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Severity of the Fire
The severity of a fuel related fire determines, in large
part, the magnitude of the fire "hazard associated with that
fuel. This involves not just the violence with which the fuel
burns, but also the heat given off by that fire, and the amount
of smoke which it produces. All three help determine how
easily the flame will spread, or how dangerous that fire will
be to person and property.
Diesel fuel fires begin slowly, due to its extremely low
volatility, with a flame spread rate over a pool of fuel of
only 0.02 to 0.08 m/s (See Table 1). At the same time, its
high heat of combustion and low heat of vaporization (a ratio
of 156:1) combine to quickly vaporize additional fuel; causing
the burn to progress much more violently. The only controlling
factor is the high boiling points of diesel fuel's
constituents. As a result, as seen in Table 3, the relative
heat release rate from a diesel fuel fire is very high. This
high heat release rate results in a high probability that a
diesel fuel fire will spread to other nearby flammable
substances, and cause serious burns to exposed individuals.
Gasoline's high volatility enables immediate eruption of a
fully developed fire. The flame spread rate over a pool of
gasoline is nearly 100 times that for diesel fuel, or
approximately 4 to 6 m/s. Once ignition occurs, the high heat
of combustion provides more than adequate heat to overcome the
low heat of vaporization (a ratio of 123:1) and low boiling
point of many of its constituents. The pool burn rate for
gasoline is thus the highest of all the fuels, and when coupled
with its high heat of combustion causes the heat release rate
for gasoline also to be the highest of all the fuels (See Table
3). As a result, gasoline represents the greatest hazard of
the four fuels for the fire to spread to other flammable
substances nearby, and represents the greatest hazard for
serious burns to individuals in the vicinity of the fire.
MIOO's low volatility causes a flame to spread over a pool
of fuel at a speed just slightly more than half that of
gasoline; and MIOO's low heat of combustion and high heat of
vaporization combine to cause the burn to progress much more
slowly. (The ratio of the heat of combustion to the heat of
vaporization is only 17:1 for M100.) For this reason, a pool
of M100 burns at the slowest rate of all four fuels, and as
shown in Table 3, the heat release rate (ignoring situational
effects such as flame geometry) is nearly one-fifth that for
gasoline. In addition, the fraction of heat emitted in the
form of radiation is less with methanol than with the other
fuels.22 since this is the main source of heat exposure to
persons and objects near a fire, the relative heat release rate
is even more favorable to methanol than the values in Table 3
suggest.
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Table 3
Relative Heat Release Rates*
Fuel
M100
M85**
Gasoline
Diesel
Heat of Heat of
Combustion Vaporization
(kJ/1) (kJ/1)
15860
18270
31970
35680
936
817
259
228
Burn Rate
(mm/min)
2.1
2.5
4.8
4.0
Relative Rate
Release Rate
l.o
1.4
4.9
4.5
* *
Ignores differences in flame geometry and radiative heat
loss
Properties approximated based on proportions of the
constituents
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As a result of the low heat release from the methanol
fire, the likelihood that the fire will spread to other nearby
combustible substances or cause injury to people located nearby
is much lower than with gasoline.- As shown in Figure 2, the
distance from the center of a burning pool of M100 where the
incident heat radiation is adequate to cause a one percent
fatality among people located near the fire (7.5 kw/m2) is
just slightly larger than the radius of the fuel itself, while
for gasoline it is 4 to 5 times the radius of the fuel
spill.16
Also of importance in avoiding personal injury with
methanol is the fact that it does not produce the suffocating
clouds of black smoke that both gasoline and diesel fuel do.
However, since methanol vapor itself is toxic, not all risk is
avoided. In addition, as discussed later, pure methanol has
the unique property of burning with an invisible flame in
daylight conditions which increases the hazard of the fire.
In situations of fuel tank explosion, the additional
hazard results from the pressure wave associated with the
explosion. Direct biological damage to humans occurs when they
are exposed to an overpressurization of about 310 kPa, while
structural damage results with an overpressurization as low as
41 kPa.17 A methanol fuel, tank if ignited will result in a
maximum pressure rise under ideal conditions as high as 620 kPa
(825 kPa for gasoline hydrocarbons) at the fuel tank surface
(decreasing to 310 kPa at 12 feet from the tank), but under
typical in-use conditions the pressure rise could be
significantly lower.17 Any hazard resulting from this
explosion may be minimized, however, by designing the fuel tank
to withstand the pressure. Testing has shown that M100 tanks
may not need to be significantly stronger than today's gasoline
tanks to withstand the pressures generated.28
MB5 likely represents a compromise between methanol and
gasoline in aspects related to the hazard of a fire once it
occurs. Its volatility is high enough to cause the fire to
develop fully immediately following ignition, but its other
properties tend to limit the severity with which it burns. Its
heat of combustion is just slightly more than that of methanol,
while its heat of vaporization is just slightly less (a ratio
of 22:1). As a result, the rate at which a pool of M85 burns
and the rate at which heat is released from the fire are
estimated to be just slightly greater than for M100 (See Table
3). Thus, as seen in Figure 2 the area effected by a pool fire
of M85 is estimated to be just slightly greater than for M100.
Ease of Extinguishing
Given enough time, and proximity to combustible materials,
any fire can cause personal injury and extensive property
damage. For this reason, the ease with which a fire can be
extinguished also becomes important.
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FIGURE 2
Fatality ana Oamaqe Distances for Methanol 4 Gasoline Pool Fires
(100* FATALITIES IN POOL)
Key: ——— IS fataltty distance
100* fatality
Note: This figure was taken in its entirety from reference 16
-------
The main difference between M100 and gasoline and diesel
fuel is that M100 can be extinguished much easier with water.
Gasoline and diesel fuel are not water soluble and are both
lighter than water. Thus, a fire with these fuels is difficult
to extinguish with water as the fuel floats to the surface
where it reignites. Only by means of spraying water as a fog
and driving the fire off of the fuel can it be extinguished
with water. However, with diesel fuel, due to its high flash
point, water may be of some benefit in getting a fire under
control if it can be used to cool the fuel below its flash
point. Unlike gasoline and diesel fuel, methanol is infinitely
water soluble. Thus, it does not float on the water, and can
be extinguished by diluting it. Large quantities of water are
necessary, however, since a methanol/water mixture is flammable
down to 21 volume percent methanol. Since water is the most
abundant and readily available substance for fire fighting,
this can be a significant benefit with methanol, especially
when fires develop in remote areas. Since M85 has only limited
solubility in water before it will separate into the two phases
of gasoline and a methanol/water blend, water may be even less
effective as an extinguishing agent for M85 than for gasoline.
An additional benefit with methanol is the low amount of
heat given off by the fire. Fire fighting personnel are thus
able to approach a methanol fire with less chance for burn
injuries, fire stroke, and heat exhaustion, and should be able
to extinguish the fire more readily.16 In addition, due to
the lack of smoke and typically low levels of products of
incomplete combustion (PICs) produced when methanol burns, the
hazard to fire and rescue teams due to smoke inhalation should
be greatly reduced below that for gasoline and diesel
fuel.16 An added concern with fighting a methanol fire,
however, is that the fire itself is considered invisible during
daylight if it involves no other combustible materials or
contaminants. This could hinder fire fighting efforts, and
represents a serious safety concern. (This topic will be
discussed further in the following section.) The main benefit
of M85 over M100 is that, as discussed below, the flame is
typically visible in daylight.
Visibility of the Flame
As alluded to above, the lack of luminosity of an M100
flame is a significant issue relative to both the severity of a
fire, and the ease with which it can be extinguished. Gasoline
and diesel fuel burn with dark yellow flames clearly visible
under any conditions. In addition, they give off large clouds
of thick black smoke which can be seen for long distances.
Thus, there is little chance that even small fires with these
fuels will go unnoticed. Methanol, however, burns with a
smokeless blue flame, which is considered to be invisible in
daylight, since it contains no carbon-carbon bonds and,
therefore, does not produce unoxidized carbon particles or
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precursors to soot particles when it burns.32 For
comparison,. M100 burns with a luminance of 0.39 foot-lamberts,
while gasoline burns with a luminance typically exceeding 300
foot-lamberts.33 The only way of knowing that a fire exists
in which only M100 is burning (no other combustible materials
or contaminants are involved) under well lit conditions is by
seeing the heat waves or feeling the heat radiation given off
by the fire. This creates the potential of people entering the
fire without realizing it. However, the heat radiated from the
fire and any other substances which become involved in the fire
may provide some warning. Testing done on actual vehicle
engine compartments revealed that within a short period of time
after ignition of the M100 fire, combustion of underhood
materials (plastics, rubbers, etc.) provided sufficient
luminosity and smoke.30 This should also be the case in
spills outdoors as vegetation burns, and possibly also in
garage areas where minor oil spills are commonplace.
To avoid possible problems due to methanol's low
luminosity, there are a number of additives which have been
tested for use to make the flame visible. Many additives will
provide luminosity, but few provide luminosity throughout the
entire burn (i.e., they burn off faster than the methanol).
However, recent efforts with various organic dyes have yielded
more positive results at concentrations in the hundreds of ppm
range.34
To date, the simplest and most successful additive for
obtaining a luminous flame has been 15 percent of a high
aromatic, high volatility gasoline as selected by Ford.3®
Testing has shown that this results in an adequate amount of
flame visibility even in broad daylight throughout the burn;
thus, the emergence of M85.35'3' Despite this there are
still some concerns with regard to its flame luminosity.
Although the addition of gasoline provides luminosity, it is
still not very intense, and its blue and yellow flame tends to
diminish in luminosity as the burn progresses, especially if
not properly blended.^5'37 For this reason, if all of its
luminosity benefits are to be realized, care must be taken to
ensure that M85 is blended properly. In addition to concerns
over its effectiveness as a flame luminosity additive, 15
percent gasoline also changes significantly the other safety
characteristics of the fuel as discussed in this paper. As a
result, additives which provide luminosity without
significantly altering the nature of methanol may be preferable.
TOXIC RISK OF FUEL TO HUMANS
Fuel toxicity to humans is an issue of great importance
when assessing the safety of a given fuel. There are many
situations in which a person may come into contact with the
fuel either through inhalation, ingestion, or dermal contact.
Thus, if the fuel causes any acute, chronic, subchronic, or
carcinogenic toxic effects to humans, the risks due to toxicity
may far outweigh any other safety concerns.
