What About Those Aerosol Sprays?
By “Awake!” correspondent in Australia
HAVE you ever wondered how so much shaving foam comes out of those small aerosol cans? They seem almost bottomless! But did you know that actually there is no foam at all inside the container?
How is that possible? Well, we will see in a moment. But for now let us say that there is much more involved in a common “spray can” than meets the eye.
These convenient and useful aerosol devices are based on quite a sophisticated technology. A key to their success is the gas or “propellant” used to push the product out of the container. This is important because it must satisfy a number of special requirements all at the same time.
A Suitable Propellant
Mere compressed air or most gases just will not do the job properly. The ideal propellant must be nonpoisonous and nonflammable. It must not affect the quality, smell or taste of the product. Neither should it corrode the aerosol’s mechanism. It has to be versatile enough to allow for the exact amount of wetness or dryness desired, also allowing for fineness of spray. It must be able to provide a wide range of pressures to suit the density of various products. And it must maintain the necessary pressure right to the last drop.
Obviously, there are few substances known that fulfill all these requirements. Gases called hydrocarbons, such as propane and butane, satisfy most of them, but they are also somewhat odorous and highly flammable. So, after much experimentation, fluorocarbon gases were found to meet the requirements best.
Under relatively low pressure, these gases become a liquid that mixes readily with many products without affecting their qualities. And a variety of fluorocarbon types can be used singly or in a mixture to provide the properties and pressures needed for individual applications.
One illustration of fluorocarbon versatility is shaving foam. As noted earlier, there is no foam as such inside the can, but, rather, a pressurized mixture of liquid fluorocarbon propellant and the fluid product. As this liquid mixture reaches the nozzle and is suddenly relieved of pressure, the propellant instantly vaporizes, forming thousands of tiny bubbles within the product that you see as foam.
So, with the press of a button, you can now dry-clean your dog, spray on a bandage, make instant hors d’oeuvres or even attempt to ward off a shark attack. In fact, more than 300 different types of products are now said to be packed as aerosols, and it is claimed that almost any product can be “aerosolized” if desired.
The versatility of fluorocarbons is such that over half of all aerosols came to use them as a propellant, while the remainder used primarily hydrocarbons and a few used other compressed gases. The fact that flammable hydrocarbons are the propellant in a high percentage of aerosols is often the reason for warnings on the containers: “USE ONLY WHERE THERE IS PROPER VENTILATION!” “DO NOT USE NEAR FLAME!”
It should be noted that these and other warnings such as “KEEP AWAY FROM HEAT!” “DO NOT STORE IN DIRECT SUNLIGHT!” “DO NOT PUNCTURE OR INCINERATE CAN!” may or may not have to do with the type of propellant. It is possible for any aerosol to explode if left near a fire or inside a car in hot sunlight. Aside from gas pressure, this could be due to the nature of the product or to other solutions that are mixed with it to give the desired texture.
While there is no uniform world aerosol safety legislation, most containers are tested at high heat and pressure, assuring relative safety. In fact, at normal room temperature, there may be less pressure inside an aerosol can than in many soft-drink containers!
Yet, with all their virtues, the popularity of fluorocarbon gases as propellants has been marred in recent years by a still-controversial scientific issue.
Aerosols and Ozone
A potential danger is said to exist each time you press an aerosol button. The culprit is not the device itself or the product in it, but the fluorocarbon propellants that make many aerosols work so well. The accumulation of these gases released over the past 30 years or so is said to be affecting the “ozone layer” high in the atmosphere.
Ozone is a highly active form of oxygen that is created in our atmosphere by the action of ultraviolet (uv) radiation on atmospheric oxygen. Ozone appears in appreciable amounts at altitudes roughly between 6 and 30 miles (10 and 50 kilometers) above the earth, with maximum concentrations between 12 and 15 miles (20 and 25 kilometers). This radiation-created layer itself acts as a shield against most of the sun’s harmful uv radiation. Increases in such radiation are charged with causing more skin cancer.
The vast amounts of fluorocarbon gas released over the years are said to be rising slowly until they finally penetrate the ozone layer. Once above the protection of this layer, the sun’s uv radiation can break down fluorocarbons, releasing chlorine atoms and chlorine oxide. In turn, these elements destroy small amounts of ozone by converting it catalytically into plain oxygen. The amount of protective ozone is thus thought to be undergoing gradual depletion.
Other potential effects of this ozone depletion are also under study. The ozone layer converts uv radiation into heat, thus directly or indirectly influencing earth’s temperature and weather patterns. Hence, it is thought that any variations in the ozone layer could affect many things on earth. Crop yields, plant growth, forests, oceans, fish and animal life are all potentially subject to any changes.
