On August 28, 1992, a cryogenic tank ruptured in Hokkaido, Japan, and is a textbook case study in the catastrophic consequences of completely isolating a cryogenic vessel.
The explosion occurred in the middle of the night at a food processing factory. The blast destroyed the upper half of the facility, damaged 25 surrounding buildings, and wrecked 39 parked vehicles within a 1,300′ radius. The largest piece of debris—a 5′ wide section of the outer shell head—was thrown 1,100′ from the site.
The vessel was a vertical, double-shell, vacuum-insulated cold evaporator (Model CE-7500) designed for liquefied nitrogen storage.
- Inner Shell: Stainless steel
- Outer Shell: Carbon steel
- Insulation: Vacuum-packed perlite in the annular space between the shells.
This was a classic physical overpressure rupture caused by the total isolation of a cryogenic system combined with ambient heat inleak.
- Total Isolation: The post-accident investigation revealed that manual block valves located immediately below the vessel’s primary relief devices—a safety relief valve and a bursting disc—had been closed. The liquid inlet and outlet valves were also shut.
- Heat Inleak: Over approximately 60 days after its last fill, ambient heat steadily penetrated the tank’s vacuum insulation.
- Pressure Accumulation: As the liquid nitrogen absorbed heat, it boiled off and expanded in a confined, completely closed system. Because the relief path was blocked, the internal pressure climbed continuously.
- Catastrophic Rupture: The internal pressure eventually exceeded the ultimate tensile strength of the inner stainless steel shell. Investigators estimated the inner shell failed at approximately 1,000 psig. The sudden release of potential energy shattered the inner vessel into seven fragments and the outer carbon steel shell into eleven main pieces.
The Hokkaido incident revealed severe deficiencies across multiple layers of safety management, highlighting why strict adherence to recognized codes and standards is non-negotiable:
- Relief System Design (No Interlocks): The system was designed with manual isolation valves below both relief devices. Crucially, there was no mechanical interlock (such as a 3-way transflow valve) or administrative control (like car-sealing or locking the valves open) to ensure that at least one relief path remained open to the vessel at all times.
- Operating Procedures: There were no documented operating manuals for the nitrogen vessel. Personnel lacked basic step-by-step instructions for safe operation, startup, and shutdown.
- Training & Competence: Operators were not given safety instructions regarding the extreme physical hazards of isolating cryogenic liquids and the inevitability of pressure buildup.
- Routine Inspections: The required daily inspections of the vessel were largely neglected, allowing the completely isolated condition to persist unchecked for roughly two months.
This incident underscores the absolute necessity of rigorous relief system management and demonstrates exactly why industrial codes heavily regulate the placement and control of block valves upstream of pressure relief devices.
Source: Gemini+