Shock triggers aging gas cylinder to burst and fragment at Nam Ngiep 1 Project
Investigations into the bursting and fragmentation of a pressurized oxygen cylinder concluded that it is highly likely that the deadly combination of shock that resulted from dropping the cylinder onto a hard surface and the inherent brittleness of the steel casing through long service caused the deadly accident in which six workers lost their lives and two more were injured at the Nam Ngiep 1 (NNP1) Hydropower Project main dam works at the end of July 2017.
According to all external experts consulted internationally, and after thorough research of similar accidents, the fragmentation feature of the bursting was found to be most unusual, as such cylinder failures normally result in the cylinder remaining intact and fracturing or splitting, rather than fragmenting. The experts were unanimous in their conclusions, and ongoing laboratory testing is expected to confirm these findings, that strength and durability were seriously diminished in the aging cylinder by the metal casing becoming brittle.
The shock of a sudden impact was concluded to be the trigger for the cylinder to fragment. Though corrosion was observed on both sides and at the fracture of the fragments of the cylinder that were recovered afterward, the exterior surface did not exhibit any obvious signs of heavy rust. Initial results from the testing of fragments of the burst cylinder in materials laboratories have already indicated weaker strength than expected and required, while early chemical tests showed results within the standard range. It is thought that internal corrosion may have resulted from water and impurities left inside the cylinder after washing and use of the cylinder for storage of various gaseous and liquid materials over its many years of service.
The police report after their intensive investigation concluded that the oxygen cylinder was accidentally dropped from the carriers’ hands and hit the concrete surface and disintegrated on impact. Experts consider this to be the trigger that caused the pressure inside the cylinder to increase and the cylinder to effectively explode into small pieces thereby causing serious damage to life and limb of those nearby.
“Immediately following the accident and to fully ensure the safety of all employees of Nam Ngiep 1 Power Company Limited (NNP1PC) and those of our contractors, all works were suspended. Following 12 days of investigation all works on Site have now resumed as normal except in the use of gas cylinders for cutting steel, until such time as all gas cylinders have been checked and certified for use,” said Mr. Yoshihiro Yamabayashi, the Managing Director of the Nam Ngiep 1 Power Company.
“This is understood to be the first accident of its kind in Laos. To prevent it happening again in the future, NNP1PC will work with authorities in Laos in order to stimulate high-level thinking that low-level workmanship and poor standard equipment lead to unnecessary and currently unnoticed safety hazards in the workplace. It is hoped and expected that this will lead to the establishment of appropriate safety standards for the use of pressurized gas cylinders in Laos,” he added.
The accident happened during the night shift on Friday, 28th July 2017 when two workers were carrying the cylinder at the time it burst, killing three workers instantly and an additional three more workers were later pronounced dead in Paksan hospital. Five other injured workers were taken to hospital but all were discharged within a few days and some have returned to work. Hearing and sight checks have been given to approximately 80 workers who were in the vicinity of the accident when it occurred. Two workers were found to have suffered possible damage to the tympanic membrane in their ears.
All six workers who died are Vietnamese nationals and worked for Song Da 5, one of the subcontractors of the NNP1 Project.
The Vietnamese families of the deceased have been compensated in accordance with Laws of the Government of Vietnam.
NNP1 is a hydropower project with the installed capacity of 290 megawatt which is under construction in the Bolikhamxay and Xaysomboun Provinces. The Project consists of the construction of two dams and two powerhouses along the Ngiep River in Bolikhamxay Province, in Lao PDR.
The construction of the re-regulation dam was impounded in May 2017. Overall progress of the project is almost 78% at the end of July 2017 and electricity generation is expected in February 2019
Photo: ©NNP1PC/Mr. Vilakhone SIPASEUTH
Minister of Energy and Mines, H.E. Dr. Khammany Inthirath, fourth from the right, and provincial government officials and NNP1PC management inspected the accident scene together at the NNP1 Project on 4th August 2017
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