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Fluorocarbons have represented only a small niche of the U.S. aerosol market for the past 2 decades. Originally, CFCs were the dominant propellant in the 1960s and 1970s. However, even prior to the 1977 EPA ban on the use of CFCs in aerosols, allowing an exception for critical uses such as metered dose inhalers (MDIs) and those products where the propellant was the active ingredient, such as dusters and signal horns, etc., there was a small erosion in the size of the CFC market for aerosol applications. Higher prices for the CFCs were a significant driver for these inroads, in spite of the non-flammability and low toxicity of the CFCs. In anticipation of consumer concern regarding the use of CFC-11 and CFC-12 in aerosols after the Rowland-Molina hypothesis was published in 1974, the trend toward replacement of CFCs by hydrocarbons was accelerated. In 1977 the EPA banned the use of CFCs in aerosols for many applications.

One option in response to the 1977 ban was to replace the CFCs by HCFCs and/or HFCs. However, the substitution ratio was low due to the higher price of these materials compared to CFCs, and the lower cost of options such as hydrocarbon propellants, reformulating using water-based blends (e.g. dimethyl ether/water) to lower flammability, and alternative delivery systems such as pumped spray.

Currently, for non-pharmaceutical aerosols, about 4.5% of the volumetric total of propellants used in the US is HFCs based on consolidated industry estimates from the hydrocarbon, dimethyl ether and HFC and aerosol product producers

Consumers select aerosol products because: they are hermetically sealed and will not leak, go stale, or evaporate; are pre-mixed for maximum formulation effectiveness; are far reaching, allowing penetration of hard to get to areas and no contact with the surface (important in obtaining uniform coatings, thorough cleaning, and where sanitary application is required); are uniquely capable of creating stable foams; and are recyclable when empty.

Competing propellants include the hydrocarbons: propane, butane, and isobutane, dimethyl ether, and compressed gases; alternative delivery systems include pumps, sticks, nebulizers, piston can systems, and roll-ons. HFC propellants are primarily used for selected applications where there is a concern about flammability, safety, or compliance with ambient air quality regulations or where there are unique performance requirements.

A metered dose inhaler (MDI) is a small, hand-held, pressurized multiple dose delivery system that delivers small doses of medication to the lungs, giving rapid symptomatic relief from asthma and chronic obstructive pulmonary disease (COPD). An MDI consists of the following components: a storage canister, a medicinal formulation containing a propellant and active ingredient, a metering valve to control delivery of a precise dose, and an actuator. When the piston is depressed to release the dose, the propellant flash evaporates, creating a fine mist of the drug suspended or dissolved in the propellant. This mist can easily penetrate into the small passageways of the lungs, where it is deposited.

The MDI is a vital therapeutic option for the estimated 300 million people worldwide who suffer from asthma and the many millions more afflicted by a variety of other respiratory diseases. Proper treatment makes a critical difference in these patients' ability to lead full and active lives. For some patients, it may mean the difference between life and death.

The parties to the Montreal Protocol have made an exception and allowed continued production of CFCs for use in MDIs, since these devices are essential for the treatment of asthma and COPD. Recognizing the need to develop alternatives to CFCs for use in MDIs, the pharmaceutical industry has undertaken a large research effort to develop alternatives. These potential substitutes must meet strict criteria. The propellant must have the following characteristics:

• Appropriate boiling point and vapor pressure, i.e., can be liquefied in a closed container at room temperature;
• Low toxicity;
• Nonflammable;
• Appropriate density;
• Good stability;
• Appropriate solvency characteristics for the drug; and
• Acceptable to the patient in terms of taste and smell.

After an extensive effort, the only two propellants found to meet these stringent criteria were HFC-134a (CF₃-CH₂F) and HFC-227ea (CF₃-CHF-CF₃). Subsequently, an extensive research and testing effort was undertaken to develop new HFC-based therapeutic formulations for use in MDIs. These potential formulations must also undergo extensive toxicological, stability and clinical testing before they can obtain regulatory approval.

While alternative drug delivery systems involving dry powder inhalers and nebulizers are also available to treat asthma and COPD, it is recognized that MDIs are the mainstay of therapy and critically needed as one of the treatment options.

Several HFC-based formulations are now available around the world. The transition from CFC-based to HFC-based formulations is just now beginning and will continue well into the first decade of the 21^st century.

In 1998 usage of HFC-134a in the manufacture of MDIs sold in the United States was approximately 0.26 million metric tons of carbon dioxide equivalents.

Tire inflators consist of an aerosol can containing a rubber latex sealant, a solvent/diluent, and a propellant. They are used to reinflate a flat tire allowing the driver to proceed to a repair station to have the tire fixed or replaced.

The advantages of using a tire inflator instead of jacking up the car and replacing the damaged tire are as follows:

1. Minimizing exposure time to hazards from rapidly moving traffic and inclement weather;
2. Reducing potential for attack by assailants; and
3. Providing a less strenuous way to temporarily repair a damaged tire, allowing the driver to effect immediate repairs that may otherwise be difficult due to age or infirmity.