Further complicating research into this matter is the fact that ozone levels can vary as much as 25 percent just between day and night. These levels also seem to follow an 11-year cycle that may be affected by sunspot activity. And though most ozone is produced near the sun-drenched equator, the gas gradually moves toward the poles. So ozone density and thickness at the poles is somewhat greater than it is in the expanse between.
With so many interdependent factors involved, scientists say that it will take five to 10 years before their preliminary findings can be confirmed, rejected or adjusted with any degree of certainty. However, it is estimated by some that if fluorocarbons continue to be released at only the present rate, the ozone level could eventually be reduced by about 7 percent, though there is a large margin for error either way.
In the meantime, because the gas rises so slowly, scientists estimate that even if fluorocarbon use were completely stopped right now, the gas already in the atmosphere would continue to rise and affect the ozone layer for another 10 years! Even then, they estimate that it would take the ozone about 65 years more just to recover half of the maximum loss, and over a century to return to normal!
Some Counterarguments
Most researchers agree that fluorocarbons do have some adverse effect on the ozone layer, and that this, in turn, affects the incidence of skin cancer. But not everyone agrees that ozone depletion is the major skin-cancer hazard. Since World War I, the disease has increased far more rapidly than population growth, and some scientists believe that ozone depletion has played only a small role, if any, in this increase.
They point to the fact that skin cancer has even increased during times when the ozone level also increased. They say that growth of the disease is more likely a result of changing life-styles. People spend more leisure time outdoors, travel to warmer climates and are more readily inclined to shed their clothes when on vacation or even while working.
These changes have exposed people to more uv radiation than in the past, say the critics, increasing the incidence of skin cancer far more than does depletion of the ozone layer. To illustrate: They point out that because of the increasing ozone density between the equator and the poles, the predicted aerosol-caused increase in uv radiation reaching earth is no greater than if a person moved from the north to the south in England.
These critics also contend that skin cancer would be combated most effectively by requiring suntan oils and lotions to include ingredients that do a better job of filtering out harmful uv wavelengths.
If Fluorocarbons Were Banned
Banning all fluorocarbons would affect many things that we take for granted. These gases are the refrigerant used for almost all cooling purposes throughout the world. Other gases would not work well in present systems.
Fluorocarbons are also the blowing agent used in manufacturing many familiar foam plastic products such as lightweight packaging, carpet backing, flooring, man-made leather and upholstery, flotation material, drinking cups, ice chests, thermal insulation and many other things. No satisfactory substitute has yet been found. Either the fire risk with other gases is too high and/or the product is inferior.
Elimination of fluorocarbons would affect the food, trucking, textile, electronic, automotive, optical, paint, printing, photography and steel industries, to name a few. Even hospitals and pharmaceutical suppliers would feel the loss.
However, aerosol use of fluorocarbons accounts for about three quarters of the total, and only a quarter is divided mainly between refrigeration and plastics. So the emphasis now is primarily on reducing nonessential use of aerosols. Many experts strongly recommend selective regulation of fluorocarbons rather than an outright ban. The state of Oregon has been selective by banning fluorocarbon aerosols as of March 1, 1977.
Are There Alternatives?
As noted before, hydrocarbons have some features required of the ideal propellant, but they are highly flammable and odorous. Some are also toxic to humans and do not always allow for a uniform spray to the last drop. They are already used extensively, where possible, for such things as cleaners, waxes, paint and automotive products. But there is no guarantee that they, too, will not be discovered to have detrimental effects on the environment.
Compressed gases, too, are being used where a solid stream or heavy wet spray is desired, such as in pesticides, toothpaste, food products and cookware sprays. But pressure inside the container declines as it empties and such gases cannot be mixed with the wide range of products that fluorocarbons can.
Mechanical pumps that many now use also seldom match the effectiveness of aerosols. The spray is not as fine or uniform, causing dripping or streaming. They may leak, and it is not uncommon to miss the target area. Air leaks can degrade some products, and many times pump systems just do not throw the spray far enough.
Wide-ranging research is under way to develop new products and to change the chemical formulas of some present ones to make them work better with flammable hydrocarbon propellants. Consumers will have to decide whether this changeover harms the quality of future products. But no doubt such items will be more expensive than those used now.
Practically every aerosol product is available in some more or less effective substitute form today. With some items you may decide to forgo the advantages of aerosol application, while with others your decision may be to continue using this convenient addition to our modern way of life. However, for the moment, in most places the choice is yours.
[Box on page 21]
• Use with adequate ventilation; avoid breathing vapor or spray mist.
• Keep out of reach of children.
• Do not spray into eyes or mouth.
• Avoid open flames.
• Do not puncture, incinerate, or store above 120° F. (49° C.).
[Diagram on page 21]
(For fully formatted text, see publication)
PUSH BUTTON
MOUNTING CUP
PROPELLANT Vapor fills void
DIP TUBE
ACTIVE INGREDIENTS PLUS LIQUID PROPELLANT