Environmental Engineering Reference
In-Depth Information
expected. The sample may be collected from a defined surface area (e.g., 1 m
)
or time period (e.g., 5 min) to provide a sufficient sampling mass to express
concentrations on a unit mass basis (e.g.,
2
g/g). Collected dust samples are
analyzed using monoclonal or polyclonal antibody procedures. Surface sam-
pling for dust mite, pet dander, and cockroach allergens is preferred when
assessing potential health risks associated with airborne allergen exposure.
Surface sampling has also been conducted for mineral fibers such as
asbestos, fiberglass, mineral wool, and ceramic fibers using vacuum or wipe
sampling techniques. The efficacy of such techniques in quantifying mineral
fiber levels in surface dusts has not been well documented.
ยต
E.
Measuring common contaminants in indoor environments
A variety of gas, vapor, and particulate-phase contaminants are measured
in indoor environments. These include contaminants suspected of contrib-
uting to IAQ/IE complaints, and contaminants such as radon, which may
pose long-term cancer risks. Contaminants associated with IAQ/IE com-
plaints include CO
, CO, HCHO, total volatile organic compounds (TVOCs),
specific VOCs, and mold. Less commonly, airborne particulate matter levels
are measured.
2
1.
Carbon dioxide
Because it is widely used as the principal indicator of ventilation adequacy,
CO
is the most commonly measured indoor air contaminant. Carbon diox-
ide measurements are made using direct-read, real-, or quasi-real-time
instruments. These include electronic instruments that can provide instan-
taneous or near-instantaneous values and, if desired, a continuous record,
and gas sampling tube systems. The measurement of CO
2
levels in electronic
instruments is based on electrochemistry. Two types of CO
2
instruments are
commonly available. These are pump-operated instruments which, on draw-
ing air through a sensing chamber, quickly respond to changes in CO
2
con-
2
centrations. Other instruments determine CO
levels by passive absorption
2
of CO
into the sensing unit. Pump-driven devices may have two sampling
ranges: 0 to 2000 and 0 to 5000 ppmv; passive samplers have a sampling
range of 0 to 2000 ppmv. Since CO
2
levels above 1000 ppmv are generally
recognized as exceeding guideline values for ventilation adequacy, there is,
in theory, no need to measure CO
2
levels above 2000 ppmv. Passive sampling
devices are relatively inexpensive (circa $500). Both dynamic and passive
battery-operated CO
2
samplers are available. Battery life in continuous oper-
ation is usually no more than an hour. Dynamic samplers can be operated
continuously using a line cord.
Dynamic CO
2
monitors are calibrated using canisters of standard con-
centrations of CO
2
and zero gas (nitrogen). Passive sampling devices are
factory calibrated and do not lend themselves to laboratory calibration.
Examples of dynamic and passive direct-read electronic instruments can be
seen in
Figures 9.1
and
9.5
.
2
