Investigation Report on Disease from Oxygen Deficiency at the Clear Water Reservoir of the Village Water Supply System, Moo 4, Nongklap Subdistrict, Nongbua District, Nakhon Sawan Province
Keywords:
Epidemiological Investigation Report , Confined Space , Toxic Gas , Clear Water TankAbstract
On April 23, 2025, the Situational Awareness Team of the Office of Disease Prevention and Control 3 was notified of an incident involving five casualties (one fatality and four injuries) inside a clear water storage tank of a village water supply system in Moo 4, Nong Klap Subdistrict, Nakhon Sawan Province. The disease investigation team deployed to the area on April 25, 2025. The objectives were to confirm the diagnosis, determine the causes of injuries and fatalities associated with working in a confined space, and identify appropriate measures for planning the prevention of confined space-related injuries and fatalities. The study methodology employed a descriptive cross-sectional epidemiological approach. This involved reviewing medical records from Nong Bua Hospital in Nakhon Sawan Province, interviewing relevant individuals, collecting data on the injured and deceased, surveying the environment, and measuring toxic gas levels under normal conditions compared to simulated conditions involving the agitation of sludge at the bottom of the tank. The results showed a total of five victims: one fatality (a 26-year-old male) and four injuries. The cause of death was asphyxiation (lack of oxygen). The incident site was a 4-meter-deep concrete clear water storage tank with an accumulation of sludge reaching 1 meter high. Gas monitoring under normal conditions showed values within standard limits. However, during the simulation involving the agitation of the sludge at the bottom of the tank, hydrogen sulfide (H2S) levels reached as high as 41.6 ppm (standard limit: 20 ppm), and ammonia (NH3) levels surged to 440 ppm. This exceeded the Immediately Dangerous to Life or Health concentration (IDLH: 300 ppm) according to NIOSH standards. In conclusion, the loss of consciousness and fatality were caused by the inhalation of high-concentration toxic gases released from organic sediments during operations. The primary root cause was working in a confined space without ventilation and adequate safety systems.
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