People have been warned to only visit Cornwall s A&E department for life threatening and emergency conditions after the Duchy s main hospital was put on black alert. The Royal Cornwall Hospital at Treliske in Truro has been raised to OPEL 4 (referring to operational pressures escalation levels ) which is the highest level of alert. It is commonly referred to as black alert , given in the most extreme pressure situations. It classed by NHS England as when a hospital is “unable to deliver comprehensive care” and usually means bed space has been filled. Cornwall Council has asked people to stay away unless in the most serious circumstances.