This month our example is Phosgene,
which has a chemical formula of (COCl2).
Phosgene is listed under the UN # (United Nations
Number) by the US Department of Transportation: UN 1076.
Phosgene CAS# is: 75-44-5.
Persons exposed only to phosgene gas
do not pose substantial risks of secondary
contamination. Persons whose clothing or skin is
contaminated with liquid phosgene (ambient temperature
below 47 °F) can secondarily contaminate response
personnel through direct contact or off‑gassing vapor.
At room temperature, phosgene is a
colorless, nonflammable gas with a suffocating odor like
new mown hay. However, odor provides insufficient
warning of hazardous concentrations. At high
concentrations it is mildly irritating.
Below 47 °F, it is a colorless,
fuming liquid; contact with the liquid can cause
frostbite. In the presence of water (sweat, saliva,
tears), the liquid or gas slowly hydrolyzes to
hydrochloric acid, which can irritate and damage cells.
Phosgene is absorbed to some extent
by the lungs, but not by intact skin. Systemic damage is
usually a secondary result of anoxia caused by loss of
lung function. It is corrosive to the lungs and intact
Phosgene is a colorless, fuming liquid below 47 °F
(8.2 °C) and a colorless, nonflammable gas above 47 °F.
At low concentrations, its odor is similar to that of
green corn or new mown hay; at high concentrations, its
odor can be sharp and suffocating. Phosgene is slightly
soluble in water and is hydrolyzed slowly by moisture to
form hydrochloric acid. It is soluble in most liquid
hydrocarbons. It is shipped as a liquefied, compressed
gas. Large quantities of phosgene should be stored in a
dry, cool, well‑ventilated, and fireproof room. Phosgene
is a combustion product of many household products that
contain volatile organochlorine compounds. Therefore, it
may contribute to the hazards of smoke inhalation in
fire victims and firefighters.
Phosgene is produced commercially by chlorinating
carbon monoxide. It is a combustion or decomposition
by-product of most volatile chlorinated compounds;
therefore, household substances such as certain
solvents, paint removers, and dry-cleaning fluids can
produce phosgene when exposed to heat or fire. Phosgene
may also be produced during the welding of metal parts
that have been cleaned with chlorinated hydrocarbons.
Phosgene is used as an intermediate in the manufacture
of many chemicals including isocyanates, polyurethane,
polycarbonates, dyes, pesticides, and
gas with musty odor at room temperature; a fuming liquid
below 47°F (8°C).
properties: Detectable odor following brief
emergency releases; odor threshold 0.4 to 1.5 ppm;
slightly irritating in high concentration. Odor
provides inadequate warning of harmful
Molecular weight: 98.9
point: (760 mm Hg): 47 °F (8 °C)
Freezing point: -198
°F (-127 °C)
Specific gravity: 1.43
(liquid at 32 °F)
pressure: 1,215 mm Hg at 68 °F (20 °C)
density: 3.48 (air = 1)
carbonic acid dichloride, carbonic dichloride, carbon
oxychloride, carbonyl chloride, and chloroformyl
OSHA PEL (permissible exposure limit) = 0.1
ppm (averaged over a 8-hour workshift)
(immediately dangerous to life or health) = 2 ppm
ERPG-2 (emergency response planning guideline) (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) = 0.2
Incompatibilities: Phosgene reacts with
moisture (water or alcohols). In water, it slowly
decomposes to hydrochloric acid and carbon dioxide. When
heated to decomposition, it will produce toxic and
corrosive fumes. Phosgene reacts violently with various
chemicals (e.g., alkalis, ammonia, amines, copper,
aluminum); it attacks many metals in the presence of
water and can also attack plastic and rubber.
Routes of Exposure:
Inhalation is the major route of phosgene exposure.
The odor threshold for phosgene is 5 times higher than
the OSHA PEL. Thus, odor provides insufficient
warning of hazardous concentrations. Phosgene’s
irritating quality can be mild and delayed, which may
result in a lack of avoidance leading to exposure for
prolonged periods. Phosgene is heavier than air and may
cause asphyxiation in poorly ventilated, low-lying, or
exposed to the same levels of phosgene gas 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
phosgene gas found nearer to the ground.
