Section 18.98 - Enclosures, joints, and fastenings; pressure testing(a) Cast or welded enclosures shall be designed to withstand a minimum internal pressure of 150 pounds per square inch (gage). Castings shall be free from blowholes.(b) Pneumatic field testing of explosion-proof enclosures shall be conducted by determining: (1) Leak performance with a peak dynamic or static pressure of 150 pounds per square inch (gage); or(2) A pressure rise and rate of decay consistent with unyielding components during a pressure-time history as derived from a series of oscillograms.(c) Welded joints forming an enclosure shall have continuous gastight welds.