Volatile Fog Testing—Does It Need Updating?March 21st, 2014 by DWM Magazine
In a recent presentation “Objective Volatile Fog Measurement,” Dave Cooper and Jonathan Herndon of Guardian Industries discussed the series of testing the two completed to determine effective methods for measuring volatile compounds in insulating glass units (IGU).
The organic components to which IGUs are exposed, such as sealants, exterior components, adhesives, muntin bars and spacers, among others, may evolve into volatile compounds. These volatiles “may condense on the inner glass surfaces and become visible,” creating a fog, Cooper and Herndon noted during the presentation.
Two tests, ASTM E2189 and CGSB 12.8, are designed to intensify the conditions which would create volatile fog. The test exposes two IGUs to constant heat and ultraviolet light for seven days in a special box with a chiller plate placed on the low-E side of each IGU. After the seven days, the IGU is visually inspected for any volatile compounds which may have condensed opposite of the chiller plate. Should the tester see anything on either IGU within seven days after they have been removed from the box, the test criterion is a fail, they said.
According to Cooper and Herndon, they posited that there are two things wrong with this method. First, “Fog box construction defined by the standard is open to interpretation. Can we make identical units fail in one box and pass in another?” Second, “When there is ‘light fog’ or haze, or a color shift, can it really be seen?” They quoted one technician who said, “I can’t see it, but I know it’s there.” They noted that the fog typically only shows up in reflection so technicians must know exactly what to look for.
After receiving highly varied results from third-party volatile testing in April 2012 for boxed units that met ASTM E2189 criteria, members of Guardian decided to conduct more in-depth testing. They determined that what is wrong with the testing is the fog box construction, specifically the fact that the construction and control of the box affects the internal conditions. Temperatures vary at different locations of the IGU. Cooper and Herndon stated that, “Glass and edge component temperature [is] dependent upon [the] distance from radiant heat source, coating type, convective cooling aspects, fan(s) position, hole(s), temperature regulation schemes, insulation within the box and surrounding environment conditions. UV wavelength characteristics and strength [include] bulb age, source voltage, distance from IG, spectral curve with respect to energy output [and] reflective surfaces within the box.”
The company began to measure various characteristics of the volatile fog boxes and found numerous inconsistencies, such as radiant energy from the bulbs, distance from bulb, infrared spectrum and intensity, temperature control, UV degradation and unspecified voltage input impacting bulb output. In a comparison of measured UV irradiance of fog boxes, eight different boxes showed eight different curves for UVC, UVB and UVA for a centered frequency for an E2189 measurement device.
While Cooper and Herndon noted that the “industry is improving upon the volatile outgassing aspect of components,” there are an increasing number of components being added to IG. Light fog may be indiscernible to the untrained eye, but a spectrophotometer may be able to measure the shift in color using the variables L* (degree of brightness scaled black to white), a* (color from red [+] to green [-]) and b* (color from yellow [+] to blue [-]). Guardian began a study to find out if a spectrophotometer could measure lightly fogged units, and if so, which is the better piece of equipment to use.
The two main devices examined were the Hunter Colorquest XE, which is a benchtop spectrophotometer that measures reflectance and transmittance at an estimated cost around $25,000. Cooper and Herndon said it was, “fairly precise and accurate [and is] utilized in many industries.”
The other device was the Konica Minolta CM-2500d, a portable spectrophotometer which measures reflectance only at an estimated $8,200. They were unsure of the instrument’s precision and accuracy, however.
The two posited that the portable Konica would make a much more feasible option for most companies, but needed to see how it held up against the Hunter Colorquest.
Following a series of tests and a live demonstration for attendees, Cooper and Herndon concluded that, though it was somewhat less precise than the Hunter Colorquest, the Konica was “suitable” for the identification of volatile fog in IG.
Herndon and Cooper used two methods of analysis—the Empirical Rule and Non-uniformity. The empirical methods included “measuring the cold plate area of the IGU before fog box exposure to determine a baseline, calculating a standard deviation and mean for L*, a* and b* values, re-measuring the cold plate area after fog box exposure and using the Empirical Rule (3-sigma) L*a*b* data to determine whether pre- and post-exposure measurements are dissimilar which would indicate fog presence.”
According to their empirical findings, before E2189 exposure, there was a low variability of color data and a steep bell curve. Following E2189 exposure, they stated there was a higher variability of color data, a wider bell curve and color values shifted toward +a*,-b* which is a purple color. Of the three units analyzed, fog was present on all three.
For the Non-uniformity analysis, Cooper and Herndon utilized the ∆E* concept under ASTM D2244 “Standard Practice for Calculation of Color Tolerances and Differences” using the formula ΔE*ab=(Δ