety cabinet for biological agents. Open use
of materials that are hazardous to humans should always
be done inside a primary containment device.
Secondary containment consists of the lab enclosure,
general lab exhaust and keeping the lab pressure
negative relative to the adjacent corridor. Best practice is
always to keep the lab door closed to maintain secondary
containment. Lab exhaust fans should run continuously
unless all hazards are removed from the lab. ANSI/ASSP
Standard Z9.5-2022, Laboratory Ventilation, requires that
air move from lower to higher hazard. Air should always
move from the corridor into the lab.
Fume Hoods and Biological Safety Cabinets
Primary containment devices should be selected
carefully and should always be used as the fi rst means
FIGURE 2 Increasing level of hazard.
Higher Education
Research
Higher Education
Science
High School
Science
Middle
School Science
Elementary
School Science
Low
Moderate
FIGURE 3 Codes and standards applicable to laboratories.
High
of protection from exposure. There are many types of
fume hoods and biological safety cabinets. Designers
should familiarize themselves with these devices
and understand how to apply them. The architect or
lab planner typically specifi es these along with the
laboratory furnishings in Division 11 of the project
specifi cations. However, in my experience, architects
who design education facilities may not be familiar
enough with these devices to apply them properly. I
normally ask the architect if I can review the fume hood
and/or biological safety cabinet specifi cation, and they
are almost always happy to have the assistance.
The location of fume hoods and biological safety
cabinets must be carefully considered. They should be
located away from doors and main traffi c aisles. Doors
and personnel movement can create cross drafts and
may decrease a hood's containment ability.1,2 Supply
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ASHRAE Journal - September 2023

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