Advisory Note - Exposure to Naturally Occurring Radon in the Workplace

Published March 2024

Summary

Relative to most other countries, radon levels in Australia are low, however there are certain industries and workplaces where radon levels may be elevated.

Australia has recommended reference action levels for radon: 200Bq/m³ for households, and 1000Bq/m³ for workplaces.

In workplaces, where radon levels exceed the reference action levels, the Person Conducting a Business or Undertaking (PCBU) of those workplaces has a duty of care to implement controls to minimise radon exposure to workers.

Due to the naturally occurring nature of radon, minimisation of radon levels using elimination and substitution principles (from the hierarchy of control) is not appropriate, however other mitigation strategies can be used to reduce the risk posed by radon where elevated concentration levels exist.

Radon is one of several hazards found in workplaces. Its control needs to be kept in perspective with all other workplace hazards and risks.

Introduction

This advisory note provides practical guidance for Persons Conducting a Business or Undertaking (PCBU) and workers about managing health and safety risks associated with exposure to naturally occurring radon in the workplace. It is not intended for sites which are regulated for radon exposure.

It contains information on the risks of radon exposure, the control measures which can be used to help eliminate or minimise, so far as reasonably practicable, a worker’s exposure to radon in the workplace, and guidance on how to implement a radon protection program.

Workers who spend all or part of the day working in high-radon concentration settings (e.g. underground mining operations, certain enclosed workplaces, natural spring spas, and tourist guides in show caves) may be exposed to elevated radon levels and the adverse health effects associated with such exposure. Exposure to radon is a normal part of everyday life. It only presents a hazard when it is concentrated well above typical levels. 

ARPANSA has developed the Australian Radon Action Plan which includes details on the future development of resources, advice and services that will be available to all affected industries and workplaces, within all Australian States and Territories, to help with the delivery of information and training for workers.

The ARPANSA Radon Action Plan can be found at Australian Radon Action Plan.

What is radon?

Radon is an inert, colourless, and odourless radioactive gas. It is formed by the radioactive decay of primordial elements that occur naturally in most rocks and soils. Radon has several radioactive isotopes which have the same chemical properties but different nuclear properties. There are three naturally occurring isotopes of which two, radon-222 (Rn-222) and radon-220 (Rn-220), occur naturally in significant amounts and decay by alpha emission. Radon is an alpha-emitter, alpha particles pose a much greater risk of harm when present inside the body through ingestion, inhalation or via an open wound. Because radon is an inert gas, it can diffuse through materials internally.

Rn-222 is part of the uranium-238 (U-238) radioactive decay chain. It is the immediate decay product of radium-226 (Ra-226). Radon-222 has a half-life of 3.8 days and has several short-lived chemically reactive decay products which decay by alpha and beta emission. Rn-222 is commonly known as Radon.

Rn-220 is commonly known as thoron and is part of the decay chain of a primordial radionuclide, thorium-232 (Th-232). Due to its short half-life, thoron can build up to relatively high levels close to its source.  Management measures and controls for radon are also generally applicable to thoron.

Radon is present in all air. Outdoor air contains very low radon levels, however within enclosed workplaces, the levels can be higher. Lower ventilation levels in some enclosed workplaces can trap radon, which is denser than air. There are places where radon levels can be very high, for example, in some caves, or in poorly ventilated underground mines.

For radon to be a source of radiation exposure, the surrounding soil or rocks must be sufficiently porous and permeable to allow radon to migrate with soil gas and enter overlying buildings or underground caverns in the case of show caves or underground mines.

Radon decays, emitting radioactivity, and turns into a series of other radioactive elements. The decay products themselves are short lived, meaning that they give off their radiation quickly. The decay products are not solids and can attach to small dust particles in the air, which can then be inhaled and lodge in the lungs.

While we usually talk about radon, most of the exposure comes from the decay products. The reason that radon is referred to, is that it is easy to measure. 

The risk of developing lung cancer from exposure to radon depends on how much radon we breathe in. The more radon there is in the air, the greater the risk. Similarly, the longer we spend breathing in that radon, the greater the risk. There is also clear and established evidence that shows that smoking increases the risk associated with exposure to radon.

Radon in Australia

Relative to most other countries, the levels of radon in Australia are very low. The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) conducted an extensive survey to determine radon levels in Australia in 1990 (Radon Map of Australia). This indicated that almost no Australian homes need to consider reducing levels of radon. 

Figure 1 indicates that average radon levels in Australia are the lowest amongst member countries of the Organisation for Economic Co-operation and Development (OECD). Most workplaces are above-ground buildings with good ventilation so, like homes, it is expected that most Australian workplaces would have very low radon levels. 

Figure 1: Mean indoor radon concentrations in OECD countries.

