CHEMICAL DATA NOTEBOOK SERIES #57: CARBON MONOXIDE
HAZARDOUS MATERIALS
Carbon monoxide is a toxic, flammable, colorless, odorless, and tasteless gas. Available as a compressed gas or as a cryogenic liquid, it is commercially valuable, used to produce ethylene; hydroxy acids such as acetic acid and propionic acid and their esters; glycolic acid, methanol, and phosgene; and groups of chemicals such as acrylates, aldehydes, and isocyanates. It also is used to form metal catalysts valuable in organic synthesis, which makes possible the production of materials that were once only found in nature. In addition, it is used to reduce metal oxides to the pure metals or to metal carbides.
PROPERTIES
Carbon monoxide has a very wide flammable range of 12 percent to 75 percent in air and an ignition temperature of 1,128°F. It has a vapor density of 0.966, and its molecular weight is 28. It has a freezing point of — 340°F, has a boiling point of — 312.7°F, and is slightly soluble in water. Its molecular formula is CX).
HAZARDS
The most widely known (and feared) hazard of carbon monoxide is its toxicity. Approximately 85 percent of all deaths in fires occur from breathing toxic combustion products, and carbon monoxide is the principal toxicant in nearly all of these deaths. Carbon monoxide is produced during the incomplete combustion of any carbon-containing material. In every fire (outside rigidly controlled experimental small fires under strict laboratory conditions) carbon-containing materials are not completely burned. Therefore, for all practical purposes, every fire will produce carbon monoxide.
The amount of carbon monoxide produced depends on many factors. It is not a coincidence that these factors include the three legs of the fire triangle.
Fuel. Any material that burns with some difficulty will produce more carbon monoxide than a material that burns comparatively easily. Therefore, methyl alcohol will produce less carbon monoxide per unit burned than will benzene, a flammable liquid that has a relatively high ignition temperature (see Fire Engineering, September 1987 for methanol and October 1988 for benzene). It is also true that when a carbon-containing material burns and liberates great quantities of black smoke, greater quantities of carbon monoxide are liberated than if a “clean” burning carbon-containing substance is burned.
The chemical makeup of the fuel is most important in determining its burning characteristics. Charcoal, almost pure carbon, will burn considerably hotter than most common woods, which are made up mostly of cellulose, a naturally occurring polymer made up of carbon, hydrogen, and oxygen. It takes more heat input to ignite a piece of charcoal than it does to ignite an identical size piece of pine, but once ignited, the charcoal will burn hotter and produce more carbon monoxide than the pine.
The physical properties of the fuel are another consideration. Is the material in very large “pieces” that will be difficult to ignite and will burn relatively slow ly, or is it in the form of a finely divided powder, a vapor, or a gas? In the former case, carbon monoxide will be formed as combustion begins, and in the latter case an explosion will occur and the generation of carbon monoxide is not as critical as the destruction caused by the explosion.
Oxidizer. If the fire is fuel-regulated (there is plenty of oxygen or other oxidizer for the combustion process to proceed unhindered, as in a fire out in the open), smaller amounts of carbon monoxide will be formed than if the fire is oxygen-regulated (there is plenty of fuel to burn, but the amount of oxygen is restricted somewhat, as in a fire in an enclosure).
A word of caution is needed here: liven though there is less carbon monoxide formed in a fuel-regulated fire per unit of fuel consumed, there probably will be more fuel consumed (the fire will be bigger) and therefore a larger overall quantity of carbon monoxide may be formed than in the interior, oxygen-regulated fire. Remember that carbon monoxide is produced in every fire, and positivepressure. self-contained breathing apparatus is required at every fire. Also remember that SCBA is required during overhaul, where harmful gases in addition to carbon monoxide are generated during the smoldering of the remaining fuels.
Hent A rule of thumb, all else being equal (the fuel is the same and in the same form and size, and there is the same amount of oxygen available to support the combustion), is that the hotter the fire, the less carbon monoxide will be formed.
Carbon monoxide is extremely dangerous. Its TLV-TWA (threshold limit value-time weighted average) is 50 ppm (parts per million in air), its STEP (short-term exposure limit) is t()0 ppm, and its 1DI.H (immediately dangerous to life and health) is 1,500 ppm. These limits are established by the American Conference of Governmental Industrial Hygienists. OSHA has established a PEL (permissible exposure limit) of 35 ppm and a ceiling limit of 200 ppm. Since it is always best to be conservative when dealing with hazardous materials, observe the lower limits (PEL and ceiling).
