CHEMICAL DATA NOTEBOOK SERIES #85: NITROGEN TETROXIDE (AND NITROGEN DIOXIDE)
HAZARDOUS MATERIALS
It is impossible to discuss nitrogen tetroxide and nitrogen dioxide separately. They exist in equilibrium with each other under certain circumstances, so it is fitting that they be discussed together. Both are members of a family of chemical compounds known as the nitrogen oxides, written NOX. As a group, these gases represent a combination of hazards to anyone exposed to them. Unfortunately. exposure is quite common to firefighters who do not wear the proper respiratory protection at fires, particularly when outside in the open air.
Nitrogen tetroxide is a toxic, oxidizing, corrosive, irritating, nonflammable, yellowish to reddish brown or dark brown gas or liquid, depending on the reference source. It has a very sharp, penetrating, pungent odor. Nitrogen dioxide has the same description.
In liquid form, the material is 99 percent nitrogen tetroxide and one percent nitrogen dioxide; in gaseous form, the material is made up of 90 percent nitrogen dioxide and 10 percent nitrogen tetroxide; and in solid form, it is 100 percent nitrogen tetroxide. In other words, as the material moves from solid to liquid to gaseous form, the result is more and more nitrogen dioxide. Since the material is usually shipped as a liquid, it is important to know the properties of nitrogen tetroxide; however, an accidental release of the liquid will evaporate rapidly, producing a great deal of nitrogen dioxide. Therefore, it is important to be aware of the properties and hazards of both materials.
Nitrogen dioxide may be shipped in cylinders as a pure product in its gaseous form. In this case, the material will be 100 percent pure nitrogen dioxide, with no nitrogen tetroxide present. However, if pure nitrogen dioxide is liquefied, it will convert to 99 percent nitrogen tetroxide.
Nitrogen tetroxide is used to manufacture nitric and sulfuric acids, as an oxidizing agent for rocket fuels, as a polymerization inhibitor for some monomers, and as a catalyst for some chemical reactions. It also is used to nitrate certain explosives and organic chemicals.
PROPERTIES
Nitrogen tetroxide and nitrogen dioxide are both nonflammable gases, so there are no flash points, ignition temperatures, or flammable ranges to discuss. However, since both materials are powerful oxidizing agents, they will radically affect any flammable or combustible materials with which they come in contact. Liquid nitrogen tetroxide has a specific gravity of 1.45, a molecular weight of 92, and a vapor density of 317. Nitrogen dioxide has a molecular w eight of 46 and a vapor density of 1.58. Nitrogen tetroxide has a boiling point of 698°F. This temperature is so close to room temperature that many classify nitrogen tetroxide as a gas rather than a liquid. It freezes at 15°F and is soluble in water. Nitrogen tetroxide’s molecular formula is N2O4, while nitrogen dioxide’s formula is NO2. Nitrogen tetroxide actually is a dimer of nitrogen dioxide; that is. nitrogen tetroxide really exists as two molecules of nitrogen dioxide chemically combined.
HAZARDS
Nitrogen tetroxide’s greatest hazard is its toxicity. Even though it rates only a “3” in the health quadrant of NFPA’s 704 System, when its toxicity is accompanied by the properties of being a powerful oxidizer and the ability to become corrosive when moist, nitrogen tetroxide becomes deadly. As nitrogen dioxide, its TLVTWA (threshold limit value-time weighted average) is three ppm (parts per million of air), and its PEL (permissible exposure limit) is one ppm. Its STEL (short-term exposure limit) as listed by the ACGIH (American Conference of Governmental Industrial Hygienists) is five ppm, while OSH A (Occupational Safety and Health Administration) lists it as one ppm.
Both nitrogen tetroxide and nitrogen dioxide may exist in pure forms that, when released, will result in certain reactions. When both materials react with moisture, nitric acid (HNO3), nitrous acid (HNO2), and nitric oxide (NO) are formed. When the nitric oxide contacts air or oxygen, it converts to nitrogen dioxide (see “Nitric Oxide,” Fire Engineering, August 1992).
It may be confusing to visualize two separate and different chemicals existing together in equilibrium or separately as pure materials, but it happens. The reactions and hazards of the two chemicals are so similar that they could be discussed as one material, but that also could be confusing. It is necessary to discuss them both since they are both deadly hazardous materials, and you must avoid all contact with them without proper eye, skin, and respiratory protection.