The International Commission on Radiological Protection (ICRP) observed that there was a significant association between lung cancer and radon exposure at levels of approximately 200 Bq/m³ (ICRP Publication 115).

Based on this publication, ARPANSA recommends the following reference levels:

• 200 Bq/m³ – for households (assuming a scenario of continuous exposure 24 hours a day, seven days a week).
• 1000 Bq/m³ –  for workplaces (assuming exposure of 40 hours per week over 50 weeks per year).

If the radon levels exceed the above levels, the appropriate state, territory, or Commonwealth radiation health authority should be contacted for advice. 

In most workplaces, radon exposure of workers is not a result of the work activities causing an increase to radon levels, rather it’s caused by the natural occurrence of radon and its physical properties. 

Where radon exposure occurs, a graded approach to managing exposure is necessary and the workplace may be considered an existing exposure situation if appropriate. Further guidance on existing exposure situations can be found in the Guide for Radiation Protection in Existing Exposure Situations - Radiation Protection Series G-2).

Suggested protection levels

Consideration of radon exposure risk requires a general, risk-based approach, as applicable to any other risk associated with WHS principles in the workplace. 

In general situations, it is recommended that mitigation actions be considered in workplaces if radon concentration levels are above the household reference level of 200 Bq/m³. If radon concentration levels below 200Bq/m³ can easily be achieved simply by encouraging a flow of fresh air, then no further radiation protection considerations in relation to radon exposure would be needed, i.e. no restrictions on exposure duration for workers.

For workplaces where the radon concentration levels fall between 200 Bq/m³ and 1000 Bq/m³, the PCBU should consider including mitigations in line with the optimisation principle as detailed below.

Where radon concentration levels in workplaces exceed the workplace reference level of 1000 Bq/m³, reasonably achievable radon protection measures are required, and should be decided upon following appropriate advice from a radiation protection advisor or local regulator. The introduction of specific, individual radon monitors, or general radiation monitors to improve understanding of the risk will provide useful information for determining appropriate protection measures. 

Depending on the individual State/Territory requirements, workers may be treated as radiation workers and their annual radiation exposure may need to be recorded in the Australian National Radiation Dose Register (ANRDR) - Australian National Radiation Dose Register

In the Australian context, there are only a limited set of scenarios which may give rise to elevated radon levels in a workplace, include:

• Highly energy efficient buildings in areas of high radon potential.
• Underground workplaces (e.g., non-uranium underground mining operations, show caves etc.).
• Workplaces with naturally elevated radon concentrations (e.g., natural spring water spas/hot springs).
• Enclosed workplaces with limited ventilation.

In all situations, where the radon concentration reference levels are exceeded, action should be taken to reduce the concentration of radon or the exposure of people to radon.

What are the health risks?

Most of the radiation exposure from radon arises from inhaling the short-lived, decay products, rather than radon itself. When produced, the decay products of radon tend to attach to airborne particles which can then be inhaled and lodge in the lung.

Radon is recognised by the International Agency for Research into Cancer (IARC) as a Class 1 carcinogen. Evidence has been obtained from pooled, large scale epidemiological studies that show there is a linear relationship between long term radon exposure and excess relative lifetime lung cancer risk.

An individual’s baseline lung cancer risk is strongly dependent on their smoking status, with current smokers having a risk of about 15% of acquiring lung cancer up to age 75, compared to 0.4% for life-long non-smokers.

There is currently no evidence to link radon exposure to cancers other than lung cancer or to other diseases. Calculations of radiation doses to organs other than the lung suggest a small, theoretical risk of cancer to other organs but these would be much smaller than the doses, and risks, to the lung.

Identifying and assessing radon exposure in the workplace

For the previously mentioned workplaces, and other workplaces where radon may be elevated, monitoring can be used to determine the radon levels. There are many ways of measuring radon in workplaces which can include the use of active or passive radon monitors.

Passive monitors are inexpensive and can be placed for extended periods, whereas active monitoring measures radon concentrations in real time and are more useful to understand the variability that can occur.

For long-term assessment (≥3months), the use of passive monitors is recommended. These monitors stay in the same location for the duration of the monitoring period. There are various commercial services that provide such monitors. For radon measurement over a shorter period (≤30 days) an active radon monitor can be used. There are several different types of active monitors available, including but not limited to the following:

• Radonova - Atmos
• Durridge - RAD8
• ADM Nuclear Technologies - SARAD Radon Scout Professional
• Bertin Instruments - AlphaE
• AirThings - Corentium Home
• SA Radiation - Radon Eye

Assistance in deciding which type of radon monitor is best suited to an individual workplace can be sought from an experienced and suitably qualified occupational hygienist (with radiation expertise), or by contacting your State/Territory radiation regulator.

