ISO/TC 85/SC 2/WG 14 - Air control and monitoring

This document focuses on monitoring the activity concentrations of radioactive gases. They allow the calculation of the activity releases, in the gaseous effluent discharge from facilities producing positron emitting radionuclides and radiopharmaceuticals. Such facilities produce short-lived radionuclides used for medical purposes or research and can release gases typically including, but not limited to 18F, 11C, 15O and 13N. These facilities include accelerators, radiopharmacies, hospitals and universities. This document provides performance‑based criteria for the design and use of air monitoring equipment including probes, transport lines, sample monitoring instruments, and gas flow measuring methods. This document also provides information on monitoring program objectives, quality assurance, development of air monitoring control action levels, system optimisation and system performance verification. The goal of achieving an unbiased measurement is accomplished either by direct (in-line) measurement on the exhaust stream or with samples extracted from the exhaust stream (bypass), provided that the radioactive gases are well mixed in the airstream. This document sets forth performance criteria and recommendations to assist in obtaining valid measurements. NOTE 1 The criteria and recommendations of this document are aimed at monitoring which is conducted for regulatory compliance and system control. If existing air monitoring systems were not designed according to the performance criteria and recommendations of this document, an evaluation of the performance of the system is advised. If deficiencies are discovered based on a performance evaluation, a determination of the need for a system retrofit is to be made and corrective actions adopted where practicable. NOTE 2 The criteria and recommendations of this document apply under both normal and off‑normal operating conditions, provided that these conditions do not include production of aerosols or vapours. If the normal and/or off-normal conditions produce aerosols and vapours, then the aerosol collection principles of ISO 2889 also apply.

The use of a continuous air monitor (CAM) is mainly motivated by the need to be alerted quickly and in the most accurate way possible with an acceptable false alarm rate when significant activity concentration value is exceeded, in order to take appropriate measures to reduce exposure of those involved. The performance of this CAM does not only depend on the metrological aspect characterized by the decision threshold, the limit of detection and the measurement uncertainties but also on its dynamic capacity characterized by its response time as well as on the minimum detectable activity concentration corresponding to an acceptable false alarm rate. The ideal performance is to have a minimum detectable activity concentration as low as possible associated with a very short response time, but unfortunately these two criteria are in opposition. It is therefore important that the CAM and the choice of the adjustment parameters and the alarm levels be in line with the radiation protection objectives. This document describes — the dynamic behaviour and the determination of the response time, — the determination of the characteristic limits (decision threshold, detection limit, limits of the coverage interval), and — a possible way to determine the minimum detectable activity concentration and the alarms setup. Finally the annexes of this document show actual examples of CAM data which illustrate how to quantify the CAM performance by determining the response time, the characteristics limits, the minimum detectable activity concentration and the alarms setup.

The use of a continuous air monitor (CAM) is mainly motivated by the need to be alerted quickly and in the most accurate way possible with an acceptable false alarm rate when a significant activity concentration value is exceeded, in order to take appropriate measures to reduce exposure of those involved. The performance of this CAM does not only depend on the metrological aspect characterized by the decision threshold, the limit of detection and the measurement uncertainties but also on its dynamic capacity characterized by its response time as well as on the minimum detectable activity concentration corresponding to an acceptable false alarm rate. The ideal performance is to have a minimum detectable activity concentration as low as possible associated with a very short response time, but unfortunately these two criteria are in opposition. It is therefore important that the CAM and the choice of the adjustment parameters and the alarm levels be in line with the radiation protection objectives. The knowledge of a few factors is needed to interpret the response of a CAM and to select the appropriate CAM type and its operating parameters. Among those factors, it is important to know the half-lives of the radionuclides involved, in order to select the appropriate detection system and its associated model of evaluation. CAM using filter media accumulation sampling techniques are usually of two types: a) fixed filter; b) moving filter. This document first describes the theory of operation of each CAM type i.e.: — the different models of evaluation considering short or long radionuclides half-lives values, — the dynamic behaviour and the determination of the response time. In most case, CAM is used when radionuclides with important radiotoxicities are involved (small value of ALI). Those radionuclides have usually long half-life values. Then the determination of the characteristic limits (decision threshold, detection limit, limits of the coverage interval) of a CAM is described by the use of long half-life models of evaluation. Finally, a possible way to determine the minimum detectable activity concentration and the alarms setup is pointed out. The annexes of this document show actual examples of CAM data which illustrate how to quantify the CAM performance by determining the response time, the characteristics limits, the minimum detectable activity concentration and the alarms setup.

