Positive isolation methods are those which remain effective even if there is equipment failure or operator error. These techniques apply not only to vessels, piping and tanks but also to pneumatic and hydraulic equipment.
The sketch shows some of the various isolation techniques that can be used to protect workers in the process industries. The process containing toxic or flammable chemicals under pressure is on the left; the open system, where the workers are present, is on the right. The order is from the least to the most secure.