Methanol Safety

Methanol, as mentioned earlier, is a colorless liquid with a mild alcoholic odor. It is widely used as a chemical intermediate and solvent by industries and is present in a variety of consumer products. This includes, for example, the blue windshield washer fluid that most motor car owners are familiar with, which is in fact composed in large part of methanol. The use of methanol not only as a windshield washer fluid but also as a deicing fluid, antifreeze or even fuel for camping cooking vessels, implies that albeit almost every house contains methanol. Even if vigilance is always required, no significant problems have been associated with its use by the general public. With its widespread usage as an automotive fuel, exposure to methanol is likely to increase. As shown by a number of studies, the risks encountered by the consumer will however remain minimal and, in any case, not greater than those associated with the use of gasoline.

Methanol, like all other motor fuels, is toxic to the human body and should be handled with the same care as gasoline or diesel fuel with regard to its adverse effects on human health. Methanol is readily absorbed by ingestion, inhalation, and more slowly by skin exposure. The ingestion of 25 to 90 mL of methanol [169] may be fatal if not treated in time (compared to 120-300 mL of gasoline). Shortly after exposure, methanol causes a temporary effect on the brain, of similar nature but of lesser strength, than that of ethanol. Methanol is eliminated from the body by metabolism (i.e., enzymatic conversion) in the liver to formaldehyde, and then to formic acid which can be excreted in the urine or further me-

202 | Chapter 11 Methanol as a Fuel and Energy Carrier CH3OH

Methanol

Alcohol dehydrogenase

HCHO

Formaldehyde

Aldehyde dehydrogenase

HCOOH

Formic acid

Spontaneous

Formate

Folate

CO2 Figure 11.13 The metabolism of methanol

Carbon dioxide in the human body.

tabolized to CO2 (Fig. 11.13). As methanol is metabolized, the most severe effects are delayed for up to 30 h, these being caused mainly by the formic acid produced, which humans metabolize very slowly. Higher concentrations of formic acid, when dissociated into formate and hydrogen ions, leads to increased acidity in the blood. Symptoms may include weakness, dizziness, headache, nausea, and vomiting, followed by abdominal pain and difficulties in breathing. In severe cases methanol poisoning may progress to coma and death. Another well-known symptom associated with methanol poisoning is that of visual impairment, which ranges from blurring to total loss of vision, and is caused by formic acid affecting the optic nerve.

Several treatments can be applied to combat methanol poisoning, and these generally lead to complete recovery if administered in timely manner. Early treatment with sodium carbonate counters the higher blood acidity and prevents or reverses vision impairment. Dialysis is effective in removing both methanol and formate from the bloodstream. In addition, 4-methylpyrazole (AntizolĀ®, fomepizol) [169, 170], an antidote approved by the US Food and Drug Administration (FDA), and operating in the same manner for ethanol ingestion, though without its side effects (it is also effective against ethylene glycol poisoning), can be administered either intravenously or orally.

Although overexposure to methanol can be dangerous to human health, it is also important to realize that both methanol and formate are naturally present in our bodies from the diet, and also as a result of metabolic processes. Methanol is ingested when eating fresh fruits, vegetables and fermented foods and beverages. Aspartame, a widely used artificial sweetener included in many diet foods and soft drinks is also partially converted to methanol during the digestion process. According to the FDA, a daily intake of up to 500 mg methanol is safe for an adults diet [171]. Methanol and formate are naturally present in the blood in concentrations of approximately 1-3 and 10 mg L-1, respectively; moreover, formate is an essential building block for many biological molecules, including components of DNA [169]. Methanol is not considered to be either a carcinogenic or a mutagenic hazard; this is in contrast to gasoline, which contains a number of chemical compounds that are considered to be hazardous, including (amongst others) benzene, toluene, xylene, ethylbenzene and n-hexane, some of which are known to be carcinogenic.

