CHEMICAL DATA NOTEBOOK SERIES #119: NITROBENZENE
BY FRANK L. FIRE
Nitrobenzene is a highly toxic, combustible, fairly reactive, irritating, oxidizing, bright yellow crystalline solid or a yellow-to-brownish oily liquid with a bitter almond or shoe-paste odor. It is used to make drugs, dyes, explosives, leather dressings, metal polishes, paint solvents, rubber chemicals, shoe polishes, and a variety of other chemicals. Products of combustion may contain the nitrogen oxides (NOx). These gases are oxidizers and highly toxic.
Nitrobenzene is classified as a toxic material; but since it will burn and has a flash point of 100°F or higher, it is also a combustible liquid. Its flash point is 171°F, its autoignition temperature is 900°F, and its lower explosive limit is 1.8 percent in air. No upper explosive limit has been reported. Its boiling point is 411.6°F, its freezing point is 42.3°F, and it is practically insoluble in water. Its specific gravity is 1.20, its molecular weight is 123, and its vapor density is 4.25. Its chemical formula is (C6H5)NO2.
Toxicity is nitrobenzene`s major hazard [as evidenced by the “3” in the left (health) quadrant of the NFPA 704 diamond], and any release should be considered highly toxic and dangerous. Breathing the vapors can cause bluish discoloration of the skin (starting in the earlobes, face, lips, and nose), convulsions, coma, dizziness, drowsiness, headache, irritability, rapid and difficult breathing, vomiting, weakness, unconsciousness, and death. Enough vapors can be absorbed through the skin to cause cyanosis and death.
The manner in which nitrobenzene kills is extremely interesting. When ingested, inhaled, or absorbed, it forms compounds with the red blood cells that renders them incapable of combining with oxygen and thereby of carrying oxygen to the body`s cells. When breathing in a “normal” mixture of air, the oxygen reacts with hemoglobin to form oxyhemoglobin. This relatively weak chemical compound serves as the vehicle for carrying oxygen to the cells, where the oxygen is “dumped” (released to the cell) and the carbon dioxide released by the cell is picked up and brought back to the lungs for disposal. A substance that prevents the formation of oxyhemoglobin is a blood asphyxiant.
The most common blood asphyxiant is carbon monoxide, the deadly gas formed in all fires involving carbon-based materials. It reacts with hemoglobin to form carboxyhemoglobin (COHb)–a much stronger compound than oxyhemoglobin–and the red blood cell bypasses the body cell waiting to exchange carbon dioxide for oxygen, depriving it of its needed oxygen.
The red blood cell makes it return trip to the lungs where it is supposed to dump its load of carbon dioxide and pick up fresh oxygen. Since the cell is still carrying its load of stable carboxyhemoglobin, it cannot pick up oxygen; it passes through the lungs and begins another trip through the circulatory system, only to disappoint more waiting body cells. As the process continues, more and more red blood cells become loaded with carbon monoxide and unable to pick up oxygen in exchange for the carbon dioxide in the oxygen-starved body cells. The body cells begin to die.
When nitrobenzene vapors are inhaled, the chemical compound methemeglobin–considerably more stable than oxyhemoglobin–is formed. When the methemeglobin in the blood reaches 15 percent, cyanosis appears and death occurs. In many cases, there may be a one- to four-hour delay before symptoms of nitrobenzene poisoning appear.
It is imperative that oxygen get to the cells before irreparable damage is done. The methemeglobin may be able to hold on to the red blood cell for four to five hours. Merely giving the victim pure oxygen, therefore, may not prevent death. It may be necessary to use a hyperbaric chamber to speed the acceptance of the tissue-saving oxygen.
The TLV-TWA (threshold limit value-time weighted average) set for nitrobenzene by the American Congress of Governmental and Industrial Hygienists is one ppm (part per million of air). The STEL (short-term exposure limit) is two ppm for 15 minutes.
Liquid nitrobenzene may be absorbed through the skin to cause cyanosis. Contact may cause the skin to smart; a short exposure will irritate the skin. Prolonged exposures may result in secondary burns and could eventually cause death.
Contact with the eyes will cause serious irritation; continued exposure could cause permanent damage.
Ingesting liquid nitrobenzene will cause cyanosis, preceded by most of the signs and symptoms of inhaling the vapors.
Nitrobenzene does not react with water and other common materials but is reactive with a variety of chemicals. Reactions with aluminum chloride and phenol mixtures, aniline and glycerine mixtures, nitric acid, nitrogen tetroxide, silver perchlorate, and strong oxidizers may be explosive. The product is generally thought to be stable in transportation.