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Fuel Toxicity
The.acute toxicity of diesel fuel relative to ingestion is
such that acute exposure may cause nausea, vomiting, cramping,
liver and kidney damage, lung irritation, and central nervous
system depression ranging from a mild headache to coma, and
death.8 If the lethal dose to rats (LD50) is extrapolated to
humans, death would result from ingestion of just 63 ml (1/4
cup) for the average adult male.3® Since diesel fuel will
often cause regurgitation, large quantities of ingested fuel
will often not stay in the stomach, thus avoiding the acute
toxicity discussed above. Unfortunately, when regurgitation
occurs, aspiration into the lungs of even small amounts of
diesel fuel may result in severe irritation with coughing,
gagging, difficulty breathing, chest pain, and chemical
pneumonitis, and bronchopneumonia.8'39
In addition to ingestion, acute effects with diesel fuel
can also result from dermal contact. Diesel fuel is considered
to be a moderate to severe skin irritant, causing irritation of
hair follicles and blockage of sebaceous glands resulting in a
rash of pimples and spots.8'40 More importantly, prolonged
or repeated exposure may result in defatting of the lipid
components of the skin. Prolonged exposure may also result in
a state of stupor (narcosis) as a result of absorption through
the skin. No information was found in the literature which
quantified the exposure necessary to result in these toxic
symptoms, however, and as a result it is difficult to make
comparisons with the other fuels. Based on what information
was available, diesel fuel would appear to be the mildest of
the four fuels in relation to skin contact. Eye contact may
result in irritation and redness; with prolonged exposure
resulting in inflammation of the eye's mucous membranes.
Acute inhalation exposure to diesel fuel vapor, though
extremely rare, may cause respiratory tract irritation, and
high levels may cause giddiness, headache, dizziness, nausea,
vomiting, incoordination, and unconsciousness.8 The
concentration in air which is considered to be immediately
dangerous to life and health (IDLH) is 10,000 ppm.17 Long
term chronic exposure to diesel fuel vapor is not known to be
carcinogenic. However, skin painting carcinogenesis bioassay
tests reveal that diesel fuel may be weakly to moderately
carcinogenic, and mutagenesis assays have yielded mixed
cesults;38.46
The acute toxicity of gasoline relative to ingestion is
such that even small amounts (5 to 10 ml) may cause a burning
sensation in the mouth, throat, and chest, and intense
irritation and burning in the gastro intestinal tract, with
nausea, vomiting, diarrhea, and abdominal pain. Ingestion of
27 to 40 ml of gasoline will typically result in additional
more serious symptoms including central nervous system
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depression, headache, dizziness, drowsiness, fever, and
transient .liver damage.13'38 Severe intoxication may result
in unconsciousness and coma or convulsions with
seizures.13,3® Estimates for the dose which is typically
fatal to the average adult range from 115-180 ml to 470 ml, but
death has been reported at a dose as low as 13 ml.38'41 In
children, the normally fatal dose is approximately 13 to 20
ml.38 In addition to the potentially severe systemic
toxicity of gasoline, it is probably even more hazardous if
aspirated into the lungs following regurgitation or belching.
Once in the lungs, even small amounts may cause severe chemical
pneumonitis, and death from lung insufficiency.13'41
The acute toxicity of gasoline skin contact is such that
minor direct contact can result in irritation, drying and
cracking of the skin, and dermatitis.13 A more severe or
repeated exposure can cause chemical burns and blistering, and
defatting of the skin due to gasoline's lipid (fatty tissue)
soluble characteristic.13 In addition, prolonged exposure
can result in absorption into the body causing systemic toxic
effects such as weight loss and lung, heart, neurologic,
kidney, and liver problems with potentially life threatening
consequences.42 As with diesel fuel, since no information
was found in the literature which quantified the exposure
necessary to result in these toxic symptoms or the rate at
which gasoline is absorbed into the skin, comparisons with the
other fuels are difficult. Eye contact with gasoline may
result in mild irritation and redness.13
The acute toxicity of gasoline vapor inhalation is such
that exposure to low concentrations may cause eye irritation,
respiratory tract irritation and burning with cough and sore
throat, central nervous system depression with headache,
dizziness, drowsiness, nausea, or mental confusion.13'43'44
Higher concentrations may cause respiratory difficulty,
accumulation of fluid in the lungs, bronchial pneumonia with
fever, and heart damage. Further central nervous system
depression may occur with muscular incoordination, blurred
vision, unconsciousness, or convulsions. Even brief exposure
to high concentrations may cause narcosis, coma, or death from
severe central nervous system depression resulting in
respiratory failure. Extremely high concentrations may cause
asphyxiation.13»45
The chronic effects of gasoline exposure are less well
known. It is believed that chronic exposure to gasoline
results in pathological changes in the lung and central nervous
system disturbances, and may result in gradual irreversible eye
damage, but other effects are uncertain.46 Information is
inconclusive regarding any mutagenic, reproductive, or
teratogenic effects. EPA has classified gasoline vapors as
being a group 2B probable human carcinogen.47 Despite more
recent information which questions the applicability of the rat
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and mouse studies on which this classification is based, EPA
has retained the B2 classification.40,47,48,49 The fact that
gasoline contains benzene, a proven carcinogen, lends support
to the carcinogenicity of gasoline vapor. In fact, gasoline's
threshold limit value (TLV) of 300 ppm and short term exposure
limit (STEL) of 500 ppra were set at least in part to protect
against the cumulative toxic effects of benzene.
With few exceptions, the acute toxic effects of methanol
exposure are the same regardless of the route of exposure.50
These symptoms, all related to systemic toxicity, occur in
three stages.
1st: Depending on the amount ingested, the first symptom
is intoxication similar to that with ethanol.
2nd: This is followed by a latent period of 10-48 hours
in which no symptoms occur.
3rd: If the exposure was significant (large) enough, and
treatment was not received, the latent period is
followed by a variety of symptoms including:
headache, nausea, vomiting, violent abdominal pain,
leg and back pain, blurred vision, sensitivity to
light, and pain in the eyes. If the exposure were
severe, symptoms can progress to severe impairment
of vision, temporary or permanent blindness, coma,
and possibly death as a result of respiratory
failure or rarely circulatory collapse. If death
does not occur, these symptoms may be followed by a
prolonged recovery period with loss of strength,
blindness, and impaired kidney function.50'51'52
The initial symptoms of overexposure to methanol result in
a manner similar to that for ethanol. However, the symptoms
following the latent period result from methanol's metabolites
in the body.53 Methanol is metabolized to formate, which is
in turn oxidized to form CO2 which is then exhaled.50'54
However, the rate of metabolism of formate is slower than for
methanol. Thus, if the level of methanol exposure is severe
enough and/or of long enough duration, the body's ability to
metabolize the formate is overwhelmed, causing formate buildup
and acidosis of the blood with the subsequent symptoms of
methanol exposure.53'54 The minimum exposure to methanol
which is estimated to challenge formate's rate of metabolism
and, thus, the point at which the toxic symptoms following the
latent period are expected to occur in humans, is approximately
210 mg/kg of body weight.55 Correspondingly the minimum
lethal dose of methanol in the absence of medical treatment
generally ranges between 300 and 1000 mg/kg, while the dose
often causing death ranges between 800 and 5000 mg/kg.55
Ingestion is the most common form of methanol poisoning in
humans. There are no additional unique symptoms relative to
ingestion. Metabolism of the methanol may be slowed and the
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latent period extended if ethanol is ingested along with the
methanol or within the first few hours thereafter. For the
average adult male weighing 70 kg,- toxic effects can begin with
ingestion of as little as 18 ml (approximately 3 to 4
teaspoons) of methanol. Ingestion of larger amounts can cause
blindness, and as little as 26 to 70 ml can be fatal. However,
there are cases described where as little as 6 ml proved fatal
while in other cases 500 ml has not resulted in any permanent
damage, and the normally fatal dose ranges from 60 to 240 ml.
Methanol is considered to be a moderate skin and eye
irritant.56 Additional symptoms of acute toxicity relative
to skin contact include defatting and a mild dermatitis on the
skin, and prolonged or repeated exposure may cause eczema,
redness, and scaling. The most severe symptoms occur if
methanol is absorbed into the skin in significant quantities to
result in the systemic toxicity discussed above. Methanol will
absorb through the skin readily at an estimated rate of 0.2
mg/cm2 per minute.57 Momentary contact with it is not a
large concern, but frequent or long term exposure can be.
Immersion of a hand (with a surface area of roughly 440 cm2)
in methanol for three hours may cause toxic effects (roughly
equivalent to a body concentration of 220 mg/kg), and immersion
for four hours could potentially cause death. Acute eye
contact with methanol has caused superficial corneal lesions,
but the real hazard to the eyes is to the optic nerve as a
result of methanol's metabolism as described above.
The symptoms related to acute inhalation of methanol vapor
include irritation of the mucous membranes, headache, and mild
eye irritation. Headaches have been reported to occur at
concentrations between 17 and 385 ppm, while the first sign of
eye irritation, eye sensitivity to light, may begin at
concentrations as low as 2.5 ppm.57 Prolonged exposure to
high concentrations can result in the systemic toxic effects
discussed above. In order for these toxic symptoms to occur,
the ambient concentration of methanol for eight hours a day
must typically be about 3000 ppm.5 8 The TLV, however, is set
much lower than this at 200 ppm, while the STEL is 250 ppm, and
the level immediately dangerous to life or health is 25,000
ppm. To put inhalation into perspective with the other modes
of exposure (assuming total absorption of the inhaled vapor), a
70 kg person breathing at twice the resting rate (20 mVday),
who is exposed to 150 ppm of methanol vapor for 15 minutes
accumulates a methanol body concentration of 0.6 mg/kg, which
is at least 500 times less than the minimum lethal dose.55
For comparison, the average person consumes anywhere from
one-half to two and one-half times this amount through the
consumption of fruits, vegetables, and alcoholic beverages in
the diet everyday.55 Using similar assumptions, the
concentration would have to be nearly 20,000 ppm in order to
achieve the minimum fatal dose (300 mg/kg) with exposure for 1
hour. The majority of methanol taken into the body is purged
within a few hours, and usually completely gone in 10 to 16
hours.59
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Available peer-reviewed literature does not provide
conclusive evidence of any long-term low-level chronic effects
associated, with exposure to methanol.53 The belief that
methanol is not toxic with low-level, long-term chronic
exposure is supported by the fact that methanol occurs
naturally in the body at a level of approximately 0.5 mg/kg
(ranging from 0.2 to 5.0 mg/kg) as a result of natural
metabolic processes, occurs naturally in the atmosphere in
minute concentrations, and is present in our daily diet.55
The average daily intake of methanol in the diet through
ingestion of fruits, vegetables, and alcoholic beverages is
estimated at 0.3 to 1.1 mg/kg with a 99th percentile as high as
3.4 mg/kg. In addition, just one can of a diet softdrink
sweetened with aspartame amounts to the ingestion of roughly
0.3 mg/kg (See Table 4).55
A few studies have suggested possible neurobehavioral,
central nervous system, reproductive, or developmental effects
of exposure to methanol at concentrations at or substantially
above methanol's TLV.62 The most plausible chronic effects
of methanol exposure are probably reproductive and
developmental due to methanol's similarity to ethanol, and the
known effects of ethanol in these areas.
