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LCQ7: Tritium exit sign

     Following is a question by the Hon Albert Ho and a written reply by the Secretary for Food and Health, Dr Ko Wing-man, in the Legislative Council today (June 1):


    Under the Radiation Ordinance (Cap 303), possession or use of tritium self-luminous exit signs (TES) requires a licence issued by the Radiation Board of Hong Kong (RBHK) unless an exemption has been granted. In reply to my question at the Council meeting of March 27, 2013, the Government advised that the United States Environmental Protection Agency (USEPA) had stated that TES were potentially hazardous and RBHK's licensing policy on "the justified use of tritium exit signs where the use of electrical power is not possible or feasible is well echoed by the USEPA". Nevertheless, I have learnt that there are other views that the Government should pay attention to. For instance, the International Atomic Energy Agency (IAEA) has classified TES containing up to 740 GBq. of gaseous tritium as category 5 (i.e. "most unlikely to be dangerous to the person"). Also, IAEAˇ¦s guidelines on "Exemption from Regulatory Control of Goods Containing Small Amounts of Radioactive Material" have stated that (i) regarding TES, "the regulatory body should only concern itself with the risk from the tritium in normal use, in accidental conditions and following disposal" and it is "not within its competence to assess the more conventional risks such as those arising from broken glass following an accident or to take decisions on the basis of these risks", (ii)  the justification relating to the use being a net benefit from the device concerned is "normally applied to a type of practice and therefore need not be applied to each and every application for authorisation or candidate for exemption... [and] the existence of a technical standard for a particular type of practice may often be taken to indicate that the type of practice is justified", (iii) "[t]he benefits from a practice could therefore be of many different types, not just possible saving of life or prevention of injury or illness, but also technical benefits, prevention of property damage, improvements in security or simply improvement in the quality of life", and (iv) the requirement for justification relates to there ˇ§being a net benefit from the particular type of device [while] to search for the best of all the available alternatives is a task that is beyond the responsibility of the regulatory body". Besides, the United States Nuclear Regulatory Commission (USNRC) has stated that (i) TES "serve an important safety function by marking exits to be used during power outages and emergencies", (ii) TES "pose little or no threat to public health and safety or security", and (iii) TES "are designed to be inherently safe so they can be used without the need for radiation training" and facilities do not need a specific licence to use TES.  In this connection, will the Government inform this Council:

(1) whether RBHK has considered the aforesaid views and practices of IAEA and USNRC; if so, of the details; if not, the reasons for that;

(2) as I have been told that since there is hardly any building requiring exit signs for emergency evacuation of its occupants is not supplied with electrical power, RBHK's current licensing policy on the justified use of TES where the use of electrical power is not possible or feasible is tantamount to a total ban on TES, of the types of buildings or premises that would be allowed to install TES under such policy; and

(3) of the buildings in Hong Kong in respect of which RBHK has issued licences for the installation of TES therein and the relevant details; if there is no such building, of the reasons for that?



(1) Tritium gas is a radioactive substance. Tritium exit sign is a self-luminous product illuminated by gaseous tritium light sources for the indication of the location of fire emergency exit. Currently, the Radiation Board (the Board) requires the use of tritium exit signs to be justified by the potential benefit of saving life and where the use of electrical power is not possible or feasible.  

     In formulating the policy on use of tritium exit signs, the Board considered that while the potential benefit of tritium signs is saving of life by providing illuminated indication of emergency egress routes in indoor premises, there exist the potential harm of increased risk of internal radiation exposure of the uninformed public by the leakage of tritium during their normal use, and potential internal radiation exposure of the public on breaking of signs because of accidents, acts of vandalism and losses or improper disposals. Another consideration is the availability of other types of luminaries that do not contain radioactive substances such as light-emitting diode and compact fluorescent lamp type luminaries. As the licensing authority with the duty to protect public health from the potential deleterious effects of ionising radiations, the Board has properly considered the availability of these alternatives in the overall balance between the risks and benefits of using tritium luminaries. Among other considerations, the Board's policy has also made reference to the regulatory practices in different countries and views from international organisations.

