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Module 8 : Pressure Hazards Pressure is defined in physics as the force exerted against an opposing fluid or thrust distributed over a surface. This may be expressed in force or weight of unit per area, such as psi (pounds per square inch). A hazard is the condition with the potential of causing injury to personnel, damage to equipment or structures, loss of material, or lessening of the liability to perform a prescribed function. Thus, a pressure hazard is a hazard caused by a dangerous condition involving pressure. OSHA defines high pressure cylinders as those designated with a service pressure of 900 psi or greater.

Boilers and pressure hazards A boiler is a closed vessel in which water is heated to form steam, hot water, or hightemperature water under pressure. Potential safety hazards associated with boilers and other pressurized vessels include the following: -

Design, construction, or installation errors


Poor or insufficient training of operators


Human error


Mechanical breakdown or failure


Failure or blockage of control or safety devices


Insufficient or improper inspections


Improper application of equipment


Insufficient preventive maintenance

High-temperature water hazards High-temperature water (HTW) is exactly what its name implies, but not hot enough to produce steam. In some cases, HTW can be used as an economical substitute for steam.

Hazards of unfired pressure vessels Unfired pressure vessels include compressed air tanks, steam jacketed kettles, digesters, and vulcanisers, as well as others that can create heat internally by various means rather than external fire. The potential hazards associated with unfired pressure vessels include 1

hazardous interaction between the material of the vessel and the materials that will be processed in it; inability of the filled vessel to carry the weight of its contents and the corresponding internal pressure; inability of the vessel to withstand pressure introduced into it plus pressure caused by chemical reactions that occur during processing; and inability of the vessel to with stand any vacuum that may be created accidentally or intentionally. The most effective preventive measure for overcoming these potential hazards is proper design.

Hazards of high-pressure systems The hazards most commonly associated with high-pressure systems are leaks, pulsation, and vibration, release of high-pressure gases, and whiplash from broken high-pressure pipe, tubing, or hose.

Cracking hazards in pressure vessels One of the most serious hazards in pressure vessels is the potential for cracking. It can lead to either a complete rupture or leaks.

Figure 1: Diagram of a typical pressure vessel showing potential points for leakage or rupture.


Module 8_Pressure Hazards