 |
||||||||||||
November 2005 Dear
All,
Randall
S. Fike, Ph.D.
The “hump” in the chromatogram is a collection of undifferentiated hydrocarbons. Even though many of the individual compounds are not discernable, collectively, they contribute heavily to the TVOC load.
Currently there is no specific US standard for the PEL
(Permissible Exposure Level) for TVOCs (Total Volatile Organic
Compounds) nor is there any specific specification as to the carbon
chain length covered. Even though research and opinions have
been published for more than 30 years, questions regarding safe
levels or whether or not methane, ethane, and similar low MW
compounds should be included still remain and are currently being
discussed in the arena of ideas. However, it is still possible
to establish reasonable, workable limits until a specific standard
is established. LEED (Leadership in Energy and Environmental
Design, USGBC) has developed a new standard for Green Buildings of
<500 ng/L after its previous standard of <200 ng/L proved
unattainable, especially in new buildings. The European
Community has tried to get around the problem of what makes up the
TVOC by using a limit of 300 ng/L with no single compound
contributing more than 10% of the total. One large US chemical
company uses the standard of <500 ng/L as their target for
non-manufacturing areas, 500-1000 ng/L as the “action level” and
>1000 ng/L as the “immediate action level”. The literature
generally seems to agree that <300 ng/L represents an
“acceptable” TVOC level and that >3000 ng/L represents a
“hazardous” TVOC level; however, few seem to want to address the
hazards involved with levels between 300 and 3000 ng/L. Part
of this problem rests in the fact that many office residents enjoy
VOC’s from perfumes and odorants (cleaning products, scented
candles, potpourri, air fresheners etc.) and work to increase the
background level while other office residents are not so inclined
and may actually suffer from nausea, headaches, and other symptoms
as a result.
Further, PATI has defined the low molecular weight limit for VOCs included in the TVOC value to include C1 and C2 halogenates and oxygenates (such as formaldehyde, and C1 CFCs) but exclude C<3 hydrocarbons. The high molecular weight limit for included VOCs is C15.
Several devices are available that do an acceptable job estimating TVOC including PID (Photoionization Detectors), AirCuity monitors, the Nose (by Pure Choice), and several others. These are especially useful for continuous monitoring or for obtaining real-time data. However, the use of GC-FID (Gas Chromatography-Flame Ionization Detector) or GC-MS (Gas Chromatography-Mass Spectrometry) will provide the most accurate and useful data although GC-FID has the drawback of not providing secondary verification of compound identity. PATI uses GC-MS in determining the TVOC value because, should a question arise as to the identity of the specific compounds contributing to the TVOC, it is possible to use the mass spectral verification feature to do a full TDT Air Scan analysis of the data without having to take another sample. This feature is included in PATI’s MoldScan Plus and GreenScan analyses where a TVOC value is reported. If the TVOC is low, usually no additional analysis is required. However, if the TVOC level is high, a full 300+ compound, TDT Air Scan® analysis can be requested.
Technical Guide to the Investigation of Indoor Air
Quality in Office Buildings: Also, do a Google or Dogpile search using “Lars Molhave” as the key words
Q. What is sub-slab
sampling?
There
are many problems associated with indoor air quality (IAQ) issues,
like musty smells, sore throats, coughs, headaches, watery eyes
etc…. And there are consequences of not recognizing IAQ
problems. John Bruce in a two part article explains some of these
issues.
Copyright © 2002-2005 Prism Analytical Technologies, Inc. All rights reserved. |
Have
a Case Study to Share? Look
for in upcoming issues: CONTACT US trappedair@pati-air.com Learn more about MoldScanPLUS™ visit us at www.pati-air.com; Acronym Helper
Do you
have your PATI Air Analytical Tool Box ? |
This November we complete our third year of
Trapped Air. We hope that you have found and continue to find
this newsletter both informative and thought-provoking. We
continue to strive to make this newsletter a forum for new
technologies, methodologies, and ideas that further the advancement
of air testing science.
Before getting into the
technical aspects of Total Volatile Organic Compounds (TVOCs), it is
important to understand what is really meant by the term. A
TVOC value is not simply the sum of the volatile organic compounds
detected in an analysis. For example, consider a radio signal
received on a car stereo. Suppose the station is playing a
flute solo. An analysis of the radio signal at any specific
moment in time would show a single note or “peak” in the signal
(apologies are extended to musically astute for ignoring the
harmonics, timbre, etc. here). If the station were coming in
clearly, that single tone would be overwhelming relative to the
magnitude of the rest of the tones. If the same station is
playing an organ solo, there might be six clear, distinct tones.
If the station were playing rock music, there would be a
distorted conglomerate of discordant tones. For the last
example, now consider a station that is coming in poorly and is
playing rock music. The static or “white noise” would nearly
overwhelm the already complex signal. In each and every case,
the radio volume might be the same, but the tonal makeup and
complexity would be vastly different. Such is the case with a
TVOC value. The value includes all of the indistinguishable
“chemical noise” as well as the recognizable compounds. As in
the radio analogy, without a significant “total signal”, there is no
radio reception; however, a high total signal could be anything from
one pure tone to nothing but loud static. So it is with TVOC,
a low TVOC usually indicates that there is no VOC problem (unless,
of course, the TVOC value is due to only a small number of
compounds); however, a high TVOC value may result from a high level
on one single compound or it may be a vast collection of low
compound levels from a chemical “soup”, or it may be anything in
between. 