Contact When phosgene gas contacts moist or wet
skin, it may cause irritation and erythema. High
airborne concentrations can also cause corneal
inflammation and opacification. Direct contact with
liquid phosgene under pressure can cause frostbite as
well as severe irritation and corrosive effects.
more vulnerable to toxicants affecting the skin because
of their relatively larger surface area:body weight
Ingestion of phosgene is unlikely because it is a
gas at room temperature.
is an irritant to the skin, eyes, and respiratory tract;
there may be minimal irritation immediately after
exposure, but delayed damage may be severe.
initial symptoms include mild irritation of the eyes and
throat, with some coughing, choking, feeling of
tightness in the chest, nausea and occasional vomiting,
headache, and lacrimation.
poisoning may cause respiratory and cardiovascular
failure, which results from low plasma volume, increased
hemoglobin concentration, low blood pressure, and an
accumulation of fluid in the lungs. Secondary systemic
damage is the result of anoxia.
Acute Exposure Phosgene
directly reacts with amine, sulfhydryl, and alcohol
groups in cells, thereby adversely affecting cell
macromolecules and cell metabolism. Direct toxicity to
the cells leads to an increase in capillary
permeability, resulting in large shifts of body fluid,
decreasing plasma volume. In addition, when phosgene
hydrolyzes, it forms hydrochloric acid, which can also
damage surface cells and cause cell death in the alveoli
and bronchioles. Hydrochloric acid release into the
mucosa triggers a systemic inflammatory response.
Phosgene stimulates the synthesis of
lipoxygenase-derived leukotrienes, which attract
neutrophils and causes their massive accumulation in the
lungs; this contributes to the development of pulmonary
edema. Following phosgene exposure, a patient may be
free of symptoms for 30 minutes to 48 hours before
respiratory damage becomes evident; the more severe the
exposure, the shorter the latency. If the initial
concentration of phosgene was high, rapid onset of
direct cytotoxicity and enzymatic poisoning may ensue.
Because phosgene is not very water soluble and
hydrolysis tends to be slow, victims inhaling low
concentrations of the gas may experience no irritation
or only mild irritation of the upper airway. Lack of
irritation allows victims to inhale the gas more deeply
into the lungs and for prolonged periods.
do not always respond to chemicals in the same way that
adults do. Different protocols for managing their care
may be needed.
Inhaling low concentrations of phosgene may cause no
signs or symptoms initially, or symptoms may be due only
to mild irritation of the airways; these symptoms
(dryness and burning of the throat and cough) may cease
when the patient is removed from exposure.
after an asymptomatic interval of 30 minutes to 48
hours, in those developing severe pulmonary damage,
progressive pulmonary edema develops rapidly with
shallow rapid respiration, cyanosis, and a painful
paroxysmal cough producing large amounts of frothy white
or yellowish liquid. Inadequate, labored respiration,
during which abnormal chest sounds are evident, may be
accompanied by increased distress and apprehension.
Insufficient oxygenation of arterial blood, and massive
accumulation of fluid in the lungs may be accompanied by
cardiovascular and hematological signs.
to phosgene has been reported to result in Reactive
Airway Dysfunction Syndrome (RADS), a chemically- or
irritant-induced type of asthma.
may be more vulnerable to corrosive agents than adults
because of the relatively smaller diameter of their
airways. Children may also be more vulnerable because of
increased minute ventilation per kg and failure to
evacuate an area promptly when exposed.
exposed persons may develop inflammation of the lungs
when reexposed to extremely low levels of Phosgene.
Flu-like symptoms such as fever, malaise, shortness of
breath, and cough can develop 4 to 6 hours after
exposure and persist for 12 hours or longer. Chest
x-rays may indicate lung changes.
sensitized individuals, asthmatic attacks can occur
after exposure to extremely low Phosgene air
concentrations (0.0001 ppm). Asthmatic reactions can be
immediate, delayed (4 to 8 hours), or both.
to Phosgene can lead to Reactive Airway Dysfunction
Syndrome (RADS), a chemically- or irritant-induced type
may be more vulnerable because of relatively increased
minute ventilation per kg and failure to evacuate an
area promptly when exposed.
Cardiovascular collapse may occur if the patient is
severely hypovolemic and hypoxemic from accumulation of
fluid in the lungs. Destruction of red blood cells in
the pulmonary circulation can cause capillary plugging
that leads to strain on the right side of the heart and
If the skin is wet or moist, contact with phosgene
vapor can cause irritation and redness of the skin.
Contact with liquid phosgene under pressure can result
in frostbite. Because of their relatively larger surface
area:body weight ratio, children are more vulnerable to
toxicants affecting the skin.