Nitrobenzene`s flash point of 171°F (the temperature at which the liquid produces vapors sufficient to form an ignitable mixture with the air near the liquid`s surface or the container) indicates it is a combustible liquid (a liquid with a flash point of 100°F or higher). This, therefore, means that if the temperature of even a small portion of the liquid nitrobenzene reaches 171°F, sufficient vapors will be liberated and ignited if an ignition source that will produce a temperature of 900°F is present. All common ignition sources produce the energy to reach this temperature; and if enough vapors have been generated, the resulting ignition may take the form of a powerful explosion. Final products of combustion of nitrobenzene include carbon, carbon monoxide, carbon dioxide, water, and the nitrogen oxides.
Since nitrobenzene is a very toxic material, a release of any appreciable quantity should be treated as a serious incident and the community`s emergency response plan must be triggered. Evacuation of all nonemergency personnel for at least one-half mile in all directions and from one to two miles directly downwind of the release must be considered from the first threat of release.
Nitrobenzene`s vapor density of 4.25 means the vapors will “hang together” for a considerable distance unless wind or some other force disturbs them. The vapors will flow along low spots in the terrain and may find an ignition source or accumulate in a low spot or an enclosed area. In any case, the consequences of such movement are serious.
Anyone caught in the vapors without respiratory protection is in danger of being quickly poisoned, and the lower explosive limit of 1.8 percent means a vapor explosion is imminent when vapors reach an ignition source. After the explosion, the burning vapors will “flash back” to the source, producing an extremely hazardous situation at the site of the spill or release.
Approach the spill or release from upwind and uphill. Although the fuel must be heated to its flash point of 171°F before enough vapors are released to form an ignitable mixture, consider that the spilled liquid might be impinging on something hot. There are also the toxic vapors to be considered, and all emergency personnel must be wearing proper respiratory protection.
Standard procedures for containing liquids must be used when the spill is large. Soil, sand, clay, and other materials may be used to build a dike to create a containment pond. Since nitrobenzene will produce toxic vapors when evaporating and the rate of evaporation depends on the surface area of the liquid (the larger the surface of the containment pond, the faster the evaporation), it may be better to dig a containment pit that will present a smaller surface area to the atmosphere while holding the same volume of liquid. The released liquid must be contained to prevent its spreading and keep it from contaminating sewers and waterways.
The proper environmental authorities (who must be alerted whenever any hazardous material is released) must be consulted to avoid possible ground water contamination. With this in mind, a shallow containment pond might be better than a deep containment pit. The use of trenches and other excavations may also be considered, always with ground water contamination in mind.
Once contained, the next concern should be to reduce evaporation so that a minimum of vapors is produced. Using firefighting foams to cover the liquid`s surface will help slow evaporation. The foams may have to be continually applied, since the foam may break down over time. A tarpaulin or other compatible cover, instead of foam, may be placed over the surface of the containment pit.
As part of the mitigation of any incident involving liquids, product may be pumped from the containment pit into an approved, empty, secure container (a tank-truck, tank car, or drum, for example). Be sure that all equipment used is compatible with nitrobenzene and that motors driving the pumps are explosionproof.
Any foam, soil, or other diking materials touching the product will be contaminated and have to be removed and disposed of in accordance with all federal, state, and local regulations. Qualified contractors, not emergency responders–who generally are not trained to clean up hazardous-materials releases–should do this work. The responsibility for cleanup lies with the shipper and owner of the material.
Once the nitrobenzene has been contained in secure containers, any material left in the pit (assuming it is not an overwhelming amount) may be removed by absorption or adsorption techniques. Absorption (the product penetrates the additive and “soaks” it, as water does a paper or cloth towel) may be accomplished with soil, clay, sand, sawdust, peat moss, fly ash, cement powder, or some commercial absorbent. The absorbent material then may be taken to a secure container and deposited, or it may be physically “squeezed” in one manner or another to force out the absorbed product. In this manner, the absorbent may be used again. The contaminated absorbent will release toxic vapors unless confined in airtight containers. Just because the liquid no longer exists in a pool or pond doesn`t mean it is gone or is no longer harmful.
In adsorption, the material, held by some physical or chemical force, adheres or “sticks” to the outside of the adsorbent. The contaminated adsorbent then must be disposed of or treated in some manner to get the contaminant to leave the adsorbing material.
All the rules for contact with nitrobenzene must be followed when handling contaminated sorbents and adsorbents. Note: Although absorption or adsorption may be used to handle a spill, absorbents usually are used for spilled product on the ground or floating on the water; and adsorbents are used for removing gases, vapors, and fumes from the air or dissolved material from water.
Waterways. Prevent product from entering sewers and waterways. In addition to contaminating the waterway, the product can pose a toxicity problem or cause an explosion downstream if the contaminated water enters an industrial facility or any other enclosed structure where an ignition source may be present. Entry into a sewer poses another explosion problem, particularly with a material with a low explosive limit. To prevent such occurrences, dikes must be built in front of the catch basins and low-lying ground leading to a waterway.
