Liquid nitrogen explosion

 https://www.safework.nsw.gov.au/__data/assets/pdf_file/0008/1054718/liquid-nitrogen-explosion.pdf

Nitrogen pipeline ruptured

Part of the pipeline network used to channel nitrogen gas at a manufacturing plant has suffered a failure and ruptured. This incident took place after the refilling of liquid nitrogen from transportation vehicle into the storage tank was done. No loss of life or injury was reported because there was no worker in that area during accident.

Investigation found (revealed) that the pipelines which are made of carbon steel, ruptured in many parts during the accident. Failures on welded part of the pipeline were also detected.

Recommendation of Improvement:

1. Welding on critical and pressurised parts should be done by a qualified welder. The process and method of welding shall meet the requirements of relevant standards.
2. Design of storage tanks and pipelines should be in compliance with the appropriate design standards and code of practice.
3. Pressure safety valve shall be installed at appropriate location on the storage tanks to prevent undetected overpressure. The safety valve must also be suitable with the range of pressure used.
4. Some metals become brittle when exposed to low temperature. This condition can cause failure to happen in a short period of time and without imminent warning. For this purpose, any metal used for pipelines and storage tank shall be suited to the type of gas/ liquid and operating temperature/ pressure, especially if it involves cryogenic process or materials.

Source: https://www.dosh.gov.my/index.php/osh-info-2/safety-alert/749-nitrogen-pipeline-ruptured

Rupture of a Liquid Nitrogen Storage Tank

On 28th August 1992, there was a catastrophic failure of a storage tank containing liquefied nitrogen. The failure resulted in the collapse of almost half of the manufacturing site and damage to houses and vehicles within a 400 metre radius. Fragments of the vessel were projected up to 350 metres, the largest of which, a section of the outer shell head was 1.5 metres wide and 8mm thick.

The tank was a double-walled vacuum-insulated ultra-low temperature storage vessel designed to operate at -196°C and 9.3 bar (maximum normal operating pressure).

The inner vessel broke into seven fragments and the outer vessel broke into eleven main fragments and numerous smaller pieces. It was discovered during the course of the investigation that most of the valves on the system were closed including the top liquid inlet, liquid outlet and the isolation valves for the relief valve and bursting disc. The vessel was therefore under completely closed conditions at the time of the accident. The bursting disc was found to be ruptured despite the closed inlet valve, however it was believed that the valve might have been closed after the disc ruptured on a previous occasion. The inner and outer shells ruptured as a result of excessive pressure under closed conditions. It was estimated that the inner shell ruptured at a pressure of 68.7 bar. The pressure reached this level as a result of heat inflow over the sixty days between its final filling and the time of the explosion.

Failures in technical measures

• Isolation valves were fitted below both relief devices without any interlocking system to ensure that one device was always protecting the vessel.
• Relief Systems / Vent Systems: relief valves, bursting discs
• There were no manuals for the operation of the nitrogen vessel. The daily inspections required on the vessel were largely neglected and no safety instructions were given to employees.
• Training: operator training
• Operating Procedures: provision of comprehensive operating procedures

Source: https://www.hse.gov.uk/comah/sragtech/caseliqnitro92.htm

Liquid nitrogen incident

 At 5:30 p.m. on February 5, 2017, an employee was responding to an emergency alarm. As he entered a space that was oxygen deficient, he was knocked unconscious. The employee was rescued from the space and was hospitalized, where he received treatment for having been exposed to an oxygen deficient atmosphere, as well as hypothermia and frostbite. His injuries resulted in amputation of an unspecified extremities. The incident investigation revealed that the space contained liquid nitrogen. 

Source:Osha.gov

Electrocution incident

On January 14, 2004, Employee #1, was contracted by the client to provide additional electrical power to boost up the power available from the utility company, which the client needed to test some special equipment. This client is involved in the manufacture and testing of cryogenic pumps and other parts used in the aerospace industry. The manufacturing and testing operations are housed in a large building. The employer had temporarily wired up additional generators to a transformer owned and maintained by the client. This temporary wiring setup including the generators and the transformer was entirely located outside in the parking area behind the manufacturing building. This testing had been completed and the employer was in the process of dismantling this temporary setup when this incident occurred. The circuits containing generators and the transformer had been completely shut down and there was no live part in the temporary wiring setup. The enclosure that housed this transformer for the temporary setup had three additional cables running through it. These cables were spliced inside this enclosure and had no connection to the transformer. These spliced cables carried Edison 4160VAC power for a 150-horse power motor used by the client as permanent equipment, which was not involved in the temporary wiring setup by the employer. It appears that the transformer enclosure was also used as a junction box for the spliced cables. Each of the spliced connections was covered with pieces of PVC pipe and some duct tape. Before the incident a coworker had tested transformer terminals and determined that there was no power in any part of the transformer. As part of the temporary setup dismantling process, Employee #1 was helping the corker to disconnect the cables from the transformer. While Employee #1 was disconnecting a cable from the transformer, one of the spliced connections was exposed, which started an electrical arc and fire. The right forearm of Employee #1 was burned in the fire before he could get away. Employee #1 suffered third degree burns to his right forearm and was hospitalized for three weeks. 

Source:Osha.gov

Asphxiation incident

Employees were tasked to fill a series of Chart MVE 1842P-150 Cryogenic Freezers in an enclosed storage room on a weekly basis. The room was not equipped with an adequate engineered ventilation system or oxygen monitoring equipment or system. On the evening of November 20, 2019, an employee began topping the bulk tanks off with liquid nitrogen when the room became filled with nitrogen gas causing the employee to collapse and eventually succumb to the oxygen-deficient atmosphere created in the room. The room was not equipped with an adequate engineered ventilation system or oxygen monitoring equipment or system. This condition exposed an employee to an oxygen deficient atmosphere while filling bulk tanks with liquid nitrogen. 

Source:OSHA.gov

Decomposition incident

 On September 21, 2003, Employee #1 and several coworkers were working at a chemical plant that deals with nitric oxide. On the day of the accident, a major leak occurred in a stainless steel distillation column. The nitric oxide leaked into the facilities surrounding vacuum jacket and into the atmosphere through a pump, which controls a high quality vacuum inside the jacket to minimize transmission of heat toward the cryogenic distillation columns. A brown cloud quickly formed and the temperature and the pressure inside the distillation column and its surrounding vacuum jacket began to rise. The leak was detected and the vacuum pump was turned off to halt the leakage of nitric oxide into the atmosphere, allowing the pressure inside the column and vacuum jacket to stabilize around 130 psi. Although stabilized, the pressure was far above the normal pressure of less than or equal to atmospheric pressure (14.7 psi). Approximately 3 hours later, an explosion occurred. The operation and process were destroyed, and debris flew through the plant. Employee #1 suffered lacerations due to flying glass and was treated at a local hospital, where he received stitches and then released. A detailed investigation determined that the cause of the explosion was most likely due to something inside the vacuum jacket initiated the dissociation of nitric oxide, a reaction that is very rapid, exothermic, and self-propagating once started. 

Source:Ohsa.gov