What is an ISOTOPE?
An “ISOTOPE” is a modified form of a primary chemical element which has an atomic structure slightly different to the primary element. All isotopes have the same chemical properties as the primary element, however they can be radioactive. Tritium gas is a radioactive isotope of hydrogen gas.
Radioactive isotopes contain atomic nuclei which are unstable and are always tending to change to a stable situation. In the process, energy is given off and this produces radioactivity. The process is called “decay”.
Radiation from radioisotopes occurs in three basic forms:
1. Alpha radiation
2. Beta radiation
3. Gamma Rays & X-rays (electro-magnetic, no mass)
It is also necessary to identify the energy level of the radiation emitted – different isotopes may emit the same type of radiation but have a far different energy level. Both the type and the energy level must be known to determine any potential health hazard. Note: the energy level is not given by the number of Curies or TeraBequerals contained within a product. Curie and Bequeral are units of measure of the radioactive material.
ALPHA particles are the heaviest atomic particle and can be hazardous to the body even if the energy is low.
BETA particles are actually electrons and have almost zero mass. Potential hazard depends on the energy level, however because beta particles are practically weightless, this level must be high before penetration of body tissues can occur. Tritium has low-level emissions that can be stopped by a sheet of tissue paper or in ¼” thickness of air. Tritium emits the lowest level of beta radiation of all isotopes (no other type of radiation is emitted) and the particles cannot penetrate even the thinnest layer of body skin.
GAMMA and X-RAYS can penetrate body tissues readily, and the hazard once again is in the proportion to the energy involved. In most commercial applications, gamma and X-ray radiation is so powerful that we use very dense materials such as lead, steel and concrete to absorb unwanted radiation.
What is TRITIUM?
Discovered in 1934, Tritium (Hydrogen 3) is a colourless, odourless gas, lighter than air, and physically almost identical to ordinary hydrogen gas. Tritium gas energizes the phosphor-coated tubes in Shield Source Incorporated (SSI) signs. The tritium’s low energy beta emissions striking the phosphor coating inside the borosilicate (pyrex) glass causes light to be generated. The phosphor coating and the glass wall absorb all beta emissions from tritium. The tritium is unable to penetrate through the glass and thus there is no radiation emitting from the signs.
Tritium beta emissions are very weak. In free air, the tritium beta particle travels about 5mm (less than a quarter of an inch) and can be stopped simply by putting a piece of paper in the pathway of the tritium. Tritium has a “half-life” of 12.3 years. This means that in 12.3 years, half of the tritium energy has decayed, or half of the energy for light production has been expended. The maximum amount of tritium in a sign is 0.80 TBq (terabequerals), thus in 12.3 years there is only 0.40 TBq remaining in the sign.
If for any reason the SSI egress sign is destroyed and the tritium gas is set free in a small closed area, anyone in that room exposed to the tritium for one hour with no change of air may receive a total dose of about 30 millirem (0.3 millisievert) or about 1/10 of the acceptable radiation dose set by the Canadian Nuclear Safety Commission for the general public. For comparison, natural background radiation from the earth and sun is about 100 millirem (1millisievert) per year. This is the most conservative or “worst case” scenario.
In a more realistic situation, the destruction of the SSI sign happens in an area where there is constant flow of air, such as corridors, large rooms and storage areas, then the radiation exposure is approximately 1/100 of the allowable dosage level as set by the Canadian Nuclear Safety Commission.
Since tritium cannot penetrate the skin, how is a radiation dose received? The radiation dose is received mainly by breathing through the lungs, where it mixes with body fluids. Tritium is not transferred to bone marrow or other body organs where it may accumulate and within a short time (from 1 to 15 days) the majority of the dose is expelled from the body through urination.
It is plain to see that potential risk to anyone in everyday conditions is very low – while the benefits of total reliability without maintenance or power consumption far outweigh any risk posed by accidental exposure to radiation.
SSI self-luminous signs are completely safe and are designed to take great abuse. They are manufactured by SSI under stringent quality control procedures and meet all requirements of the Canadian Nuclear Safety Commission.
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 insure that they will stand up to extremely tough handling.
The potential risk to anyone in everyday conditions is very low – while the benefits of total reliability without maintenance or power consumption far outweigh any risk posed by accidental exposure to this radiation.
What happens if a sign breaks?
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. These signs would not be End User Exempt by the Canadian Nuclear Safety Commission if there were any chance that they posed a health risk to the public in a normal accident event. In fact, self-luminous signs have been used extensively throughout Canada and the United States for more than 25 years without incident.
How are they disposed of?
The Canadian Nuclear Safety Commission allows for the use, possession, transfer and disposal by unlicensed facilities. We will accept the return of any Shield Source Incorporated self-Luminous sign that was sold in Canada. Contact us for Disposal information.