The LC50 listed for nitrogen tetroxide is 315 ppm for 15 minutes’ exposure. The LC50 for nitrogen dioxide is listed variously as 88 ppm for four hours, 30 ppm for one hour, and 1,000 ppm for 10 minutes. The different values represent tests done on different animals at different times by different researchers. The correct LC50 is less relevant than the fact that nitrogen dioxide is a highly toxic material. Breathing nitrogen dioxide can be instantly fatal in concentrations of 5,000 ppm or higher. Exposure to lower concentrations over a period of time can cause a range of problems—from drowsiness and dizziness to irregular respiration and rapid death, with a variety of symptoms between these extremes.
One of the major dangers of nitrogen dioxide is that an unprotected victim may breathe a fatal dose before realizing it. Even if the amount inhaled is not instantly fatal, a victim may die anywhere from eight to 48 hours later. The victim may feel fine until symptoms resembling those of a heart attack begin. The nitrogen dioxide dissolves in the moisture of the lungs to form nitric acid. This acid slowly destroys the oxygen-absorbing capabilities of the alveoli, resulting in a shortage of oxygen to the heart, producing all the symptoms associated with a heart attack and usually ending in death.
Inhaling nitrogen tetroxide and/or nitrogen dioxide gas will irritate the bronchia, pharynx, and sinuses, causing choking, coughing, cyanosis, constriction of the bronchial airways, headache, irregular breathing, shortness of breath, slowing of the heartbeat, pulmonary edema, asphyxiation, and death. In addition to the delayed reactions mentioned earlier, other side effects are possible. They include increased possibility of pulmonary infection due to decreased normal resistance to such infections, decreased flow of air in the respiratory system; an increase in problems for people with asthma, bronchitis, or other respiratory disorders; and the formation of fibrotic lesions in the lungs one to six weeks after other problems have occurred.
If liquid nitrogen tetroxide comes in contact with the eyes, it will cause permanent damage, just as will nitrogen tetroxide and/or nitrogen dioxide gas. Irritation of the nose and throat also will occur when these gases are inhaled.
If liquid nitrogen tetroxide comes in contact with the skin, it will cause serious burns and possibly irreversible damage. Exposure to nitrogen tetroxide and/or nitrogen dioxide gas will irritate the skin.
Inhalation of nitrogen tetroxide is highly unlikely, but it undoubtedly would cause severe burns to the mouth, tongue, esophagus, and stomach. Death would likely follow all the symptoms that occur when a person ingests a corrosive substance.
Nitrogen tetroxide and nitrogen dioxide are powerful oxidizing agents. They will not burn, but they will support combustion vigorously. Materials that burn easily, such as the vapors of flammable and combustible liquids and other combustible materials, usually will burst into flames (or explode) in the presence of these oxidizers. Since the normal mode of ignition for gases and vapors is an explosion, the presence of nitrogen tetroxide and/or nitrogen dioxide will increase the power of the explosion. The ignition of other combustibles will be considerably easier, since the presence of oxidizers such as these two gases is similar to adding extra oxygen to the air. For instance, the lower flammable (explosive) limit (LFI.) of all flammable and combustible gases, as well as that of fumes and dusts, will be lowered when oxidizing gases are present. It is important to realize that the presence of oxidizing gases (in addition to the presence of oxygen in the atmosphere) makes every release of nitrogen tetroxide and nitrogen dioxide a potentially explosive situation. Since oxidizing gases are nonflammable, the tendency is to treat them as nonhazardous and assume they will dilute the amount of oxygen present. This mistake can produce fatal results.
The corrosiveness of nitrogen tetroxide and nitrogen dioxide occurs when they contact moisture in any form. Nitric acid, nitrous acid, and nitrogen dioxide are always formed when nitrogen tetroxide contacts moisture, and the two acids also are formed when nitrogen dioxide contacts moisture. Both nitric acid and nitrous acid are highly corrosive, but there is an increased hazard in that both are oxidizing agents themselves. Consider the hazards of these acids in addition to the hazards of nitrogen tetroxide and nitrogen dioxide. Where nitric and/or nitrous acids are formed, heating and agitation will release the gases that formed them. Metals exposed to these acids will be oxidized quite rapidly, and the possibility exists that explosive hydrogen gas will be liberated in the reaction.
At low (but above the STEL) concentrations, nitrogen tetroxide and nitrogen dioxide will irritate the eyes, nose, throat, and lungs when inhaled over long periods of time.
NONFIRE RELEASE
Any release of nitrogen tetroxide or nitrogen dioxide should activate the community’s emergency response plan. Containers may hold product as either a liquid or a gas, and releases in either form will be highly hazardous.
