Total Volatile Organic Compounds (TVOCs) in the Air
(What does TVOC really mean?)

Randall S. Fike, Ph.D.
Prism Analytical Technologies, Inc. (PATI)
Chief Technical Officer

Understanding TVOC

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.

Note in the following chromatogram the difference in TVOC makeup as compared to the identifiable compounds.

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.

TVOC PELs

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.

The recognized symptoms above 3000 ng/L generally include drowsiness, eye and respiratory irritation, general malaise, headache, nausea, and exacerbation of symptoms of respiratory ailments.  Some data suggests that high TVOC levels amplify the hazardous effects of specific, harmful VOCs.  In addition, there is some empirical information from IH consultants who perform medically driven environmental investigations, which indicates that typically acceptable levels are too high by a factor of two or more for chemically sensitive individuals.

Prism Analytical Technologies, Inc. (PATI) has worked with the available literature, large chemical companies, and many IH consultants active in the IAQ field as well as using our own consultative data correlating symptoms to TVOC levels to establish the following table defining the limits and effects of TVOC concentrations:

 

 

 

 

 

 

 

 

 

Measuring TVOC and How PATI Measures and Reports TVOC

Several devices are available that do an acceptable job estimating TVOC including PID (Photoionization Detectors), AirCuity monitors, XXXX, 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.