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the biological agents to destroy; however, as toxins rather TABLE 2-9 Determination of
than viable organisms, they may be washed away and diluted Biological Event Emergency Response
to safe levels with soap and water. Biological Event
Gaseous decontamination, or fumigation, applies to en- Information Needed to Determine Appropriate
closed spaces. The primary choices for destroying bacteria Emergency Response
and viruses are chlorine dioxide, methyl bromide, para Estimated population exposed to levels of
formaldehyde, ozone, vapor hydrogen peroxide, and ethylene concern as determined from:
Affected area information (see below)
oxide. Any gas or vapor that can kill bacteria is also harmful Population data
to humans. Chlorine dioxide was used in 2001 to remediate Estimated affected area as determined from:
anthrax in the Hart Senate Office Building and the Brentwood Quantity and infectivity
U.S. Postal Distribution Center. The remaining disinfectant Location of release and contagiousness
Wind direction and strength
gas was later broken down by the addition of sodium bisul-
Topography
fate. Vapor hydrogen peroxide was successfully used by the Surface sampling
Department of State to decontaminate a mail sorting facility Possible exposure pathways as determined from:
in Sterling, Virginia, in 2002. Particularly in the cases of an- Agent type
thrax spores, administering vaccines may sometimes be more Physical form and formulation
practical than complete decontamination.
After decontamination, removal or cleanup of the disin-
fectant is required. Wide area decontamination would require the physical state of the organism, and in particular, the like-
close coordination with the U.S. EPA. The use of large lihood of the organism being suspended in air. Weaponized
quantities of liquid chlorine (i.e., bleach), in particular, will biological agents have been treated such that their physical
be subject to EPA and similar state requirements. These re- properties favor aerosol dispersion. This quality makes their
quirements may include containing runoff, measuring water re-suspension into the air a greater threat than is posed by
quality, and possibly sustained holding of runoff water with the naturally occurring forms of the organisms.
other treatment until acceptable levels of both the initial con-
taminant and any added decontaminants are reached. The
Quantity and Persistence
EPA has released an alert relative to environmental liabilities
caused by mass decontamination runoff. The quantity of a biological agent released and its disper-
sal and likely exposure routes determine the area over which
people may be infected. The persistence determines the du-
2.2.2 Emergency Response Needs ration of the risk of infection. The quantity of a viral or bac-
terial agent is increased orders of magnitude in an infected
Regardless of the cause of a biological release, from an
individual, while the quantity of a biological toxin is not in-
emergency response perspective, the primary considerations
creased after release. Biological agents that do not survive
for response management are biological agent type and for-
long in open environments may still be very persistent over-
mulation, quantity and persistence, exposure route, disper-
all if they are contagious and can be easily transmitted from
sion, and population density in the area at risk. These factors
person to person.
and their interrelationship are further discussed below. Table
An upper range estimate of the quantity of the release of a
2-9 delineates some of the information needed in a biologi-
biological agent in transport cannot be easily determined
cal event to decide the appropriateness of transportation
based on the container size. Often infectious material consti-
goals for evacuation, isolation and checkpoint establishment,
tutes only a small proportion of contaminated medical
and provision of supplies to the contaminated area.
wastes. Pure bacterial or viral cultures are shipped in small
quantities because the receiving institution generally can
culture more of the organism as needed, thereby reducing
Agent Type and Formulation transportation concerns. In the event of a biological weapons
attack, estimating the release quantity and associated area
The type of agent, its associated infectivity and conta- with concentrations of concern is difficult and made more
giousness, and its formulation are key factors in assessing difficult when there is a delay between exposure and recog-
the threat posed to human health. The health risk to an ex- nition of an attack (i.e., observable symptoms).
posed population is also affected by the quantity of the agent
released and the likely exposure route (i.e., whether the par-
ticle size will permit inhalation into the lungs). Similarly, in- Exposure Routes
formation on the biological agent type and formulation also
determines what is needed to protect emergency response Inhalation is the exposure route of greatest concern, and this
and cleanup personnel adequately. Formulation relates to is likely to be a primary form of exposure for agents dispersed
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as aerosols with droplets in the 1- to 5-m-diameter range. storage in a small municipality or a specific building is viewed
This size range can be achieved by using either a solid or a liq- as more credible, but difficult to reach without site-specific
uid preparation. Because all the biological threat agents exist knowledge and access. Alternatively, disruption of the water
as solids, the liquid preparation is actually a slurry of particles disinfection process may lead to unhealthy levels of biological
in solution. Optimal dispersion occurs when the slurry is disease agents. Intentional contamination of passenger drink-
atomized such that only a few organisms are present in each ing water within the transportation system is possible, but
liquid droplet. Because of the high surface-area-to-volume would probably not be a very large event in terms of injuries
ratio of these small particles, the liquid evaporates leaving the or casualties.
