A radiation accident occurred in Samut Prakan Province, Thailand in January–February 2000. The accident happened when an insecurely stored unlicensed cobalt-60 radiation source was recovered by scrap metal collectors who, together with a scrapyard worker, subsequently dismantled the container, unknowingly exposing themselves and others nearby to ionizing radiation. Over the following weeks, those exposed developed symptoms of radiation sickness and eventually sought medical attention. The Office of Atomic Energy for Peace (OAEP), Thailand's nuclear regulatory agency, was notified when doctors came to suspect radiation injury, some 17 days after the initial exposure. The OAEP sent an emergency response team to locate and contain the radiation source, which was estimated to have an activity of 15.7 terabecquerels (420 Ci), and was eventually traced to its owner. Investigations found failure to ensure secure storage of the radiation source to be the root cause of the accident, which resulted in ten people being hospitalized for radiation injury, three of whom died, as well as the potentially significant exposure of 1,872 people.
Background
Cobalt-60 (60Co) is a synthetic radioactive isotope of cobalt, with a half-life of 5.27 years, and emits highly penetrating gamma rays. It is commonly used as a radiation source for radiotherapy and equipment sterilization in hospital settings, and also has industrial uses. The device involved in the Samut Prakan accident was a rotational Gammatron-3 teletherapy unit, manufactured by Siemens and imported to Thailand in 1969. It was licensed for and installed at Ramathibodi Hospital in Bangkok; the radiation source involved was a replacement installed in 1981, with an initial radioactive activity of 196 TBq (5,300 Ci). At the time of the accident in 2000, its activity was estimated to have decayed to 15.7 TBq (420 Ci). The licensing of radioisotopes and nuclear material for import, export, possession and use in Thailand is regulated by the Thai Atomic Energy Commission for Peace and its working body, the Office of Atoms for Peace (OAP), formerly known as the Office of Atomic Energy for Peace (OAEP). In principle, the licensing process would involve annual safety inspections, but due to lack of personnel and resources, such inspections were not always properly performed, nor were regulatory and control protocols strictly enforced. The hospital retired the radiotherapy unit in 1994 and acquired a new one from Nordion via its Thai agent Kamol Sukosol Electric Company (KSE). The old unit and its 60Co source could not be returned either to its original German manufacturer Siemens, which had stopped producing or servicing them, or to the Canadian supplier Nordion, which was not the original manufacturer. Consequently, the hospital sold the old unit to KSE, which already had another licensed unit in storage. Neither the hospital nor KSE informed the OAEP of the transfer. In 1996 an OAEP inspection found that KSE had three unlicensed units in its warehouse, which had been licensed for the storage of a single unit in 1988. KSE's lease of the warehouse was terminated in 1999. KSE subsequently returned the licensed unit, while moving the three unregistered units to an unused car park in Bangkok's Prawet District, which was owned by its parent company. The car park was fenced, but the fence had been breached and nearby residents regularly entered to play football in its empty areas. KSE notified the OAEP of its transfer of the licensed unit, but did not mention the other three, which remained orphan sources.
Accident
On 24 January 2000, the part of the radiation therapy unit containing the radiation source was acquired by two scrap collectors, who claimed to have bought it from some strangers as scrap metal for resale. They took it home, planning to dismantle it later. On 1 February, the two, together with another two associates, attempted to dismantle the metal part (a 97-kilogram; 214 lb, 42-by-20-centimetre; 16 x 8 inch lead cylinder held in a stainless steel casing), which was the unit's source drawer. Using a hammer and chisel, they only managed to crack the welded seam. Two of the men then took the metal piece, along with other scrap metal, to a scrapyard on Soi Wat Mahawong in Phra Pradaeng District, Samut Prakan Province. There they asked a worker at the scrapyard to cut open the cylinder using an oxyacetylene torch. As the cylinder was cut open, two smaller cylindrical metal pieces, which had held the source capsule, fell out. The worker retrieved the two pieces and kept them in the scrapyard, but was unaware of the source capsule itself. The lead cylinder was returned to the scrap collectors for them to complete the disassembly. That same day, the four men present when the cylinder was opened (two of the scrap collectors and two scrapyard employees) began to feel ill, experiencing headaches, nausea and vomiting. The scrap collectors succeeded in taking the lead cylinder apart, and took the parts to sell at the scrapyard the next day. The scrapyard employees continued to feel sick during the following week, and on 12 February the scrapyard owner, believing the metal to be causing the illness, asked the scrap collector to take it elsewhere, and had the two smaller metal pieces thrown away. By mid-February the symptoms of those involved were worsening. The symptoms included burn wounds, swollen hands, diarrhoea, fever, and hair loss. One of the scrap collectors went to Samut Prakan Hospital on 15 February and was admitted the next day, while the two scrapyard employees were also admitted, on 16 and 17 February. The scrapyard owner's husband was admitted to Bangkok General Hospital on 17 February due to epistaxis (nosebleeds), while the scrapyard owner, her mother, and her maid (all of whom lived across the street from the scrapyard and sometimes entered) also began to feel ill. A stray dog that was often seen in the scrapyard died. Two of the patients at Samut Prakan Hospital were admitted to the surgical ward, while the other was admitted to the medical ward. All were nauseated and vomiting, and two of them were showing leukopenia (low white blood cell count). Reviewing the cases on 18 February, the doctors realized their symptoms were likely caused by radiation exposure, and notified the OAEP.
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