If nitrobenzene enters a waterway or sewer, immediately notify all downstream users (do not forget sewage treatment plants). Since nitrobenzene is not soluble in water, the product (in a stream of other moving water) will be moving downstream with the water. The product can be removed from the water by building small dams that allow the water to flow over while the nitrobenzene is trapped at the bottom so it can be pumped out. If possible, divert all contaminated water to a large containment area, where it can be treated for safe removal of the product by adding an adsorbent or using aeration (removing dissolved fluids from the water by agitation–usually accomplished by bubbling air through the solvent, water in this case). Agitation may also be accomplished by disturbing the water by causing it to go over waterfalls, stirring it vigorously, or pumping it into the air and letting it fall back to the water surface. Aeration techniques release contaminant vapors into the air, and care must be taken to limit exposure and prevent explosive accumulations.
Containers containing nitrobenzene or any combustible liquid or gas must be cooled as quickly as possible with unmanned appliances positioned as far away as possible. The containers will be subject to a rapid rise in internal pressure when confronted by the radiated heat of a fire or the impingement of flames, even if the pressure-relief device is operating properly (which might be bad in the case of a toxic material). This rapid rise in pressure could result in the container`s catastrophically failing, presenting the additional hazards of shrapnel and a fireball.
Consider any release of nitrobenzene a serious toxic explosion and fire hazard. If vapors from evaporating nitrobenzene are allowed to reach the lower explosive limit (LEL), any suitable ignition source will produce an explosion. Many firefighters dealing with spills of flammable or combustible liquids expect only a fire on ignition of the vapors and usually are not prepared for a violent, lethal explosion or the accumulation of toxic vapors.
If escaping (through the pressure-relief valve or a leak) vapors are accidentally ignited, do not extinguish them until the flow of fuel can be stopped. It may be wiser to let a toxic material like nitrobenzene burn rather than to spread to a populated area. Deliberately burning the vapors of a flammable or combustible liquid (or flammable gas) is a strategy that must be considered when a toxic material is involved. However, the incident commander in reaching a decision must consider the consequences of a deliberate ignition, including property damage (which, of course, is secondary to the threat to human life).
Firefighting foams, carbon dioxide, dry chemical, and water spray or fog–depending on the size and nature of the spill, the availability of extinguishing agents, and prevailing weather conditions–can be used to extinguish pools of burning nitrobenzene.
PROTECTIVE CLOTHING AND EQUIPMENT
Choose protective clothing and equipment–including rubber boots, gloves, face shields, splashproof safety goggles, and other impervious and chemical-resistant clothing–that will prevent skin and eye contact. Total encapsulating suits with self-contained breathing apparatus (SCBA) with full face piece or the equivalent are needed when participating in an incident involving a nitrobenzene release.
Total encapsulating suits made of butyl rubber, polyethylene, ethylene vinyl alcohol, TeflonTM, and VitonTM may offer protection. As always, contact the manufacturers of the suits and nitrobenzene for their recommendations. Keep in mind that the degree of protection offered by the suit is affected also by the thickness of the material, integrity of the seams, concentration of the product contacted, and length of time and concentration of the contact.
Inhalation. Move the victim to fresh air and keep him/her warm and calm. If the victim is unconscious, administer artificial respiration. (Caution: Administering mouth-to-mouth resuscitation may expose the first-aid provider to nitrobenzene in the victim`s lungs or vomit.)
Ingestion. If the victim is conscious, administer large amounts of water, and induce vomiting. Never force an unconscious person to drink or to vomit.
Eye contact (liquid or vapors). Immediately flush the eyes with water for at least 20 minutes, occasionally lifting the eyelids. Get immediate medical attention.
Skin contact. Remove all contaminated clothing as soon as possible. Wash the affected body areas with large amounts of soap and water. Get immediate medical attention. Place all contaminated clothing in a closed container for storage until it can be laundered or discarded. If clothing is to be laundered, inform the individual performing the operation of the contaminant`s hazardous properties. Discard all contaminated leather goods. n
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IDENTIFICATION NUMBERS AND RATINGS
(Chemical Abstract Services)
(Registry of Toxic Effects of Chemical Substances)
(United Nations/North America)
(Chemical Hazard Response Information System)
(Resource Conservation and Recovery Act of 1976)
(Standard Transportation Commodity Code)
(U.S. Department of Transportation)
NFPA 704 Rating
(National Fire Protection Association)
(International Maritime Organization)
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FRANK L. FIRE is the vice president of marketing for Americhem, Inc. in Cuyahoga Falls, Ohio. He`s an instructor of hazardous-materials chemistry at the University of Akron as well as an adjunct instructor of haz mats at the National Fire Academy. Fire is the author of The Common Sense Approach to Hazardous Materials and an accompanying study guide, Combustibility of Plastics, and Chemical Data Notebook: A User`s Manual, published by Fire Engineering Books. He is an editorial advisory board member of Fire Engineering.