We know about CO — is HCN really that dangerous? Here are some quotes that tell the story;
“Exposure to smaller concentrations can initially cause respiratory activation — manifested by rapid breathing and tachycardia — in an attempt to compensate for lack of oxygen. Early manifestations include headache, anxiety, blurry vision and loss of judgment. As cyanide accumulates further, signs and symptoms of poisoning reflect the effects of oxygen deprivation on the heart and brain. These include cardiac dysrhythmias, seizure, coma and death. The time between exposure and incapacitation or death is typically minutes, but varies depending on the concentration of cyanide and other toxicants.” — Obrien, DJ, Walsh, DW, Cyanide and Smoke Inhalation, 2010
“Not all HCN and CO related fatalities are caused by asphyxiation. Many cardiac related fatalities that we’re experiencing may very well be related to CO and HCN exposures over time.” — Todd Shoebridge, Carbon Monoxide and Hydrogen Cyanide Make Today’s Fires More Dangerous, Firefighter Nation, Feb 14, 2012.
“Another under appreciated effect of exposure is the death of individual cells. Even if the entire organism is not killed by a given exposure, such exposures can kill individual cells in an organism. The cells most susceptible to this effect are those in the heart and brain. As time goes on, the cumulative effects of such cell death at repeated exposures can result in chronic heart and nervous system disease.”
— Jean Marie McMahon, MD in Smoke Cyanide and Carbon Monoxide: The Toxic Twins of Smoke Inhalation, Cyanide Poisoning Treatment Coalition, 2009.
Is HCN really that prevalent? Again, here’s what the experts have to say;
A burn study sponsored by the Fire Smoke Coalition and Tarrant County College, Fort Worth, Texas in March of 2011 found significant levels of HCN were evident in open-air sampling of an outdoor burn. The highest levels were recorded at incipient start of fire and smoke production and during the smoldering period as the fire wound down but were evident in harmful amounts throughout the burn and after. HCN was also found present in areas there was no smoke.
An eight-month study in which monitoring for CO and HCN at fire calls responded to by the Columbia, SC Fire department was conducted in 2008. It resulted in air monitoring measurement results from approximately 40 structure fires. It found “staggeringly high HCN levels at almost every scene.” Worst offenders for HCN production in that study were; “Pot on a stove/cooking fires (average small kitchen fire produced 75 ppm of HCN), car fires, dumpster fires and in overhaul operations. That study resulted in writing an SOG to address the problem, which details the use of PPE, SCBA and metering in every fire response. That SOG is being shared and is available by online search.
We can’t afford to relax when the smoke is gone. Both gases are long lived and not easy to break up so they tend to be present in dangerous amounts for some time after more volatile gases have dissipated and the active fire and the smoke is gone. That creates the need to keep PPE and SCBA equipment intact until metering can show neither HCN nor CO are present well after the smoke is gone. It’s important to note studies have shown that while frequently found in the same places the presence of CO or HCN doesn’t necessarily predict the presence of the other.
The soot and particulate matter we get covered with also present a danger. Lightly hosing off your outer gear should be a standard practice — especially before going into a rehab or other “clean” environment. Be aware that a person being rescued from a fire or to whom you are providing medical services may be off-gassing an unacceptable amount of HCN that has been absorbed into the soot and particulate matter covering them — or even from their clothing and skin.
How long after a fire do we need to be concerned? Only monitoring can tell you. A firefighter recently shared they found only CO in an apartment building after the fire was out but found HCN in the next four adjacent apartments. HCN is very stable. While CO breaks down eventually to become CO2, HCN needs to be washed or blown away— it doesn’t break down. Many materials including our skin, from which it continues to off-gas for some time after the fire and smoke are gone, also readily absorb it.
How much is too much? The numbers for acceptable exposure keep coming down as scientists gain more knowledge about CO and HCN but the amount of HCN that can cause harm is very low. We also have to consider that when combined with CO both gases are more dangerous. The current Short Term Exposure limit (STEL) recommended by NIOSH is 4.7ppm. This is also the ceiling limit of exposure recommended by the American Conference of Industrial Hygienists. OSHA still uses 10ppm as their short term exposure limit but EPA lists 10ppm as creating possible adverse medical impacts in as little as 30 minutes. HCN is estimated to be 26 to 35 times more toxic than CO.
There is a significant perimeter around an active fire that is not safe. The only way to know you are outside the perimeter of danger is to use air monitors. Live air sampling is the only safe way to pick a spot to set up command, EMS, rehab, etc. Continuous monitoring is the only way to know it continues to be safe.
We need to address this increased risk! Metering and using SCBA and PPE that limits the exposure of eyes and skin should be considered a minimum while working in and around any active fire, see Air Management (NFPA 1404). Atmospheric monitoring to determine when the air is safe to doff SCBA should include HCN. Air monitoring should be used to be sure areas set up for rehab, command and other operations are outside — and stay outside the perimeter of danger for those gases at any active fire. Only metering can confirm pump operators and others near an active fire are safe. We need to be aware that off-gassing from gear worn into a fire or victims rescued from an active fire may put you in danger. The bottom line is the only way to assure your crews safety, as well as your own is through constant air monitoring any time you are out of SCBA and PPE at any active fire scene and on into overhaul, clean up and investigation.
Promote standard operating guidelines (SOGs or SOPs) for your department if yours doesn’t already address these two very dangerous “toxic twins” (CO and HCN). One resource is an organization called the Fire Smoke Coalition. They offer web-based education, training programs — even an “ask the expert” service. They are available at www.FireSmoke.org.
There are some new technologies available in monitors. Our company has developed an HCN monitor that does not need to be calibrated and offers several years of warranted service. There are also several brands of HCN detectors as standalone devices or in combination with other gases that can be considered.
Knowledge regarding HCN is relatively new but it is compelling and ignoring the inherent danger it presents has the potential to shorten our lives. Knowledge is your basic defense. Learn more at the conferences, through the Fire Smoke Coalition, NFPA and others. Make sure your SCBA and PPE equipment is intact and up to date. Check into monitoring devices to protect yourself and your team. Your successful and long life may depend on it!