Application Note AP-238
Toxic Twins (HCN & CO) in FIRE OVERHAUL
Barriers to change within the firefighting community include a
“smoke eater” culture where many firefighters shun using safety
equipment, such as gas-detection instruments, or keeping their
breathing apparatus on for longer periods while on-scene or during
fire-overhaul operations. Many firefighters consider smoke-filled
uniforms or soot-covered faces a badge of honor, and not the telltale
signs of exposure to dangerous gases and particulates that are
known carcinogens.
OVERVIEW
Today, with the proliferation of plastics and synthetic
polymer building materials, the risk of a significant
hydrogen cyanide (HCN)-poisoning component in
victims of enclosed-space fire smoke inhalation has
increased.1
Death by smoke inhalation has been known since antiquity. In some
ancient conflicts, captured enemy soldiers were executed by placing
them in cages over fires fueled with green wood. Although CO
(carbon monoxide) poisoning as a cause of serious poisoning or
death in smoke inhalation victims has long been recognized, it was
only in the 1960s to 1980s when the potential for a significant HCNpoisoning component contributing to or, in some cases, being the
major cause of serious poisoning or fatality in smoke inhalation
victims began to be recognized.2
1
Alarie Y. Toxicity of fire smoke. Crit Rev Toxicol. 2002;32:259-289.
Stefanidou M, Athanaselis, S. Toxicological aspects of fire. Vet Human Toxicol.
2004;46:196-199.
2
Wetherell JR. The occurrence of cyanide in the blood of fire victims. Journal of
Forensic Science. 1966;11:167-173.
Birky MM, Clarke FB. Inhalation of toxic product products from fires. Bull NY
Academic Med. 1981;57:997-1013.
Clark CJ, Campbell D, Reid WH. Blood carboxyhaemoglobin and cyanide levels in
fire survivors. Lancet. 1981;1:1332-1335.
Jones J, McMullen MJ, Dougherty J. Toxic smoke inhalation: Cyanide poisoning in
fire victims. Amer J Emerg Med. 1987;5:318-321.
RAE Systems by Honeywell 877-723-2878
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One of the largest studies, conducted by the University of Cincinnati
(UC), reveals that firefighters face increased risk for certain cancers.
The study analyzed data on 110,000 mostly fulltime firefighters from
information culled from 32 previously published scientific reports in
order to correlate cancer and health risks for the profession.
“We believe there’s a direct correlation between the chemical
exposures firefighters experience on the job and their increased risk
for cancer,” says Grace LeMasters, PhD., a co-author of the study
and professor of epidemiology and biostatistics at UC.3
The study found that firefighters are twice as likely to develop
testicular cancer and have higher rates of non-Hodgkin’s lymphoma
and prostate cancer than non-firefighters, and confirmed that
firefighters are at greater risk for multiple myeloma, a cancer that
begins in the plasma cells in bone marrow.
These and other studies reveal new, blunt warnings regarding the
health dangers of fire smoke, as well as the danger of breathing fire
smoke toxins in the fire overhaul process.
3
News Release from UC Health News, University of Cincinnati (10 Nov 2006)
“Firefighters Face Increased Risk for Certain Cancers.” Release on findings
reported in the Journal of Occupational and Environmental Medicine about a study
by Grace LeMasters, PhD, Ash Genaidy, PhD, and James Lockey, MD.
1
Application Note AP-238
OVERHAUL AND HIGH HCN LEVELS
Overhauling is the late stage in a fire-suppression process
during which the burned area is carefully examined for remaining
sources of heat that may re-kindle the fire. This activity often
coincides with salvage operations to prevent further loss to
structures or their contents, as well as fire-cause determination
and preservation of evidence.
During this stage of firefighting, there is no fire and little to no
smoke in the environment, and firefighters are likely to work
“barefaced” (remove their self-contained breathing apparatus,
or SCBA).
