1. it's not particle board. The surface material is probably lauan plywood, but the substrate will be aluminum framing. If it has broken loose due to weight, I personally would use an anchor type fastener/molly on at least a few of them.
They are typically rated for 200lbs but the problem is when that is not evenly distributed and secured. Way back in the back like that...rule of thumb is always at least 5 times. When we rate our LP tank, we have to test for 5 times the actually weight due to bouncing. So that 50lbs tool box becomes 250lbs pretty darn quick.
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