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Comment by alexhutcheson | Hacker News Reader

There is good evidence that the rubber "safety" matting that's common on new playgrounds causes significantly more long-bone injuries (broken arms and legs) than previous surfaces like wood chips. Kids test the limits and play up to the point of pain, so they'll leap off structures onto rubber matting in a way that they wouldn't do onto wood chips or pea gravel. In the name of "safety", we're using surfaces that prevent scrapes and road rash, but have higher risk of more significant injuries when you account for the change in kid behavior.

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I suspect the bone injuries come from the traction you get on those mats more than perceived safety. In the gravel if you put your arm out to catch a fall, it slips (and you scuff up your palms, learning not to do that next time), whereas on rubber mats it sticks and can end up taking the whole force of your fall.

Why not use rubber mulch then? Lots of playgrounds already use it, and it offers the cushioning of wood chips and the "softness" of rubber matting.

I think he means wood chips hurt, so kids don't jump off things from so high, so its less likely to break bones.

My understanding (not an expert) is that it's a combination of less high jumps/falls because "wood chips hurt", and reduced long bone injuries for the jumps/falls that due occur due to differences in the way the material responds to the impact. Wood chips slide and absorb some of the kinetic energy, while rubber matting (and probably rubber chips?) stay in place and rebound the energy back.

As a kid there was gravel under the monkey bars. Not sure if it taught you not to fall (I did fall, a lot!), but it definitely hurt when you did!

I visited a playground made of some kind of rubber mulch, maybe chippered tires. The sun was out in force (hot summer day, 10k ft). You could see the haze of chemicals hovering over the chips as they offgassed, as well as smell them.

I'd like to see that evidence.

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