Probably I mis-remembered and my slapdash attempt at finding a source was in error (which makes twice in two days for me, embarrassingly.) I remember of the st

Probably I mis-remembered and my slapdash attempt at finding a source was in error (which makes twice in two days for me, embarrassingly.) I remember of the studies perhaps better than I remember the studies, but the gist is that there's a hierarchy of playground surfaces. I thought it was: grass < sand < wood < rubber but I suppose it's more like grass < wood < sand < rubber Regardless, sand does appear to be considered acceptable by CPSC guidelines[1], in which they recommend ATSM F1292 tested wood fibers, pea gravel, sand, rubber mulch, non-CCA-treated wood mulch, and recommend against asphalt, concrete, carpet not tested to ATSM F1292, dirt, grass, and CCA-treated wood mulch. Apologies for the error, and thanks for the correction. [1] - https://www.cpsc.gov/s3fs-public/325.pdf https://www.cpsc.gov/s3fs-public/325.pdf