Since HTO is the most frequently used water tracer, as an example, the possible dose to the operating personnel in the case of a worst case accident is discussed.

In the case of spillage of HTO, some of the water will evaporate and there will be tritiated vapour in the air. As vapour can be inhaled, a spillage of the total volume of HTO should be considered as the worst case scenario.

In the injection cylinder, the 2000 GBq of HTO will be diluted to approximately 75-100 mL. If this water evaporates and mixes with 500 m3 of air (e. g. a volume of air 10 m x 10 m x 5 m), the tritium concentration in the air will be 4 GBq/m3 or 4 MBq/L. If a person stays in this atmosphere for one minute and inhales 20 L of air and the entire vapour in the inhaled air is retained in the lungs, the intake of tritium will be 80 MBq. The annual limit of intake of tritium (from HTO) by professional workers as recommended by the ICRP is 1000 MBq. Thus, the calculated figure in the example above corresponds to approximately 8% of the annual limit of intake.

The worst case scenario for intake will occur if a beam of HTO is directed towards the faces of the operators handling the injection equipment. However, the operators will wear visors, masks and protective clothing, and they are well trained to deal with such situations. Taking into consideration that the total release of tracer can hardly occur unless there is a serious accident in the vicinity or some serious breakdown of the injection equipment at the time of injection, the worst case scenario described is very unlikely to arise. An accident causing destruction of injection equipment and the release of tracer will probably be more dangerous than the release of the radioactive tracer.

The concentrations of tracer in the sampled water will be very low. For HTO, it will be in the range of 200-300 Bq/L at maximum (top of the tracer recovery curve). For other tracers which have been injected in lower quantities, the concentration will be correspondingly lower. Sampling will not require any special protection equipment such as breathing apparatus or rubber gloves.