RADIATION SAFETY

RADIATION SAFETY


Safety issue of tritium watches

Safety issue about GTLS:

GTLS is very safe to use. The electron emitted during the beta decay process carries very low level energy with a maximum of 18.6KeV(Kilo electron volt). The average energy is only 5.7KeV. It has very short range, a few mm in air, 0.9um in water and 0.6um in human tissue. This low energy level means that the penetrating power of the emitted particles is very weak. They can be easily stopped with a piece of paper. They cannot penetrate into human skin.

The tritium in a watch is confined inside the borosilicate glass vials. As mentioned in the last paragraph, beta particles from tritium can be stopped by a piece of paper, hence, they can be sealed inside the glass vial totally and cannot escape into the atmosphere. The vials are set onto the dial and hands inside a watch. The crystal of the watch further protects the vials from being smashed.

If we break all the glass vials inside a watch (typically 14 to 15 pcs with a total radiation content of less than 25mCi) and inhale all the tritium gas inside, the total radiation content inhaled is similar to the amount of radiation we would ingest by consuming a banana every day, during a period of one year. A banana absorbs minerals in the soil as it grows. Among these minerals is Potassium 40. K-40 is also radioactive.

In our normal social activities, we are exposed to far more dose of radiation than the absorption from a watch with all GTLS broken. For example, a flight from coast to coast in USA exposes us to 0.2mSv. An x-ray taken exposes us to 0.3mSv. A watch with all GTLS broken exposes us only to less than 0.01mSv.


Safety standard:

According to contamination test carried out on watches based on 8.3.2 section of the ANSI N43.4, the average result detected is around 0.6 nCi tritium per 24 hours. This is an extremely low figure. The standard is not to be more than 50nCi tritium per 24 hours.

Further elaboration:

Ci = curie It is a unit of radioactivity

1 Ci = 37,000,000,000 Bq

Bq = Becquerel

1 Bq = 1 disintegration per second

1 nCi = 37Bq

0.6 cCi = 22.2 Bq


According to the Canadian safety limit of tritium content per litre of drinking water, the limit is 7000Bq per litre and an average human would drink around 530 litres per annum.

The limit stipulated by the World Health Organization is even 10,000Bq per litre.

The total contact by wearing such a watch for a year is only around 8100 Bq, barely more than the limit on 1 litre of drinking water.

Please note that the radioactivity detected from a watch is not inhaled or ingested in contrary to water which is taken into the body.

Therefore, wearing such a watch can be considered as hazard free.

The instrument used for detecting the leakage of tritium is called a liquid scintillation counter. It is a very expensive piece of instrument usually found only in radiation laboratories in universities or department of oncology in a hospital. We, being a legal assembler behind a lot of famous brands, will have a piece of such equipment coming in very soon. By then, we can carry out contamination test on the request of our customers.


Legal issue:

GTLS, in its raw state as a glass vials, is subject to very strict legal restriction due to its radioactive nature. When using GTLS in a watch, the T25 rule must be respected. It is required by law that a watch using GTLS must bear a ?T25? mark on the dial telling people that this watch contains GTLS with radioactivity not more than 25 mCi(millicurie).

Some countries have very strict rules on the radiation content of a watch as well as the distribution of GTLS watches. Please ask us for details.


Radiation safety:

Although the tritium in a watch, due to the very small quantity, does not pose any substantial hazard to human health, we have to be very careful and watchful. On the one hand, it is because tritium itself is dangerous. On the other hand, it is a professional rule to be careful in dealing with radioactive substances.

During the assembly of GTLS watches, extremely high priority is placed in the enhancement of radiation safety. Heavy investment has been input into our radiation workshop which is now considered the best of its kind in the territory.

Staff are well trained in the handling of GTLS. Every one of them has been individually certified fit for radiation work by the Government of Hong Kong. Every one of them is provided with a personal whole body dosimeter to keep track on their exposure to radiation. The average monthly exposure of each staff is only around 0.20 mSv (Sep 2010) while the allowed limit is 1.67mSv per month.