In planning for the school year, I check for safety considerations on the National Science Teachers Association website, at www.nsta.org/portals/safety.aspx#elem
Of course, each class of children is different, and I won’t know until September if any of the four-year-olds still put small objects in their mouths, or if any of the children have allergies. I’ll use the links to find safety guidelines, but once I know my class I’ll be able to know which hazards particularly apply to my students. Wearing safety goggles when working with substances such as Borax solutions which  might splash and get into children’s eyes is good practice but requires teacher vigilance to make sure children keep them on!
Some of the dangers I’ve seen occur (which I did not predict) are:

• Children blowing into a plate of dry sand that we were looking at using magnifiers and getting sand in their eyes. Now I give children just a pinch of sand into their palms and caution them not to blow or it may get into their eyes. I could also have the children use safety goggles but they find it hard to use the magnifiers at the same time.
• Children standing on a group of marbles (on purpose) and slipping. Now I only give out two marbles per child.
• Children falling when they slipped on the edge of a scarf while dancing around a room with a tile floor. We moved the scarves to a carpeted area.
• I forgot that a child had contact allergies to wheat and brought in a container of Tenebrio beetles and their babies (mealworms) which live in a bedding of oatmeal and wheat bran. Luckily another teacher remembered before I opened the container and the class just observed the insects inside.
• Children flinging dirt up into the eyes of the next child. Now I model how to dig towards oneself before we hand out the large soup spoons we use as trowels. It also helps to enthusiastically say, “Oh look at all that good dirt you are digging up! Save that dirt right next to the hole so you can use it to put back around the flower bulb/roots after you plants.”

I hope you’ll share some safety tips with all the Early Years readers by commenting below.
Washing hands after handling dirt, or other substance which may have harmful bacteria, viruses, or molds, or animals such as guinea pigs or slugs, is one of the easiest safety precautions to put into use, but it does take time. It makes sense to have a sink in every early childhood classroom and two or three might be even better! Can you suggest ways to make hand-washing go faster or an activity to do while waiting to wash?
Peggy