HALON AND THE OZONE LAYER
1 What Is the Ozone layer?
At the outer edge of the earth's atmosphere there is a thin layer of invisible, naturally occurring gas that is critical to life on earth. It is the stratospheric ozone layer. This layer protects life on earth from the harmful rays of the sun.
2 What Causes Reductions Of The Ozone Layer?
When certain chemicals used on earth escape into the atmosphere they are broken down by solar radiation and release chlorine and bromine atoms, which, in a chain reaction, destroy ozone molecules. This reaction occurs more frequently than natural ozone replenishment, resulting in a thinning of the ozone layer.
3 Is The Ozone Layer Threatened?
Atmospheric measurements reveal that the ozone layer is getting thinner, and that at certain times of the year a hole in the ozone layer appears over Antarctica. Some people believe this reduction is due to solar or volcanic activity, but most scientists believe that certain man-made chemicals are major contributors to the problem. These chemicals include the chlorofluorocarbons (CFCs) found in refrigerators, solvents and blowing agents for foams, and the Halon used for fire fighting.
4 How Damaging Is Halon to the Ozone Layer?
A compound's ability to destroy ozone depends on many factors, including the amount of chlorine and/or bromine that it contains. To aid in comparing compounds, scientists have developed a relative scale called the ozone depletion potential (ODP). Common refrigerants, like those found in refrigerators and in automobile air conditioners, have been assigned the value 1 as a reference. Halon 1301 has the value between 10 and 16, meaning it has 10-16 times the more potential for destroying the ozone layer.
Halon use worldwide is significantly less than that of CFCs, so even though it is more damaging to the ozone layer, there is not as much of it released into the atmosphere. In fact, it is estimated that overall Halon accounts for less than 20% of ozone depletion.
5 Halon's Role in Stratospheric Ozone Depletion
The Halon covered by EPA Rule 40 CFR Part 82
, Subpart H contains the chemical element bromine (Br) and also, in the case of Halon 1211 specifically, chlorine (Cl). Br and Cl both contribute to stratospheric ozone destruction. The earth's stratosphere is a layer of the atmosphere that begins between 5 and 11 miles above the earth's surface and extends up to about 30 miles above the earth's surface. Ninety percent of the ozone in the earth's atmosphere is found in the stratosphere. The characteristics of Halon and other human-made chemicals that can deplete ozone (e.g., chlorofluorocarbons, or CFCs) enable them to reach the stratosphere, where they break down and the Cl and Br from them can destroy ozone. Halon is a major source of bromine in the stratosphere.
6 Stratospheric Ozone Destruction is a Health Risk
Ozone in the earth's stratosphere protects the earth from the penetration of harmful ultraviolet (primarily UV-B) solar radiation by absorbing most of this harmful UV-B, allowing only a small amount to reach the earth's surface. Without the filtering action of the ozone layer, more of the Sun's UV-B radiation would penetrate the atmosphere and reach the earth's surface. Increased UV-B radiation can lead to increased incidence of certain skin cancers and cataracts, as well as other human health and environmental consequences.