Symptoms of carbon monoxide poisoning include confusion, dizziness, headaches, nausea, weakness of limbs, unconsciousness, and death. Exposure to carbon monoxide in the amount of 400 ppm (0.04 percent) over 2 to 3 hours or 600 ppm (0.06 percent) over 1 hour will cause headaches and discomfort. Exposure to 1,000 to 2,000 ppm (0.1 percent to 0.2 percent) will produce throbbing in the head in about 30 minutes; staggering in 90 minutes; and headaches, confusion, and nausea in 2 hours. Unconsciousness will result if exposed to 2,000 to 2,500 ppm (0.2 percent to 0.25 percent) for 30 minutes, and death will usually result in 1 hour at exposure levels of 4,000 ppm (0.4 percent). These numbers are only averages, and response to vary -ing levels of exposure depends on such human characteristics as age, state of health, presence of alcohol or drugs in the body, and recent accumulative exposures to carbon monoxide (as in firefighting). Certainly higher concentrations of carbon monoxide will produce the above results faster than the times given, and extremely high concentrations of carbon monoxide may prove fatal in minutes.
Toxicologists classify carbon monoxide as a blood asphyxiant. Normally red blood cells pick up oxygen in the lungs, travel through the circulatory system via the arteries, and exchange their oxygen for the carbon dioxide held as a waste product by the body cells. The blood cells then travel via the veins back to the lungs, where they give up carbon dioxide and pick up more oxygen for another trip to the body cells. Since blood cells have an affinity for carbon monoxide 200 to 300 times stronger than for oxygen, when one molecule of carbon monoxide is mixed with 200 to 300 molecules of oxygen in the lungs, the carbon monoxide rather than the oxygen will attach itself to the red blood cell. The red blood cell will travel through the body without exchanging oxygen for carbon dioxide. When the cell returns to the lungs it refuses to pick up fresh oxygen because of the attached carbon dioxide. It then starts another useless trip through the body. As brain cells become deprived of oxygen they are destroyed, and eventually death occurs unless the cycle can he broken.
IDENTIFICATION NUMBERS AND RATINGS
CAS
(Chemical Abstract Services)
630–08-0
STCC
(Standard Transportation Commodity Code)
4905709
RTECS
(Registry of Toxic Effects of Chemical Substances)
FG3500000
UN/NA
(United Nations/North America)
Compressed gas, 1016; cryogenic liquid, 9202
CHRIS
(Chemical Hazard Response Information System)
CMC
DOT
(U.S. Department of Transportation)
Flammable gas
NFPA 704 Rating
2-4-0
A relatively unknown property of carbon monoxide is its flammability, which reduces the amount of this toxic gas produced in a fire, fimergence responders might get into trouble if they treat compressed carbon monoxide as any other compressed gas and overlook its flammability.
A hazard of carbon monoxide in its cryogenic liquid form is that it exists at — 312.7°F. Serious damage will occur if the liquid contacts any body tissue. Hie liquid also will produce a tremendous amount of gas as it vaporizes.
NONFIRE SCENARIO
Carbon monoxide in its pressurized gaseous form is stored in cylinders. These cylinders should never be stored next to cylinders containing oxygen or any other oxidizer, and the storage area must be free of possible ignition sources. It also should be equipped with carbon monoxide detectors to warn of any leak. All carbon monoxide cylinders should be grounded when in use.
In any release of a hazardous material. notify the proper environmental authorities immediately. However, in a situation where a toxic gits such as carbon monoxide is being released, the damage to the environment will probably be very light, and the threat to human life will be significantly greater. Therefore, when approaching the incident scene, have evacuation procedures for all exposed persons in the immediate area in place. Approach from upwind and eliminate all possible ignition sources. Keep unnecessary personnel out of the area, and make sure personnel use SCBA.
Since the molecular weight of carbon monoxide is 28 (and the average molecular weight of air is 29), the resulting vapor density of the gas is very close to 1.0. Therefore, the carbon monoxide will not dramatically rise or fall in relation to air unless it is very cold (as in gas evolving from the cryogenic liquid form) or very warm (as in a container of compressed carbon monoxide that is being heated by conduction or radiation). In the case of the cryogenic liquid, the gas will act as if it were heavier than air (because it is at that temperature), and the hot gas will act as if it were lighter than air (again, because it is when hot). At ambient temperature the carbon monoxide will neither rise nor fall but will mix evenly with the air.
If a cryogenic container is leaking liquid carbon monoxide, the liquid will slowly release great quantities of gas as it warms up above its boiling point. If the cryogenic container is leaking above the liquid level, gas will evolve, but more slowly than if the liquid were spilled. This is because cryogenic liquids are self-insulating and do not contain very much energy to promote evaporation. If a container of compressed gas is leaking, far more carbon monoxide will be released in a given amount of time because of the pressure under which the gas was contained. Notify the shipper, the manufacturer, and the buyer of the product immediately of any release. Their aid in mitigation may prove invaluable.
