如果已经对公共阀门的位置和/或安全阀的间距进行了评估，则操作员可以评估公共阀门的位置和/或安全阀的间距，以确定公共阀门之间的关系。

This report examines prior studies that have been conducted to define the relationship of block valves on gas transmission pipelines to public safety, assesses the relationship of valve spacing and valve operator type on public safety and evaluates if valve spacing/valve operator type, or valve location can improve public safety.