On March 13, 2007, Employee #1, a subcontractor, performed maintenance on commercial foodservice 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 Nitrogen cylinder 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.
Here are the requirements from ASME B31.3 leak test (e.g. pressure testing)…
(emphasis by me)
345.5 Pneumatic Leak Test
345.5.1 Precautions. Pneumatic testing involves the hazard of released energy stored in compressed gas. Particular care must, therefore, be taken to minimize the chance of brittle failure during a pneumatic leak test. Test temperature is important in this regard and must be considered when the designer chooses the material of construction. See para. 345.2.2(c) and Appendix F, paras. F323.4 and F345.5.1.
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.
345.5.3 Test Fluid. The gas used as test fluid, if not air, shall be nonflammable and nontoxic.
345.5.4 Test Pressure. The test pressure shall be not less than 1.1 times the design pressure and shall not exceed the lesser of
(a) 1.33 times the design pressure
(b) the pressure that would exceed 90% of the pressure described in para. 345.2.1(a)
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).