In the overhaul process, the smoldering fumes of a recently
doused fire can be filled with dangerous and toxic gases and
vapors that threaten the life and health of firefighters involved in
the fire overhaul operations. As firefighters sift through piles of
materials of take down rafters and walls, poisonous gases such
as CO, sulfur dioxide (SO2), hydrogen cyanide (HCN), nitrogen
oxides (NO and NO2), formaldehyde, benzene and phosgene
are released from the materials or are churned and become
airborne particles that can be inhaled.
Direct exposure to these dangerous aerosols and particles
during fire overhaul present a real risk for immediate harm or
acute and chronic health problems, including heart failure and
cancer.
HCN & CO, THE “TOXIC TWINS”
All firefighters are aware that where there’s smoke, there’s CO.
But more recent studies have revealed that high HCN
concentrations are be found in fire smoke. Even worse,
firefighters are routinely exposed to dangerous levels of cyanide
at fires without realizing it.4
A 2007 NIOSH publication, "Preventing Fire Fighter Fatalities
Due to Heart Attacks and Other Sudden Cardiovascular Events,"
noted that HCN is formed by incomplete combustion of any
substance that contains carbon and nitrogen (both naturally
occurring and synthetic) and that airborne concentrations
exceeding those of established occupational exposure limits
occur in structural fires. It also acknowledges that HCN impairs
cellular use of oxygen, which can result in cellular hypoxia and a
variety of cardiac manifestations.5
HCN is created when materials such as laminates, synthetics,
foams, plastics, and wood burn. Many of these materials are
found in furniture and upholstery in homes and offices, and as a
result, the smoke of a typical residential or office fire today is
more toxic than ever.
Cyanide is an invisible gas that cannot be detected by the color
or the amount of smoke emitted by a fire. It can only be detected
through metering and monitoring. Exposure to large amounts of
cyanide can cause convulsions, unconsciousness or rapid
death. CO, also only detectable using a sensor device, can
cause tissue hypoxia when inhaled, which prevents the blood
from carrying sufficient oxygen, and can cause dizziness,
nausea, headache and, at higher concentrations, convulsions,
tachycardia and death. When inhaled together, the so-called
“toxic twins” can have a synergistic effect, experts say, causing
even more harm.i
4
http://inletemergencyservices.files.wordpress.com/2010/07/hydrogencyanide1.pdf
Jankovic J, Jones W, Burkhart J, et al. Environmental study of firefighters. Ann
Occup Hyg. 1991;35:581-602.
Brandt-Rauf PW, Fallon LF, Tarantini T, et al. The health hazards of fire fighters:
exposure assessment. Br J Ind Med. 1988;45:606-612.
Gold A, Burgess WA, Clougherty EV. Exposure of firefighters to toxic air
contaminants. Am Ind Hyg Assoc J. 1978;39:534-539.
Purser DA, Rimshaw P, Berrill KR. Intoxication by cyanide in fires: A study in
monkeys using polyacrylonitrile. Arch Environ Health. 1984;39:394-400.
Breen PH, Isserles S, Westley J, et al. Combined carbon monoxide and cyanide
poisoning: A place for treatment? Anesth Analg. 1995;80:671-677.
5
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2
Application Note AP-238
As part of a composition of materials, HCN is relatively safe.
But when the material is heated, it becomes a concern:
• HCN is 35 times more toxic than CO.
• HCN can enter the body by absorption, inhalation or
ingestion and targets the heart and brain.
• HCN often incapacitates the victim within a short period
of time.
• HCN is again produced after the flame is out and the
materials continue to off-gas. In other words, HCN may
be present even if smoke is not visible.
HEALTH EFFECTS OF TOXIC TWINS (CO AND HCN):
HCN and CO in fire smoke are at least additive toxicants and
may indeed be synergistic (having greater toxicity than predicted
from the concentrations of either toxicant alone). Clinically, this
was observed in smoke inhalation victims in the classic Paris,
France, study, where some fatalities were associated with blood
CO and HCN concentrations, neither of which were predicted to
cause death.6
CO attaches to the oxygen molecules in the body, preventing
oxygen from reaching vital organs, which causes suffocation
after a short period of time.
