Overexposure of radiation workers

After an engineer and two operators had completed the logging operation and prepared the rig floor for lifting the logging source, logging tools were brought back to surface. The two radioactive logging sources, Cs-137 and Am241-Be, were unloaded from the logging tools by the engineer.

Unknown to the engineer, the Cs-137 source (54 GBq) was not secured in its shielding and was left lying on the rig floor. The two source shields, one unknowingly empty, were brought down from the rig floor and secured inside the logging truck. The barriers and radiation signs that erected prior to lifting the logging tools were removed.

An operator remained on the rig floor to dismantle the logging tools. He spent approximately 5 minutes kneeling next to the tool box preparing the tools for dismantling the logging tools. It was presumed that during this time the logging source was (unknowingly) in close proximity to his lower leg.

After this period of time, and seeing that the signs had been removed, the drilling crew consisting of two drillers went up to the rig floor to help the operator dismantle the tools.

After spending approximately 10 minutes on the rig floor dismantling the tools, a driller saw the logging source lying on the floor next to the well, approximately 1m from where he was standing. Not knowing what it was, he picked it up and inspected it for around 45 seconds, before handing it to the operator. The operator inspected the source and after seeing the serial number realised it was a logging source. Confirmed by another operator, the source was placed back to the shielding.

All personnel were admitted to a regional hospital for monitoring and released after three days. About 7 days after exposure, operator #1 noticed hair loss on his lower left leg. After a further 8 days (15 days after exposure) he developed a rash on that area followed by painful ulceration.

Calculated doses were as follows.

Engineer - 0.18 mSv whole body dose
Operator #1 - 2.7 mSv whole body dose, 4-13 Sv equivalent dose to leg, 510 mSv to hand
Operator #2 - 53 mSv equivalent dose to hand
Driller - 0.9 mSv whole body dose, 570 mSv equivalent dose to hand.

The nature of the leg injury to operator #1 suggested a dose of about 15 Gy to the skin and nearby tissue.

Location: Queensland field site west of Chinchilla
Event date: Fri, 28-02-2014
Nuclear event report
Legenda & explanation