aerosolized particles suspended in air. Dry agent can also be Food contamination is also possible. Although only isolated
released after it is treated to result in a majority of particles cases of intentional food poisoning have occurred, several
within the appropriate size. Bacterial spores are ideally suited single accidental food poisoning events with chemical agents
for this dry method because their nominal size is within this within the last decade have sickened thousands of people, sug-
range and they are inherently stable. Vegetative bacteria, gesting the effects that could be achieved with intentional food
viruses, and toxins are better suited for liquid formulations, but poisoning.
can be prepared as dry agent as well.
Particle size is critical for two factors. First, if the particles
are too large, they quickly fall to the ground and are no longer Dispersion and Population Density
an aerosol threat. Table 2-4 in the chemical subsection high-
lights sedimentation rates for various-sized particles in stag- The density of the population in the area at risk affects the
nant air. The second factor is that the size of a particle affects means for communicating instructions and the choices of
its ability to cause infection. In general, particles greater than transportation-related responses. The number of individuals
10 m in diameter are trapped by nasal hairs and released at risk during a biological event depends on the population
with exhaled air or sneezing. Particles less than 10 m in di- density and the area over which health-threatening levels of
ameter are referred to as "inhalable" because they may pass contamination are dispersed. Health-threatening levels are
into the upper portions of the lungs, which contain many determined by the type of the agent and the exposure route.
branched passageways. These passages (i.e., bronchi and Dispersion of the initial release is determined from the phys-
terminal bronchioles) are lined with mucus and cilia. The ical form of the released agent (i.e., aerosol or particles),
mucus traps particles, and the cilia gradually push particles up topology and meteorology (i.e., rain and wind currents), and
and out of the lungs within about a day. These particles are the quantity released. For contagious agents, dispersion will
then swallowed. Stomach acids can destroy many types of bi- also follow the path of infected individuals.
ological agents, thus preventing infection. The smallest parti- Aerosols and fine particles from a biological release may
cles (e.g., less than 2.5 m in diameter) are referred to as be dispersed by natural wind and wind generated from
"fine" or "respirable" particles. Fine particles may pass into traffic. The particles dispersed by wind will eventually be de-
the deepest portions of the lungs (i.e., respiratory bronchioles, posited onto surfaces. The atmospheric dispersion of small
alveolar ducts, and alveolar sacs) and may be removed by particles and aerosols is affected by many factors, such as en-
macrophages over many days, allowing time for bacteria ergy in the dispersion (i.e., fire, heat, explosion), height of re-
growth and the development of an infection. Bacteria are lease, presence of obstructions (e.g., buildings, hills, and
typically 1 to 5 m in diameter, while viruses are generally mountains), and weather conditions (wind speed and direc-
0.5 m or less. To put these sizes in perspective, the particle tion, temperature, humidity, rain, and cloud cover). The most
size of some common substances is shown in Table 2-5 of the important factors are wind speed, wind direction, energy and
chemical subsection. height of release, and the presence of obstructing structures
Biological agents either not released as an aerosol or released or natural features.
as large enough particles to settle on the ground pose greatly re- Weaponized biological agents travel with the wind for
duced inhalation risks. Biological agents generally cannot cause many miles before being deposited on the ground. The actual
infection by skin absorption unless there are open wounds. A number of infected individuals may be greater in areas of
notable exception to the inability of biological agents to pass lower contamination because these areas are much larger
through uninjured skin is mycotoxins, biological toxins pro- than high contamination areas. Sampling, within enclosed
duced by molds. Mycotoxins act quickly, similarly to chemical structures and in strategically determined outdoor locations,
blister agents. They can be distinguished from blister agents by is the most effective way to identify the extent of contami-
a lack of odor and by a yellow, red, green, or other color associ- nation. Both surface and air collections are made in areas
ated with oily droplets. of high contamination, but in areas of lower contamination,
As discussed in the chemical subsection, effective contam- typically only air collections are made because significant
ination of the drinking water supply of a city-sized population amounts are often not found on distant surfaces.
is not generally viewed as a credible threat by terrorism ex- Secondary releases of an agent can be caused by two dis-
ports. However, an attack on post-purification drinking water tinct mechanisms. The first is by the introduction of wind or