HCN, on the other hand, targets the central nervous system,
cardiovascular system, thyroid and the blood, causing firefighters
to become disoriented and agitated, and to lose focus on the
task at hand. Some have even fought against colleagues
attempting to rescue them. Others have run away from their
rescuers, and at times, run deeper toward the seat of the fire
until they become physically exhausted and overcome by smoke
or thermal injuries. This is why you hear of so many firefighters
who become lost and disoriented, and/or take off their masks
once they’re out of air.
Acute exposure to HCN can result in symptoms such as
weakness, headache, confusion, vertigo, dyspnea and,
occasionally, nausea and vomiting. Respiratory rate and depth
usually increase at the onset, and eventually cause the victim
to gasp for breath. Coma and convulsions occur in some cases.
If a firefighter gets to the point where they lose color and become
ashen, or cyanosis is present, it usually means that respiration
has ceased or has been inadequate for an extended amount
of time.
SCBA is a firefighter's best friend when it comes to protecting
against HCN. For years, wearing an SCBA was optional or
considered taboo. Nowadays, in most departments, it is
mandatory, but a question still remains: When is it appropriate
to remove the SCBA?
After the flames are out, HCN might still be present, but we can't
see it or test for it. Should SCBA be worn until the atmosphere is
completely free of HCN? The answer is yes, but how do
firefighters know if or when the air is clean, since the four most
commonly used gas detectors generally do not have an HCN
sensor in them?
SOLUTION: TREAT A FIREGROUND LIKE HAZMAT
Because a growing number of firefighting experts consider
structural fires HazMat hot spots, calls for greater teamwork
between HazMat and firefighters during common structural fires
are increasing. Many departments now have a standard
operating procedure (SOP) for using gas-detection equipment
during structural fires, including using standalone instruments or
wireless systems that allow on-scene agencies with compatible
systems to share data.7
While fire, HazMat and special operations teams utilize a
variety of detection instruments today, wireless gas detectors
offer key benefits to fire-service agencies. These include fast
deployments, centralized command monitoring and data
sharing with other on-scene units or off-site experts
http://www.firesmoke.org/wp-
Levin BC, Paabo M, Gurman JL, et al. Effects of exposure to single or multiple
combination of the predominant toxic gases and low oxygen atmospheres
produced in fires. Fundam Appl Toxicol. 1987;9:236-250.
7
Pitt BR, Radford EP, Gurtner GH, et al. Interaction of carbon monoxide and
cyanide on cerebral metabolism and circulation. Arch Environ Health. 1979;34:345349.
RAE Systems book “Wirelessly Networked Chemical & Radiation Detection
Systems: Essential Technologies and Applications for Increased Safety in
Continuous Gas and Radiation Monitoring.” 2012 http://www.amazon.com
6
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content/uploads/2012/07/SacramentoOverhaulSOG.pdf
3
Application Note AP-238
QRAE 3: VERSATILE 4-GAS OVERHAUL MONITOR
The RAE Systems QRAE 3 is an
affordable, personal protection gas
monitor developed by RAE Systems
with a dedicated configuration for
fire overhaul applications, with CO
and HCN sensors (model
PGM2530).
This model is available either with
an integrated pump (as shown in the
picture) or as a natural diffusion
model. QRAE 3 also provides the
following features: Datalogging
capability, policy enforcement
features and man down alarm capability with real-time remote
wireless notification.
QRAE 3 (model PGM-2530) allows firefighters to be aware of risks
in their environment by measuring the presence of CO and HCN. Its
unique wireless option provides extra safety when working in
extremely dangerous environments, as real-time data are available
on EchoView Host or on a computer running ProRAE GuardianTM
software. This means that firefighters in the safe area can monitor
their peers and work in concert with them to provide enhanced
situational awareness and support.
