Inert

Glass, and as a result foam glass too is an inert material, and that "means waste that does not undergo any significant physical, chemical or biological transformations. Inert waste will not dissolve, burn or otherwise physically or chemically react, biodegrade or adversely affect other matter with which it comes into contact in a way likely to give rise to environmental pollution or harm human health. The (...) ecotoxicity (...) must be insignificant, and in particular not endanger the quality of surface water and/or groundwater;" – see: Government Decree 213/2001 (XI. 14.)