Many people use the term, wood mulch, for what's used in a lot of publicly accessible playgrounds, yet this is not what it should be. Engineered Wood Fiber (EWF) is specially made for playground safety surfacing, and it's often a more uniform size and shape of particulate, often tumbled to remove any sharp edges or splinters, and yet it's impossible to get them all. We've got 8 INFOto pages of unfavorable issues common to wood products, none of which are great for playground safety surfacing, particularly when it adversely affects the level of safety.
Wood products attract a number of undesirable elements to playgrounds, they require periodic churning and topping off to maintain their fall safety, and really should be replaced every two years, according to the NRC. Wood products continue to deteriorate over time with exposure to weather and natural elements, which dramatically lowers fall impact safety.
Some of the most common things that love wood products include termites, rodents, bugs, microbes like mold, mildew, fungus and bacteria. Probably not what anyone had in mind when selecting EWF for their playground surfacing. It had to be installed to a 12" depth for far less than the #1 safest fall injury protection that a 6" thickness of US Rubber Mulch provides at the maximum allowable 17' fall height, with resulting test data around 700 HIC over the drops. Nope, there's no way EWF is going to be to achieve and maintain anything close to that level of fall safety over it's entire life span, much less match the 25 years or more that rubber mulch lasts, while requiring usually no more than 5% to 10% top off every 3 to 5 years.