M85, due to its newcomer status, has not been studied in
any detail, but its toxicity is expected to be merely a
combination of that for gasoline and methanol, with the precise
effects dependent on the type of exposure.56 Since both
methanol and gasoline are central nervous system depressants,
the methanol may serve to enhance the toxic effects of gasoline
just as ethanol does.40
Relative to ingestion, since gasoline comprises only 15
percent of the volume of M85, only if extremely large amounts
are ingested will the acute systemic toxic effects of gasoline
ingestion be expected to occur. However, it may be possible in
some situations, especially if regurgitation occurs, for enough
gasoline to be aspirated into the lungs where it could
potentially result in death (See discussion of gasoline
toxicity). Typically, the main concern with M85 ingestion will
result from the 85 percent of it which is methanol, for which
the discussion above applies. In instances where regurgitation
occurs shortly after ingestion, however, the chances of any
methanol poisoning are greatly reduced.
The area of skin contact is an area where synergistic
effects of methanol and gasoline on the toxicity of M85 are
currently expected to occur. Testing done with M85 has shown
that methanol's rate of absorption into the skin is higher than
with M100 alone, thus representing a higher likelihood for
systemic toxic effects.63 It is hypothesized that this may
be due to the gasoline content drying out the skin allowing the
methanol to be absorbed more readily. Aside from this aspect
M85 is not known to cause any unique effects with respect to
skin or eye contact.
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Table 4
Methanol Body Burden for .Selected Situations
Extracted from Health Effects Institute Information55
Exposure Scenario
Minimum Lethal Dose
Personal Garage
Self-Service Refueling
12-Ounce Diet Beverage
Dietary Intake of
Aspartame (w/o diet
beverages)
Background Body
Burden
Assumed
Condition
600 mg/m3, 15 min.
Twice resting
breathing rate
100 mg/m3, 5 min.
Twice resting
breathing rate
100 mg/m^, 5 min.
Resting breathing
rate
50 mg/m^, 4 min.,
Twice resting
breathing rate
555 mg aspartame/1
Normal Diet
Added Body
Burden
of Methanol
300 mg/kg
1.8 mg/kga
0.1 mg/kg
0.03 mg/kg
0.04 mg/kg
0.3 mg/kgb
0.3-1.1
mg/kg/day
0.5 mg/kgc
a. Assumes all inhaled methanol absorbed across respiratory
epithelium; in all probability, less (appx. 60 percent of
inhaled) is absorbed.60
b. Assumes all aspartame-derived methanol crosses gut mucosa
instantaneously; because of the time required for
hydrolysis and transport, peak measured levels reach 70-75
percent of the value in the table.61
c. Based on value of 0.73 mg/1 of blood.60
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With respect to inhalation, since roughly two-thirds of
the vapor produced by M85 exposed to the atmosphere is gasoline
hydrocarbon- (See flammability discussion), the acute toxic
effects of M85 are expected to most closely resemble those of
gasoline. Nevertheless, if the exposure is severe enough, it
is possible that symptoms caused by both exposure to gasoline
and methanol may develop.
Long-term chronic effects of exposure to M85 is also
expected to be most similar to that for gasoline. Due to the
limited amount of work done with M85, there is not a TLV
specified strictly for M85.
Exposure and Overall Risk Assessment
As discussed above, all of the fuels are toxic to humans,
but in order to perform an appropriate comparison between the
fuels it is necessary to take into account not only the fuel
toxicity itself, but also the potential exposure to the fuel.
In addition, traits of the fuel such as odor, taste, and color
all become important for immediate detection of possible toxic
hazards.
Ingestion
Ingestion represents the most likely cause of serious
acute toxicity due to the ability to get large quantities of
fuel into the body quickly. All of the fuels pose a toxic
threat if a sufficient amount of fuel is ingested.
Despite its wide use as a fuel, little information was
found in the literature relative to ingestion of diesel fuel,
possibly due to the fact that it is handled by a limited number
of people in a limited number of applications. In addition,
its strong taste, color, and odor may tend to discourage
accidental and intentional ingestion.
Due to the offensive nature of gasoline (i.e., taste and
odor), one would not expect gasoline ingestion to be common.
However, due to its widespread use and large number of
applications there are many instances in which accidental
ingestion occurs. It has been estimated based on American
Association of Poison Control Centers (AAPCC) information that
there are 35,000 incidences of gasoline ingestion
annually.64 Roughly 39 percent of these instances are as a
result of siphoning accidents, while an additional 36 percent
occur as a result of accidental exposure to children under 6
years of age.54 Most of the pediatric exposures are related
to improper storage of gasoline in and around the home or to
storage of fuel for use in lawn and garden applications.
Despite the large number of ingestions, the amount typically
ingested is apparently small since only 16.4 percent of
reported incidents are managed by a health care facility, and
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only 2 percent experience a "moderate" or "major" (life
threatening) medical outcome.64 Despite the number of severe
exposures, only one known death occurred in 1987 which may have
been attributable to gasoline ingestion.64 Siphoning
accidents, though likely to result in toxic symptoms, are not
likely to result in death (unless aspiration occurs), since the
average "mouthful" of fluid is only approximately 80 ml (range
of 55 to 110) while the usually fatal dose ranges from 115 -
180 ml to 470 ml.38,41,64
AAPCC data reveal that in 1987 there were 1601 reported
incidences of acute exposure to methanol (all exposures, no
differentiation was made in the data between ingestion and
other types of exposure).64 These exposures are likely to
have resulted from ingestion or skin contact to canned heat,
de-icers, duplicator fluid, gas-line antifreeze, paint
strippers and removers, model airplane fuels, pipe sweeteners,
or windshield washing fluids. Roughly 53.2 percent of these
exposures were treated in a health care facility, however, only
5.575 percent resulted in "moderate" or "major" health effects
(0.375 percent in death).64 Since these exposures are not
related to the use of fuel in motor vehicles, it is difficult
to compare these data with that for gasoline.
Based on the available information, it has been estimated
that the number of fatalities due to ingestion of motor fuels
would increase by as much as 195 per year if methanol were to
replace gasoline.64 It was further assumed, however, that
this number could be significantly reduced if certain
precautions are taken in the implementation of methanol as a
fuel.64 Some of these precautions will require specific
action on the part of authorities, but others will likely be an
automatic part of a methanol fuel program. If methanol
vehicles are equipped with flame arresters on the fill pipe and
vents to minimize the ignition hazard, most siphoning accidents
should be precluded. If methanol is not used in lawn mower
applications (or marine applications) then the exposures
associated with such a use should also not occur. These
include siphoning exposures to adults attempting to obtain fuel
for lawn mower use, and pediatric exposures associated with
lawn mower refueling containers located in areas accessible to
small children. In addition, methanol being a polar substance
is not an effective solvent for oils and greases which are
non-polar. As a result, the ingestions resulting from gasoline
stored in and around the home for this purpose should also not
occur as frequently with MIOG. Educational efforts, fuel
additives to provide distinguishing characteristics such as
taste, odor, and/or color to pure methanol, and other methods
may also be effective at minimizing the risks associated with
methanol fuel ingestion.
As historical data have shown, however, methanol may be
more likely to be ingested intentionally than the other fuels.
Although it causes a burning sensation in the mouth and
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irritates the gastro-intestinal system, M100 does not have an
unpleasant odor or taste, nor will it typically cause
regurgitation. Therefore, M100 presents no natural barriers to
-intentional drinking. In addition, since methanol has no
taste, color, or odor to identify it, it has the potential to
be ingested unintentionally more readily than the other fuels.
Although there is an effective treatment for methanol
ingestion, it will not be given unless the person knows he/she
has the need for it. For these reasons there have been a
number of different additives proposed for M100 to give it
taste, odor, and color.»65'To date, the most common
additives to methanol for fuel use in the United States have
been the addition of various hydrocarbons as in M85. Much
smaller amounts than 15 percent gasoline can accomplish this
task, however, with some estimates stating that as little as l
to 2 percent hydrocarbon can deter against its ingestion.67
M85 possesses a taste, color and odor similar to that of
gasoline. However, for many of the same reasons as for M100,
it is not as likely to be ingested. Siphoning from motor
vehicles should be prevented if flame arresters are used, and
its presumed lack of use in lawn/garden applications will
reduce the frequency of ingestion by children. It is expected
that M85 will not be as good a solvent for oils and greases as
gasoline since most of it is methanol (a polar substance vs
non-polar for oils and greases). Thus, its availability in and
around the home is likely to be less than with gasoline today.
As a result, despite the fact that toxic concerns with M85
result from both its methanol and gasoline fractions, as long
as appropriate precautions are taken, the frequency of
exposures is expected to be lower than for gasoline today.
Skin and Eye Contact
There are many possible instances in which people may ccme
into direct bodily contact with these fuels. Some are
accidental such as spitback while filling a fuel tank, whil'S
others involve negligent use of the fuel such as use as
solvent to clean oil stained hands. As discussed earlier, a.l
of the fuels can result in toxic effects, but due to the short
term nature of most skin contact, acute effects tend to be mu::i
more rare than with ingestion. In addition, for the general
public, skin contact is not likely to be a frequent enough
event to result in chronic effects.
Little information was found in the available literature
concerning the frequency of skin and eye contact with diesel
fuel. It has been suggested by persons involved with the
heavy-duty diesel vehicle industry that diesel fuel tends to be
handled rather carelessly due to its low flammability. If this
is indeed the case, then the incidences of skin contact may be
unproportionately high compared to its sales volume. However,
the toxicity information presented earlier suggests that the
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effects of skin and eye contact tend to be less severe with
diesel fuel than with the other fuels and, thus, the overall
hazard may nevertheless be small.
Due to gasoline's wide use, any situation which allows for
skin contact may represent a significant problem nationwide.
Of the 13,028 exposures to gasoline reported to the AAPCC in
1987, roughly 11.4 percent were due to skin contact, and 19.5
percent due to eye contact.64 However, only 1.6 percent of
the dermal exposures and 1.1 percent of the ocular exposures
resulted in "moderate" effects, and only 1 dermal and 1 ocular
exposure resulted in "major" effects (no deaths were
reported).64 The most likely event leading to acute dermal
toxic effects (or even possibly chronic) with gasoline is its
misuse as a solvent for cleaning oils and greases from the
hands. Splashes on the skin evaporate quickly and, if
infrequent tend to be of little concern. (Some components of
gasoline evaporate slowly, but these are often washed off due
to the unpleasant odor of gasoline.) Except in the case of a
severe accident resulting in massive and prolonged dermal
contact (in which case all the fuels would be likely to cause
death), only with continued and/or severe misuse as a solvent
is exposure likely to be severe enough or frequent enough to
result in the toxic effects discussed above.
