Now that's a load .....

I currently own a Polycystal Rack with 3 shelves and was wondering what the load capacity is for one of the shelves that are placed in the middle - The shelves are the Ultra High Density version and are supported by 4 brass pins in which the selves can be adjusted....any idea of just how much weight can be placed on one of those shelves / pins before it collapses - don't want to find out the hard way and come home to that mess or hear it in the middle of the night. Tough one as Polycrystal is no longer in business