     Apart from the United States Environmental Protection Agency (USEPA), the Board is also aware and has duly considered the discussion and views on the safety of tritium signs by the International Atomic Energy Agency (IAEA) and the United States Nuclear Regulatory Commission (USNRC) mentioned in the question. A consolidated summary is as follows:

(a) The classification of tritium signs as "most unlikely to be dangerous to the person" (i.e. Category 5) is based on the Safety Guide on "Categorisation of Radioactive Sources" (Safety Guide) issued by IAEA in 2005.  However, the Safety Guide also pointed out that even if the radioactive sources (including tritium) are at the lower end of the categorisation system, these sources could give rise to doses in excess of the dose limits if not properly controlled, and therefore it is still recommended to be kept under appropriate regulatory control. Besides, the categorisation is only based on the immediate injuries that could be caused by a radioactive source when effective control on the source cannot be exercised. Possible delayed health effects on human body, for example, radiation induced cancers which is a secondary consideration, are not taken into account (Note). In this respect, the Board has considered that it is not adequate to solely base its consideration on the above categorisation system of IAEA for regulating the use of tritium signs.  

(b) Besides, although there are opinions from USNRC that the tritium signs pose little or no threat to public health and safety of security and they are designed to be inherently safe, past incidents in the United States (US) have shown that the safety of the signs could be compromised without much difficulty by tampering leading to the breakage of the tritium tubes inside the signs.  These incidents of damaged signs had resulted in contamination of areas and risk of radiation exposures to the public.  

(c) As for the publication "Exemption from Regulatory Control of Goods Containing Small Amounts of Radioactive Material", it is a technical document of IAEA issued in 2012, which aimed to initiate discussion on the issues needed to be considered in relation to exemption from regulatory control and thus should not be taken as a guiding principle. In fact, IAEA had issued in 2014 the General Safety Guide no. GSG-5 "Justification of Practices, Including Non-Medical Human Imaging" which stated that "alternative methods, not involving the use of radiation, of achieving the same or similar objectives may exist and should be taken into account when reaching a decision on justification."

     In view of the aforesaid, the Board's policy has indeed taken into account the international guidelines promulgated by IAEA and the practice on the use of tritium signs in US including the relevant views of USNRC and USEPA, which are both legitimate regulatory bodies in US. The present policy of the Board on controlling the use of tritium signs is consistent with the relevant international guidelines of IAEA and is commensurate to the potential harms of tritium signs.

(2) The Board has provided specific guidelines about its policy on the use of tritium signs including the requirement that "supply of electricity is not possible or feasible". The guidelines are available in the website of the Board. It provides that the Board will carefully consider all factors based on the Principle of Justification, among which the possibility or feasibility of electrical power supply is one of the considerations. In doing so, the Board will consider relevant factors such as building structural constraints on installing electrical wiring around the emergency exit; difficulty in using electricity due to special circumstances in places like tunnels, mines and quarries or locations where inflammable or explosive gas is present.

(3) Persons applying for use of tritium signs should provide reasons and necessary information, with supporting documentation to the Board, of the use of tritium signs for the proposed location of installation. The Board will consider each application based on the information provided against the Board's policy on use of tritium exit signs. Some approved applications in the past include the installation of tritium signs at premises with the possible presence of inflammable vapour and the installation of tritium signs at moveable partitions. These cases had provided sufficient evidence on substantiating the difficulty in the supply of electricity because of the risk of ignition of the inflammable vapour or of the structural constraint on installing electrical wiring respectively.  

Note: Please refer to Appendix II, in pages 30 and 33 of the IAEA Safety Guide No. RS-G-1.9 on "Categorisation of Radioactive Sources".

Ends/Wednesday, June 1, 2016
Issued at HKT 16:39


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