As I have written about numerous times… PRESSURE TESTING a process is not only a “good idea” – it is REQUIRED for those of us in the process safety world. It is a critical path in process safety, ensuring our “primary containment” system (e.g. piping) was installed properly and can withstand process pressures. But with these tests comes some inherent risks and as in the case of OSHA Case File #310715214, we see how catastrophic an error can be. We can also see why the piping RAGAGEPs require TWO (2) independent means to ensure the process piping circuit being tested is NOT over pressurized.
345.5.2 Pressure Relief Device. A pressure relief device shall be provided, having a set pressure not higher than the test pressure plus the lesser of 345 kPa (50 psi) or 10% of the test pressure.
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345.5.5 Procedure. The pressure shall be gradually increased until a gage pressure that is the lesser of one-half the test pressure or 170 kPa (25 psi) is attained, at which time a preliminary check shall be made, including examination of joints in accordance with para. 341.4.1(a). Thereafter, the pressure shall be gradually increased in steps until the test pressure is reached, holding the pressure at each step long enough to equalize piping strains. The pressure shall then be reduced to the design pressure before examining for leakage in accordance with para. 345.2.2(a).
In this tragic case, On March 13, 2007, Employee #1 (subcontractor) was performing maintenance on commercial food service equipment. He was in the kitchen area of a single-story restaurant, attempting to locate the source of a refrigerant leak in an ice cream storage dipping cabinet. Employee #1 connected a cylinder containing pressurized nitrogen to the dipping cabinet’s refrigeration system via a hose without using a pressure reducing device, such as a pressure regulator or pressure relief valve. The cylinder’s internal pressure of approximately 2,200 psig was considerably in excess of the dipping cabinet’s maximum test pressure of approximately 150 psig. This disparity overpressurized the dipping cabinet’s refrigeration system and caused it to explode. The upper part of the compressor broke off and struck Employee #1 in the head, killing him.