By Jetty Middelkoop
In December 2003, after a fire in a cacao beans warehouse in Wormer (a Province in North Holland, the Netherlands), it happened again. Newspapers quickly reported that the whole area near the burning warehouse had been evacuated due to high levels of hydrogen cyanide and carbon monoxide, causing serious alert. True, the area had indeed been evacuated as a precaution. But not due to excessively high amounts of hydrogen cyanide or carbon monoxide, but because of the expectation of a long time exposure to a smelly gas. Air monitoring had shown the presence of hydrogen cyanide and carbon monoxide. But a peak value of 0.4 parts per million (ppm) hydrogen cyanide can hardly be called in excess of safe exposure levels--the Permissible Exposure Limit (OSHA PEL) is 10 ppm, the Short term Exposure Limit (NIOSH STEL) is 4.7 ppm! Is this is an example where the media disseminated the "urban legend" that a cacao beans fire produces large clouds of hydrogen cyanide? In this article, I hope to debunk this misconception.
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| Fig. 1 A cacao beans fire | Fig. 2 Roasted cacao beans (cocoa beans) |
Hydrogen cyanide (HCN) is the gaseous form of the liquid cyanic acid. It is an extremely flammable and extremely poisonous compound. The literature describes its smell as characteristic bitter almonds-like odor. (I wonder how many people know how bitter almonds smell like.) At room temperature, hydrogen cyanide is a liquid, which evaporates very easily. That is why a hydrogen cyanide leak is so dangerous: it quickly develops into gas, which is very detrimental when inhaled. The liquid form is a sure way to commit suicide quickly. Breaking a glass capsule filled with this between one's teeth is a suicide method not limited to murder mystery books. Hydrogen cyanide is not only dangerous when swallowed or inhaled, but also through skin exposure. Because of its fatal effects in all exposure routes, responders to hydrogen cyanide leaks should wear personal protective equipment that provides the highest degree of protection. Hydrogen cyanide completely dissolves in water, and thus it can be easily precipitated with a water spray in case of a release.
Where does the name "cyanide" come from?
Its name does not come from its color. Hydrogen cyanide is colorless--not cyan.
Nor is it true that persons exposed to it turn blue. What happens: their
lips and nails may turn a bit blue-ish, but their skin will turn red. These symptoms
are caused by an excess of oxygen in the blood--and oxygen rich blood is red.
The cyanide (CN) in the hydrogen cyanide binds to iron, manganese and copper in
important enzymes in the body to develop "iron blue"- a blue
colored bond between cyanide and iron, manganese or copper. Hence, the name
"cyanide".
In case of cyanide poisoning, there is enough oxygen in the blood, but the body is unable to use it. The enzymes that should have delivered it to all kinds of energy processes in the body cells have ceased to work. It is like starving in a pile of food. As the cells are no longer supplied with oxygen, they die quickly. Symptoms of cyanide poisoning are: headache, dizziness, nausea, vomiting, painful spasms, fast breathing, anxiety, unconsciousness, coma and death. A concentration of 35 ppm leads to a slight irritation of the upper respiratory track and mucous membranes. A concentration of 100 ppm leads to unconsciousness and heavy spasms, and the victim's breath has a strong smell of bitter almonds. If victims do not receive immediate medical care, they will die within half an hour. A concentration of 300 ppm will kill a victim within minutes.
In nature. Cyanide is found in many vegetables. I even read somewhere that 10% of all the plants on earth contain cyanide compounds. I think this is a bit exaggerated, but a short search on internet provided an impressive list of natural products which contain cyanide compounds, for example: tobacco (smoke), heated spinach, fresh bamboo shoots, cassava, sago, lima beans, line seed, peanuts, coffee beans, apricot seeds, almond seeds (especially in the bitter type, less in the sweet), the seeds of apple, cherry, grape and peach, beech nuts, walnuts, mountain-ash berry, Yew, bird cherry, rubber tree, eucalyptus leaf, clover and some mushrooms.
But where in these products is the cyanide located? Well, mostly in certain sugar compounds, called glycosides, and there are many kinds of these to be found.. Most of them are not harmful or even useful, like saponin in the Soapwort flower plant (Saponaria officinalis). However, there are three groups of glycosides which can be very harmful. These are:
Plant cells do not contain pure cyanide, but compounds in which cyanide is incorporated. The cells also contain an enzyme which is capable of disconnecting the cyanide from the glycoside. In the intact cell, the cyanide glycoside and the enzyme do not come in contact with each other. When plant cells are damaged, they can come in contact and the cyanides are then released. Animal enzymes, too, can release cyanide from the cyanide glycosides. Plants use cyanide glycosides as protection against gluttony. An animal which starts eating such a plant is either deterred by the bitter taste, or eats on and becomes ill and/or dies. The amount of cyanide glycosides in a plant depends very strongly on the species, age and environmental factors, such as frost or drought.