ISO 16639:2017 provides guidelines and performance criteria for sampling airborne radioactive substances in the workplace. Emphasis is on health protection of workers in the indoor environment. ISO 16639:2017 provides best practices and performance-based criteria for the use of air sampling devices and systems, including retrospective samplers and continuous air monitors. Specifically, this document covers air sampling program objectives, design of air sampling and monitoring programs to meet program objectives, methods for air sampling and monitoring in the workplace, and quality assurance to ensure system performance toward protecting workers against unnecessary inhalation exposures. The primary purpose of the surveillance of airborne activity concentrations in the workplace is to evaluate and mitigate inhalation hazards to workers in facilities where these can become airborne. A comprehensive surveillance program can be used to - determine the effectiveness of administrative and engineering controls for confinement, - measure activity concentrations of radioactive substances, - alert workers to high activity concentrations in the air, - aid in estimating worker intakes when bioassay methods are unavailable, - determine signage or posting requirements for radiation protection, and - determine appropriate protective equipment and measures. Air sampling techniques consist of two general approaches. The first approach is retrospective sampling, in which the air is sampled, the collection medium is removed and taken to a radiation detector system and analysed for radioactive substance, and the concentration results made available at a later time. In this context, the measured air concentrations are evaluated retrospectively. The second approach is continuous real-time air monitoring so that workers can be warned that a significant release of airborne radioactivity may have just occurred. In implementing an effective air sampling program, it is important to achieve a balance between the two general approaches. The specific balance depends on hazard level of the work and the characteristics of each facility. A special component of the second approach which can apply, if properly implemented, is the preparation of continuous air monitoring instrumentation and protocols. This enables radiation protection monitoring of personnel that have been trained and fitted with personal protective equipment (PPE) that permit pre-planned, defined, extended stay time in elevated concentrations of airborne radioactive substances. Such approaches can occur either as part of a planned re-entry of a contaminated area following an accidental loss of containment for accident assessment and recovery, or part of a project which involves systematic or routine access to radioactive substances (e.g. preparing process material containing easily aerosolized components), or handling objects such as poorly characterized waste materials that may contain radioactive contaminants that could be aerosolized when handled during repackaging. In this special case, the role of continuous air monitoring is to provide an alert to health physics personnel that the air concentrations of concern have exceeded a threshold such that the planned level of protection afforded by PPE has been or could be exceeded. This level would typically be many 10's or 100's of times higher than the derived air concentration (DAC) established for unprotected workers. The monitoring alarm or alert would therefore be designed not to be confused with the normal monitoring alarm, and the action taken in response would be similarly targeted at the specific site and personnel involved. The air sampling strategy should be designed to minimize internal exposures and balanced with social, technical, economic, practical, and public policy considerations that are associated with the use of the radioactive substance. A comprehensive air sampling strategy should also consider that the air sampl

ISO 2889:2010 sets forth performance-based criteria and recommendations for the design and use of systems for sampling of airborne radioactive materials in the effluent air from the ducts and stacks of nuclear facilities. The requirements and recommendations of ISO 2889:2010 are aimed at sampling that is conducted for regulatory compliance and system control. If existing air-sampling systems are not designed to the performance requirements and recommendations of ISO 2889:2010, an evaluation of the performance of the system is advised. If deficiencies are discovered, a determination of whether or not a retrofit is needed and practicable is recommended. It can be impossible to meet the requirements of ISO 2889:2010 in all conditions with a sampling system designed for normal operations only. Under off-normal conditions, the criteria or recommendations of ISO 2889:2010 still apply; but for accident conditions, special or separate accident air sampling systems can be necessary.