Anyone who enters the “hot zone” must be protected with the proper clothing and eye and respiratory protection. Apparatus drivers must be careful not to drive into a cloud of gaseous nitrogen tetroxide or nitrogen dioxide, even if all personnel are protected. Taking in a corrosive oxidizing agent will cause the apparatus engine to race and corrode instantaneously.
Approach from upwind and uphill, as you would if a flammable gas were present. The fact that the gas is toxic, oxidizing, and corrosive makes it even more dangerous than a flammable gas.
Nitrogen tetroxide and nitrogen dioxide are both reddish brown-colored gases, but they might be diluted to the point at which the color is not visible. This should not be interpreted as a safe situation, since all hazards still may be present.
If a gas release is detected, a fine spray or water fog will sweep the gases from the air. Of course, all runoff water must be contained, since it will be acidic. Contain the flow of liquid nitrogen tetroxide by forming a containment pond or leading the liquid to a containment pit. There may be no safe way to slow the evolution of gas, since the boiling point of liquid nitrogen tetroxide is below 70°F. Adding water to dilute the released liquid may increase the evolution of gas. Experimenting on the scene with a small amount of nitrogen tetroxide (in a safe place) may indicate whether dilution is a possible mitigation technique.
Adding sorbents such as cement powder, clay, fly ash, and other compatible sorbents may help slow the evolution of gas and will help prevent contamination. One reference cites calcium carbonate as a suitable sorbent.
You can attempt to neutralize the liquid, but only soda ash (sodium carbonate) and lime (calcium oxide) are listed as suitable for this purpose. Be aware that calcium oxide, which is water-reactive, is itself a very hazardous material and may be too dangerous to use. In any event, before attempting to neutralize any corrosive material, first experiment on a very small amount, away from the release site.
Nitrogen tetroxide cannot be allowed to enter a sewer system. Sewers are notorious for containing organic material (fuel), and the addition of an oxidizer such as nitrogen tetroxide or nitrogen dioxide will produce a potentially explosive situation. In such a case, immediately warn all sewage treatment facilities downstream.
Prevent liquid nitrogen tetroxide from entering waterways as well. The liquid will sink to the bottom and begin to react with the water, forming nitric and nitrous acids and nitric oxide. The more water there is and/or the faster it is moving, the faster the nitrogen tetroxide will be diluted to a safe level. Slow-moving streams may be diverted to low-lying areas where the acidic water can be neutralized. The presence of toxic gases makes all areas near the waterway dangerous to anyone without respiratory protection.
Any entry into water usually will result in the death of aquatic animals and waterfowl. If the water contaminated is used for drinking or in industrial operations, warn all downstream users immediately. Environmental experts must monitor the water and determine when it once again is safe to use.
IDENTIFICATION NUMBERS AND RATINGS
CAS
(Chemical Abstract Services)
nitrogen tetroxide: 10544-72-6
nitrogen dioxide: 10102-44-0
STCC
(Standard Transportation Commodity Code)
nitrogen tetroxide: 4920360
nitrogen tetroxide/nitric oxide mix: 4920370
nitrogen peroxide: 4920350
nitrogen dioxide: 4920340
RTECS
(Registry of Toxic Effects of Chemical Substances)
nitrogen textroxide: QX 1575000 (gas), QX 1580000 (liquid)
nitrogen dioxide: QW9800000 (gas), QW9805000 (liquid)
UN/NA
(United Nations/North America)
nitrogen tetroxide (liquid or gas): 1067
nitrogen peroxide: 1067
nitrogen textroxide/nitric oxide mixtures shipped as poisonous gas, n.o.s.: NA 1955
nitrogen tetroxide/nitric oxide mix: UN 1975 (no poisonous gas nomenclature attached)
nitrogen dioxide: 1067
CHRIS
(Chemical Hazard Response Information System)
nitrogen tetroxide: NOX
nitrogen dioxide: NOX
RCRA
(Resource Conservation and Recovery Act)
nitrogen tetroxide. P078
nitrogen dioxide: P078
DOT
(U.S. Department of Transportation)
nitrogen tetroxide: 2.3, poison gas nitrogen dioxide: 2.3, poison gas
NFPA 704 Rating
nitrogen tetroxide: 3-0-0-OXY
nitrogen dioxide: 3-0-0-OXY
IMO
(International Maritime Organization)
nitrogen tetroxide: 2.3, poison gas nitrogen dioxide: 2.3, poison gas
FIRE SCENARIO
Containers of nitrogen tetroxide or nitrogen dioxide impinged on by fire must be cooled by water applied from unmanned appliances placed as far away as possible. If the containers become heated, they will release oxidizing gas, which in effect will “feed” the fire. If overheating produces internal pressures above the design strength of the container, the container will fail catastrophically. A sudden influx of oxidizer to the fire will cause the flames to flare to several times their size before the release. It is possible for a failure of a container holding liquid nitrogen tetroxide to become a BI-EVE (boiling-liquid, expanding-vapor explosion). Although the nitrogen tetroxide itself will not ignite, the effect would be the same as if a massive amount of oxygen were released into the fire.
