AIR BAGS
Air bags have been mandatory in automobiles since 1998 and have decreased the risk of dying in an accident by nearly 30 percent. The tech- nology behind air bags was first proposed during World War II to pre- vent injuries during a crash landing in an aircraft. Typically, air bags are located on the steering wheel or on the dashboard. They are intended to slow a passenger’s speed to zero with little or no damage to the person. The air bag is made up of three major components. The bag is made of a thin nylon or equivalent fabric, which is folded compactly behind the dashboard or inside a small space in the center of the steering wheel. It typically contains a small amount of cornstarch or talcum powder to keep the nylon pliable during storage. The inflation system consists of a reac- tion between sodium azide and potassium nitrate to produce a large vol- ume of nitrogen gas to inflate the bag. The sensor, which indicates the collision, is located in the bumpers of the automobile. The sensor is a switch that closes an electrical circuit when a collision above ten to fifteen miles per hour is detected. The electrical circuit triggers the chemical reaction in the inflation system and the air bag inflates in under one- twenty-fifth of a second. The reaction of the inflation system is so fast that the air bag is inflating at over 200 miles per hour! For this reason, it is important that passengers be seated at an appropriate distance from the air bag to avoid potential injuries from the air bag itself. Air bags can seriously harm children from the rapid inflation, and it is recommended that children under the age of one year not ride in the front seat of a vehicle equipped with air bags.
FUEL ADDITIVES
Since the mid 1920s, gasoline for consumer engines has contained the additive tetraethyllead, which improves fuel performance by preventing “knocking” in the cylinders of the engine. This knocking or preignition reduces engine efficiency, damages pistons, and reduces the power out- put of the internal combustion engine. Tetraethyllead, the most com- mon fuel additive of the past century, is a toxic liquid that killed more than fifty chemical workers during its early development and manufac- turing. Nevertheless, motor companies, oil companies, and the govern- ment authorized the manufacture and used of tetraethyllead in gasoline throughout the world.
In the late 1960s, new antipollution initiatives were enacted to reduce nitrogen oxides, carbon monoxide, and lead pollutants from automotive exhaust. Nitrogen oxides were responsible for the brown haze that hung over cities that can still be seen today. The advent of the catalytic con- verter, a small canister that contained heavy metal catalysts embedded on a ceramic support, helped oxidize carbon monoxide and reverse the reac- tion that produced nitrogen oxides. However, lead in the exhaust stream deactivated the catalysts in the catalytic converter. The only solution was to remove tetraethyllead from the gasoline.
Since the 1970s, tetraethyllead has not been added to gasoline, and oil refiners were pressed to increase the octane value of gasoline. One op- tion involved externally oxygenating fuels by adding alcohols such as methanol, ethanol, and tertiary butyl alcohol as well as ether combina- tions such as methyl tertiary butyl ether (MTBE). The petroleum indus- try preferred MTBE to alcohol blends because it was somewhat easier to handle. Ethanol was seen as a viable solution but has long been resisted by the petroleum industry. Along with boosting octane, oxygenated fuels have lower hydrocarbon and carbon monoxide emissions and have been used to fight city smog since the late 1980s. The reformulated gasolines (RFGs) proposed by the petroleum industry reduce pollutants such as hydrocarbons, toxic aromatic compounds, and nitrogen oxides from the combustion of gasoline. RFGs reduced hydrocarbon emissions by at least 15 percent in major cities and reduced the cancer risk associated with gasolines with high benzene content.
Reformulated gasoline blends have several advantages over gasohol (gasoline-alcohol mixtures) and MTBE blends. RFG blends evaporate less readily because they have a lower vapor pressure, and they have lower benzene and sulfur contents. Gasoline blends, as well as other petroleum distillates, are an inhalation hazard to humans. Hydrocarbon distillates have been shown to cause cancer in laboratory animals. The products from the combustion of gasoline, specifically carbon monoxide and nitrogen oxides, have been linked to the dissipation of the protective ozone layer
surrounding the earth and are responsible for a significant number of health problems in cities plagued with smog.
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