1. Sudden Release of a Cryogenic
A cryogenic liquid is a chemical that
is normally a gas at room temperature but is liquefied
under pressure. The liquid is stored in a tank or other
container under pressure. The tank may or may not be
refrigerated. Examples of cryogenic liquids are
chlorine, anhydrous ammonia, fluorine, and hydrogen
fluoride. Of course these chemicals can be stored under
pressure as a gas, but if the pressure is great enough
or if the chemical is refrigerated, the chemical will
liquefy. A much greater amount of chemical can be stored
in a tank as a liquid than as a gas because the density
of the liquid is greater than the gas.
What happens if a hole is punched
in the tank or a connecting valve or pipe is sheared
off? The pressure inside the tank is suddenly released.
The liquid inside the tank boils. Gas and liquid escape
rapidly out the tank hole or sheared pipe. Depending
upon the dynamics, the liquid escaping from the hole or
pipe could be in the form of an aerosol or fine
droplets. Some of the droplets may settle forming a
liquid pool near the opening. If the droplets are small
enough, they will be carried as an aerosol with the
escaping gas. When the tank pressure is released and the
liquid evaporates, the air around the hole will chill.
The cold air containing the aerosol will tend to settle
near the floor (ground) and spread out from its source.
Dust can be released from explosions,
including the collapse of buildings and structures.
Weather conditions may blow dust from the ground. There
are environmental laws on the books that limit fugitive
Industrial fires, especially those
involving chemicals, can release many particulates to
1- "Dirty Bomb"
A “dirty bomb” is the purposeful
release of radioactive isotopes into the environment. A
terrorist may strap a container of a radioactive isotope
in powder form to a conventional explosive and detonate
the material. The radioactive isotope could also be
dissolved or slurried in liquid form. The setup of such
a device would probably be very risky to the terrorist
as the handling of any radioactive material is very
dangerous. If the “explosion” results in minimal damage
or if lead shielding is found at the explosive site,
this is a tip-off. A car bomb could also be seeded with
radioactive material. Confirmation is made by using
radioactive detection equipment.
2- Chemical Warfare Agents
The PEAC tool contains a menu where
the user can pull up a screen listing many chemicals
which may be used as chemical warfare agents. Some are
common industrial chemicals such as phosgene and
hydrogen cyanide which serve many legitimate uses.
Others such as Sarin and VX have no legitimate use and
are banned by the international chemical weapons treaty.
Some are very odorous and choking but others may have a
mild pleasant odor or odorless and could easily be
inhaled or applied to the skin with the person unawares.
One drop of VX applied to intact skin is sufficient to
A terrorist using such a weapon must
find a way of getting the chemical agent into the air
where it might be inhaled or contacted with the skin as
from contaminated clothing. One way is setting off an
explosive device by a container of the material. Another
way is using a small pressurized tank dispersing as an
aerosol. There is concern that crop dusting equipment on
small planes could be used.
The United States once had a
military program which included the development of
binary weapons. Two chemical components each of which
was relatively benign when mixed together form Saran or
VX. The mixing was done in a delivery bomb) dropped from
the air. The military D2PC model had a component which
predicted downwind dispersion and nearby ground spray of
chemical agents delivered by several different kinds of
bombs. Depending upon the bomb and height and the
chemical, different portions of the agent might be
sprayed on the ground or remain airborne and travel
Rouge governments potentially may
invest in technologies which allow the chemical agent to
be more easily handled, or smuggled, or dispersed into
the air. The chemical warfare agent might be mixed with
a carrier solvent or adsorbed onto a fine powder for
dispersion as an aerosol or dust. The technologies are
the same as those employed for pesticide application or
even in the food processing industry. For example, there
has been recent concern on the part of the U.S. military
that Iraq may have developed a VX powder, where the VX
chemical is adsorbed unto a fine silicon dioxide “mists”
roughly on the order of 0.01 microns (or less) in
diameter, which may allow the chemical to be inhaled as
a gas. The chemical VX in its pure form is a very
viscous liquid with a very low vapor pressure, and is
not easily inhaled.
