What type of microscopy is used to analyze samples in asbestos testing?

The correct choice for analyzing samples in asbestos testing is transmission electron microscopy. This technique is essential due to its ability to visualize the fine structure of asbestos fibers, which are typically much smaller than what can be resolved with other types of microscopy. Transmission electron microscopy utilizes a beam of electrons that passes through the sample, allowing for a high-resolution image that can reveal the unique fibrous characteristics and dimensions of asbestos fibers, which is crucial for accurate identification and quantification.

The other types of microscopy, while useful in various contexts, do not offer the same level of resolution needed for asbestos analysis. Phase-contrast microscopy is more suited for viewing live cells or transparent specimens but lacks the resolution required for detecting smaller particles like asbestos. Scanning electron microscopy is useful for surface morphology but may not provide the interior details necessary for identifying specific fiber types or assessing their effects. Optical microscopy, while commonly used, generally cannot achieve the magnification levels needed to clearly differentiate asbestos fibers from other materials.

Thus, transmission electron microscopy is the preferred method for its high level of detail and ability to identify and analyze asbestos fibers accurately.