This month our example is Methyl
Bromide, which has a chemical formula of
CH3Br. Methyl Bromide is listed under the UN
# (United Nations Number) by the US Department of
Transportation: UN 1062 and has a CAS # of 74-83-9.
Persons exposed only to methyl
bromide gas do not pose substantial risks of secondary
contamination; however, some methyl bromide may permeate
clothing. Persons whose clothing or skin is contaminated
with liquid methyl bromide (temperatures less than
38.5°F) can secondarily contaminate others by direct
contact or through off gassing vapor.
A gas at room temperature, methyl
bromide readily penetrates skin, cloth, and other
protective materials such as rubber and leather. It is
nonflammable and toxic at low concentrations.
Methyl bromide is odorless and odor
provides no warning of hazardous concentrations.
However, because methyl bromide is odorless and
nonirritating, a lacrimator (an agent that irritates the
eyes and causes tearing), most commonly chloropicrin at
2%, is often added as a warning agent.
Methyl bromide is absorbed well by
the lungs and to some degree through intact skin. Oral
exposure is rare because methyl bromide is a gas at room
temperature, but it may be absorbed by the
gastrointestinal tract. Exposure by any route can cause
bromide is a colorless gas at room temperature and a
liquid below 38.5°F (3.6°C) or when
compressed. It is usually shipped as a liquefied,
compressed gas. It is odorless and nonirritating at low
concentrations and has a musty or fruity odor at high
concentrations (greater than 1,000 ppm).
bromide is produced by adding sulfuric acid to a mixture
of sodium bromide and methyl alcohol. Methyl bromide is
used primarily as a pesticide to fumigate soil, spaces,
structures, and commodities. It is also used as a
methylating agent, low-boiling solvent, and oil
extractant in chemical syntheses. Less toxic chemicals
have replaced it as a refrigerant and fire-extinguisher
Colorless; gas at room temperature and liquid below
properties: Inadequate; musty or fruity odor
at greater than 1,000 ppm; eye and throat irritation at
greater than 500 ppm.
Molecular weight: 95.0
point (760 mm Hg): 38.5°F (3.6°C)
pressure: 1420 mm Hg at 68°F (20°C)
density: 3.4 (air = 1)
solubility: Water soluble (0.09% at 68°F) (20°C)
Flammable, but only in the presence of a high energy
monobromomethane, isobrome, and methyl fume.
Standards and Guidelines
ceiling limit = 20 ppm (skin)
(immediately dangerous to life or health) = 250 ppm
ERPG-2 (the maximum airborne concentration below which
it is believed that nearly all individuals could be
exposed for up to 1 hour without experiencing or
developing irreversible or other serious health effects
or symptoms which could impair an individual’s ability
to take protective action) = 50 ppm
Incompatibilities: Methyl bromide
reacts with strong oxidizers, magnesium, aluminum, tin,
zinc, and alloys. It attacks aluminum to form aluminum
trimethyl, which is spontaneously flammable.
Routes of Exposure:
Most exposures occur by inhalation and by absorption
through the skin. Odor is not an adequate indicator
of the presence of pure methyl bromide and does not
provide reliable warning of hazardous
concentrations. Because pure methyl bromide lacks
adequate warning properties, significant exposure can
occur before symptoms are evident.
bromide is 3 times heavier than air and can accumulate
in poorly ventilated or low-lying areas. Under adverse
conditions, it can remain in the air for days after
application as a fumigant. Fatalities have occurred
among pesticide appliers and building occupants who were
exposed during the application process or who
prematurely reentered fumigated buildings.
exposed to the same levels of methyl bromide as adults
may receive larger doses because they have greater lung
surface area:body weight ratios and increased minute
volumes:weight ratios. In addition, they may be exposed
to higher levels than adults in the same location
because of their short stature and the higher levels of
methyl bromide found nearer to the ground.
Contact Methyl bromide gas easily penetrates most
protective clothing (e.g., cloth, rubber, and leather)
and skin. Prolonged retention in clothing and rubber
boots may lead to chemical dermatitis and severe burns.
Skin absorption may contribute to systemic toxicity.
Children are more vulnerable to toxicants absorbed
through the skin because of their relatively larger
surface area:body weight ratio.
