Even for simple construction, the sequence must be considered

Thread Content

Source: Team Safety. Everyone has heard the saying “Haste makes waste,” and similar situations often arise in both life and work. Today, I’ll tell you a story about a construction project that was not carried out in order, which resulted in a flash explosion. It was in April 2003, during the major maintenance period in the Factory South Area; our workshop had to conduct maintenance and inspection on a high-pressure gas tank with a diameter of 1 meter and a height of less than 2 meters. To do this, it was necessary to grind out the weld seams on the tank. At this point, the entire gas pipeline network has been subjected to steam purging and cooking, and the liquid separation tank has its middle manhole opened for natural ventilation; however, the unit responsible for removing debris has not yet begun working. For the construction of this type of equipment inspection project, the normal procedure is to first use steam for steaming in order to remove any flammable materials from within the tank, then clean up the residues left in the tank, and finally grind the weld seams in preparation for the inspection. This time, the contractors in charge of the grinding work thought that the project was relatively small, so they wanted to assign someone casually to finish the job quickly so they could move on to other tasks. They therefore persuaded a supervisor in the workshop: since the tanks had already been properly sterilized, it didn’t matter whether cleaning or grinding was done first. With his approval, they began carrying out the work. The workshop technicians contacted the laboratory staff to conduct a gas analysis of the separation tank; the results were satisfactory, and accordingly, work permits for entering the container and permits for working with fire were issued. The construction party assigned one worker to go into the tank to grind the weld seams. After entering through the manhole, the worker dragged tools such as grinders into the tank, located the welds, and began grinding them. Soon, a loud explosion was heard, and an explosion occurred inside the tank. The worker emerged from the manhole, rolling and crawling, with his hair and eyebrows burned by the fire; his face was red, and the synthetic fabric of his pants stuck tightly to his legs due to the fire, causing burns to his ankles which had no underwear to protect them. He was so terrified that he trembled all over. When the supervisor arrived at the manhole with a fire extinguisher ready to put out the fire, he found that the fire inside the tank had already been extinguished. Afterward, we conducted an analysis of the reasons, and the main one was that the construction was not carried out in accordance with the prescribed sequence. Only steam cooking was carried out in the separation tank, and the combustible gases in the gas phase space inside the tank were completely removed; therefore, the gas analysis inside the tank was satisfactory. However, the residues accumulated at the bottom of the tank were not cleaned up. The steam only vaporized the oil and gas on the surface of these residues. When workers entered the tank, they disturbed the residues at the bottom, causing the gas contained within them to be released. This gas reached its explosive limit, and an explosion occurred when it came into contact with the open flame generated by the grinding machine. If the residue had been removed first as required before grinding, this flash explosion accident would not have occurred. Fortunately, there was only a small amount of combustible gas released from the residue in the tank, and no continuous combustion occurred. Furthermore, this construction worker was not wearing the proper personal protective equipment; he was dressed in synthetic pants and nylon socks, which stuck to his legs when fire broke out, causing burns to his calves and ankles. Fortunately, the lining of the bag is cotton; otherwise, the damage could have been worse. Therefore, to ensure construction safety, it is necessary to organize work in strict accordance with regulations, as each preceding process often serves as the foundation for the next one. Those seemingly simple construction tasks cannot be ignored; accidents often occur unexpectedly. No matter how simple the task, it should still be carried out in order.