Methanol's use as a motor vehicle fuel will also result in
skin and eye exposures. However, since it is not a good
solvent for cleaning oils and greases due to its polar nature,
and since it is not as likely to be used in other applications
(lawn mowers, boats, etc.), the frequency with which skin and
eye contact occur is likely to be less than with gasoline. In
addition, since its toxicity relative to the skin or eye is not
significantly greater than that of gasoline, the number of
cases with "moderate" or "major" effects seen with gasoline in
the AAPCC data is not expected to be significantly greater with
methanol. Splashes on the skin evaporate quickly, and as a
result are not of long enough duration to be of concern. Only
if methanol is maintained in contact with the skin such as with
methanol soaked clothing are concerns likely to arise.
Nevertheless, since methanol does not have a distinctive odor
or color which might tend to deter against frequent intentional
or careless skin contact, or speed cleanup of accidental skin
contact, additives such as odorants, colors, or dyes to
methanol in addition to educational efforts, may be beneficial.
The situation relative to skin and eye contact with M85
should be virtually the same as with M100. As discussed above,
M85 may be absorbed through the skin slightly faster than M100,
but in most situations this is not a significant difference.
Also, M85 may be a slightly better solvent for greases and
oils, and as a result possibly also more likely to be used on
the hands for this purpose. However, M85 possesses the odor of
gasoline, and as a result an additive for this purpose may not
be necessary.
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Inhalation
Inhalation of fuel vapors can represent a serious health
hazard. Although the number of - exposures by inhalation is
large, seldom is it to a high enough concentration or of a long
enough duration to result in acute toxicity. The most common
instances where acute inhalation exposure to motor vehicle
fuels are known to occur today are in intentional abuse
situations such as "gas sniffing", and in personal accident or
spill situations where exposure to high concentration is
maintained for long periods of time. The largest risk from
inhalation of motor vehicle fuels may come as a result of
possible long-term chronic exposure. Thus, even low
concentrations in the background air we breathe can conceivably
be a toxic hazard.
The extremely low volatility of diesel fuel causes there
to be concern of acute toxicity due to inhalation only in
situations such as an individual lying in or near a pool of
diesel fuel, or if a heating source is vaporizing the fuel.
Thus, only chronic concerns are likely with diesel fuel.
Although it may be possible that diesel fuel is a weak to
moderate carcinogen with long-term chronic exposure based on
skin painting bioassay tests, once again, due to the extremely
low volatility, exposures tend to be very minor, and any
possibility of chronic effects is minimized.40
The properties of gasoline (high volatility, low diffusion
coefficient, and high vapor density) suggest that acutely toxic
concentrations of vapor would be more common with it than with
the other fuels. Despite this, natural ventilation apparently
limits exposures except in the most severe circumstances.
Sampling performed in the breathing zones of persons at service
stations revealed that time weighted exposures were 8.2 ppm or
less, and when averaged over the entire working day were less
than 2 ppm.68 Only approximately 8.3 percent of the 13,028
exposures to gasoline reported to AAPCC in 1987 were inhalation
related, and of these just 5.1 percent (60) resulted in
"moderate" effects and 0.4 percent (5) resulted in "major
effects". In addition, one death was reported as a result of
gasoline "sniffing", and one death possibly related to
inhalation.64 Most reported instances of severe inhalation
exposure are as a result of either intentional abuse as with
gasoline sniffing or direct exposure to spills.64
Low concentration exposures to gasoline are extremely
common (refueling, vehicle exhaust, ambient air, etc.). While
these events are typically not of an acutely toxic concern,
they may be of a chronic concern. Gasoline vapor is considered
by EPA to be a group B2 probable human carcinogen which was
estimated to result in as many as 68 incidences in 1986, and is
suspected of causing various other chronic effects (See earlier
discussion).69 In addition, gasoline vapor contains benzene,
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a group A human carcinogen which was estimated to cause as many
as 1.55 cancer incidences in 1986 (as will be discussed later,
roughly 70' percent of these are projected to be due to benzene
in vehicle exhaust, with the remainder due to evaporative and
refueling emissions and other direct emissions).73 as a
result, the chronic effects of gasoline inhalation exposure far
outweigh the acute effects.
Due to a similar use pattern, the frequency of inhalation
exposure with M100 may be similar to that with gasoline today.
Due to methanol's much lower volatility, however, the level of
exposure is expected to be much lower; 30 percent by volume of
that for gasoline based on volatility alone. (The actual
concentration will be a strong function of the specific
situation.) In addition, the high diffusion coefficient and
low vapor density of methanol tend to limit concentrations and
speed their dispersion. Based on this information, and
discussion of the AAPCC data on gasoline earlier, it appears
that the situations most likely to result in acute exposure
with gasoline are less likely to occur with M100. It is not
expected to be abused as is gasoline (gasoline sniffing), and
it should be less prone to flow into low areas where it may
accumulate, or stay along the ground where already unconscious
people may be exposed. Most other likely exposures, as with
gasoline, are not expected to be significant enough to lead to
acute toxic effects. The time weighted average methanol
concentration in the breathing space of attendants refueling
methanol vehicles is roughly just 2 ppm.50 The results of
modelling done for a variety of other situations (street
canyons, roadways, tunnels, personal garages) using emission
rates from malfunctioning methanol vehicles (first generation,
low technology vehicles compared to the vehicles likely to be
introduced in the future) reveal that only in the worst case
situation (malfunction idle in a personal garage) is the
ambient concentration expected to exceed the STEL. However,
since the TLV is based on an 8 hour exposure, and the garage
scenario exposure lasts for only approximately 15 minutes, the
TLV is not exceeded.70 Thus, as shown in Table 4 the
expected body burden caused by even the worst case scenario
still only produces an exposure less than one-hundredth the
minimum lethal dose. In addition, it is much more likely that
the TLV for carbon monoxide (CO) will be reached before that
for methanol. Testing done in the LA garage where M85 vehicles
have been operated for a number of years demonstrated that
concentrations of CO reached levels as high as 30 percent of
the TLV, while those for methanol were less than 1
percent.71'74
Since chronic effects are not presently considered to
result from exposure to low levels of methanol, and since it is
not considered to be carcinogenic, even though some exposures
related to vehicle exhaust emissions may be slightly more
severe with methanol, the toxic risk is expected to be much
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less. In the few studies which have suggested that some
chronic effects may exist with methanol similar to those that
exist with, ethanol, the concentration has typically been well
above normal exposures, and has greatly exceeded the expected
ambient concentration of less than 1 ppm.74
Despite the lack of situations leading to toxic exposure,
a unigue concern with methanol is that it does not have a
distinctive odor at the concentrations at which it can be a
health hazard. Thus, a person could be inhaling a toxic
concentration of methanol without knowing it until the symptoms
(mucous membrane irritation, eye irritation, headache - refer
to earlier discussion) began to show. Estimates vary widely on
what the odor threshold is for methanol with some estimates as
low as 3.3 ppm and other estimates as high as 6000 ppm, but a
reasonable estimate is probably approximately 2000 ppm.57
This is ten times the level of methanol's TLV, but is still
below the minimum concentration thought to be capable of
causing acute methanol toxicity (3000 ppm). To alleviate this
potential problem, there has been some consideration of the
addition to the fuel of odorants. A wide variety of possible
odorants exist; including gasoline in very low concentrations.
M85, once again, appears to represent a compromise between
Ml00 and gasoline. Due to a similar usage pattern the types of
exposures may be similar to those for gasoline, but due to its
lower volatility, the level of exposure should be lower; 77
percent by volume of that for gasoline based on volatility
alone. Roughly two-thirds of "M85 vapor" is composed of
gasoline hydrocarbon, and as a result, exposed M85 fuel
produces roughly 90 percent by volume of the methanol vapor as
does M100, and 50 percent by volume of the gasoline hydrocarbon
vapor as does gasoline.73 (Note that actual emissions can be
quite different from these estimates as they will vary
depending on the specific situation.) M85 also represents a
compromise in its vapor dispersion properties, but is probably
most similar to gasoline due to the large fraction of "M85
vapor" which is gasoline hydrocarbon.
Also, as a result of the large fraction of vapor which is
gasoline hydrocarbon, the practice of "gasoline sniffing" is
not eliminated. In addition, high concentrations of gasoline
hydrocarbon may build up in low areas or along the ground. But
since less gasoline hydrocarbon is given off from M85 than from
gasoline, acute effects from exposure are less likely than with
gasoline.
Chronic effects resulting from exposure to M85 may be of
greater concern than the acute effects. The cancer risk of M85
is expected to be in proportion to the fraction of emissions
which are gasoline hydrocarbon. Based on the above discussion,
the hydrocarbon portion of "M85 vapor" is estimated to be
approximately 50 percent of that from gasoline, thus, roughly
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50 percent of the cancer incidences estimated to result each
year from exposure to gasoline vapor may also be expected with
M85. Due' to the high aromatic content of M85's gasoline
fraction (roughly 40 percent compared to approximately 30 for
standard gasoline), benzene emissions from M85 should represent
a proportionately greater fraction of the hydrocarbon
emissions. Incorporating the greater fuel volume requirement
for M85 (roughly 65 percent) results in the conclusion that
roughly 68 percent of the evaporative and refueling benzene
emissions from gasoline and 68 percent of the cancer incidences
associated with them should also be expected to occur with
M85. The actual number could be even higher due to the greater
tendency for benzene to evaporate when mixed with
methanol.40»75
ENVIRONMENTAL HAZARD
Each year billions of dollars are spent in an effort to
clean or maintain various aspects of the environment. Without
such expenditures we would pay a penalty either in public
health or quality of life. Of this money, a significant amount
goes toward cleaning up the land, water and air due to leaks,
spills and emissions from petroleum fuel sources. If another
fuel is to replace petroleum, it too will have to be evaluated
on this basis. If it proves much less hazardous, it could be a
great economic and social benefit. If it proves much more
hazardous, it may deter its implementation.
