Friday, June 29, 2012

Burning Plastic Can Kill You

Just as a PSA-- a firefighter friend of mine was recently hospitalized for several days after responding to a fire and unknowingly inhaling hydrogen cyanide (HCN). The 'fire' was a plastic dish that an elderly woman had mistakenly put on a stove, and which melted, ignited, and gave off hydrogen cyanide. It wasn't much of a mess but it was still enough to almost kill someone. DO NOT BURN OR MELT PLASTIC.

You can also take this as a good reason to rationalize the use of plastics on the whole.

Everyone knows fires contain lots of things that are dangerous to breathe-- carbon monoxide, smoke, too-hot air, etc.  HCN poisoning is rapidly becoming a major concern for firefighters; a lot of good people --residents, neighbors, and firefighters alike-- have been sent to the hospital over the last few years with HCN poisoning.

With the increased use of plastic in the last couple decades, particularly in building materials themselves (PVC pipe, plastic-based carpet, vinyl tile) fires are actually becoming even more hazardous than they used to be, since the air in and near the buildings is saturated with toxic (and I MEAN toxic) vapors,  fumes, and particulates.(footnote 1)  This is one reason SCBA tanks and full-face respirators have become standard turnout equipment for fire crews rather than specialty kit, and why departments able to afford them in these days of eagle-squeezing budgets are issuing HCN alarms to their first responders.

During the 2003 Station Nightclub fire in Providence, Rhode Island, which killed 100 people-- and which my brother survived, may any gods who might be listening be thanked-- the fire generated enough carbon monoxide and hydrogen cyanide to turn the place into a gas chamber in NINETY SECONDS.(footnote 2)
Building materials or plastic products don't typically contain HCN itself (unless, as a remote possibility, as a dye) but hydrogen cyanide itself is very flammable and solid HCN will probably burn to nothing before it can become a hazard, if nothing aerosolizes or evolves it to a gas.

The atmospheric problems are created when the compound forms as a combustion byproduct, e.g. the vinyl component in polyvinyl chloride (PVC) reacts with the nitrogen in the atmosphere or another nitrogen compound. The vinyl chloride donates the hydrogen and carbon, the ammonia donates the nitrogen and more hydrogen, and the fire provides the energy to fuel the reaction.   A related reaction can also generate hydrochloric acid (HCL) gas, using hydrogen and the chlorine component.

This article from Fire  sums up some of the hazards of HCN in the atmosphere.  You can get dangerous quantities of HCN from even very small and apparently insignificant incidents-- case in point, what happened to my friend.  A plastic dish on a stove almost killed him.

If significant concentrations are inhaled, it can be extremely dangerous within very short time windows, since HCN poisoning shuts down cell respiration.  HCN poisoning Initial symptoms of cyanide poisoning can occur from exposure to 20 to 40 ppm, including weakness, headache, mental confusion, vertigo, fatigue, anxiety, shortness of breath, and sometimes nausea and vomiting (your body is trying to detox itself). The mental weakness is a killer because it hinders your ability to recognize the problem and escape.
10 minutes' exposure in an atmosphere of ~300 milligrams per cubic meter of air will kill you.  2200 milligrams per cubic meter will kill you in ONE minute.   HCN gas has a bitter almond odor with an air odor threshold concentration of about half a part per million.  Unfortunately, your sense of smell won't save you because if there's burning plastic around, it'll stink enough to mask the HCN odor.

The current Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for hydrogen cyanide is 11 mg per cubic meter as an 8-hour time-weighted average (TWA) concentration.
The American Conference of Governmental Industrial Hygienists (ACGIH) has assigned hydrogen cyanide a not-to-be-exceeded ceiling limit value of 4.7 ppm (5 mg/cubic meter of air. NOTE THE DIFFERENCE. (Footnote 3)

The standard treatment (in the US, at any rate) is a small inhaled dose of amyl nitrite, followed by intravenous sodium nitrite, followed by intravenous sodium thiosulfate, usually in conjunction with supplied oxygen to keep the cell respiration and the lungs going and to keep off cyanosis or hypoxia.

Hydrogen cyanide IS naturally occurring and is found in some foods, e.g. apple seeds  and almonds, but when ingested and digested it is harmless, unless you have chronic exposures like people in Africa who eat lots of cassava roots for thirty years and don't get enough Vitamin B.  Ferrocyanide compounds are very stable and can be consumed safely-- they don't degrade, get metabolized, or bioaccumulate in the human body, they just go out the other end.

Be safe, everyone.


Footnote 1 - I can't stop myself from being pedantic here.  Vapors and fumes are different things.  Vapors are the gas form of liquids; a fume is very small airborne particles that have cooled from a very hot vapor or aerosolized solid (usually from metal, e.g. the workplace hazard 'metal fume fever'). The difference between a vapor and a fume is important when designing ventilation systems or selecting respirators.

Footnote 2 - I use the gas chamber term with all seriousness, because the Zyklon B gas used in the gas chambers Nazi death camps like Auschwitz was essentially HCN adsorbed to a carrier, and which had been a commercial pesticide before the Nazis decided that certain racial elements were pests.

Footnote 3 - Lemme just note here-- as a professional working in the environmental industry, it is my very considered opinion that most OSHA standards are unscientific and indefensible crap, based on a limited set of knowledge that mostly hasn't been updated since the 1970s, and that they are not sufficiently protective... and when I say that I mean protective of ME and my coworkers.  Unless faced with a regulatory requirement I can't argue my way past, I use the ACGIH standards because they have an additional thirty years' worth of research and toxicology experience behind them, and as a result of that, are usually much more stringent than OSHA's.  At one point about fifteen years ago, OSHA tried to adopt the ACGIH's standards as OSHA's own, but the legal people and ACGIH (who weren't thrilled with the idea) shot the idea down and told OSHA they couldn't copy the product of a private organization, and to do their own damn homework.

1 comment:

unstrung said...

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