Hazards of Pressure, Steam, and Electricity

Upon completion of this chapter the student should be able to  

On April 27, 1865, the side-wheeler steamer Sultana, overloaded and carrying more passengers than it should, steamed up the Mississippi River. The Sultana carried more than 2,000 Union soldiers, many bound for home after being released from Confederate prison camps. Quick repairs had been made to the vessel s boilers at Memphis. A few miles north of Memphis, the boilers blew up and tore the Sultana apart, hurling men and parts of the vessels hundreds of feet. An estimated 1,700 soldiers died either from the explosion or from drowning. The pressures at which the Sultana s boiler normally operated, and even the pressure at which it ruptured so violently, would be considered low compared with boiler pressures commonly used today. 

It is not necessary to have much pressure to create conditions where serious injuries and damage can occur. It is commonly and mistakenly believed that injury and damage will result only from high pressures, however, there is no agreement on the definition of the term high pressure beyond the fact that it is greater than normal atmospheric pressure. 

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Steam, and other vapour heating systems, are intrinsically safe as the temperature cannot exceed the saturation temperature at the supply pressure. Other heating systems rely on control of the heating rate to limit the maximum process temperature. Electrical heating systems can be particularly hazardous. 

Examples of common safe practices are pressure relief valves, vent systems, flare stacks, snuffing steam and fire water, escape hatches in explosive areas, dikes around tanks storing hazardous materials, turbine drives as spares for electrical motors in case of power failure, and others. Safety considerations are paramount in the layout of the plant, particularly isolation of especially hazardous operations and accessibility for corrective action when necessary. 

Hazardous features to be considered will include pressure relief handling of hazardous materials such as acids and alkalis protection from steam and other high-temperature fluids and electrical classification for handling solvents or protection from water ingress, high speed rotating machinery, and noise levels. 

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