Refueling a motor car with methanol at a service station equipped with an usual refueling system is only expected to result in low-dose exposures (23-38 ppm during the refueling process [169]) to the general public. By inhalation, a small oral intake of 2-3 mg of methanol is thus expected during a typical refueling. For comparison, this is much less than drinking a single 0.35-L can of diet soda containing 200 mg of aspartame, which will produce some 20 mg of methanol via the body's digestive system. Using vapor recovery systems, exposure to methanol during refueling can be further reduced to the 3 to 4 ppm level , adding only insignificantly to the methanol balance of the body. Even considering a worst-case scenario involving a malfunctioning vehicle in an enclosed garage where the methanol concentration is estimated to reach 150 ppm, a 15-min exposure would only add some 40 mg to the body's intake, or the equivalent of drinking 0.7 L of diet soda. Exposure to methanol can be readily minimized through the correct design of fueling systems and fuel containers.

In order to avoid spills, spill-free nozzles have been developed which makes it virtually impossible for the consumer to come into contact with methanol during refueling. Nevertheless, in case of contact with the skin, the affected area should be washed thoroughly with water and soap. To avoid accidental ingestion of methanol, the addition of distinct taste and odor agents should be considered. A dye may also be added to give methanol fuel a distinctive color. As indicated, however, by the 35 000 annual cases of gasoline ingestion in the United States alone (mostly through mouth siphoning when fuel is transferred from one tank to another), the unpleasant taste and smell may not be enough to prevent accidents. Thus, refueling systems should also be designed to make siphoning impossible and to allow only the vehicles themselves to be refueled with methanol. Other containers not meant specifically to contain methanol, the improper labeling of which could lead to mistakes or misuses, should be prohibited. In order to prevent the accidental ingestion of methanol by some heavy drinkers or the ill-informed public, the name "methyl alcohol" should also be avoided for methanol in order to minimize possible confusions with ethyl alcohol (i.e., ethanol). Above all, commonsense precaution in handling methanol should make its use safe.

Fire and explosion are major hazards associated with the use of transportation fuels, and these are also of concern for methanol safety. Compared to gasoline, methanol's physical and chemical properties significantly reduce the risk of fire. Combined with its lower volatility, methanol vapor in air must be four times more concentrated than gasoline for ignition to occur. If it does ignite, methanol burns about four times slower than gasoline and releases heat at only at one-eighth the rate of gasoline fires. Because of the low radiant heat output, methanol fires are less likely to spread to surrounding ignitable materials. In tests conducted by the EPA and the Southwest Research Institute [108], two cars - one fueled by methanol and the other by gasoline - were allowed to leak fuel on the ground adjacent to an open flame. Whilst the gasoline ignited rapidly, resulting in a fire that consumed the entire vehicle within minutes, methanol took three times longer to ignite and the resulting fire damage affected only the rear part of the car. The EPA has estimated that switching fuels from gasoline to methanol would reduce the incidence of fuel-related fires by 90%, saving annually in the United States more than 700 lives, preventing some 4000 serious injuries, and eliminating property losses extending to many millions of dollars [172]. Methanol has been the fuel of choice for Indianapolis-type race cars since the mid-1960s because, in addition to achieving superior performances, it is one of the safest fuels available. Unlike gasoline fires, methanol fires can be quickly and easily extinguished even by simply pouring water on them. Methanol burns with little or no smoke, reducing the risks of injuries associated with smoke inhalation and allowing a better visibility around the fire, enabling easier fire fighting. Methanol's combustion generates a light blue flame that is visible in most situations, but may not be easily seen in bright sunlight. In a majority of fires, however, the burning of materials other than fuel, such as upholstery, engine oil and paint, would impart the color of the flames, making them visible

Methanol Temperature Protection
Figure 11.14 Comparative fuel-related fires, deaths and injuries. (Source: U.S. Environmental Protection Agency, EPA 400-F-92-010.)

in any situation. In confined areas such as fuel tanks and reservoirs, an ignitable methanol/air mixture can form at ambient temperature. This property of methanol is however unlikely to lead to fires or explosions even in the event of a collision, and has been addressed by simple fuel tank modifications or addition of a volatile compound which makes the vapor space in the tank too rich to ignite [120].

In summary, compared to gasoline, methanol fires are far less likely to occur, and are much less damaging when they do (Fig. 11.14).

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Responses

  • TANELI
    What are the side effects of methyl alcohol exposure?
    8 years ago
  • VICTORIA
    How does methanol affects optic nerves?
    8 years ago

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