Tritium - the driving force behind our self-luminous products
What is tritium?Tritium gas (chemical symbol H-3) is an isotope of hydrogen gas, and is colourless, odourless, and lighter than air. Tritium is a radioactive 100% beta emitter and decays by sending out an electron with a half-life of 12.32 years. Most physical characteristics are the same as hydrogen, but the atoms in tritium are slightly different, causing them to emit low energy radiation in the form of beta particles, or electrons. Tritium is considered “user friendly” because it has the lowest energy rating of any radioisotope and is most commonly found in the stratosphere but is also created in nuclear reactors.
Are betalights radioactive?No, because no radiation is emitted by the product. It contains radioactive material, but the product itself is not “radioactive.” In the tritium devices (GTLD), tritium gas is hermetically sealed into Borosilicate glass tubes, like a miniature fluorescent lamp. The glass completely stops all radiation. Actually, tritium beta emissions are so weak that even in free air, the particle can only travel less than 1/4 inch. A sheet of tissue paper will stop it.
What happens if the tubes break?If tritium is released from broken tubes, the product could emit a very small amount of radiation. First of all, Tritium illuminated products are very tough and it is hard to break tubes in an installed device. Government regulations for exit signs require that they pass drop tests from 8 feet to concrete! But let’s assume somebody strikes one with a hammer ... Repeatedly. We will assume the most conservative, or the “worst case scenario.” We can calculate the potential radiation dose assuming that all 10 Tubes of an exit sign are broken, which in practice would require the outer case and all inner parts to be broken. Released tritium gas will behave exactly like hydrogen-it’s very light and dilutes rapidly in air which reduces the amount anyone can breathe. But we assume that somehow, a person is standing with his/her face literally inches away from the sign, breathing hard for at least 5 minutes during and after a breakage and absorbs all the tritium. Under these extremely conservative and unrealistic conditions a person might get a radiation dose about the same as a tooth x-ray.
How is light produced from tritium?The electrons emitted during the decay process (beta particles) from tritium energize a phosphor compound which is coated on the inside of the glass tubes. Phosphor has the property of emitting light when stimulated by electrons, and is used in old television tubes and fluorescent lights. The surface of the tritium tube emits light continuously when the phosphor layer is energized. The mechanism is exactly the same as in an electrical fluorescent lamp, except that electrons are provided by tritium instead of by electrical current. The energy of tritium electrons is much less than those generated in electrical lamps, which is why you can’t see tritium tubes glow except in dim light or darkness.
TRITIUM EXIT SIGNS
How do you determine the life of tritium device or exit signs? Tritium gas, like other radioisotopes, decays at a known rate. This rate is usually specified by the “half-life,” which is the time taken to decay to half the initial energy. For tritium, this is 12.32 years. In addition, we know the minimum brightness required to meet national and local codes for tritium exit signs. With these two figures, we can calculate exactly the right amount of tritium required in a new sign to produce light for the guaranteed period before the minimum brightness is reached. We offer signs with up to 20 years of guaranteed useful life before replacement is needed.
Tritium escape sign vs. Everyday radiation
Average dose in millisievert (mSv)
In the Code of Federal Regulations, Title 10, Part 20, the U.S. government has set the acceptable limit for radiation exposure from man-made sources at 300 millirem per year for the general public. Therefore, as shown in this graph, in the unlikely event that a self-luminous sign is broken, there is no significant health risk.
Sign brightness & luminous life of tritium illuminated products We offer models with guaranteed useful life ranging up to 20 years or more before replacement is required. Loss of brightness results from the known radioactive decay of tritium, which loses half its energy in 12.3 years. We can therefore accurately predict the rate of loss of brightness of signs, and adjust the initial brightness to give the luminous life required. The minimum brightness for self-luminous exit signs is defined in National Fire Protection Association Life Safety Code 101 (1997). Thus, the amount by which the initial brightness exceeds this figure will determine the useful life before replacement is required.
Radiation testing during service Not required. Such testing is specifically exempted under 10CFR Part 31.5 (c) (2) (ii) for devices containing tritium. However, testing is required for fire safety reasons, just as for electrical signs. Inspectors like the fact that each tritium sign carries an easily read “replacement date” so they and the user know exactly when replacement is required, just as for fire extinguishers.
Hazardous and/or explosive atmospheres Self-luminous exit signs will not cause or contribute to the ignition of any hazardous or explosive atmospheres. A self-luminous tritium exit sign’s illumination is not dependent upon the use of any electrical power, either internal or external. Since the sign does not require electrical power, the potential for arcing at any contact point is eliminated. Also as there is no requirement for a power source, there are no elements or filaments to glow or become hot, which may cause ignition. Betalight self-luminous Exit signs meet the requirements for use in hazardous atmospheres/ locations where flammable petrochemical vapors and/or pulverized dust exist or has the potential to exist. These hazardous location emergency lighting fixtures are typically used aboard vessels, gas plants, off-shore oil platforms and paint spray booths as specified in the National Electric Code; Article 500, Class 1, Class 2 and Class 3 conditions. The signs comply with the ATEX 114 requirements.
Disposal of tritium self-luminous signsTritium self-luminous signs powered by tritium gas lights have a guaranteed maximum operating life before replacement is required. The replacement date is clearly marked on each product, on a label located on the lower edge of the housing frame for easy visibility. SPECIAL DISPOSAL IS REQUIRED. CONTACT BETALIGHT B.V. AT LEAST ONE MONTH BEFORE THE REPLACEMENT DATE, NEW SIGNS SHOULD BE ORDERED TOGETHER WITH A REQUEST FOR AN RGA NUMBER TO RETURN THE OLD UNITS FOR DISPOSAL. Upon receipt and installation of the new sign, securely pack the old unit in the container received with the new sign, and return to the nominated disposal location advised by Betalight b.v.
Disposal fees: If a replacement self-luminous tritium sign is purchased from Betalight b.v. the disposal fee will be waived. Betalight b.v. will accept any manufacturers signs for exchange on a one for one basis i.e buy one, return one. Betalight b.v. will accept any manufacturers signs for disposal only for a fee per sign, pre-paid disposal fee. If an LED or Photoluminescent exit sign is purchased from Betalight b.v. a reduced disposal fee per sign shall apply on a one for one basis. Betalight b.v. reserves the right to revise disposal fees and policy without notice. Disposal of defective signs During its working life as marked on the label for each product, if a broken or defective sign, i.e. one in which the light sources appear unlit or unevenly illuminated in darkness, Betalight b.v. should be contacted to arrange for replacement and return of the defective sign. Betalight b.v. offers an unlimited guarantee to replace any faulty product, unless damage has been caused by obvious mistreatment or abuse.
Clean-up of contamination from leaking or broken signs If necessary, this is done by washing surfaces with ordinary soap and water. Contact Betalight b.v. for a detailed procedure. Our experience is that leaking exit signs are extremely rare, and the amount of tritium released from a leaking sign would be very unlikely to cause contamination of the local area above levels which are allowed under regulations for “unrestricted” (public) areas. Though this amount may be above background (the level of radiation that exists naturally in all buildings), it is not hazardous. However, if required, it can readily be removed by the means described.