Fog Testing

Introduction

Volatile compounds with lower molecular weights may evolve during heating in enclosed spaces, such as car interiors. These fumes can also condense over cooler objects, such as windshields, displays, or lenses, to cause low visibility and an unappealing sight. Fog testing helps manufacturers assess this risk and increase the selection of materials that meet the industry-established criteria for safety and performance. It is particularly important for dashboards, interior trims, headliners, seals, and other components made of polymers, as they are often subjected to sunlight or elevated temperatures during usage.

Methodology

A typical method of fogging test, as specified in ASTM G85, involves heating a sample of material within a sealed container or system to a specified temperature, with a cooler (usually made of glass or aluminum) nearby. When this material is heated, it off-gasses, allowing any volatile materials to collect on the cold surface and produce a visible fog or residue. Fogging propensity may be quantified optically (perception of the sharpness of a pattern grid viewed through the fogged plate)  or gravimetrically (change in weight of condensed material). These standards are commonly characterized as DIN 75201, ISO 6452, and SAE J1756, which differ in their suggested test conditions and measuring criteria, depending on the application.

Instrumentation

Fog test assemblies and fog test chambers with fine temperature regulation, heating plates or oil baths, coolable collection plates made of glass or aluminum, and optional optical light sources can be used for visual comparison. In more sophisticated systems, haze meters or photometers can be utilized to measure the transmission of light through the fogged surface, with analytical balances employed in the gravimetric technique.

Strengths

Fog testing offers a straightforward method for identifying potential off-gassing issues in heated materials. It makes interiors appear secure and free from visual dilapidation throughout the product’s lifetime. This testing is crucial in meeting international automobile and consumer product requirements and is very important in controlling materials, approving suppliers, and confirming products.

Limitations

Fog testing is used to measure volatile organic condensation in a controlled environment, where it fails to produce all sorts of emissions, including those that are not easily condensed. It does not consider odor or health-related VOC unless in combination with chemical assessment. Additionally, disparities in testing methods (visual vs. gravimetric) may lead to discrepancies, and test data may not accurately reflect actual conditions in time-related exposure.