In non-ruminating mammals like humans who have acid stomach fluid, small amounts of cyanide that enter the body with food are converted into less damaging compounds. Ruminators such as cows and sheep hardly have any acids in their stomach fluids. As a result, their stomachs cannot break down cyanides. For this reason, the amount of cyanide compounds in animal feed is closely monitored. The liver, too, can turn limited amounts of cyanides into the less damaging thiocyanate at low intake rates. All animals get in trouble when their intake of cyanide is higher than their break down rate.
In manmade products. Cyanide is used in rodenticides and insecticides (gassing). It is also used in the production of artificial materials such as insulation material (polyurethane foam), clothes and home textiles (polyamides, polyacrylic nitril, acryl). It can be found in galvanizing baths and even in certain food additives. High concentrations of cyanides can be found in the soil and in cesspools around old gas factories (factories that make gas from coal).
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| Fig. 3 Cassava is an example of a vegetable that contains cyanide glycoside. The threedouble bonded Nitrogen on the right with its adjoining Carbon (not visible, it is positioned on the "crossroads") can be set loose and turned into HCN. |
Cyanide glycosides can be rendered harmless by heating or flushing with water for quite some time. Some jungle tribes take the cyanide out of their sago flour by treading it for a long time while repeatedly throwing water over it. Most of the cyanide will then be flushed away with the "tread-water". Long time storage can also reduce the amount of cyanide. This is what happens with walnuts, beechnuts and peanuts. This explains why one can eat many more dried nuts than fresh nuts before getting symptoms of cyanide poisoning. Finally, many cyanide-containing food products are made safe for eating by boiling them and pouring off the water.
When products that contain cyanide are burnt, the release of cyanide is enhanced. If the burning product is of herbal origin, this will not lead to a cloud of hydrogen cyanide -- only to traces of hydrogen cyanide in the smoke. The reason for this is that plants only contain a limited percentage of cyanide glycosides -- plants need to do much more than just frighten off potential eaters, and for all these other processes the plants need many more other compounds. Based on this, I hope never to read in the media again that a cacao beans fire lead to an enormous hydrogen cyanide plume! Or will the media in the future also pay attention to hydrogen cyanide risks in case of a taxus hedge fire, a fire in a nut shop or in a storage of cattle fodder? For manmade products, it can be quite a different story. These products normally only serve one goal, and thus they can contain a much larger percentage of cyanide compounds than plants can. If polyurethane foam is burnt for example, you should certainly reckon with a high concentration of hydrogen cyanide in the smoke depending on the temperature of the fire! An example of this is the fire that broke out several years ago on the airport of Düsseldorf (Germany). Sixteen people died then. The high concentration of hydrogen cyanide released when the ceiling insulation burned contributed to the death of several of these victims.
Finally, not only cyanide glycosides can lead to the production of hydrogen cyanide when burned. Also other chemical compounds that contain carbon (C) and nitrogen (N), can partly be turned into hydrogen cyanide. This is certainly true for amines and amides. That is why you can get hydrogen cyanide from the burning of wool. But this is another subject, which I will not deal with here, or my article would grow much too long. And besides, that would also bring me too far away from my primary subject: a cacao beans fire. So if you are interested in this new subject, just contact me! Always at your service - and if I do not know the answer directly, I will look it up.
More info
Emergency Response Card for Hydrogen Cyanide (PDF)
| About the Author | |
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Jetty Middelkoop is a chemical advisor for the fire department of Amsterdam, The Netherlands. Part of her spare time she spends as a volunteer fire fighter in her home town. Before becoming a chemical advisor, she was head of the Radiological Protection Service of the Dutch Ministry of Defense for several years. Ever since, Class 7 is her favorite Dangerous Goods Hazard Class. Dangerous goods not only are a means to earn a living for her, they are also her hobby. She likes to spread the knowledge of dangerous goods as wide as possible. She collects pictures of dangerous goods accidents to use them in her lectures. She welcomes suggestions for articles and accident pictures. Email: middelkj@brandweer.amsterdam.nl |