The release of carbon monoxide in any form is quite dangerous to human (and animal) life, so evacuate as far downw ind as possible. High-pressure water fog or spray may be used near the leak to disperse the vapors.
If carbon monoxide liquid is leaking from a container, prevent it from entering waterways. Although the cryogenic liquid will boil as it enters the water, enough carbon monoxide may dissolve to endanger aquatic life. There is also danger that water contaminated with the toxic and flammable gas may be drawn into an industrial operation and produce tragic results. Notify all dow nstream users of the water immediately.
If the liquid enters a sewer system, certainly all animal life there will be eliminated, and there also is a danger of serious explosion if the gas is within the flammable range and a suitable ignition source is present. The danger of explosion will be spread rapidly, so warn and evacuate the sewage treatment plant at once.
SYNONYMS
carbonic oxide carbon oxide exhaust gas flue gas monoxide
Techniques to slow the evolution of gas from the liquid include covering the contained liquid with sheets of canvas, rubber, or plastic. These materials will instantly become very rigid, and the slightest movement w ill cause them to break. Straw or hay also might slow’ evaporation. However, keep in mind that anything added to the cryogenic liquid will warm it up and increase evaporation. Consult the shipper and manufacturer of the product for safe mitigation techniques. They can help determine whether the liquid may be contained and salvaged.
Deliberate ignition of the gas is an effective technique to convert carbon monoxide to carbon dioxide, but it can be used only if there is no threat of explosion and spread of fire. If deliberate ignition is used, sweep the immediate area with fog or highpressure spray patterns to cleanse the air of explosive carbon monoxide vapors. Consider the relatively high lower flammable limit (12 percent), since there will be enough gas in the air to produce an explosion. Originate ignition as near to the leak as possible.
FIRE SCENARIO
If carbon monoxide containers are being threatened by radiated heat from the fire or are being impinged on by flames, cool the containers with water thrown from as far away as possible by unmanned appliances. Pay attention to the sound of gas escaping from vents, since any sudden increase could signal an impending BLEVE. Any leaking gas will probably be burning. and a burning gas flame should never be extinguished unless the flow of gas can be stopped immediately after extinguishment. The preferred method of fighting gas fires is still to stop the flow of fuel first!
If a container of cryogenic carbon monoxide is threatened by fire, it will be protected somewhat by its container where there is a container inside a container separated by an insulating air space. Water applied to the outer container will not cool the inner container and may be useless. A cryogenic container that is weakened after exposure to extreme heat is very dangerous. Failure of this container first will release great quantities of super cold liquid capable of destroying body tissue, then will produce enormous quantities of highly toxic and explosive gas.
Whether the container holds compressed carbon monoxide gas or cryogenic carbon monoxide liquid, the incident commander will have to decide whether to fight the fire or to withdraw, protecting exposures.
PROTECTIVE CLOTHING AND EQUIPMENT
Protect against carbon monoxide gas with respiratory equipment. Use positive-pressure, self-contained breathing apparatus in handling carbon monoxide incidents, whether the origin of the gas is from a compressed gas cylinder or from a cryogenic container. If a cryogenic container is leaking, avoid all contact with either the liquid or gas. Frostbite will occur with contact by the very cold gas as it escapes the container, but instant tissue destruction will occur with any contact of the skin by the cryogenic liquid. Any turnout gear or equipment will become extremely brittle on contact with the cryogenic liquid and will shatter easily.
FIRST AID
Remove any person who has been exposed to carbon monoxide immediately to fresh (not cold) air. Place the victim on his stomach with his face turned to the side. Administer oxygen immediately. If the victim is not breathing, start artificial respiration at once and simultaneously administer oxygen. The carbon monoxide will be removed from the bloodstream much faster if a mixture of 7 to 10 percent carbon dioxide in oxygen is administered. The carbon dioxide will act as a powerful respiratory and cardiac stimulant and will cause the victim to breathe more deeply, thus hastening the elimination of the carbon monoxide from the bloodstream. Administer this mixture for 1 5 to 30 minutes. Immediate medical attention is absolutely necessary.
Ingestion of the cryogenic liquid is unlikely. Severe and possible irreparable damage to the mouth, esophagus, and stomach will occur. Seek medical attention immediately.
Contact of the cryogenic liquid with the skin will cause severe frostbite and tissue damage. Remove frozen clothing with caution to avoid further tissue damage. Wash the affected area with large quantities of water. Do not use warm or hot water, and do not rub frostbitten areas.
Contact of the cryogenic liquid with the eyes will cause severe damage. Wash the eyes with large amounts of cool w ater for at least 15 minutes, occasionally lifting the lids. Seek immediate medical attention.