High vapor concentrations cause tearing and
increased presence of blood in the eye. Contact with
liquid phosgene may result in clouding of the cornea and
In severe cases, phosgene may cause hemolysis that
results in the plugging of pulmonary capillaries. Most
hematologic changes (e.g., hemolysis, methemoglobinemia,
bone marrow suppression, and anemia) can be detected by
standard blood tests.
In cases of high exposures, phosgene may be directly
cytotoxic to the liver, causing necrosis and loss of
In cases of high exposures, phosgene may be directly
cytotoxic to the kidneys, causing necrosis and loss of
Nausea and vomiting may occur following exposure to
Sequelae If the patient survives the initial 48
hours after exposure, recovery is likely. Sensitivity to
irritants may persist, causing bronchospasm and chronic
inflammation of the bronchioles. Pulmonary tissue
destruction and scarring may lead to chronic dilation of
the bronchi, lobular emphysema, regions of atelectasis,
and increased susceptibility to infection.
to phosgene has been reported to result in Reactive
Airway Dysfunction Syndrome (RADS), a chemically- or
irritantinduced type of asthma.
ExposureA group of workers who were exposed daily to
high levels of phosgene showed an increase in mortality
and morbidity from inflammation of the lungs, chronic
inflammation of the bronchioles, destruction of alveoli,
and impaired pulmonary function. Chronic exposures to
low levels of phosgene may lead to chronic pneumonitis,
which may resolve or lead to pulmonary edema.
exposure may be more serious for children because of
their potential longer latency period.
Carcinogenicity Phosgene has
not been classified for carcinogenic effects.
Reproductive and Developmental
Effects No information was found pertaining to
reproductive or developmental hazards caused by phosgene
exposure. Phosgene 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
Phosgene in the database. The following figures show the
screens displayed for chemical properties, Figure 1 for
the PEAC-WMD for Windows application and Figure
2-4 for the PEAC‑WMD for the Pocket PC
Figure 1 - Using the Lookup By:
Name for Phosgene using the PEAC-WMD for Windows
Review of the information displayed
in the chemical properties screen whether in Figure 1
(above) or Figures 2-4 (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 Phosgene
using the PEAC-WMD for Pocket PC application
Figure 3 – The top portion of the
Chemical Properties Data Display Screen
Figure 4– 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
Phosgene as the involved chemical we’ll set the location
to be a chemical manufacturing facility located in
Houston, TX. The date is December 11, 2003, about 1:30
AM with a temperature of 55°F, a
wind speed of 5 mph with a clear sky. The release
involves a portable tank that has a 1-inch transfer
valve knocked off by a forklift. The facility response
team responds and by the time they have arrived, a pool
of liquid has formed about 25’ in diameter. 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 Houston and set the date and time to the
proper values, otherwise you’ll compute different
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 5. 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 Houston in December and
the temperature about 55°, wind is set for 5 mph,
clear skies and the terrain is Urban/Forest
since it’s an industrial setting.
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
Pool Diameter of 25 ft and a Pool
Depth set to the default depth of 0.4”.
Figure 5 – Calculating a PAD using the
PEAC‑WMD System for December 11th
By pressing the right arrow at the
top of the screen, the PEAC system will display a screen
as shown in Figure 6. This calculates a PAD
(Protective Action Distance) based on the default
Level of Concern the IDLH of 2 ppm. This
evacuation or standoff distance is based on the toxicity
Figure 6 – Default PAD for Phosgene
using the IDLH of 2 ppm
With a wind speed of 5 mph the
downwind evacuation or PAD extends about 1 mile. If the
wind speed was slower so that stable atmospheric
conditions were established, the downwind evacuation
distance will be impacted. To see the effect, click on
the left arrow [|] at the top
of the screen until you return to the meteorological
input screen. As shown in Figure 7, select a wind speed
of 2 mph rather than 5 mph.
Figure 7 – Change the wind speed
to 2 MPH
Then click on the right arrows [}] at the top
of the screen until a new PAD screen is displayed. The
results of the new calculations are shown in Figure
Figure 8 – PAD under stable
As can be seen in Figure 8, the
evacuation distance has increased substantially when
stable atmospheric conditions are present, hence the
term “worst case conditions”.
The user should be aware that stable
atmospheric conditions may exist during night with low
winds. These conditions can present serious problems
with respect to toxic clouds and their behavior.
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/.