What characteristic does glass blocks exhibit despite their limited strength?

Glass blocks, despite their limited structural strength, exhibit the characteristic of being able to withstand fire. The unique properties of glass blocks allow them to provide a certain level of fire resistance, making them suitable for use in fire-rated walls or partitions. They can help to control the spread of flames and smoke, which is a crucial factor in fire safety and building design.

In contrast, while glass blocks may be waterproof to some degree, this does not fully capture their primary characteristic related to fire. Although they may offer some insulation properties, their main function in fire-related applications is not insulation but rather their ability to resist fire. They are not typically designed to be load-bearing elements, as their limited strength means they are not intended to support significant weight. Thus, the key quality of glass blocks in the context of fire safety is their ability to withstand fire.