3- Biological Warfare Agents
The news has focused attention on
powders containing anthrax spores delivered in letters
addressed to people in government. Some of the spores
apparently escaped the letters as a few postal workers
developed inhalation anthrax. Anthrax spores are very
resistant to drying and sunlight, and may remain
infectious for years, even decades. Roughly 8000 to
50000 spores are required to infect a healthy adult by
inhalation, but the dose for the elderly could be much
less. Anthrax is not contagious with normal human
Tularemia or rabbet fever is
normally transmitted to humans by infected flies,
mosquitoes, or ticks. Rabbits and other small animals
might serve as the host species in nature. Only a few
tularemia bacteria, perhaps 10 or less, can infect a
human. The bacteria can live for weeks even months in
contaminated dust outside the infected insect or animal.
This property makes it possible for a dangerous dust
containing the bacteria to be produced from animal or
insect parts or excrement. Inhalation tularemia has a
higher fatality rate than if acquired through an insect
There are a number of viral and
bacterial diseases that are normally transmitted through
the bite of a tick or by inhaling dust containing
excrement or saliva of infected rodents. Infected ticks
and their droppings can be ground to produce an
infectious dust which may be inhaled. They have
potential for producing a bioterrorist weapon. Some
viruses and bacteria do not live outside the host long
and are susceptible to drying. Other dusts may remain
infectious for many months, depending on the agent and
how it is preserved.
Small pox is a highly contagious
disease for which there is no cure. It is most
contagious when the initial rash develops. Transmission
is by direct contact or indirectly through contact
through objects that an infected person has also
contacted (e.g. the phone, money, papers, etc.). It can
also be spread in a confined area by inhalation.
Fortunately, the virus does not survive very long
outside the human host, but still can be infectious for
hours. The infected terrorist himself might serve as the
So Why not Model the Release?
There are many ways for aerosols and
dusts to be released. A terrorist may release the dust
or aerosol in a building or airplane or subway. There
are models available for specific applications such as
the release of hydrogen fluoride or a chemical warfare
agent released as a gas out in the open. If the aerosol
or dust is fine enough, it will behave as a gas and a
gas model can be used to estimate a downwind
Gas dispersion models would be almost
useless in predicting downwind dispersion in release of
biological weapons, especially if only a few organisms
can infect a person. The release also might take place
inside buildings or other confined areas. The release
quantity would probably be unknown.
When an industrial or transportation
accident occurs, the chemical released and perhaps even
the quantity is known (at least the tank size is known).
There is probably an appropriate gas dispersion model
that can be used. With a terrorist activity, the
material released and quantity is unknown.
More important to the first
responder is to establish that an incident has taken
place, and what the material is. What can be done to
protect the public and emergency personnel? How long
will the location be contaminated? Individuals exposed
to the contamination will need to be located and tracked
down to make sure they do no spread the contamination,
whether the contamination is a radioactive isotope or a
communicable disease or a chemical warfare agent.
Persons exposed to contamination may need to be isolated
in addition to being treated. There is also the matter
of decontamination and cleanup. These issues will likely
take center stage.
Establishing that a
Terrorist Incident has Taken Place
Any suspicious explosion should be
checked for radioactivity. Any package unusually heavy
for its size should also be checked for radioactivity. A
person exposed to a lethal dose of radiation or a
chemical warfare agent or to a deadly disease may feel
fine at the moment but later die a horrible death.
Sometimes the first clue that an
incident has occurred is when a large number of people
become sick, especially with similar symptoms. A single
case of an uncommon disease should also be investigated.
Epidemiologists and law enforcement officers need to
work closely on this. The Military Medical Technology
(volume 6 issue 8, 2002, pages 32-34) has published
a number of questions law enforcement officers and
epidemiologists should ask when investigating an
illness/sickness outbreak. These are repeated here.
Epidemiology is the study of the incidence and
distribution of diseases in large populations, and the
conditions influencing their spread and severity.
Questions Law Enforcement Officers
Might Ask (from Military Medical Technology, with
- What do you think made you ill?
- When did you start feeling sick
- Do you know of anyone else who
became ill or died?
- Have you had any medical treatment
in the last month? What is the name of your health
care provider? Where were you treated? Are you taking
- Where do you live and work (or go
- Did you attend a public event?
(Sporting event, social function, restaurant, etc.).
What did you eat there?
- Have you or your family members
traveled more than 50 miles in the last 30 days?
- Have you or your family members
had any contact with an individual who has been in
another country in the last 30 days?
- Have you seen anyone with an
unusual device or anyone spraying something? Anyone
with laboratory equipment or other suspicious
activities? These questions might in particular be
asked in context of a public event or a location where
the public may assemble.
- Have you detected any unusual
odors or tastes?
- Have you noticed any sick or dead
animals or birds?
This information should be provided
to public health officials.