Hydrocarbons, dimethyl ether, or HFC-134a are used as the propellant. However, highly flammable propellants such as hydrocarbons have been linked to deaths and injuries caused by explosions occurring in the repair shop when a torch was used to repair a brake drum adjacent to the inflated tire.

These developments led to reformulation to ozone depleting compounds by Nationwide Industries in the 80's, the recall and eventual withdrawal from the market by STP and Prestone brands in the early 90's and subsequent reformulation to HFC-134a by Pennzoil in 1999.

The main reason for using a hydrofluorocarbon as a tire inflator, in this case HFC-134a, is to avoid potential injuries involving explosions when using a highly flammable propellant.

Total yearly usage in N. America is estimated to be approximately 3.1 million metric tons CO₂ equivalent.

Electronics cleaning aerosols consist of a solvent such as a hydrochlorofluorocarbon (e.g. HCFC-141b), a hydrofluorocarbon (e.g. HFC-43-10) or a hydrofluoroether (e.g., such as CH3-OC4F9), or a hydrocarbon. HFC-134a or carbon dioxide are used as propellants in order to ensure nonflammability. A finer spray is achieved when using HFC-134a rather than carbon dioxide.

These formulations are used primarily for spot rework to remove residues from high value components while minimizing potential damage due to incompatibility, thereby ensuring the proper functioning of the component subsequent to the cleaning process.

Use of these aerosol products for electronics cleaning helps to ensure the proper functioning of high value components and systems, reducing the frequency and expenses associated with malfunctions, failures, and/or warranty rework. HFC-134a is used as the propellant to reduce flammability in those niche applications where a finer spray characteristic is desirable.

The estimated volume of HFC-134a propellant is low because compressed gases are acceptable for most applications. The HFC propellant contribution is approximately 0.1 metric tons CO2 equivalent.

The estimated total volume of HFC-43-10 and HFE-7100 used in aerosols is very low due to their high costs. Since the breakdown between use of these two solvents is uncertain, an approximate GWP of 900 is chosen to represent the market mix. This results in a contribution of 0.4 million metric tons CO2 equivalent for North America.

These products consist entirely of propellant, which is the active ingredient. They are used for:

1. Removal of dust from hard to reach space and crevices for maintenance of electronic components including computer components, imaging equipment, and high technology equipment in the laboratory, optics, and laser sectors;
2. Removal of dust and/or particles from electronic components during the repair or manufacturing process;
3. Freezing of circuit components to test for dead faults;
4. Industrial gum removal by freezing; and
5. Marine and industrial safety alarms

In the first and second instance, the spraying of propellant gas against plastic substrates, especially in the presence of dust could create a static charge that would function as an ignition source. In the second instance hot soldering irons are quite often present in the vicinity, also constituting a potential source of ignition. In the third instance there are energized circuits potentially constituting a source of ignition. In the fourth instance, there could be a buildup of static charge and/or potential sources of ignition nearby. In the fifth instance, such alarms are used in inherently hazardous locations, often to signal for help due to fire.

HFC-134a is used in dust removal and circuit freezing because it is non-flammable, thereby eliminating the potential of fires in the presence of sensitive and/or energized electronic equipment. In some applications, notably office dusters, HFC-152a has proved to be an effective, lower GWP replacement. Although HFC-152a is moderately flammable, dusters have been developed utilizing this propellant that would not require a flammable label on the container according to 16 CFR 1500.3 (c) (6), and do not require special warehousing attention according to NFPA 30B. However, in service and manufacturing areas, where duster use is more than incidental and sources of ignition are more prevalent the totally non-flammable HFC-134a is mandated for reasons of worker safety.

HFC-134a and HFC-152a are more effective dusting agents than hydrocarbons or compressed gases on an equivalent volume basis due to the their higher molecular weight. Compressed nonflammable gases, such as CO₂ and nitrogen, are not a viable option, since a very heavy, thick walled cylinder would be required to handle the pressure (more than ten times the maximum pressure rating of an aerosol can). If the propellant were solely in the gas phase, the pressure and thus the spray characteristic would change as the contents are discharged and the number of discharges per can would be severely reduced. The energy required to liquefy a compressed gas, so as to achieve a reasonable number of discharges, would be prohibitive. Also, the cost of using such a thick walled cylinder along with a valve capable of handling the high pressure would cost in the neighborhood of $100.

Compressed air from a mechanical compressor may be considered an alternative. However, compressed air is inherently dirty and moist and, to provide equivalent functionality, an air compressor would be required to maintain a high-pressure level continuously so as to be available for intermittent sprays. Compressor systems are subject to continuous leakage through reed valves, check valves, hoses and fittings, tank fittings and the gun. When the cumulative effect of these leaks causes tank pressure to drop below a minimum level, the compressor cycles on to rebuild the level. The energy requirement has not been tested but is expected to be significant. Additionally, compressors typically cost hundreds of dollars and are not very portable.