The best location for radon monitors within underground or indoor workplaces is typically within the main working areas and transit routes. 

If elevated radon concentrations are identified, the PCBU must pursue measures to ensure any exposure to workers is reduced to as low as reasonably achievable, following the hierarchy of control principles.

Where radon exposure is confirmed through monitoring, careful management is needed, applying a graded approach. 

The principles of radiation protection should also be considered, those being:

• Justification – all exposures, or risk of exposures to workers resulting from operations undertaken in high radon workplaces must be justified. The benefits of the operation must outweigh the detriment of exposure or risk of exposure.
• Optimisation – all exposures, or risk of exposures to workers, must be optimised to ensure that any actual or likelihood of exposure, and the number of people exposed, is as low as reasonably achievable (ALARA) and dose constraints applied where appropriate.
• Dose Limits – following justification and optimisation considerations, the actions of the PCBU must ensure that no dose exceeds the applicable dose limit for members of the public (1mSv/yr). A higher dose limit applies for 'radiation workers’ (20 mSv/yr), however workers in the industries covered by this guidance are generally not considered radiation workers. 

Managing the risks

Radon exposure risks can be managed using the same approach as other WHS risks and follow a systemic approach including:

• Identifying hazards.
• Assessing the risks – understanding the nature of harm that could be caused by the hazard, how serious the harm could be and the likelihood of it happening.
• Controlling the risks – implementation of the most effective control measures that are reasonably practicable in the circumstances.
• Reviewing control measures to ensure they are working as planned.

Figure 2 shows a systemic approach for identifying and managing radon exposure. The decision box titled ‘Is control justified?’ determines whether there is a need to take protective measures (e.g. remedial actions and/or protective actions). 

This strategy should follow the principles of the hierarchy of control (Figure 3) where possible.

Figure 2: A systemic approach for identifying and managing radon exposure risk.

Further guidance on the risk management process can be found in the SafeWork Australia (SWA) Code of Practice: How to manage work health and safety risks.

Controlling radon exposure

Due to the natural occurrence of radon, the elimination or substitution tiers from the hierarchy of controls may not be practical. The remaining elements of the hierarchy of control may be more appropriate (See figure 3 with examples).

Figure 3: Hierarchy of Controls Pyramid.

For engineering controls, implementation of effective ventilation techniques could be introduced into areas with high radon potential. The use of such controls could be informed by receiving specialist advice.

In addition to the engineering controls, some workplaces may be able to reduce exposure to radon by managing local occupancy to high radon areas (administrative controls). This includes implementing limited access to affected areas, reducing the time which workers spend in high radon areas, and reducing the frequency that workers are required to be in high radon exposure locations. 

If any residual risk remains after engineering and administrative controls have been implemented, further risk minimisation could be achieved by combining control measures such as engineering and administrative controls and/or the introduction of personal protective equipment for workers.

Information, training, and instruction

The PCBU of a workplace that may have radon exposure potential has a duty of care to provide information, training and instruction that is suitable for the nature and risks of the work, and the controls being put in place to manage those risks. 

Raising awareness and providing training and instruction to workplace safety officers, health and safety representatives, supervisors, underground workers, and new workers is essential to the success of a workplace radon protection program.

A workplace training program can:

• Improve knowledge and understanding of radon, what it is, and what risks to consider.
• Improve knowledge and understanding of the radon protection control measures in place.
• Raise worker’s awareness about the workplace radon protection program and policy.
• Provide a forum for feedback from workers.

Topics many include:

• Introduction to radon
• What radon is and how it may affect a worker’s health if exposed to high concentration levels.
• Factors that may increase the level of risk for workers (i.e. smoking, or the amount of time spent in high radon concentration locations).
• The controls used to mitigate the risk of radon exposure to workers in elevated risk workplace settings.

Workplace radon protection policy

A radon protection policy records how the radon risk at a workplace will be managed.

A radon protection policy can outline:

• the hazards, risks, and radon control measures at the workplace.
• information and training requirements.
• responsibilities at the workplace.
• review processes.

When radon control measures have been implemented, they should be monitored and reviewed regularly. Supervision should also be provided to ensure the control measures are used effectively and are complied with.

Where possible, the monitoring of radon control measures should be incorporated into existing audit tools used in the workplace, including work health and safety inspections, on-site supervisor reports and checklists.

The radon protection policy should also:

• consider establishing a system for collecting regular feedback from workers, for example through surveys or focus groups.
• ensure workers and their representatives are consulted and feedback is considered before making changes.

A sample radon protection policy is provided at Appendix A – Sample radon protection policy but this should be used as a guide only and each workplace should tailor a policy to suit the needs and practicalities of their organisation.

Further information

Appendix A – Sample radon protection policy

Sample radon protection policy