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Farm and Home Biosecurity
Consumer/General Public and Livestock/Row Crop Producer
Air Handling Systems
Weapons of Mass Destruction (WMD) Prevention Task Force Information Paper
Summary
Release of a toxic chemical into an air handling system is a credible threat.
Simple measures taken immediately on learning of the release might lessen
harmful effects. Use of military and commercial chemical-biological detectors as
"in-line" monitors is deemed unlikely to benefit because the response
time is longer than the time needed for the toxic substance to be spread through
the air handling system.
Key Findings
- Most structures in the US have an air handling system (residences, office
buildings, shopping centers, commercial establishments, transit systems,
airports). Each system has one or more air intakes and a blower or some similar
device that moves the air through the system (typically, the ventilation
system).
- Release of a toxic chemical into an air handling system is a credible
threat because (1) toxic chemicals are readily available in quantities and in
forms making them easy to disperse into the air handling system, (2) most air
intakes are readily accessible, (3) few air handling systems have any in- line
filters that would be effective at removing these chemicals, and (4) any release
would be spread throughout the entire system within five minutes or less.
- Release of a biological pathogen is a less credible threat because (1)
the pathogens are difficult to obtain in the quantities and forms needed to
mount an attack and (2) many pathogens would be knocked down by the
"roughing" filter present in many air handling systems and by physical
settling likely to occur within the ventilation system.
- Military and commercial detection equipment is unlikely to benefit if
used as an "in-line" monitor within the air handling system.
- Benefits will be derived from the simple measures of (1) turning off the
air handling system (for an external release) or opening up the air handling
system to full outside make-up air (for an internal release) and (2) moving
occupants away from windows, elevators, courtyards, and stairwells and into
interior rooms.
Adversary's Capabilities: Hydrogen Cyanide (HCN)
Intelligence assessments have focused attention to hydrogen cyanide as a
potential chemical weapon for use against, in particular, air handling systems
(that is, released within a building or other confined space or introduced into
an air intake such that the hydrogen cyanide is spread throughout the building
or space via by air handling system). Fueling such assessments are
open-literature reports of improvised devices involving compounds intended to
evolve hydrogen cyanide gas on mixing.
- The threat that hydrogen cyanide might be used against air handling
systems is credible.
- Hydrogen cyanide is a colorless liquid that rapidly evaporates under
ordinary temperature and weather conditions. The hydrogen cyanide vapors (that
is, a gas) have a faint almond odor; however, 20% of humans are incapable
of detecting hydrogen cyanide at any concentration.
- The toxicity of hydrogen cyanide is equivalent to that of chlorine but
is significantly less than that of military chemical warfare agents. Hydrogen
cyanide is less toxic by inhalation than by ingestion. The poisoning effects
of hydrogen cyanide are not cumulative. An exposed person who survives can be
expected to suffer no serious, long-term ill health effects from the hydrogen
cyanide (by contrast, chlorine and many other toxic industrial chemicals often
cause such long-term effects).
- Factors working against use of hydrogen cyanide are
- (1) the quantities required, with larger air handling systems
requiring massive (multiple tank-car loads) quantities;
- (2) the "lighter than air" quality of hydrogen cyanide,
meaning the vapors rise and rapidly dissipate if the operational situation
permits (as is the case in an open area or when the air handling system is
turned to full outside make-up air);
- (3) the relatively rapid biological turn-over of hydrogen cyanide,
which means a human can tolerate a low dose over a long time with no or
little ill health effects but will rapidly succumb to a massive, single dose
(as is achieved in a "gas chamber"); and
- (4) the rapid degradation of hydrogen cyanide to relatively non-toxic
substances in the presence of water, such as the moisture in the air or from
a water sprinkler system.
- It is extremely difficult (some authorities report
"impossible") to achieve a lethal concentration of hydrogen cyanide
out-of-doors.
- Factors working in favor of its use are
- (1) its availability as liquid hydrogen cyanide, which has many
legitimate industrial uses and
- (2) the ability to make gaseous hydrogen cyanide "in-situ"
by mixing a cyanide salt (such as sodium or potassium cyanide, which are
available commercially) with certain acids (note: specifics have been
omitted intentionally). Chlorine is a more readily available industrial
chemical than is hydrogen cyanide. Devices for in-situ release of hydrogen
cyanide can be neutralized with copious amounts of water, but the simplicity
of such devices plus the ability to pre-position such devices make them a
credible threat to air handling systems.
Preventions
- Immediate, low- or no-cost measures:
- Building and system managers (for example, subway and tunnel systems)
should be instructed to cut off the air handling system immediately upon
being advised of the release of a toxic substance external to the
building. This simple measure will stop the spread of the toxic
substance throughout the building.
- Building and system managers should be instructed to place the air
handling system on "full (or 100%) outside air" immediately upon
being advised of the release of a toxic substance internal to the
building. This simple measure will dilute the toxic substance already
within the air handling system and will speed up its removal from the
building.
- Building occupants should be instructed to seek "shelter in
place" in areas where air movement is low. Occupants should be
instructed to stay away from windows and to avoid places where air movement
is brisk (for example: elevator shafts and stairwells). Occupants should be
instructed to remain inside, under cover.
- Building and system managers should be advised that military and
commercial detectors for toxic chemicals and biological pathogens are of
little or no use as in-line monitors within an air handling system. The
response time of currently available detectors is too slow to impact the
spread of any toxic substance within the building or system. These detectors
might have value as a diagnostic tool post-exposure of the building or
system occupants and as a tool for determining when the outside air is safe
for use following shut-off of external air intake.
- Building
•and
system managers should activate the water sprinklers if advised of an
in-building release of hydrogen cyanide, chlorine or other toxic industrial
chemicals. The water will mix with these chemicals to form less toxic
substances, removing them from the air.
- Near term measure:
- Building and system managers should consider design and equipment
modifications to make external air intakes less accessible. Options include
installation of false or decoy intakes, camouflaging the actual intakes, and
relocating the intakes to less accessible areas.
WMD Prevention Task Force Point of Contact
Benjamin C. Garrett
Chief Chemist
FBI Hazardous Materials Response Unit (HMRU)
Quantico, VA
Office: 703-632-4653
Pager: 888-771-6861
PaperNo. 2: Air Handling Systems
10-06-2001, Version 2 Back to Consumer/General Public
and Livestock/Row Crop Producer |
