Well now here starts another grate debate ! Play sand VS. Reptile grade sand. Most reptile sands are milled so that the grain actually becomes smoother or round. Play ground sand is a silicate sand which still has it's jagged edge and actually is easier to cause impaction. With that said there is no 100% safe substrate in my opinion. There are those substrates that you definitely want to stay away from.. ie. Corn cob and walnut shell for instance. Silicate sands can also be very dusty which can cause respatory problems.(washing does help) I have used many different types of substrates and as for sands I have never had a problem with a fine grade milled reptile sand.