Emissions
Motor vehicle emissions are a primary source of air
pollution, particularly in metropolitan areas, and the problems
which they cause are a real concern when considering a new
fuel. In fact, the ability of methanol to reduce one of our
most severe air quality problems today, ozone, is the main
reason why EPA is interested in methanol as an alternative
fuel. The effectiveness of methanol at reducing the ambient
levels of ozone is currently the focus of a great deal of
effort both within EPA and elsewhere. Due to the complexity of
the topic, it will not be addressed further in this report, but
the reader is instead referred to references 74, 76, and 77 for
further information. Other emissions such as carbon monoxide
(CO), carbon dioxide (COo), the oxides of nitrogen (NOx),
and the oxides of sulfur (SOx) will also be impacted to some
degree with the use of methanol instead of gasoline or diesel
fuel. In most cases the impacts are favorable toward
methanol. The discussion of these emissions, however, is also
left for other studies. The emissions which will be briefly
discussed here, are those which are considered to be air toxics
(particulate, benzene, formaldehyde, and 1,3 butadiene). Since
a large portion of the exposures of the general public to motor
fuels is from inhalation of the products of combustion in the
exhaust of the vehicles, these emissions are of great
importance in assessing the toxicity of the different fuels
(evaporative emissions were addressed earlier).
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Particulate
Particulate emissions lead to poor visibility, soiling of
anything it precipitates on, and more importantly can cause
premature mortality, aggravation of bronchitis, and reversible
declines in lung function. For these reasons EPA has set a
national ambient air quality standard for particulates smaller
than 10 microns in diameter.78 Particulate emissions from
mobile sources represent approximately 15 percent of the
national emission inventory, and are likely the most
troublesome emissions from diesel vehicles. Particulate
emissions from diesel vehicles are typically 20 to 100 times
greater than from gasoline, M100, or M85 vehicles, and are a
particular concern from buses and trucks that operate primarily
in urban areas where public exposure is very high. Particulate
in the exhaust of diesel vehicles results from the incomplete
combustion of the heavy hydrocarbons in the fuel, and is
composed of elemental carbon and a wide variety of condensed
and/or adsorbed fuel and lubricant components and other varied
combustion products.69 Over 90 percent of diesel particulate
is less than 1 micron in diameter and is thus small enough to
be inhaled and deposited deep within the lungs.69 The
organics adsorbed onto diesel particulate have been found to be
mutagenic in a variety of bioassays. In addition, testing with
rats has shown that when diesel exhaust is inhaled chronically
at high concentrations it results in lung cancer in rats.
Based on these studies, diesel particulate was estimated to
have resulted in 176 to 860 incidences of cancer in 1986, but
as shown in Table 5 this is expected to decrease substantially
already by 1995 as a result of EPA's more stringent particulate
standards.69 To add additional perspective to the problem of
diesel particulate, it is worth pointing out that diesel fuel
represents only approximately 20 percent of the total motor
fuel consumption in the United States.
A gasoline vehicle emits far less particulate than a
diesel vehicle, and what is emitted is far less noticeable
since it is difficult to see with the naked eye. Nevertheless,
particulate emissions from gasoline (also known as the products
of incomplete combustion) are considered to be mutagenic and
possibly carcinogenic, and were estimated to cause from 1 to
176 cancer incidences in 1986 depending on the method used (See
Table 5).69. The main concern with gasoline particulate
emissions appears to result from high molecular weight organics
such as polycyclic aromatic hydrocarbons (PAHs) including
benzo(a)pyrene.
Due to MIOO's simple chemical structure, and lack of
impurities and additives, carbonaceous particles, PAHs, and
other products of incomplete combustion (PICs) are not as
likely to form with the combustion of M100 as with gasoline and
diesel fuel. In fact, it is mainly the potential for
significant particulate emission reductions which is causing
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Table 5
Summary of Risk Estimates.5' ^
Motor Vehicle Pollutant
U.S Cancer Incidences/Year*3
1986 1995c
Diesel Particulate
178 -
860
106
- 662
Formaldehyde
46 -
86
24
- 43
Benzene
100 -
155
60
- 107
Gasoline Vapors
17 -
68
24
- 95
Other Gas Phase Organics
1,3-Butadiene
236 -
269
139
- 172
Acetaldehyde
2
1
Gasoline Particulate
1 -
176
1
- 156
Dioxins
NDd
ND
Asbestos
5 -
33
ND
Vehicle Interior Emissions
Cadmium
Ethylene Dibromide
ND
<1
1
ND
<1
<1
Total
586 - 1650
355 - 1236
a The risk estimates are 95% upper confidence limits.
b The risk estimates for asbestos, cadmium and ethylene
dibromide are for urban exposure only. Risks for the
other pollutants include both urban and rural exposure.
c The total risk in 1995 is slightly underestimated. Due to
inadequate information and the sensitivity of future risk
to control decisions which have not yet been made,
projected risk estimates were not made for some of the
pollutants.
d ND = Not Determined.
NOTE: The risk estimates are upper bound estimates;
therefore, they are not intended to represent actual
numbers of cancer cases but rather can be used to
rank the mobile source pollutants and to guide
further study.
Taken in its entirety from reference 69.
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the heavy-duty industry (particularly the urban transit bus
industry) to consider methanol as an alternative fuel. Some
particulate emissions may occur with methanol due to factors
such as- the incomplete combustion of lubricating oils, but the
magnitude of these emissions (as well as those resulting from
any potential additives) in production vehicles and their
carcinogenic risk is yet to be determined. Due to the
concentration of gasoline in M85 and the particulate emissions
associated with it, a fraction (as of yet not completely
established) of the cancer incidences associated with gasoline
can also be associated with M85.
Benzene
As discussed briefly earlier in the paper, benzene
emissions represent a serious health hazard due to their
carcinogenic potential. Based on several epidemiology studies
which demonstrated its potential to cause leukemia in humans,
EPA has classified benzene as a group A human carcinogen.
Annual incidence estimates associated with all motor vehicle
related benzene emissions range from 100 to 155 for 1986 (95th
percentile confidence limit) but are projected to decrease to
60 to 107 by 1995 as hydrocarbon emissions are controlled (See
Table 5).69
Eighty-five percent of all benzene emissions (and hence
also incidence estimates) are estimated to be motor vehicle
related, and 97 percent of these are estimated to be gasoline
related (only 3 percent diesel fuel related).69 Of the 85
percent, roughly 70 percent comes from the exhaust, while 14
percent are evaporative emissions, and 1 percent refueling
emissions. Benzene occurs in the exhaust of gasoline vehicles
mainly as a result of the incomplete combustion of benzene and
other aromatics in the liquid fuel. Hence, any fuel which
contains either benzene or aromatics is expected to result in
significant benzene exhaust emissions.
M100 contains no benzene or other aromatics, and therefore
is not expected to cause any benzene related cancer incidences.
M85 contains 15 percent of a highly volatile, high
aromatic gasoline. Thus, M85 contains approximately 6 volume
percent aromatics of which approximately 0.3 volume percent is
benzene. In addition, due to the lower heat of combustion of
M85, roughly 65 percent more fuel will have to be used to get
the same mileage. Based on this and the fuel concentrations,
as much as 35 percent of the benzene emissions and related
cancer incidences that occur as a result of the exhaust of
gasoline vehicles may also occur if M85 vehicles replace
gasoline vehicles. Actual benzene emissions and related cancer
incidences, however, will be a strong function of the design of
the production M85 vehicles.
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Formaldehyde
Formaldehyde, a colorless pungent gas, is a common
emission from many different combustion processes. Even small
concentrations of formaldehyde may irritate exposed membranes
of the eyes, nose, and respiratory tract, and may cause various
other acute effects including headaches, nausea, and possible
death. Formaldehyde is not expected to result in systemic
toxic effects under any expected exposure scenarios. Due to
its potency as an irritant, formaldehyde has a very low TLV of
1 ppm, and a STEL set at 2 ppm. However, a level of concern of
0.5 ppm has been chosen by EPA for future work.72 Since
formaldehyde's odor threshold for most individuals ranges from
0.08 to 0.4 ppm, concentrations of a toxic concern should be
detectable. Based on various animal and human epidemiology
studies formaldehyde is classified by EPA as a group 51
probable human carcinogen.
Roughly 50 to 90 percent of ambient formaldehyde is
estimated to result from photooxidation in the atmosphere of
other hydrocarbons from motor vehicles (including exhaust,
evaporative, and refueling emissions). Approximately 35
percent of this is estimated to occur as a result of the
combustion of fuels in motor vehicles, since motor vehicles are
responsible for about 35 percent of total hydrocarbon
emissions.69 Only 10 to 50 percent of ambient formaldehyde
is estimated to be directly emitted formaldehyde.79 However,
since 91 percent of the human exposure to formaldehyde is
estimated to be due to indoor formaldehyde (formaldehyde is
used in many industrial applications and is emitted from many
common construction materials and home furnishings), current
mobile sources are estimated to contribute only about 3 to 4
percent to an individual's total exposure to formaldehyde, and
direct motor vehicle emissions of formaldehyde less than 2
percent.79 Despite the small fraction of formaldehyde
exposure which is attributable to mobile sources, the annual
incidences of cancer associated with that exposure is estimated
to be rather large. As shown in Table 5, all mobile source
(both gasoline and diesel) related formaldehyde was estimated
to result in 46 to 86 incidences in 1986 (decreasing to 24 to
43 by 1995).69
Formaldehyde emissions from gasoline vehicles are roughly
1 to 4 percent of the total hydrocarbon emissions depending on
vehicle class.69 For well maintained, late model, light-duty
gasoline vehicles this corresponds to approximately 4.4
mg/km.79 Despite this relatively low emission rate,
modelling of public and private garage scenarios indicates that
concentrations approaching and exceeding levels capable of
causing acute toxic symptoms are possible. However, exposures
in these situations are typically of short duration and thus
not usually a serious concern. As discussed above, much of the
ambient formaldehyde (and thus carcinogenic hazard) associated
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with gasoline vehicle emissions occurs as a result of the
photooxidation of the other highly reactive hydrocarbons
emitted in.the exhaust (as well as evaporative, and refueling
emissions).
Despite the fact that overall hydrocarbon emissions are
lower with diesel vehicles than with gasoline vehicles, the
direct formaldehyde emissions in the exhaust are estimated to
be roughly 2 to 3 times those from gasoline vehicles because
they do not utilize catalysts.79 However, due to the
decrease in total hydrocarbon emissions, the total ambient
formaldehyde contribution (including photochemically generated
formaldehyde) of a diesel vehicle may not be significantly
greater than that for a gasoline vehicle.
Very little information exists on formaldehyde emissions
from production M100 vehicles. One data source that does exist
is on heavy-duty bus engines. This information suggests that
engine-out formaldehyde emissions from current technology M100
vehicles may be as much as 10 times that from comparable diesel
vehicles (i.e., as much as 20 to 30 times that from comparable
gasoline vehicles), but with the use of a proper catalyst
(possible with methanol due to the small amount of particulate
matter in the exhaust), the formaldehyde emissions can be as
low or lower than from comparable diesel vehicles.79 On the
other hand, if formaldehyde emissions from M100 vehicles are
assumed to be similar to those from M85 vehicles (for which
most LDV information exists), then formaldehyde emissions from
light-duty M100 vehicles is roughly 3 to 7 times that of
comparable gasoline vehicles.79
Despite the increase in engine out formaldehyde emissions
from methanol vehicles over that from gasoline vehicles,
modelling suggests that the low reactivity of methanol in the
atmosphere causes ambient concentrations of formaldehyde to be
similar with M100 and M85 vehicles to those with gasoline
vehicles.74 Thus, there is not expected to be a significant
change in mobile source formaldehyde related cancer incidences
with the substitution of methanol for gasoline as the primary
motor fuel.
