It's a framework called OpenVDB [1], which we use to represent and manipulate volumetric data (level sets). It stores the data as a sparse hierarchical grid with (from a practical perspective) infinite dimensions, and allows very efficient iteration and local manipulations of the grid.

I'm not an expert on how it is implemted exactly, but I believe the way it uses Blosc is by saving leaves of the VDB grids in blosc-compressed chunks, which are loaded into memory directly and only decompressed on-demand when the data is accessed, then re-compressed when the leaves are processed.

[1] https://www.openvdb.org