Considerations when selecting tiles for pool designs include tile size and dimensional ratios. Large format glass tiles have been known to fracture along the waterline as a result of thermal shock. Long rectangular shapes can be less stable at the center of the tile, prone to fracturing especially if installation methods are substandard.
I study each product and imagine how the shape, thickness, and design will function in a pool environment. Then I look to the manufacturer for product testing and recommendations. While the industry actively develops and revises standards for glass tile manufacturing and specification in pools, the bottom line is to work with manufacturers that have a good quality track record and knowledgeable (accessible) technical staff.