1,3-Butadiene
1,3-Butadiene is a photochemically reactive compound which
is estimated to comprise 0.35 percent of gasoline vehicle
exhaust.69 Based on animal data, 1,3-butadiene is classified
by EPA as a group B2, probable human carcinogen. As shown in
Table 5, mobile source 1,3-butadiene emissions were estimated
to result in 236 to 269 cancer incidences in 1986, but this
number is projected to decrease to 139 to 172 by 1995.
Due to the difficulty in measuring 1,3-butadiene
separately from n-butane, until recently data on actual
emissions from current gasoline vehicles was extremely scarce,
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and it remains scarce with diesel vehicles. In addition,
nothing has yet been published as to the concentration of
1,3-butadiene in the exhaust of M100 and M85 vehicles.
However, due to the general lack of hydrocarbon emissions in
the exhaust of methanol vehicles, 1,3-butadiene is not expected
to represent as large of a fraction of methanol vehicle exhaust
as gasoline vehicle exhaust.
Leaks and Spills into Water
Leaks and spills of hazardous materials into water are a
common occurrence and represent a potentially significant
environmental hazard. Often spills on land drain into lakes,
rivers, and streams, where the effect is the same as if the
spill had occurred directly into the water. In addition, since
much of the transportation of petroleum fuels is done over
oceans and rivers, the chance for massive spills from tankers
and barges also exists.
The effects of petroleum spills and petroleum-derived
fuels on aquatic environments are fairly well known - oil films
stretching for miles, ruined beaches, surface fires, dead fish
and water fowl, and many more.®® While petroleum fuels are
for the most part not soluble in water and, as a result, spread
out over long distances on the surface in a thin layer, some
components are soluble in water and are extremely toxic to
aquatic life.81 In 1957, a tanker spill of diesel fuel in a
small bay in Mexico resulted in near total destruction of the
bay, and other spills have resulted in destruction of
commercial fishing grounds.®1 In addition, many of the toxic
effects of petroleum fuels on aquatic life not killed by
exposure are not reversible and remain for years. An estimate
of the retention time of soluble petroleum components in
coastal marshlands of France following a tanker spill is
considered conservative at 7 to 12 years.81 These long-term
effects follow extensive cleanup operations involving
containment of the spill using physical barriers, suction-pump
recollection, chemical surfactant dispersal, detergent
application, or absorption to straw, floating pellets, or other
material, and later removal or degradation of larger residue.
Since the majority of gasoline components evaporate readily,
the need for extensive spill cleanup may not be as necessary as
with other petroleum fuels; however the heavier components
evaporate much more slowly.
In general, methanol is significantly less toxic to marine
life than petroleum fuels, and many of the effects of
short-term exposure are temporary and reversible.82 Most
aquatic life can survive concentrations of less than one volume
percent of methanol for brief periods of time (some as high as
10 percent), although few can survive long term exposure to 500
ppm.82.83 since methanol is infinitely soluble in water, a
spill in open water disperses rapidly, especially in situations
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with strong currents, tidal action, and wave action. As a
result, concentrations outside the immediate spill area tend to
remain below toxic concentrations, and even in the spill area,
the toxic concentrations are short-lived (although severe).
Simulation of a large-scale (10,000 ton), open-sea, methanol
spill revealed that the concentration near the spill site would
be reduced to less than 0.36 percent within an hour of the
spill.84 A similar simulation of a 10,000 kl/hr spill on a
coast (at a pier) revealed that even in the severe case where
the wind was blowing toward the coast, the concentration was
less than 1 percent at the spill site within 2 hours after the
spill was stopped and 0.13 percent after 3 hours.84 If these
results are extrapolated to rivers, the methanol concentration
can be expected to be reduced even faster due to the greater
effects of currents and eddys.
In addition to its rapid dispersion, complete elimination
from the environment occurs as a result of methanol's rapid
biodegradation (decomposition of methanol as a result of
natural processes). There is a wide variety of naturally
occurring marine and terrestrial microbes which metabolize
methanol.85 As a result, recolonization of methanol spill
sites is very rapid (a matter of months) with no long-term
effects, while the effects of petroleum spills may require
years to disappear.82 Part of the explanation for the
comparative resilience of aquatic habitats to methanol may be
due to the fact that methanol occurs naturally in both drinking
and surface water and, as such, is not a foreign substance to
these environments.
Cleanup of methanol spills on water should not require the
extensive efforts and costs associated with petroleum fuel
cleanup and is generally much more effective. Small spills
usually do not require cleanup, but rather require only
monitoring and isolation of the area for several days, allowing
natural biodegradation to complete the task.82 Larger spills
require the removal of dead organisms, and cleanup may be
accelerated by aerating the water to promote aerobic (as
opposed to anaerobic) degradation and/or inoculating the water
with nonpathogenic bacteria, such as the naturally occurring
Pseudomonas fluorescens, which metabolize methanol.8*'82
M85 has not been studied in any detail, but it is not
likely to be an advantage over M100. When spilled in the
water, the methanol portion will dissolve into the water and
quickly disperse as with M100 while the majority of the
gasoline components will rise to the surface where they can
evaporate (and/or be cleaned up). Those gasoline components
that are water soluble will act exactly as with gasoline with
the exception that there is much less of them (although a
greater fraction of the gasoline in M85 will likely dissolve in
the water due to the cosolubility with methanol 18).
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Leaks and Spills on Land
Leaks and spills on land arise from a wide variety of
sources. Many of these are minor, involving the spillage of
only a few gallons or less of fuel such as from small fuel
containers or vehicle fuel tanks. Other instances which are of
more concern involve spills from overturned tanker trucks,
leaks from pipelines, or leaks at refineries, fuel terminals,
or well sites. Among the more frequent spills on land are
those from underground storage tanks. These alone accounted
for 12,444 reported incidences of release between 1984 and
1986, and most releases are never reported.85'87
Gasoline and diesel fuel are very toxic to terrestrial
plant and animal life. Since they are composed of many
different compounds including many additives, their toxicity,
fate, and transport in soil is extremely variable. Once
spilled, they are retained in the soil by capillary forces, by
adsorption onto soil particles, by evaporation in soil air, and
by dissolution in soil water.88 Their main route of
dissipation is through evaporation. Since diesel fuel
evaporates much more slowly relative to gasoline, much more of
the spilled fuel will be absorbed into the soil tending to make
its effects of longer duration. A wide variety of organisms
exist in the soil which can degrade hydrocarbons. Degradation
rates vary depending on the soil acidity, nutrient content,
temperature, moisture content, and oxygen content.88 Oxygen
content is the dominant variable, since, although some studies
indicate that anaerobic degradation occurs, it is at a
significantly slower rate than aerobic degradation.88
Aerobic conditions can quickly become anaerobic once
degradation begins and the available oxygen is used up,
especially if the soil is near saturation with water. In
addition, the products of anaerobic degradation may themselves
be toxic.88 Thus, absolute recovery of soil ecosystems
contaminated with gasoline or other petroleum fuels is a very
slow process which can last for years as a result of slow
degradation and disruption of successional organisms.89
Because of the slowness of the natural processes, damage
from leaks and spills of petroleum fuels is in large part a
function of the rate and extent to which cleanup efforts are
undertaken.40 However, the cleanup of a petroleum spill site
is difficult, and itself can last for years. The most common
technique for land cleanup is excavation of the contaminated
soil with subsequent disposal at a land fill site.88
Although still controversial, the use of biorestoration may be
a preferable alternative since it eliminates the contamination,
not merely transferring it to a new medium. It also does not
require massive soil removal, but may instead require extremely
long periods to complete cleanup. Due to the expense of such
spill cleanup processes, many spills in the past have not been
cleaned up and have merely been left to the natural processes
of dissipation.
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M100, like the petroleum fuels, is very toxic to plant and
animal life. Grasses, mosses, and other plants are quickly
killed by. surface saturation with methanol; and few of the
organisms in the spill area can withstand even brief exposure
to high concentrations of methanol.81'83 However, the toxic
effects of an M100 spill are much shorter lived than for
petroleum fuels for a variety of reasons. First, M100
evaporates completely much more quickly than diesel fuel and
even quicker than gasoline (gasoline's heavier components
evaporate slowly). This causes less fuel to be absorbed into
the soil, and thus, less fuel must undergo decomposition.
Second, M100 is completely water soluble, and as a result,
disperses to non-toxic concentrations much faster than
petroleum fuels. Third, M100 is easily decomposed both
aerobically and anaerobically by naturally occurring
micro-organisms living in the soil which move into the area
following a spill.90'91 As a result, analysis of the lateral
and vertical movement of methanol spills shows penetration to
be limited to the immediate spill area.81 Fourth, M100
occurs naturally in the environment in low concentrations,
causing many organisms to be more tolerant o£ it than of
petroleum fuels. As a result, growth can return to a spill
site before the methanol is entirely dissipated.
Experimental information shows that much of the subsoil
life has returned to a spill site just one week following
surface saturation with M100.81 As much as 90 percent
recovery of subsoil life is possible within 3 weeks with M100,
as opposed to 50 percent recovery in 3 to 12 months with
gasoline spills.In a field study, methanol applied to the
surface of a scattered black-spruce heath community disappeared
within one week as a result of evaporation, percolation, and
biodegradation.91 In an effort to assess just the
biodegradation rate of methanol, soil samples taken at various
depths at three different locations in the United States were
contaminated with methanol. Results indicated that methanol
concentrations of 1000 mg/1 added to soil placed in sealed
tubes (no dispersion, or influx of oxygen or additional
microbes) would degrade to non-measurable levels in less than a
year, and complete degradation of 100 mg/1 in 30 to 60
days.92 As with gasoline, aerobic degradation of methanol is
more rapid than anaerobic, but both are apparently much faster
than with gasoline.
Since the effects of a methanol spill are generally of
short duration, nothing is typically done to clean up a spill
site. If, however, the spill is massive, and a cleanup period
faster than that of the natural process is required, the
techniques used for cleanup of petroleum spills on land should
also be effective (as long as groundwater is not affected),
including injections of the various methanol decomposing
bacteria.89
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Unfortunately, since M85 is a new fuel there have been no
studies conducted to determine its actual impacts on land.
