【Mistakes We Made Over the Years】018 Incorrect connection of air supply for diaphragm pump

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This post was last edited by 68589544 on 2017-5-17 at 13:32. Yesterday, the circulation pump of the company’s refrigeration unit was switched over, and during this process the pressure in the low-temperature water network increased. A device’s underground tank was cooled by low-temperature water, and the safety valve installed at the inlet to this water opened due to overpressure. Since it was located in an underground tank, the leak was detected only late, resulting in the loss of more than ten tons of low-temperature water. Since the leaked low-temperature water is relatively clean, it was decided to use a diaphragm pump to pump it back into the low-temperature water system in order to reduce losses. When I arrived at the site, I found that the maintenance team had already connected the temporary diaphragm pump, as well as the inlet and outlet pipelines and the air supply. At that time, I sensed something was wrong, but I couldn’t recall what it was. On my way back to the office, I realized what the problem was: the air supply for the diaphragm pump was connected to nitrogen. I returned to the site immediately; the maintenance team had just started the nitrogen startup pump. I told them to stop working, to switch the gas supply to industrial air, and shared with the people on site a case I had seen before. In June 2001, a petrochemical plant in Hunan Province carried out expansion and renovation work on its facilities. The construction unit is carrying out earthwork pile-digging operations inside the production facility, with the workers using pneumatic hammers powered by compressed air. The pile hole is a shaft with a diameter of 1.3 m and a depth of 11 m. On the first day of construction, everything proceeded normally. On the second day, the well was dug to a depth of 3 meters; before starting work, tests were conducted for oxygen levels, combustible substances, and toxic substances (oxygen level: 19.7%, no detectable amounts of combustible or toxic substances), and a permit for equipment entry was obtained. When the work began, 5 minutes after the workers descended into the well, they experienced symptoms of chest tightness and dizziness. They thought it was due to physical discomfort, so they came back up to the surface and had someone else take over the work. Even after the replacement, the workers down in the well continued to suffer from chest tightness and dizziness. The supervisor realized that something was wrong and reported it to the safety officers. Safety officers arrived at the scene and immediately took samples from the well for analysis. The results showed an oxygen content of 10%, while no combustible materials or toxic substances were detected. After questioning the construction workers and inspecting the construction tools, it was found that the air supply for the pneumatic hammer had been incorrectly connected to the nitrogen pipeline. Cause analysis: The direct cause of the accident was that the construction unit used the gas source without the consent of the production unit, diverting nitrogen as a power source to drive the pneumatic hammer. On the first day of construction, the well hole was shallow and the nitrogen concentration was not high, so the workers did not feel any effects. On the second day, as the depth of the well hole increased, the nitrogen emitted by the pneumatic hammer accumulated inside the well, reducing the oxygen level and causing the workers to experience symptoms of suffocation. Lesson: When construction teams enter chemical production facilities to carry out work, they must not use the production equipment on site (switches, valves, buttons). If it is indeed necessary to use the equipment within the facility, this must be done with the approval of the person in charge of the facility’s operations, and under the supervision and assistance of the production operators. Diaphragm pumps and pneumatic hammers operate on similar principles, both converting the pressure of air into mechanical energy. They are typically driven by industrial air (compressed air); nitrogen can be used in well-ventilated areas, but it must never be used in areas with poor ventilation or in confined spaces, as this can lead to suffocation accidents.