Moving Beyond TVOC - Reasons to avoid the use of TVOC as Pass/Fail criterion for assessing VOC emissions from products
Total Volatile Organic Compounds (TVOC) has a long history as a metric for determining the acceptability of the emissions of VOCs from building products and furnishings. The first significant program to rely on a TVOC criterion was the Carpet & Rug Institute’s (CRI) Green Label Program that evolved out of the Carpet Policy Dialog between the carpet industry and the US EPA.The TVOC criterion was later incorporated into the U.S. Green Building Council’s LEED rating systems and was adopted by the commercial furniture industry. More recent VOC emission test method and acceptance standards have focused instead on individual VOCs that may pose health hazards to individuals at low concentrations. Examples of such programs in North America are the California Department of Health Services' Standard Practice (a.k.a. Section 01350), which recently was revised to Standard Method Version 1.1, and CRI’s Green Label Plus program. TVOC values are still reported, but pass/fail determinations are based on the emission levels of individual compounds of concern. There is an urgent need to expand such determinations of acceptability beyond a select number of individual VOCs to encompass the broader range of chemical emissions that may impact health. TVOC is again being proposed to fill this gap and may be appealing to many because of its presumed simplicity. In my opinion, we should avoid this temptation and move on the more difficult, but certainly achievable, task of focusing on the toxicity of individual compounds. The following are my primary arguments against the use of TVOC as a Pass/Fail metric.
TVOC measurements may be grossly inaccurate and therefore the TVOC concept is unsuitable as a PASS/FAIL metric. Individual compounds' instrumental responses relative to toluene, the surrogate standard of choice, vary dramatically. Some common VOCs have an order of magnitude lower response per unit mass than toluene. Other compounds have higher response ratios. Even within a class of compounds (e.g., alkane hydrocarbons) the response per unit mass can vary substantially depending upon their chromatographic retention times with early eluting compounds having lower response ratios than late eluting compounds. Individual VOCs also are measured with very different levels of precision. Thus, there is no way to determine the accuracy and precision of TVOC measurements made across different mixtures of VOCs characteristic of the broad range of products and materials being assessed. This problem with TVOC is well recognized by true experts. In particular, ISO 16000-9, the emission test method most widely used in Europe and other regions outside of the US clearly states. "The sum of emitted compounds, TVOC, should be regarded only as a factor specific to the product studied and only to be used for comparison of products with similar target VOC profiles." One of the big changes that is needed in the reporting of VOC emissions is to include estimates of uncertainty. In fact, reporting of uncertainty is dictated by ISO/IEC 17025 quality management systems if requested by the customer. The use of TVOC moves the process in the completely opposite direction toward unknowable uncertainty.
Product certification programs can, and should, be progressive with respect to public health concerns. TVOC may be a useful tool for such certification programs. For example, the monitoring of TVOC for a specific product over time (in keeping with the ISO 16000-9 precaution) may provide useful information on manufacturing variations within or among production facilities assuming the VOC profiles are similar. However, this is not a substitute for assessing the potential impacts of the individual compounds comprising these emissions. There are many different lists of toxic chemicals that can be used by certification programs as the basis for such assessments. The fact that a publically available method and guideline document only contains a relatively short list of chemicals of concern should not be a limiting factor. MBDC's Cradle-to-Cradle program is one example of a proactive certification program that considers the environmental and human health issues associated with chemicals used the in the manufacturing of products. It should be noted that a significant downside to this particular program is the lack of transparency with respect to how the toxicology judgments are made. It also might be argued that the success Greenguard's Children & Schools program in the marketplace is, in part, related to their use of an expanded list of individual chemicals of concern.
Assuming there was a more accurate and precise measure of the quantity of total VOCs emitted by a product, there still is a need to establish an acceptable level. The Greenguard Indoor Air program uses a guideline of 500 µg/m3 modeled to a small room. The Greenguard Children & Schools program uses a guideline of 220 µg/m3 modeled to a typical school classroom. The 500-µg/m3 value has some historical precedence, but in reality these numbers are simply 'pulled out of a hat.' The chemicals used in manufacturing products are undergoing rapid change. When the TVOC metric was first implemented as a metric for the Carpet & Rug Institute Green Label program in 1989, the chemicals used in manufacturing included aromatic and chlorinated hydrocarbon solvents. Today in the 21st century, most products do not use these traditional solvents because of concern regarding their toxicity. Instead, we have an increasing emphasis on 'Green Chemistry' and widespread use of water-based solvent systems. Generally, these chemicals have lower toxicity than the solvents they are replacing but they also have lower vapor pressures. Due to their low vapor pressures, the off gassing of these solvents occurs more slowly than for aromatic solvents, for example. Thus, total VOC emissions will be higher, but in many cases toxicity can be presumed to be lower. The use of a TVOC metric may, therefore, penalize products and inhibit government's and industry's efforts to switch to more sustainable chemistry. These efforts are better served by focusing on the toxicity of the individual compounds.
US Proponents of TVOC have repeatedly pointed to European product testing methods and certification programs as a precedent for the use of TVOC. While it is true than many European programs do contain a TVOC requirement, the values are often considerably higher than the values the proponents would like to impose on the US. The most widely used European assessment document, the German AgBB () scheme, relies mainly on criteria for a list of about 190 individual chemical substances. The AgBB TVOC criteria at 3 days is 10,000 µg/m3, or 20 times a proposed 500 µg/m3 value measured at 7 or 14 days (note that a direct comparison is complicated by different testing methods and modeling assumptions, but the magnitude of the difference is approximately correct). Clearly the dominant European assessment criteria focus on individual VOCs, NOT on TVOC.
Proponents of TVOC argue that there are tens of thousands of individual chemicals emitted by building products and furnishings that may be affecting our health, and due to this overwhelming number only a metric like TVOC is practical. This is far from the truth. There are many hundreds of chemicals in petroleum distillate fractions, e.g., Stoddard solvent. Over the years, there has been a shift away from these solvent mixtures to simpler, manufactured mixtures with better controlled volatility and elimination of compounds that are of particular concern because of their toxicity. The true number of chemicals that are frequently emitted by building products and furnishings probably number several hundred. If this universe of chemicals can be identified (not difficult), it is a much more manageable task to evaluate the toxicology data to see which chemicals are of real concern for the general population and at what levels.
Proponents of TVOC also argue that there are many potential synergistic relationships among VOCs and that, again, only the use of TVOC can guard us against this danger. Such arguments regarding synergism are not founded on fact. For example, while the hedonistic value of odor response can vary depending upon the mixture of chemicals, odor receptors are very specific for particular chemical functionality and size. The mammalian sensory perception system (Trigeminal) is much more generalized. However, the effects for VOCs with low reactivity (i.e., most of the VOCs that are measured by conventional methods) have been shown to be additive in both animal and human studies. If there is a highly reactive VOC in the mixture, the sensory response is controlled by the reactive chemical, not the mixture.
Al Hodgson, Co-founder and Research Director, Berkeley Analytical Associates