However, M85 would appear to be more hazardous than M100 and
possibly even gasoline. This is evidenced by the results of a
field study in which the return of vegetation was slower
following a low level methanol blend spill than with either
gasoline or M100.19 Not only may the methanol carry the
gasoline further distances, causing more to enter the soil
rather than evaporating, but also some of the methanol
decomposing bacteria may be totally intolerant of
gasoline.8*'90 The result is a larger area which may be
affected by both the gasoline and the methanol and a longer
time over which both components remain toxic.
Groundwater and Drinking Water Contamination
One of the major threats of spills to both land and water
is that the fuel will contaminate groundwater and other
drinking water supplies. Roughly half of the United States'
drinking water is supplied by groundwater, including all or
part of the drinking water for 34 of the 100 largest
cities.87,93 Although spills have been one of the more
visible environmental threats, leaks from underground storage
tanks is probably of greater importance to groundwater. There
are an estimated 796,000 underground storage tanks in the U.S.
today.86 New York state and Maine have estimated that at one
point as many as 19 and 25 percent respectively of their
underground gasoline tanks were leaking.*3 of the 12,444
reported incidences of release of material from underground
storage tanks between 1984 and 1986, an estimated 45 percent
involved leaks to the groundwater.86 Thus, more than 70,000
underground storage tanks may be leaking to groundwater, and an
estimated 29 percent of the drinking water supplied to large
cities is contaminated with volatile organic compounds.93
Due to the strong odor and taste of petroleum fuels, even
concentrations as low as 1 ppm can render drinking water
supplies unpalatable.93 Thus, even small leaks or spills can
ruin large water supplies. In addition, thirteen compounds
commonly found in gasoline are regulated as hazardous chemicals
under the Comprehensive Emergency Response, Compensation and
Liability Act (CERCLA) due to their toxic nature.88 Most
gasoline and diesel fuel components are not soluble in water
(only 25 to 250 mg/1 for gasoline) and, as a result, float on
top of the water in the underground aquifer. However, benzene,
toluene, and xylene, (BTX), three of the hazardous chemicals
regulated under CERCLA, represent the majority of the soluble
fraction of gasoline in water.18 Although expected to occur,
biodegradation of gasoline and diesel fuel in the relatively
anaerobic conditions of an underground aquifer is very
slow.88 Therefore, contaminated areas will remain so for
long periods of time.
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Cleanup of petroleum spills to groundwater takes two
forms, both of which are necessary if groundwater is to be used
-as••a drinking source. The first, stage of cleanup consists of
removing undissolved gasoline from the upper level of the
aquifer (free product plume) through the use of trenching with
skimmers or filter separators, or the use of a pumping well
system with oil/water separators.88 The second stage
consists of removing hydrocarbons dissolved in the water
through the use of air stripping towers or carbon adsorption,
or both, although biorestoration is also receiving increased
attention for this purpose.88 Given proper design and
implementation, all of these techniques can ideally remove
greater than 99 percent of the spilled fuel, however, it may be
years before the effectiveness approaches this level. Carbon
adsorption also lends itself for use in removing small
concentrations of dissolved hydrocarbons in the water at the
point of entry into homes.88 The level of cleanup necessary
is that which will achieve compliance with the current and
proposed drinking water standards for benzene, toluene, and
xylene are 5 ug/1 (5.65 ppb), 2.0 mg/1 (2.3 ppm), and 0.44 mg/1
(0.51 ppm), respectively.
Biorestoration of groundwater involves the addition to the
contaminated aquifer of indigenous microorganisms that have
been selectively adapted or genetically altered to degrade
gasoline components dissolved in groundwater (at present still
a very controversial technique). Biorestoration tends to be
oxygen limited and, as a result, various pumping, injection,
and circulation pumping systems that mix the contaminated water
with oxygen, nitrogen, phosphorus, and growth substrates are
needed in addition to the microorganisms.8®
Due to its relatively short-term effects on aquatic and
terrestrial life, the main concern of methanol spills relates
to the possibility that concentrations toxic to humans may
occur in groundwater and other water supplies used for drinking
water. Unlike the petroleum fuels, since methanol is not
considered to be carcinogenic and is not presently known to
result in long-term effects due to chronic exposure to low
level concentrations, high concentrations in groundwater
capable of causing acute toxic effects are the major concern,
although EPA is evaluating possible adverse effects of low
concentrations. Since methanol dissolves completely in water,
high concentrations may be possible; and, since M100 has no
odor, taste, or color, potentially toxic concentrations will be
undetectable (although drinking water supplies are not rendered
unpalatable). If it is assumed that toxic effects begin with
exposure to 210 mg/kg of methanol, that the maximum average
water intake of an adult is two liters per day, and that this
is all ingested in 8 hours, then the methanol concentration in
the drinking water would have to be roughly 9200 ppm in order
for toxic symptoms to occur. To receive the minimum lethal
dose of 300 mg/kg, the corresponding water concentration would
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have to be roughly 13,000 ppm. Methanol concentrations of this
magnitude, in drinking water derived from either surface water
or groundwater are not expected under any credible scenario,
however.90 As discussed above with open water spills,
methanol's complete solubility in water combined with naturally
occurring currents, dispersion, and biodegradation cause
concentrations to fall below 1300 ppm within 3 hours in even
the most severe situations. In cases where drinking water
supplies are derived from groundwater, due to the rapid
evaporation and biodegradation of methanol, spills on land tend
to remain localized and, due to its susceptibility to aerobic
and anaerobic biodegradation, groundwater contamination
problems should be minimal.81'92
With the exception of biorestoration, the cleanup
techniques used for groundwater contamination with gasoline are
not expected to be effective for cleaning up methanol
contamination.18'94 Because methanol is completely soluble
in water, there is not expected to be a large free product
plume that can be removed with the use of trenches or pumping
techniques. In addition, methanol's water solubility,
polarity, and low molecular weight render air stripping and
carbon adsorption techniques ineffective.8® Fortunately, due
to its speed of biodegradation, methanol contamination may
often be removed naturally faster than gasoline contamination
using active cleanup techniques. In addition, biorestoration
techniques similar to those being developed with gasoline may
cause methanol cleanup to be even quicker.
While these findings are encouraging, it is clear that
further study is necessary to determine if in fact under
certain extreme conditions concentrations toxic to humans may
be possible in groundwater. If this possibility cannot be
precluded, it may be necessary to add components to the fuel
such as a dye to provide an identifiable characteristic to
drinking water if it contains a toxic concentration of methanol.
Due to the uncertainty in our understanding of groundwater
processes and the lack of information with M85, it is difficult
to assess the relative hazard of M85 to that of the other
fuels. Once in the groundwater, M85 should separate into free
gasoline, which floats on top of the groundwater, and methanol
(along with small concentrations of certain gasoline
components) dissolved in the groundwater itself.94 For a
number of reasons, the actual gasoline contamination may be
greater than might first be expected. In limited testing the
addition of just 20 percent methanol to gasoline caused the
amount of naphthalene (a component of gasoline) retained in the
soil (and thus able to move to groundwater) to decrease by more
than half.18 In addition, since methanol is water soluble
and gasoline is cosoluble with methanol in water at low
concentrations of water, the gasoline in M85 may be carried
further distances, causing groundwater to be affected more
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frequently.86,90 Limited testing has also demonstrated that
the solubility of xylene and naphthalene in water is increased
by 266 percent and 335 percent, respectively, with the addition
of just 20 percent methanol to gasoline.1® Thus, the effect
of M85 on groundwater may be more severe than with either M100
or gasoline.
Cleanup techniques for removing M85 contamination from
groundwater will likely involve the techniques used for
gasoline. Due to the presence of the gasoline, the potential
problem related to the inability to detect even toxic
concentrations of methanol in groundwater should no longer be
of concern. Although not yet confirmed, the taste and odor of
the gasoline should serve as an adequate warning and is likely
to persist in the groundwater at least as long as the methanol.
SUMMARY AND CONCLUSIONS
Transportation fuels affect many aspects of our lives. As
a result, safety concerns with those fuels are important when
considering changes to the Nation's transportation system.
Thus, the recent emphasis on methanol as an alternative to
gasoline and diesel fuel raises questions as to the effect
methanol would have on public and environmental safety.
The largest public safety and environmental health
concerns with transportation fuels today result from the
flammability of gasoline and long-term inhalation exposure to
air toxic emissions from gasoline and diesel vehicles.
Methanol fuels (particularly M100) can go a long way in
reducing the risks associated with today's fuels. Only a
fraction of the fires that occur with gasoline today are likely
to occur with M100, and the frequency and severity of serious
personal injury and property damage with the fires which do
occur will tend to be lower. In addition, available
information suggests that a large share of the cancer
incidences estimated to occur as a result of emissions from
today's motor fuels would also not occur with methanol fuels
(especially M100).
Despite these safety advantages, there are also safety
concerns and uncertainties unique to methanol which will need
to be addressed if methanol is used as a fuel. One such
concern is the lack of a luminous flame when M100 burns in
certain situations. Based on available information, the
fraction of M100 fuel fires which will be invisible is not
expected to be large, but further study is necessary to
properly quantify this. In addition, the added hazard which an
invisible flame represents and the effectiveness of additives
to enhance the luminosity of M100 fires also need to be studied
further in order to properly quantify the hazards of methanol
fires. Recent research has produced promising results with
luminosity additives, which if successful could completely
eliminate any concern over flame invisibility.
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A second unique concern with M100 is that due to its low
volatility, and high £lammability limits it is flammable inside
fuel tanks. Although a valid concern, it is nevertheless a
concern with solutions. Available information suggests that,
since ignition sources are limited in fuel tanks, ignition is
not expected to be a frequent occurrence, and that a number of
fuel tank design precautions, such as the use of flame
arresters and modified in-tank electrical devices, can be taken
to limit even further the chance for ignition. Additional
information suggests that, were ignition to occur, the severity
of the explosion is much milder than might be expected, and
once again proper fuel tank designs may be able to minimize
much of the risk. For these reasons, any potential increase in
risk with M100 resulting from fuel tank flammability can be
minimized through the utilization of proper vehicle design
considerations on the part of motor vehicle manufacturers.
The third area where concern may arise with the
substitution of M100 for petroleum fuels is accidental
ingestion of the fuel. M100 is tasteless, odorless, and
colorless, and toxic if small amounts are ingested. These
properties have led to projections of large increases in
injuries and fatalities resulting from accidental ingestion if
M100 replaces gasoline unless certain precautions are taken.
Precautions likely to be part of any methanol fuel program
include: requiring the use of flame arresters on vehicles to
prevent many siphoning related exposures; preventing the use of
pure methanol in lawn and garden applications to eliminate many
siphoning and pediatric exposures; adding compounds to methanol
to provide a taste, color, or odor; and instituting a public
education program. In addition, properties of methanol itself
such as its low solubility with oils and greases will limit its
misuse for these purposes and reduce accidental exposures.
