Late Stage of an Emergency
Depending on the magnitude of the release, it may be necessary to continue to monitor the food-chain for some weeks or even months until any interdiction on foodstuffs has been lifted, and assurance is obtained that levels of radioactivity are returning to normal and arrangements for monitoring can return to those specified for the routine background monitoring programme.
If the release is a major one, monitoring in the post-accident situation will be concentrated on foodstuffs. Even if the wind direction has carried activity away from Hong Kong it will still be essential to monitor foodstuffs entering Hong Kong and to provide reassurance that contaminated supplies are not reaching the public. This may involve setting up monitoring posts at the road, rail and port entries for foodstuffs. Monitoring may be carried out in bulk on each load of produce to provide rapid screening. This system should be backed up by sampling consignments for more stringent analysis in the laboratory, and results of such analyses should be compared with the results of bulk monitoring on the sampled consignment. This will provide evidence that the bulk screening methods are adequate.
It will also be necessary to monitor foodstuffs at markets within Hong Kong to check that controls are working. Clearly this procedure would require a great deal of manpower, although in general the equipment required will be simple and no great degree of skill will be required by personnel carrying out this work provided they are suitably supervised and instructed. In the case of meat, however, checking may require laboratory preparation and testing of samples.
8.4 Monitoring Instrumentation and Equipment
Alerting Instrumentation
The environmental monitoring fixed stations at Sha Tau Kok and Yuen Ng Fan are reasonably well-situated to provide early detection of airborne activity approaching Hong Kong. The island of Ping Chau would be an excellent position for a further monitoring station since it is located only 13 km from Daya Bay and lies in the path of any release carried towards Hong Kong. It is therefore recommended that a fixed monitoring station be installed at this location. Even with three monitoring stations it is possible that a narrow plume could arrive in Hong Kong undetected. It is therefore recommended that a minimum of a further five monitoring stations be installed. One to cover the 'gap' between the Sha Tau Kok and Ping Chau stations, one to cover the 'gap' between the Ping Chau and Yuen Ng Fan stations, the third station located on the coast, due east of the High Island reservoir. The fourth on the east side of Kowloon and the fifth on the east side of Hong Kong island.
The use of high pressure ionisation chambers in these stations is supported. Alternatively stations could be developed using Geiger-Muller detectors. The dose rate range of these stations should be at least zero to 1 milligray per hour, (effectively 1 millisievert per hour).
The detection system based upon these detectors must be designed to ensure high reliability. If necessary, consideration should be given to the use of redundancy in detectors, electronics and communication systems.
It would clearly enhance the usefulness of these stations in an emergency if the dose rates from each of the stations, rather than just an alarm signal, could be transmitted to the Monitoring and Assessment Centre at the Royal Observatory, so that data on dose rates may be plotted from the start of an incident.
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