Ingestion of methyl bromide is unlikely because it
is a gas at room temperature.
bromide is a neurotoxic gas that can cause convulsions,
coma, and long-term neuromuscular and cognitive
to high concentrations of pure methyl bromide may cause
inflammation of the bronchi or lungs, an accumulation of
fluid in the lung, and irritation of the eyes and nose.
Tearing agents added to methyl bromide to provide
warning of its presence can also cause these symptoms,
even at very low concentrations.
contact with high vapor concentrations or with liquid
methyl bromide can cause systemic toxicity and may cause
stinging pain and blisters.
Exposure Methyl bromide methylates the
sulfhydryl groups of enzymes, causing cellular
disruption and reduced glutathione levels. Cellular
disruption, primarily in the CNS, results in progressive
dysfunction. In sublethal poisoning, a latency period of
2 to 48 hours can occur between exposure and onset of
symptoms. Methanol, a metabolite of methyl bromide, may
also contribute to the neurologic and visual effects,
but this is only likely to be significant at high levels
do not always respond to chemicals in the same way that
adults do. Different protocols for managing their care
may be needed.
The most serious effects of acute inhalation
exposure involve the CNS. Depending on the concentration
and duration of exposure, initial neurologic effects may
be delayed for 2 or more hours after exposure and may
include headache, nausea, vomiting, dizziness, malaise,
and visual disturbances. Examination may reveal
involuntary movements of the eyes, dilated pupils,
slurred speech, trembling of the extremities during
movement, impaired gait, impaired sensation of touch,
brain damage (i.e., cerebellar abnormalities), motor
deficits, and decreased reflexes. Neuropsychiatric
abnormalities often occur after acute exposure, although
onset may be delayed for days to weeks. In some cases,
mental disturbances may predominate with only mild
neurologic signs and no seizures; in others, severe and
prolonged seizures may occur. Motor and cognitive
deficits may persist indefinitely.
Neurologic Peripheral neuropathy may develop after
acute exposure to methyl bromide and may persist
Respiratory symptoms are the most likely
nonneurologic effects of acute methyl bromide
inhalation. Throat irritation, chest pain, and shortness
of breath are common. Severe exposures may cause
inflammation of the bronchi or lungs and an accumulation
of fluid in the lungs, which may be delayed 24 hours or
longer after exposure. Death may result from respiratory
or cardiovascular failure.
certain chemicals can lead to Reactive Airway
Dysfunction Syndrome (RADS), a chemically- or irritant
induced type of asthma.
be more vulnerable because of relatively increased
minute ventilation per kg and failure to evacuate an
area promptly when exposed.
Acute inhalation of high concentrations can cause
rapid, ineffective beating of the heart.
Protein and blood in the urine, scant urine
production, absence of urine production, and
accumulation of urea and other nitrogen wastes in the
blood due to death of kidney cells have been described.
Complete recovery is usual.
Elevated liver enzymes in serum and jaundice occur
occasionally after acute exposure.
Eye exposure to liquid methyl bromide or to high
concentrations of vapor may cause corneal irritation and
Contact with either liquid or high vapor
concentrations can cause stinging pain, redness of the
skin, and blisters characteristic of second-degree
burns. Because of their relatively larger surface
area:body weight ratio, children are more vulnerable to
toxicants absorbed through the skin.
Sequelae Peripheral nerve damage, speech difficulty,
and neuropsychiatric sequelae such as impaired gait,
involuntary movements of the eyes, tremors, involuntary
muscle jerks, seizures, decline in mental abilities, and
severe mental disorders (i.e., psychoses) may develop
weeks after exposure.
Exposure Repeated exposures have been
associated with peripheral neuropathies, especially
sensory neuropathy, impaired gait, behavioral changes,
and mild liver and kidney dysfunction. Visual impairment
secondary to atrophy of the optic nerve has been
reported. Chronic exposure may be more serious for
children because of their potential longer latency
The International Agency for Research on Cancer has
determined that methyl bromide is not classifiable as to
its carcinogenicity to humans.
Developmental Effects Methyl bromide is not
considered a reproductive or developmental toxicant. No
human data are available; one study of experimental
animals (rats and rabbits) did not find teratogenic
effects at levels below those causing maternal death.
