Chances are, if your parents wouldn't allow you to have a mouse, rat or guinea pig as a pet, you knew someone who did at some point. You may remember they normally made their bedding, or nesting areas to sleep, out of wood chips and shavings, that could be purchased at the local pet store. Any of these would chomp on whatever they had available, often gnawing on pieces of wood or other materials within their enclosures.
Wood is a natural organic material that pretty much most rodents prefer to make their nest with, and within, which isn't great news for anyone choosing or already has engineered wood fiber (EWF) for the playground safety surface. Finding rodent nests within playgrounds with EWF is more common that many might be willing to admit. In one playground, the founder of our company discovered at least one snake living within the EWF, because it didn't have a need to go anywhere else for food, given the number of rodents nesting there.
If this isn't bad enough, the rodents help to break down the EWF into a fine dust that offers nearly zero fall impact protection, into which their fecal waste gets blended, along with any zoonotic pathogens or parasites, thet spread and multiply rapidly with moisture. This microbial infested soup is absorbed into the remaining EWF, which spreads it far and wide throughout the playground.
This is just one of a myriad of reasons EWF might not be the best choice for safety surfacing on your playground, and it's always a good idea to compare all available surfaces, learning what the good and bad points are for each one, along with the respective fall safety, longevity, required maintenance, upkeep, removal & replacement costs, sp the best educated decision is most likely achievable.