The Chilca Incident – industrial over-exposure

The Chilca Incident

The IAEA have published a very detailed review of this event and the learning to be gained from it. https://www-pub.iaea.org/books/IAEABooks/11095/The-Radiological-Accident-i

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A serious radiological accident occurred in Peru around midnight on 11 January 2012 during non-destructive testing in the district of Chilca, in the Cañete Province of Lima. An iridium-192 source in a radiography camera being used to test pipeline joints became stuck inside the guide tube, resulting in three workers being overexposed to ionizing radiation.

Pipes were being welded together and a radiography camera was being used to determine the quality of the welds. The equipment used consisted of a 192Ir source inside a shield (see picture). When an exposure is required a remote winding mechanism is used to move the source from inside the shield, along a tube and into collimator – this produces a beam of gamma rays that are used to make the measurement.

The process involves attaching the collimator and guide tube to one side of the pipe being tested and an unexposed film to the other side of the pipe, then retreating, winding

Device used to store and deploy radiation source

the source out, making the exposure and then winding the source in and repeating. The blackening of the film shows where gamma rays have been less well attenuated and can highlight defects in the weld or pipe wall. The team of three took 97 exposures during a night shift. Finishing at 02:20 on 12 January 2012.

The company provided the workers with a kit that included a set of tools and equipment for operational and personal safety. However, the two assistants, Co-worker 1 and Co-worker 2, left their personal dosimeters in the transportation vehicle; thus, Worker 1 was the only worker wearing a personal dosimeter. None of the workers used alarming dosimeters or direct reading dosimeters. They did not adequately test that the source was returning to the shield at the end of each exposure.

At the end of the shift, when the equipment was being dismantled, it was discovered that the source had not returned to its housing.

At 02.30 worker 1 was sick and he continued to be sick for the next few hours. In the course of the night co-worker1 experienced fatigue and co-worker 2 dizziness.

On investigation it was found that some of the films were overexposed.

On 15 January 2012 erythema (redness of the skin or mucous membranes, caused by hyperemia (increased blood flow) in superficial capillaries which occurs with any skin injury, infection, or inflammation and is a symptom of radiation burning) appeared on the left hand index finger of Worker 1. The company then realized that the workers had been overexposed to radiation.

The Peruvian Institute of Nuclear Energy (IPEN) was alerted and responded by recommending hospitalisation of the three workers. A formal request for assistance (the first of three as the situation developed) was sent from IPEN to the IAEA on 20 January 2012 under the Convention on Assistance in the Case of a Nuclear Accident or Radiological Emergency (the Assistance Convention) for dose reconstruction and medical advice. International support helped to understand the medical conditions of the exposed workers and determine their treatment, to understand the doses received and to consider further actions.

The prodromal symptoms of the three were carefully recorded and they were subjected to close examination and observation. The three patients were classified in accordance with the Medical Treatment Protocols for Radiation Accident Victims (METREPOL) system. This considers neurovascular, haematological, cutaneous and gastrointestinal issues and rates each person on a scale of 1 (minimum severity) to 4 (maximum severity) for each. Consideration of the symptoms displayed, the time to onset and their severity allows the doctors to estimate the dose and dose distribution received by a patient and this allows them to predict the course of their illness and to determine the most appropriate treatment.

Worker 1 was the most severely exposed to radiation during the accident. He received a significantly heterogeneous whole body dose of 1.8 Gy (with 75% of the body having received a dose in the range of 4 Gy), as well as doses ranging from 20 to 50 Gy to the extremities of both hands. He was subject to a programme of care and investigation in Peru, Chile and in France. He received reconstructive surgery and cell therapy (mesenchymal stem cells (MSCs) or MSC injections) but still had to have parts of his hand amputated on day 101 after the event.

It was concluded that the work had been badly managed. The trained radiological protection officer was not present, the equipment had been assembled by an untrained person, no attempt had been made to confirm the correct retraction of the source, there were no alarming dosimeters and two of the team were not wearing the supplied dosimeters. This shows poor application of rules and guidance and a poor safety culture.

An observation was that “significant time (6 d) was taken to recognize the radiological nature of the accident, despite the availability of substantial evidence and clinical manifestations. Consequently, as has happened in many other radiological accidents, valuable time was lost before the workers were given appropriate medical evaluation and treatment.” It is suggested that doctors should be trained to suspect and to identify the effects of radiation when patients present with the symptoms of acute radiation syndrome or their case history suggests it is possible.

It was observed that there were problems associated with the analysis of samples and with the sending samples by airline as they demanded confirmation that they were not dangerous. There were also delays with treatment, particularly treatment abroad, on cost grounds, the workers lacking insurance.

The important message here is that these accidents happen and are continuing to happen. Could it happen in the UK? We would like to think not but it only takes a few mistakes with this type of equipment to result in over-exposure. Would it be detected more quickly? We would like to think so. There is at least a suggestion that the workers involved were not open with their initial reports as they feared blame for failing to work to procedures more than they feared the consequences of overexposure and delayed treatment.

This could happen in any county in the UK. It is worth being aware of that and considering how the local authority would react to an event in their area.

Author: Keith Pearce

Emergency Planning and Health Physics consultant and author

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