What is the best safest way to clean carpet on OSB flooring?

The "safest" way to clean carpet is with a dry cleaning product like Capture. You can find it in most home improvement stores. You spray a light mist of pre-cleaner solution on the carpet and then sprinkle a powder. After lightly brushing the powder into the carpet with the brush included in the kit. Let it sit for 30 minutes and vacuum up. If you are looking to have it professionally cleaned, look for someone who uses a carbonated process It leaves less water on the floor. The rental machines you find at the grocery and the home improvement store should be avoided. They leave far to much water on the carpet and will cause your carpet to break down quicker.