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Occupational exposure: Borehole logging
Exploration workers must be trained in the correct use of borehole logging devices containing radiation sources. Not following procedures may result in exposure to high levels of ionising radiation.
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Oil, gas, and mineral exploration workers use borehole logging devices containing sealed radioactive sources to measure the density and porosity of geological formations surrounding the borehole. Sources used for borehole logging could deliver large amounts of radiation in a short time. Workers may be exposed to significant radiological health hazards including potential lethal doses if:
- safety procedures are not followed
- inadequate training and supervision
Or during the following activities:
- fault/jam occurs while operating the borehole logging device
- recovering lost sources
- transferring the source to the shielded transport container.
The main source of exposure for workers using borehole logging devices containing radioactive sources is by external exposure from the sealed radiation source in the device. Once the source of radiation is stored in the appropriate shielded transport container, the exposure stops.
External exposure from the sealed radioactive source that emits gamma or neutron radiation can interact with your body that may result in health effects that could result in serious injuries.
Internal exposure from sealed radioactive sources due to ingestion or inhalation under normal operating conditions is unlikely. However as these sealed radiation sources age there may be leakage of radioactive material creating a pathway for intake into the body. Good inspection and maintenance practices are essential to ensure workers using borehole logging equipment containing radiation sources remain safe to use.
Table 1: Possible health effects
|Dose range (millisieverts)||Description||Possible health effects|
|Up to 10||Very low dose||None observed or expected (typical background range)|
|10–100||Low dose||Plausible health effects but not observed|
|100–1000||Moderate dose||Increase risk of cancer
Acute effects at higher end of range (above 500 mSv)
|Above 1000||High dose||Acute effects (burns, vomiting)
Death possible at very high doses (above 5000 mSv)
No health effects have been observed or are expected to be observed at the very low doses normally received in this occupation.
Ionising radiation has been proven to cause harmful short term effects at moderate and high doses received in short periods of time, above 500 mSv, with an increased risk of cancer shown to occur for long term exposures of above 100 mSv.
Moderate and high dose can occur in borehole logging incidents. With relevant controls in place the risk from normal exposures are very low and comparable with the risks of exposure from background and medical radiation exposure.
In Australia most workers receive very low doses, however there have been borehole logging incidents that have resulted in severe radiation health effects. These incidents have been caused by one or more for the following factors: human error, technology factors, and organisation factors.
Case Study: Australian Radiation Incident Register: Borehole Logging Incident1
A serious incident occurred in Australia in 2014 involving borehole logging source. This incident was reported to the Australian Radiation Incident Register (ARIR).
Due to human error while transferring sources between the borehole device and the shielded transport container workers:
- failed to place all the sources in the shielded transport container
- failed to perform a radiation survey of the area before removing the area barriers and warning had been removed
As a consequence work continued in the area and three workers received high doses in the short time before the source was identified. The workers were hospitalised for three days for monitoring and blood tests. Further blood tests were performed every two days for the remainder of the month.
Following this incident, the responsible company and one worker were subject to prosecution.
In Australia the use of borehole logging devices containing radiation sources is regulated. Each state and territory is responsible for enforcing their respective radiation safety act and regulations in their jurisdictions. The Australian government is responsible of enforcing the radiation safety act and regulations of commonwealth entities only.
Organisations/employers are responsible for:
- devising, implementing, and regularly reviewing their radiation management plan
- regulatory compliance
- induction and ongoing training of workers, including contractors
Workers are responsible for:
- following radiation protection practices specified in the radiation management plan
- complying with legitimate instructions of the employer or designated radiation safety officer
- participating in radiation protection training
All Australian jurisdictions have uniform annual limits for public and occupational exposure to ionising radiation: 1 mSv for the public and 20 mSv for workers who are occupationally exposed. Despite this, there are different definitions of who is ‘occupationally exposed’ and who should wear personal dosimeters. You can further discuss occupational radiation exposure with your facility’s Radiation Safety Officer or the relevant jurisdictional regulator.
For a pregnant radiation worker, the dose to the unborn child is restricted to the same as a member of the public – 1mSv. (See Management of Pregnant Workers Exposed to Ionising Radiation factsheet)
- Code of practice for the safe use of sealed radioactive sources in borehole logging
- Australian regulators
- The Australian Radiation Incident Register