Question: Very simply, do you wear one or two foot straps to protect against ESD?
Answer: You should wear two foot straps, for the purpose of continuous grounding. Additionally, the floor should be conductive or the foot straps will not work. The intent of the grounding straps, be it foot straps or wrist straps is to reduce the static electricity potential in the human body, so when working with ESD sensitive products, they will not be destroyed.