Methyl bromide is not included in Reproductive and
Developmental Toxicants, a 1991 report published by
the U.S. General Accounting Office (GAO) that lists 30
chemicals of concern because of widely acknowledged
reproductive and developmental consequences.
In using the PEAC application we
access information for the chemical by first locating
Methyl Bromide in the database. The following figures
show the screens displayed for chemical properties,
Figure 1 for the PEAC-WMD for Windows application
and Figure 2-5 for the PEAC‑WMD for the Pocket PC
Figure 1 - Using the Lookup
By: Name for Methyl Bromide using the PEAC-WMD for
Review of the information displayed
in the chemical properties screen whether in Figure 1
(above) or Figures 2-5 (below), show chemical properties
values discussed earlier at the top of this discussion.
As you can see below, the published toxicity values,
e.g., IDLH, ERPGs, and the TEELs (Temporary Emergency
Exposure Limits) published by Department of Energy are
provided. We will use the IDLH as the Level of Concern
when we develop the PAD a little later.
Figure 2 – Selecting Methyl
Bromide using the PEAC-WMD for Pocket PC
Figure 3 – The top portion of the
Chemical Properties Data Display Screen
Figure 4– The middle portion of
the Chemical Properties Data Display Screen
Figure 5– The bottom portion of
the Chemical Properties Data Display Screen
A benefit of using the PEAC tool is
assistance in the development of an evacuation zone for
those chemicals that produce a toxic vapor cloud. If
transported as a compressed liquefied vapor it will be
released from a container as a vapor or aerosol or a
liquid that will rapidly vaporize. As with most of our
examples, AristaTek creates a scenario for a spill or
release of the specific chemical, and then we work
through the development of a PAD (Protective Action
Distance) to demonstrate how the PEAC system works.
For our hypothetical scenario using
Methyl Bromide as the involved chemical we’ll set the
location to be a chemical manufacturing facility located
in Baton Rouge, LA. The date is November 11, 2003, about
9:30 AM with a temperature of 75°F, a wind speed of 10 mph with a
partly cloudy sky. The release involves a portable tank
that has a 1” transfer valve knocked off by a forklift.
The PEAC tool can provide guidance with regards to toxic
vapor cloud that is released. If you decide to follow
along as we proceed through these examples, remember to
set the location to Baton Rouge and set the date and
time to the proper values, otherwise you’ll compute
different values. Also it should be understood that the
examples shown below assume that no fire is involved,
otherwise the Methyl Bromide might ignite.
As seen at the top of the data
display screens, there is a yellow icon displayed; this
is the PEAC icon for notifying the user that a
Protective Action Distance can be calculated. Clicking
or tapping on the PAD icon will display a screen as
shown in Figure 6. Following through the screens, we
provide information on the Meteorology, Container Size,
and Type of Release (Source). The following figures
demonstrate how we would work through our scenario to
see what our Protective Action Distance should
It’s Baton Rouge in November
and the temperature about 75°, wind is set for 10
mph, partly cloudy skies and the terrain is
Urban/Forest since it’s an industrial
We have selected from our list
of container sizes the Portable Tank
selection; this gives some quick dimensions
that should get us close to the right size.
We have selected a Hole or
Pipe Release for the type of release with a
1” Hole Diameter.
Figure 6 – Calculating a PAD using the
PEAC‑WMD System for November 11th
By pressing the right arrow at the
top of the screen, the PEAC system will display a screen
as shown in Figure 7. This calculates a PAD
(Protective Action Distance) based on the default
Level of Concern the IDLH of 250 ppm. This
evacuation or standoff distance is based on the toxicity
of Methyl Bromide.
Figure 7 – Default PAD for Methyl
Bromide using the IDLH of 250 ppm
If we felt that the IDLH was not a
conservative enough concentration to provide adequate
protection to the public, we can quickly compute another
PAD using another Level of Concern concentration. For
instance, we could select the ERPG-2 value from the
pop-up list as shown in Figure 8. The results of the new
calculations are shown in Figure 9.
Figure 8 – Selecting another Level
of Concern from the pop-up list
Figure 9 – The PAD calculated
based on the ERPG-2 LOC of 50 ppm.
Substantial portions of this
discussion were adapted from the Agency for Toxic
Substances and Disease Registry (ATSDR) Web site for
Medical Management Guidelines at: http://www.atsdr.cdc.gov/.