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Tritium Self-luminous Timepieces
Regulatory control on self‐luminous timepieces containing gaseous tritium light sources (GTLS)
There are available on the market luminous watches, of various brand names and from different countries. The dials of these watches, in particular the hands and the numerals, but in some models also the bezel and the crown, may glow in the dark and therefore render them legible in such situations. The majority of these luminous watches use common or proprietary phosphorescent chemical compounds (phosphors) that absorbs and stores light energies during daytime, either from sunlight or artificial lighting, and then re‐emit the energy in the form of light in the dark.
There is however one type of luminous watches that are self‐luminous by incorporating different radioactive substances with the phosphorescent material, so that the energy released by the radioactive substance could continuously excite the phosphorescent material to give out visible light. As this type of self‐luminous watches contain radioactive substances, placing them on the market has to be under certain regulatory control, in Hong Kong as in other countries alike. Originally these watches or timepieces are meant for use by military and emergency personnel, and certain professionals such as divers and mountaineers, even astronauts in space explorations, who might need to work in harsh conditions and dark environments. In the old days, radium paint was commonly used. Over the years, tritium paint and promethium paint had been used, but they are also phasing out and becoming obsolete in consumer timepieces. Nowadays, common self‐luminous watches use GTLS.
While abundant information on self‐luminous watches could be found by searching on the internet, the following ‘Questions and Answers’ aims at providing specific information on self‐luminous watches using GTLS, and gives an overview of the local regulatory control, including exemptions granted to certain aspects, of the marketing of this type of timepieces.
FAQ on tritiuim self‐luminous timepieces
Q1
What are these self‐luminous watches using for illumination?
Self‐luminous watches normally use radioactive materials to energize some sort of phosphors to give out visible light so that people can read the time in the dark. The most common self‐luminous watches available on the market now use GTLS to illuminate the hands, the dial numerals, and sometimes also the crown of the wrist watch.
Q2
What are GTLS and how do they work?
GTLS are sealed glass vessels that give off light in various colours. Usually it is green light because the human eye is most sensitive to its wavelength. To fabricate GTLS, the glass vessel is coated with luminous matter (different phosphors depending on the colour) on the inner wall, and then it is filled with the radioactive tritium gas and sealed airtight. The beta particles emitted by the tritium during its decay will come into contact with the coating. The phosphor will absorb the energy of the beta particles and converts it into visible light.
Q3
Is there any restriction imposed by the Radiation Board on the activity of tritium in these watches?
Yes. For GTLS watches generally available in the market, each individual timepiece shall not contain more than 1 GBq of activity of tritium gas in total.
Q4
How is this level of 1 GBq chosen?
1 GBq is the exempted level for tritium recommended by the International Atomic Energy Agency in their Basic Safety Standards.
(Reference:International Atomic Energy Agency (IAEA) Safety Series No. 115, Basic Safety Standards, Schedule I, Table I‐1).
This is also the level adopted by Switzerland.
(Reference: Office Fédéral de la Santé Publique (OFSP), Division Radioprotection / RL / 4 mai 2009).
As to other countries, two recent European Commission publications: ‘Radiation Protection 146’ and ‘Radiation Protection 147’, have made available information provided by European Union member states and candidate states in a recent review of availability of consumer products in about 30 European countries. For timepieces (normally watches) incorporating GTLS, the activities reported were up to 1 GBq.
(Reference: EC, Radiation Protection 146: A Review of Consumer Products Containing Radioactive Substances in the European Union, 2007; EC, Radiation Protection 147, Guidelines for the Regulatory Control of Consumer Products Containing Radioactive Substances in the European Union, 2007, in particular Annex I)
Q5
What is the policy of the Radiation Board on the marketing of these self‐luminous watches using GTLS?
There are several aspects about placing GTLS watches in the market: import, manufacture and sale of these watches by companies, and possession and use of these watches by members of the public.
Any person/company who intends to import, manufacture and distribute GTLS watches is required to apply for and be granted a Radioactive Substance Licence for relevant and specified purposes. As to companies which retail these GTLS watches directly to consumers, the Radiation Board has granted an exempted quantity of 1,000 GBq for possession. As each watch is to contain no more than 1 GBq of tritium gas, this exempted quantity would mean about 1,000 watches. Individual members of the public in possession of GTLS watches are also granted the same exempted quantity. A notice of the exemption has been published in the Gazette.
Q6
What is the basis of the Board’s licensing and exemption policy on the marketing of GTLS watches in Hong Kong?
The Board’s policy on the marketing of GTLS watches takes into account of both the International guidance and local practice.
For the protection of those workers who may be required to handle GTLS directly or GTLS watches in bulk quantities, importers/distributors and manufacturers of GTLS watches are not exempted from the requirements of the Radiation Ordinance (Cap. 303) and its subsidiary Regulations, and have to be licensed accordingly.
As to exemption granted to retailers and individual consumers, Regulation 15(1) of the Radiation Ordinance provides the Board the power to grant exemptions, inter alia, to the possession and use of specified radioactive substances for justified purposes. The current exemption policy is in compliance with the principles and criteria laid down by the IAEA for exempting practices and sources within practices from requirements of the Standards, including those for notification, registration or licensing.
(Reference: IAEA Safety Series No. 115, International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources, 1996, Schedule I, Exemptions)
Q7
What is the Board’s policy on watches with more than 1 GBq of tritium?
Sale, possession and use of watches that incorporate more than 1 GBq of tritium per timepiece that are designed for specific purposes and to be used by specific professionals will need to be justified by the applicant and be assessed by the Board on a case‐by‐case basis. The assessment will certainly include the consideration of the justification principle in the use of radiation and of the imposition of more stringent standards and requirements for the testing of the product.
