New Tool to Validate Chamber Protocols

April 6, 2011

Berkeley Analytical (BkA) is participating in studies to develop a new diffusion-based reference tool for small-scale, volatile organic compound (VOC) emission testing of interior building products and other materials. A scientific article on the pilot study of this reference tool has just been published (Howard-Reed, C. et al., Building and Environment 46: 1504-1511, 2011). Please email us if you would like a copy for your reference. The research program was created by the National Institute of Standards and Technology (NIST) and Virginia Tech (VT). They are developing a diffusive reference material and an associated mechanistic model into a test standard that laboratories will be able to use to validate the performance and accuracy of their VOC emission tests.

This approach is intended to supplement or replace more traditional inter-laboratory studies (ILS), i.e., round robin, studies that are often used for laboratory performance evaluations. The central advantage of the new approach is that the VOC source is well characterized and its emissions are accurately predicted by the diffusion model. The pilot study in which BkA participated is leading to improvements in the approach and effectively demonstrated the potential of the source and model combination to serve as a useful laboratory validation tool.

The source consists of a thin polymer that is loaded with a known amount of a reference VOC. For the initial studies, toluene is being used as the reference. The toluene emission rate from this source is predicted using a mechanistic mass transfer model in which the key parameters controlling emissions are measured rather than obtained by curve fitting. By use of the model, predicted chamber concentrations can be obtained for a wide range of chambers and chamber operating conditions. Thus, measured results can be compared directly to predicted values. By comparison, the traditional ILS statistical approach of constructing frequency distributions of measured results is always inconclusive as there is no way to determine which laboratory’s results are correct. Additionally, if the source becomes commercially available, a laboratory can use it at any time without having to depend upon the availability of a sponsored study involving many laboratories (typically ten or more).

In the pilot study, VT prepared two batches of their reference material saturated with and emitting toluene at a known rate. The four-laboratory pilot study showed that the reference material was uniform in composition and sufficiently stable as the rates of toluene emissions within and between production batches were consistent. It was concluded that this approach has the potential to reduce inter-laboratory uncertainty in VOC emission measurements to under ten percent, a significant improvement over current ILS approaches.

The pilot study also identified several opportunities for improvement, which have been incorporated into an expanded international pilot is now in progress. It is anticipated that the project will be expanded by 2013 to include more types of VOC references to be produced in larger batches for broad distribution to international testing laboratories.

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Sincerely, The Berkeley Analytical Team