Should a heated container vent nitrogen tetroxide or nitrogen dioxide and the gases increase the fire’s intensity, all attempts at extinguishing the fire may be futile. It may be better to concentrate on protecting exposures until the fuel and the oxidizer arc consumed. In any event, your only action may be to cool the fire with the application of water.
Although all fires produce large quantities of heat, fires supported with “extra” oxidizers will burn even hotter. The tremendous heat may prevent you from getting as close to the fire as firefighting normally dictates.
Firefighters are exposed to the nitrogen oxides at every’ large fire, during which additional oxygen reaches the fuel because the draft created by the thermal column above the fire pulls more and more air through the fire. Since nitrogen makes up “8 percent of the air, a tremendous amount of nitrogen is pulled through the fire with the oxygen. As more oxygen supports the fire, more nitrogen is exposed to the fire. Nitrogen is considered by many to be an inert gas — and at normal temperatures and pressures, it is. However, when raised to the temperatures produced by large fuel-regulated fires and in the presence of oxygen at these same temperatures, nitrogen is oxidized into the various nitrogen oxides, including nitrogen tetroxide and nitrogen dioxide. Any firefighter not wearing respiratory protection, even outside, will be exposed to these toxic gases and may have serious —even fatal —reactions up to 72 hours later. Thus, you should wear respiratory protection at all times on the fireground.
PROTECTIVE CLOTHING AND EQUIPMENT
Protective clothing and equipment should prevent nitrogen tetroxide and nitrogen dioxide from coming in contact with the skin or eyes. This means protective gear should be made of materials that are impervious to nitrogen tetroxide and nitrogen dioxide and that also will not absorb them. Neoprene, nitrile rubber, or butyl rubber gloves and boots; chemical splashproof goggles; and face shields may suffice for very low concentrations, but total encapsulating suits are recommended for all exposures. Compatible materials may include chlorobutyl rubber and polyethylene. One reference lists only Saranex® as suitable for contact with nitrogen dioxide and makes no recommendation for nitrogen tetroxide. Consult manufacturers of protective clothing to make sure their products will offer protection and to determine the length of time protection will be maintained. Contact manufacturers of nitrogen tetroxide and nitrogen dioxide for their recommendations. Respiratory’ protection in the form of positive-pressure, self-contained breathing apparatus is required.
FIRST AID
Inhalation. Move the victim to fresh air and keep him/her calm and warm. If the victim’s breathing has stopped or becomes labored, administer artificial respiration, being aware that such action might expose the first-aid giver to the material in the victim’s lungs and/or vomit. Seek medical attention immediately, as oxygen must be administered as quickly as possible. The victim must be kept under close medical supervision for at least 72 hours and should have weekly medical examinations concentrating on expected pulmonary problems.
SYNONYMS
nitrogen tetroxide:
dinitrogen dioxide
dinitrogen tetroxide
nitrito
nitrogen di-dioxide
nitrogen dioxide
nitrogen dioxide, liquid
nitrogen (VI) oxide
nitrogen peroxide
nitrogen peroxide, liquid
nitrogen tetroxide, liquid
NTO
oxides of nitrogen
red oxide of nitrogen
nitrogen dioxide:
dinitrogen tetroxide
nitrito
nitrogen peroxide
nitrogen peroxide, liquid
nitrogen tetroxide
Eye contact. Flush the eyes immediately with water for at least 15 minutes, lifting the eyelids occasionally. Seek immediate medical attention.
Skin contact. Wash the affected body areas with large amounts of soap and water after removing and isolating contaminated clothing. Skin irritation will continue after washing, so seek immediate medical attention.
Ingestion. If the victim is conscious, make him/her drink large quantities of water immediately, but do not induce vomiting. Never try’ to make an unconscious person vomit or drink anything. Seek immediate medical attention.
