It doesn’t help that this "Threat Condition Orange" perfectly
coincides with the administration’s desperate attempts to link
al Qaeda with Saddam Hussein, but let’s leave politics aside for
Houston press has reported
that Lowe’s and Home Depot stores throughout
Harris County have sold out of the plastic sheeting, duct tape,
and other supplies recommended by the Office of Homeland Defense
(OHD) in order for citizens to be better prepared in the event
of an terrorist act. It’s the same all over the nation.
This is a very serious health issue.
"Place a dry cleaning bag over your head and await further
instructions." This may as well have been the instructions
by the time they filtered down to Betty Sue in Omaha. But we all
know Betty Sue doesn’t have anything to worry about, does she?
Well, she does if she follows the instructions from OHD.
The cause for most
concern is the OHD plan for "What
to do during a chemical or biological attack":
Seek shelter in an internal room, preferably one without windows.
Seal the room with duct tape and plastic sheeting. Ten square feet
of floor space per person will provide sufficient air to prevent
carbon dioxide build-up for up to five hours.
And Good Morning America’s
Home Improvement Editor, Ron Hazelton, assured
Don’t worry about running out of air. Every ten square feet of
floor space will last an adult about 5 hours. And don’t leave the
room until you get instructions from the Emergency Broadcast System
to do so.
notice the discrepancy in the phrases "to prevent carbon
dioxide build-up" and "don’t worry about running out
of air." Hazelton is actually correct (probably accidentally)
that the amount of oxygen corresponding to a ten square foot space
is probably sufficient (though marginal) to sustain an adult for
about five hours, but the critical issue is not oxygen consumption,
but carbon dioxide generation and accumulation. The OHD statement
is correct in identifying carbon dioxide accumulation as a concern,
but its conclusions are surprising, to say the least.
an eight-foot ceiling (yielding eighty cubic feet per person)
and a subject metabolic rate of 800 BTU/hr, after five
hours the partial pressure of carbon dioxide (ppCO2) would be ~67
mm Hg (if the initial ppCO2 were zero). It cannot be understated: this
is very high.
800 BTU/hr (3.36 kcal/min) is not unreasonable for a very excited
person in a hot and humid enclosure with elevated carbon
dioxide (more on that in a moment). For this case, a bare (but
irresponsible) minimum might be 600 BTU/hr (corresponding to a
ppCO2 level of 50 mm Hg after five hours). Consider that NASA Environmental
Control and Life Support (ECLS) engineers typically assume a waking
metabolic rate of 450 BTU/hr for moderate intravehicular activity,
and this is with very physically efficient subjects (astronauts)
not using major muscle groups (e.g., legs) in microgravity.)
in mind that the maximum operational limit for the Shuttle Orbiter
is 7.6 mm Hg, and is actually lower for the International
Space Station. The NASA Spacecraft Maximum Allowable Concentration
(SMAC) for carbon dioxide is 10.0 mm Hg for a one-hour period.
Similar values can be found among the literature of the various
NASA Bioastronautics Data Book (Second
Edition, pp. 48–49) indicates that after only 80 minutes, at
a ppCO2 level of
~18 mm Hg, the subject can experience "mental depression,
headache, dizziness, nausea." At ~45 mm Hg (after 80 minutes),
the subject experiences "marked deterioration leading to dizziness
and stupor, with inability to take steps for self preservation.
The final state is unconsciousness." (The level in our case
would not reach 45 mm Hg after 80 minutes, but the threshold of
the aforementioned symptoms would be at a much lower CO2 level
at the end of five
Industry literature is similar.
The W.E. Kuriger Associates
web page titled "Carbon
Dioxide Fact Book," states that,
Several studies have
indicated that CO2 does not seriously impact human health until
levels reach approximately 15,000 ppm [7.5 mm
Hg]. … At extremely high levels, i.e., 30,000 ppm [15 mm Hg] (these
concentrations are usually never reached in a standard home), the
symptoms can include nausea, dizziness, mental depression, shaking,
visual disturbances and vomiting. At extremely high levels, loss
of consciousness may occur. … Finally, CO2 is an asphyxiate, a
condition in which an extreme decrease in the amount of oxygen
in the body, accompanied by an increase of carbon dioxide, leads
to loss of consciousness or death. Concentrations of 100,000 ppm
[50 mm Hg] or more of CO2 can produce unconsciousness or death.
And carbon dioxide is hardly the only physiological concern.
One would probably pass out from heat exhaustion before he passed
out from exposure to high carbon dioxide concentrations.
probably not a bad assumption to consider the system adiabatic
(no heat transfer — there would be very little heat transfer via
conduction, which is the only mechanism for heat transfer to the
environment in this scenario), and considering the thermal capacitance
of the subject (the thermal capacitance of the surrounding air
is only about 1% of that of the subject), suffice to say that the
subject would have very serious core temperature problems long
before five hours time (a three, four degree elevation per hour?)
within about ten to fifteen minutes after being in this enclosure
the air would
become saturated, that is, 100% relative humidity
(and condensate would start forming on the plastic). As the air
temperature and humidity increases (deteriorating the mechanisms
for rejecting the subject’s metabolic heat), and carbon dioxide
levels increase, and as oxygen is depleted (at the end of five
hours, at 800 BTU/hr the subject would be at an altitude equivalency
of ~19,000 feet (0.47 atm.), at 600 BTU/hr ~14,000 feet (0.60
atm.)), his metabolic rate will increase, in turn increasing the
metabolic heat and perspired and respired water vapor he generates,
creating a vicious cycle.
And, of course, children and elderly can withstand much less of
this kind of environment than adults.
Perhaps the worst aspect of the dissemination of this information
is that the balance of the press, including network news broadcasters, didn’t
even mention a time limit at all.
Other aspects of the
OHD statement are very odd — how many folks are wealthy enough
to have an inside room with no windows (other than a closet,
which would, according to their recommendations, only
be sufficient for one person)?
And plastic sheeting?
That’s awfully vague. Surely there are permeability
and robustness issues here. The
Washington Post reported that in a local D.C. hardware
store "plastic dropcloths were being evaluated with one aim
in mind: Would they work to seal a room?" Good question, but
Considering that only
a very tiny proportion of the population (and obviously no one
at the Office of Homeland Security) are trained
to make these calculations and decisions, and remembering that
a significant portion of the population doesn’t know their "right
hand from their left," may God bless them, the instructions
from the OHD are cause for very serious concern.
So please give
this wide circulation — there is a high
likelihood that there are plenty of folks already out there
sitting in an enclosure that they believe to be safe, unknowingly
endangering the lives of themselves and their children.
Brian Dunaway [send him mail] is a chemical engineer and a native Texan.