Thus, the societal risk of ingestion of motor fuels should not
be significantly greater with M100 than with gasoline.
In addition to human health and safety concerns, there are
a number of environmental safety concerns which exist today
with petroleum fuels. Spills of fuel onto land and into the
water result in serious disruption of plant and animal life in
the spill areas, sometimes for many years. Spills which impact
groundwater can prevent its use as a drinking water supply for
many years due to palatability, long-term toxicity concerns,
and slow natural biodegradation. Although cleanup is possible,
cleanup to EPA's current and proposed drinking water standards
may also take years and incur great costs.
In comparison, although also toxic to plant and animal
life, the effects of M100 spills onto land and into water are
comparatively short lived, especially with spills into water.
Relative to spills which effect drinking water, it would appear
that there is a tradeoff between the long-term toxic effects
and palatability concerns with gasoline and the potential for
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severe short-term toxic effects if high concentrations of
methanol occur in groundwater which is used as a drinking water
supply.. Due to the lack of hydrogeologic information relative
to methanol, it is not yet known' whether its concentration in
groundwater would be likely to reach toxic concentrations, but
the speed at which it biodegrades may result in faster natural
cleanup of M100 contamination than invasive cleanup of gasoline
contamination. In addition, it may be possible to add
compounds such as dyes to methanol to provide a recognizable
characteristic to groundwater should a potentially toxic
concentration exist.
Based on the available information, in all the areas
discussed above M85 would appear to represent a compromise
between gasoline and M100. M85 is not nearly as effective as
M100 at decreasing the frequency of fire which exists today
with gasoline, and its concern relative to air toxics, while
less than for gasoline and diesel fuel, is greater than with
M100. However, M85 burns with a luminous flame, and is not
expected to be flammable in fuel tanks in typical situations.
Relative to ingestion, accidental ingestion patterns will
likely be similar to those of M100, with the added benefit that
the gasoline fraction serves as an effective odorant and taste
deterrent. Less toxic additives, however, can be found to
serve the same purposes in M100. In groundwater most concerns
with M85 are likely to result from the long-term effects of its
gasoline fraction. The lack of available information, however,
limits the certainty of these conclusions.
The most important conclusion to be drawn is that the
magnitude of the potential safety benefits with M100 coupled
with the ability to minimize many of the concerns should result
in improved overall public and environmental safety with the
use of M100 instead of petroleum. The difference between M100
and M85 is less clear, but M100 is likely more advantageous in
terms of overall risk. Although a significant amount of work
remains to be done in many areas before firm conclusions can be
drawn, the unresolved issues do not appear to be serious enough
to prohibit the use of methanol as an alternative fuel to
petroleum.
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Occupational Health Services Inc., September, 1985.
52. "Clinical Toxicology of Commercial Products", Robert
E. Gosselin, M.D., Ph.D., Harold C. Hodge, Ph.D., D.Sc., Roger
P. Smith, Ph.D., Marion N. Gleason, M.Sc., Fourth Edition, 1976.
53. "An Evaluation of the Human Health Effects of
Automotive Methanol Vapors," Dr. Kathleen Nauss, Health Effects
Institute, Presentation at the Methanol Health and Safety
Workshop, South Coast Air Quality Management District, November
2, 1988.
54. "Metabolism, Ocular Toxicity and Possible Chronic
Effects of Methanol," Dr. Kenneth McMartin, Presentation at the
Methanol Health and Safety Workshop, South Coast Air Quality
Management District, November 2, 1988.
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55. "Automotive Methanol Vapors and Human Health: An
Evaluation, of Existing Scientific Information and Issues for
"Future Research," Health Effects Institute, May 1987.
56. "A Critical Review of the Toxicity of Methanol
Fuel," Dr. John Clary, Presentation at the Methanol Health and
Safety Workshop, South Coast Air Quality Management District,
November 2, 1988.
57. "Methanol Health Effects," Midwest Research
Institute for EPA, EPA-460/3-81-032, December, 1981.
58. "Alcohols Toxicology", William W. Wimer, John A.
Russell, Harold L. Kaplan, Southwest Research Institute, 1983.
59. "A Review of the Toxicity of Methanol", Dr. John J.
Clary, Presented at the First International Conference on
Methanol, May, 1983.
60. "Biological Monitoring of Persons Exposed to
Methanol Vapors," V. Sedivec, et.al., Int. Arch. Occup.
Environ. Health, 48: 257-271, 1981.
61. "Blood Methanol Concentrations in Normal Adult
Subjects Administered Abuse Doses of Aspartame," L.D. Stegink,
et.al., J. Toxicol, Environ. Health, 7: 281-290, 1981.
62. "Risk Assessment for Health Effects of Methanol
Vapor," J. Michael Davis, Ph.D., EPA, Presentation at the
Methanol Health and Safety Workshop, South Coast Air Quality
Management District, November 1-2, 1988.
63. "The Percutaneous Absorption of Methanol after
Dermal Exposure to Mixtures of Methanol and Petrol", D.G.
Ferry, W.A. Temple, and E.G. McQueen, Proceedings, Fifth
International Alcohol Fuel Technology Symposium, Volume 3, 1982.
64. "Acute Exposure to Methanol in Fuels: A Prediction
of Ingestion Incidence and Toxicity," Dr. Toby Litovitz,
National Capitol Poison Center, October 31, 1988.
65. Conversation with Ake Brandberg, Dr. Eng., Svensk
Drivmedelsteknik AB, June 25, 1987.
66. Briefing to Charles L. Gray Jr., Director Emission
Control Technology Division, EPA/OAR/OMS, by Angela Linder,
Chemical Engineer, EPA/OAR/OMS/ECTD/SDSB, May, 1989.
67. "Methanol Fuel Modification for Highway Vehicle
Use," Union Oil Company of California for U.S. Department of
Energy, Final Report, HCP/W3683-18, July, 1978.
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68. "Gasoline Vapor Exposures at a High Volume Service
Station," Christine A. Kearney and David B. Dunham, Mobil Oil
Corporation-, Am. Ind. Hyg. Assoc. J. 47(8): 535-539, 1986.
69. "Air Toxics Emissions and Health Risks from Motor
Vehicles," Jonathan M. Adler and Penny M. Carey, U.S. EPA, AWMA
Paper No. 89-34A.6, July, 1989.
70. "Projected Air Concentrations of Methanol,"
Presentation by Penny M. Carey, U.S. EPA at the Health Effects
Institute Workshop on Fetal Toxicity of Methanol and Carbon
Monoxide, October 3, 1988.
71. "LA County Mall Garage Emissions Study," Ken Smith,
Californian Energy Commission, Presentation to the Advisory
Board on Air Quality and Fuels, December 1, 1988.
72. "Regulatory Support Document: Proposed Organic
Emission Standards and Test Procedures for 1988 and Later
Methanol Vehicles and Engines," EPA/OMS/ECTD/SDSB, July 1986.
73. "Characterization of Emissions from Vehicles Using
Methanol and Methanol-Gasoline Blended Fuels," Peter A. Gabele,
James 0. Baugh, Frank Black, Richard Snow, JAPCA 35:
1168-1175, 1985.
74. "Quantitative Estimate of the Air Quality Impacts of
Methanol Use," Armistead Russel, et.al., Carnegie Mellon
University, for the California Air Resources Board, April, 1989.
75. Methanol Informational Brochure, Alberta Gas
Chemicals Ltd.
76. "Motor Vehicle Emission Characteristics and Air
Quality Impacts of Methanol and Compressed Natural Gas,"
Jeffrey A. Alson, Jonathan M. Adler, Thomas M. Baines, U.S.
EPA, Office of Mobile Sources, Chapter 8 of a book published by
Greenwood Press and Edited by Daniel Sperling, January, 1989.
77. "Effects of Emission Standards on Methanol
Vehicle-Related Ozone, Formaldehyde, and Methanol Exposure,"
Michael D. Gold, Charles E. Moulis, EPA/OAR/OMS/ECTD/SDSB, APCA
Paper No. 88-41.4, June, 1988.
78. "Revisions to the National Ambient Air Quality
Standards for Particulate Matter," EPA Federal Register Vol 52,
No. 126, pp. 24634-24750, July 1, 1987.
79. "Formaldehyde Emissions From Mobile Sources and
Potential Human Exposures," Charles E. Moulis, U.S. EPA, AWMA
Paper No. 89-34A.1.
80. "Preliminary Perspective on Pure Methanol Fuel for
Transportation," EPA 460/3-83-003, September, 1982.
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81. "Overview of Environmental Impacts from Methanol
Fuel Spills", Dr. Peter D'Eliscu, West Valley College, 1981.
82. "An Environmental Assessment of the Use of Alcohol
Fuels in Highway Vehicles," Argonne National Laboratory,
December, 1980.
83. "Environmental Consequences of Methanol Spills and
Methanol Fuel Emissions on Terrestrial and Freshwater
Organisms," Dr. Peter Neal D'Eliscu, Department of Biology,
University of Santa Clara.
84. "Toxicological Research of Methanol as a Fuel Power
Station: Demonstration Tests for the Environmental Safety of
Methanol," New Energy Development Organization.
85. Methanol as a Transportation Fuel: Assessment of
Environmental and Health Research," Lawrence Livermore
Laboratory, June 18, 1979.
86. "Technical Support Document: Methyl Tert-Butyl
Ether," Draft Final, Michael W Neal, et. al. , Syracuse Research
Corporation for the Office of Toxic Substances, Feb, 1987.
87. "Underground Leakage of Hydrocarbons, An Overview of
a Potential Fire Problem," Martin F. Henry, Fire Journal,
March, 1981.
88. "Cleanup of Releases of Petroleum USTs: Selective
Technologies," EPA/530/UST-88/001, April, 1988.
89. Letter to Charles R. Imbrecht, Chairman, California
Energy Commission, from Dr. Peter D'Eliscu, Department of
Biology, West Valley College, April 28, 1987.
90. Conversation with Dr. Peter D'Eliscu, West Valley
College, July 20, 1987.
91. "Summary Review of Health Effects Associated with
Methanol: Health Issue Assessment," Bryant and Parkinson,
EPA/OAQPS, September, 1987.
92. "Biodegradation of Methanol and Tertiary Butyl
Alcohol in Subsurface Systems," J.T. Novak et.al., Water Sci
Tech, Vol 17, pp 71-85, 1985.
93. "Update on the Underground Leakage Problem,"Martin
F. Henry, Fire Journal, January, 1986.
94. "Storage and Handling of Gasoline-Methanol/Cosolvent
Blends at Distribution Terminals and Service Stations," API
recommended practice, API Publication No. 1627, First Edition,
August, 1986.
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