How do they work?

Self-Luminous Exit Signs are illuminated with a light source that consists of glass tubes, internally coated with phosphor and filled with tritium gas.  Tritium gas (H3) is an isotope of hydrogen that emits low energy radiation in the form of beta rays, or electrons.  These electrons stimulate the phosphor coating causing the tubes to continuously emit light.  The mechanism is exactly the same as an electrical fluorescent lamp with the only exception being that the electrons are provided by the tritium rather than by an electric current. They require no external energy source and as such are the most energy efficient lighting product available today.

How long will they last?

Our Self-Luminous Signs are available with a ten-year, twelve-year, fifteen-year or twenty year effective life. Replacement dates are clearly marked on each unit.  The effective life of the sign is dependent upon the signs ability to meet the National Fire Protection Associations minimum luminance requirement of 0.06 footlamberts (0.21 cd/sq m) as measured by a colour corrected photometer.  Because tritium decays at a known rate, we are able to calculate the initial brightness required in order to meet the minimum luminance requirement at different points in time.  Therefore, the effective life of a self-luminous sign is dependent upon the amount of tritium (measured in curies) that we put into the sealed sources that light our signs

Are Self-Luminous Signs Radioactive?

Although tritium is a radioactive isotope, our products emit no radiation.  The gas is hermetically sealed into glass tubes.  The beta emissions from the tritium gas are completely contained within the tubes.  There is absolutely no risk of radiation exposure from normal use of our product.  Great care is taken in the construction of our signs to ensure that they will stand up to extremely tough handling.

What happens if the signs break?

Keep in mind, for this to occur the outer frame and inner protective housing would also have to be destroyed.  In this scenario, the released tritium gas would rise and dilute rapidly in the air.  If, however, somehow a person were trapped in a 10ft X 10ft room with a sign in which all of the tubes had broken, their radiation exposure would be similar to that received from a dental x-ray. 

What is our warranty?

Our Self-Luminous Products are warranted against any defects in material or workmanship for the rated life of the product.  We agree to replace any product FREE OF CHARGE that does not meet our stated specifications.

How are they disposed of?

It is unlawful to abandon or dispose of Self-luminous signs except by transfer to persons specifically licensed by the Nuclear Regulatory Agency or by an Agreement State. They cannot be thrown in the trash.  We are licensed and will accept the return of any Self-Luminous sign, regardless of manufacturer.

What is Tritium?

Tritium (H³) is an isotope of hydrogen gas.  It can be man-made, but is also a naturally occurring substance produced by the action of solar and cosmic radiation on the gases of the upper atmosphere and by the decay of natural radionuclides in rocks and soil.  It is a colourless, odorless gas, lighter than air.  It is present in air and water all over the earth and is regularly ingested and breathed by everyone.  All humans contain trace amounts of tritium and other naturally occurring radioisotopes.

Many isotopes are stable and retain their structure indefinitely.  However, some isotopes are not stable and are said to be radioactive.  Radioactivity can be defined as the spontaneous decay of a nucleus to form another nucleus and a nuclear particle.  Tritium is one such radioactive isotope.  As the tritium nucleus decays it emits an electron, causing energy to be released in the form of a beta particle.  A new nucleus is then formed with two protons and one neutron thereby becoming a form of non-radioactive helium.

A common way to express the rate of decay of a radioactive element is in terms of its half-life.  Half-life is defined as the time required for the decay of one half of a sample of a radioactive substance.  Tritium has a relatively short half-life of 12.33 years.

Tritium’s beta emissions are very weak.  No other primary radiation is emitted.  In fact, tritium emits the lowest level of beta radiation energy of all isotopes.  The beta particles are easily stopped by a thin layer of any of any solid material and are unable to penetrate our body’s skin.  Humans can only be exposed to radiation from tritium after it has somehow entered the body.  It can do this readily only when the tritium gas is chemically in the oxide form.  If inhaled as gas, tritium is almost immediately expelled from the lungs because the body cannot absorb it.  

What is the risk of exposure?

The light sources used to illuminate a self-luminous sign consist of borosilicate glass tubes, internally coated with phosphor, filled with tritium gas then sealed.  As the tritium gas decays, it emits beta particles that energize the phosphor, causing it to emit light.  The beta particles are completely contained within the glass tubes which are protectively housed within the frame of the sign.  In a normal use situation, there is absolutely no risk of radiation exposure from a self-luminous sign.

These signs are designed and tested to withstand great abuse.  Radiation exposure could only occur if the self-luminous sign were somehow broken and one or more of the internal light sources were also broken causing the tritium gas to escape.  If this were to occur, an individuals’ exposure would be dependant on how may of the signs’ light sources (GTLS) broke (up to 15 possible), how large a volume of air and how many air exchanges occur per minute, and the exposure time of the individual affected.

The chart that follows compares the potential radiation exposure from a broken self-luminous sign with examples of the everyday radiation that we are exposed to in the course of our normal existence.