CROSS-SENSITIVITY
Due to the chemical make-up of many manufactured materials,
today’s fires reach hotter temperatures faster, flashovers occur
more rapidly and the resulting smoke is much more toxic. Other
chemicals that can also be found in fire smokes include carbon
monoxide, nitrogen dioxide, polynuclear aromatic hydrocarbons,
formaldehyde, acid gases, phosgene, benzene and dioxins.
In short, the smoke is a highly complex mixture of solids, fumes
and gases that are produced due to thermal decomposition
of materials, or in other words, are produced when these
materials burn.
RAE Systems by Honeywell 877-723-2878
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It is really important to understand potential cross-sensitivity
phenomena that can occur while using electrochemical sensor
technology. RAE Systems has characterized the cross-sensitivity
by performing tests on its sensors. The following table shows
cross-sensitivity due to chemicals found in this particular
application (fire overhaul). For other cross-sensitivity values on
CO and HCN sensors, refer to RAE Systems Technical Note
TN-114.
CO Sensor Cross-Sensitivity From Potential Chemicals in
Fire Overhaul Applications
Compound
Benzene
Hydrogen chloride
Ammonia
Naphthalene
Sulfur dioxide
Nitrogen monoxide
Nitrogen dioxide
Vinyl chloride
Hydrogen sulfide
Acrylonitrile
Formic acid
Acetaldehyde
Toluene
n-Heptane
Glutaraldehyde
Formaldehyde
Hydrogen cyanide
Hydrogen fluoride
Hydrogen bromide
Isocynates
Acrolein
Concentration
(ppm)
5
10
35
125
5
35
5
10
15
10
100
50
20
100
20
5
10
15
15
0.13
20
Output
(ppm
equivalent)
0
0
0
0
0
-4 ~ 0
0
0
0
0
0
0
0
0
0
0
0
0*
0*
0*
0*
*Notes: Estimated from hydrogen chloride, acrylonitrile and
glutaraldehyde, respectively.
CO sensors were tested under the following conditions: ambient
temperature 25˚ C with a relative humidity of 63%.
4
Application Note AP-238
HCN Sensor Cross-Sensitivity From Potential Chemicals in Fire Overhaul Applications
Compound
Benzene
Gasoline
Formaldehyde (HCHO)
Hydrochloric Acid (HCl)
Ammonia (NH3)
Carbon Monoxide (CO)
Sulfur Dioxide (SO2)
Nitrogen Dioxide (NO2)
Nitric Oxide (NO)
Ethylene
Hydrogen Sulfide (H2S)
Vinyl Chloride
Acetaldehyde
Toluene
Acrylonitrile
Phosphine
Phosphine
Formic acid
Glutaraldehyde
Naphthalene
Hydrogen Bromide2
Hydrogen Fluoride3
Acrolein4
Isocyanates5
Concentration (ppm)
Output (ppm equivalent)
Cross-Sensitivity
5
100
5
15
35
300
5
5
35
100
15
10
100
10
20
5
100
100
20
1251
15
15
20
0.13
0
0
-0.7
0
0.5
0
1.5
-3
-1
0
30
0
0
0
0
9
181
0
0
0
0
0
0
~0
0%
0%
-14%
0%
1%
0%
30%
-60%
3%
0%
200%
0%
0%
0%
0%
181%
181%
0%
0%
0%
0%
0%
0%
~0%
*Notes: Unless otherwise specified, the ambient temperature is 20 ˚ C ±5˚ with a relative humidity of 50% to 85%.
Naphthalene is a white powder and volatile. Vapor pressure increases with temperature.
Based on theoretical estimation, at 25˚ C, about 125 ppm naphthalene can be emitted.
2 Estimated from HCl result.
3 Estimated from HCl result.
4 Estimated from glutaraldehyde and acrylonitrile result.
5 Estimated only. Based on theoretical estimation, methylene bisphenyl isocyanate is 0.13 ppm vapor saturation at 25˚ C.
1
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6
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