Non-flammable, portable signaling horns that meet Coast Guard prescribed decibel ratings has long been an important part of boating safety. Similarly, warning horns are used in remote areas of chemical plants, refineries, and construction sites to summon help in emergencies. Non-flammable gum removers promote worker safety in hotels and institutional buildings. There are no known equivalent substitutes for HFC-134a in these applications.

These products play a key role in the successful and safe operation of manufacturing and maintenance process for selected segments of industry. They are used primarily where potential sources of ignition may be present and user safety would be compromised by use of less efficient, highly flammable, VOC products.

The North American volume of HFC-134a used for these applications has been estimated to represent about 5.0 million metric tons of CO2 equivalent. For certain dust removal where HFC-152a can have sufficient flame suppression, the volume has been estimated to represent about 0.1 million tonnes CO2 equivalent. The share of 152a vs. 134a in the office duster segment appears to be growing, which could serve to reduce the total contribution to climate change from this category.

These aerosol formulations contain lubricants such as silicones or fluoropolymers. The inside of the mold is sprayed to facilitate the release of injected or laid-up material, usually a plastic or a synthetic fiber, to avoid having any of the material sticking to the surface. Propellants include HFC-134a, and dimethyl ether. HFC-134a is used as a propellant in many instances to avoid flammability, since the mold release aerosol is sprayed on hot surfaces.

These aerosol products using 134a play a key role in avoiding flammability incidents in the injection molding and textile industries. The volume of HFC-134a used for this application has been estimated to contribute less than 0.7 million metric tons CO2 equivalent.

Major categories include personal products such as hair care items, antiperspirants and deodorants, household products, spray paints, and automotive products. For many products, alternative, often less expensive, delivery systems exist side by side with an aerosol counterpart. The aerosol form continues due to consumer preference for its performance and functionality.

Propellants used in these products include hydrocarbons, dimethyl ether, compressed gases and HFC-152a.

A major driving force for incorporating HFCs in these products in the U.S. has been compliance with standards set by U.S. EPA under the Clean Air Act Amendments. These standards have limited content of photochemically reactive volatile organic compounds (VOCs) in consumer products as part of the effort to reduce ambient ozone, one of the most health-damaging of irritants in smog. Additionally, some jurisdictions, notably in California and some northeastern states have promulgated regulations more stringent than the EPA standards in order to attain mandated ambient air quality levels that are uniquely difficult due to geography and topography.

Formulators of consumer products whether in aerosol, pump spray, solid forms, or liquids have had to deal with reductions in VOC content by the substitution of non- or exempted, low reactivity, VOC products for such common ingredients as alcohols, mineral spirits, and hydrocarbon propellants. The list of non-VOC materials includes water and most solids. The list of exempted materials includes acetone, CFCs, HCFCs, HFCs, and very low volatility liquids such as viscous oils.

The practical list for many products has been reduced to water, acetone, and HFCs, due to functionality and environmental requirements. For many personal products, the toxicity of acetone has limited its use, leaving water and HFCs as the only major VOC substitutes available to the formulator.

Due to the price disparity between HFCs and water, we find that HFCs are predominantly used where high levels of water are deleterious to the intended use of the product. A typical example would be antiperspirants, intended to prevent moisture. Other niche applications have been in finishing hair sprays for very fine hair where the weight and curl straightening impact of water cannot be overcome by other means. Some very highly effective insecticides require HFC use where active ingredient compatibility and crevice penetration issues with water are a problem.

Limited use of HFC propellants will play a role toward reducing the VOC content in consumer product aerosols, thereby reducing the amount of organic material present in the atmosphere that can be photochemically oxidized to produce smog and deteriorate air quality. A U.S. state's failure to adequately reduce VOCs can lead to a loss of matching Federal Highway funds. This action would have a great impact on state economies by either delaying the repair and construction of new highways, and/or requiring increased in taxes, and/or requiring reprioritization of key budget items.

The volume of HFC-152a used for these applications in North America has been estimated to contribute approximately 0.9 million metric tons CO2 equivalent.

Virtually all marketers of formulated consumer products have chosen HFC-152a over HFC-134a when they have needed to use an HFC because of its significantly lower GWP. These stewardship decisions have been reinforced in informal discussions with producers and EPA.

Unlike refrigeration, air conditioning, and foam applications, the use of aerosols entails primarily the dispersal of chemicals, and the indirect contributions from this spraying would be minimal. Therefore, instead of carrying out LCCP analyses, estimates have been made for the amount of greenhouse gas emitted expressed in units of million metric tons of carbon dioxide equivalents. The estimated embedded energy and GWP of the fugitive emissions associated with manufacturing the Aerosol propellant is included in these figures.

In the preceding discussion, an estimate was provided of the total North American annual carbon dioxide equivalent emissions for each of the primary aerosol propellant applications that use HFCs. Table 11-1 summarizes this information.

Table 11-1: Summary of Fluorocarbon Aerosol Propellant Application and North American Annual Emissions