CHEMICAL DATA NOTEBOOK SERIES #75: NITRIC OXIDE
HAZARDOUS MATERIALS
Nitric oxide is a toxic, oxidizing, reactive, corrosive, irritating, nonflammable, colorless gas with a sharp, acrid, pungent, irritating odor. It is used to manufacture a wide variety of chemicals, most notably nitric acid. It also is used as a bleaching agent, which is a function of its oxidizing power. It is so toxic that it is shipped in containers with no safety relief devices. Once released from its container into the atmosphere, it reacts chemically with the oxygen in the air to convert to nitrogen dioxide and nitrogen tetroxide. These two gases plus nitric oxide are members of a group of gases known as the nitrogen oxides.
PROPERTIES
Nitric oxide, nitrogen dioxide, and nitrogen tetroxide are nonflammable; they have no flash point, ignition temperature, or flammable range. They, however, very vigorously will support combustion and other oxidation reactions.
Liquefied nitric oxide has a specific gravity of 1.27, a molecular weight of 30, and a vapor density of 1.03. It melts at — 263.2°F, boils at — 2416°F, and is not soluble in water. Its chemical formula is NO.
On some occasions, nitric oxide may be shipped as a mixture with nitrogen tetroxide. The shipping name for this mixture may be “poisonous gas, n.o.s.”
HAZARDS
One seldom would come in direct contact with nitric oxide. This means that the reactivity, oxidizing power, and corrosiveness might be meaningless to anyone exposed to the gas. Nitric oxide is so reactive that the instant it contacts oxygen in the atmosphere (or any other source), it reacts chemically to become nitrogen dioxide and nitrogen tetroxide. These two gases also are classified as toxic, corrosive, and powerful oxidizing agents and are reddish-brown, in contrast to the colorless nitric oxide. This implies that whenever nitric oxide is released into the atmosphere, it rapidly converts to two other dangerous gases. Many of the hazards presented are hazards of nitrogen dioxide and nitrogen tetroxide. Thus, the hazards of nitric oxide will be presented as if there had been no conversion to nitrogen dioxide and nitrogen tetroxide gases, and then the hazards resulting from the conversion will be stated.
Toxicity is the major hazard of nitric oxide. Its TLV-TWA (threshold limit value-time weighted average) is 25 ppm (parts per million of air). The TLV-TWA for nitrogen dioxide is 3 ppm. The STEL (short-term exposure limit) for nitrogen dioxide is 5 ppm for 15 minutes, as established by the ACGIH (American Conference of Governmental Industrial Hygienists) but only 1 ppm for 15 minutes as established by OSHA (the Occupational Safety and Health Administration).
Obviously, different organizations charged with the safety and health of American workers cannot always agree on the amount of exposure that would harm an unprotected person. This discrepancy, however, is not a very serious problem for emergency responders. When it comes down to the numbers generated by these organizations, even when, as in the case of nitrogen dioxide, one organization lists a value that represents a 500 percent difference in toxicity (STEL of 5 ppm vs. 1 ppm), the numbers represent a warning for workers. These low numbers mean that a worker in a company in America must not be exposed to a level above the I LVTWA for eight hours a day, 40 hours a week, or the STEL of 1 ppm (or 5 ppm) for any 15-minute period. If the concentration of nitric oxide, or any other hazardous material under discussion, rises above these limits, you must wear devices that protect your respiratory system. The differences are insignificant for two reasons. First, the absolute numbers (1 or 5 ppm) are very’ small: 1 ppm is 0.0001 percent, and 5 ppm would be 0.0005 percent in air. This amount is so small that it is reached in almost any situation where nitric oxide is used. Second, in any accidental release of nitric oxide or any other toxic gas, the concentration in air near the point of release always will be higher than the TLV-‘I*WA and STEL. The point is that while minor differences in values may be important to safety managers of companies using nitric oxide, they are not important in a release because the concentration of nitric oxide may be 1,000 to 10,000 times higher. Thus, emergency responders always must he protected.
The only time you would be in an atmosphere of nitric oxide is when you are directly in front of a discharge of the gas. Of course, this exposure would prove fatal in a very short time to anyone without the proper protection.
The effects of breathing nitrogen dioxide (the major reaction product created when nitric oxide mixes with air) can be instantly fatal in concentrations of 5,000 ppm or higher. Ix>wer concentrations over a period of time cause a series of problems ranging from drowsiness and dizziness to irregular respiration to rapid death, with a variety of symptoms between these extremes.
One of the major dangers of nitric oxide is that when it converts to nitrogen dioxide, an unprotected victim may breathe a fatal dose before he or she realizes it. Even if the amount inhaled by the victim is not instantly fatal, he or she may die anywhere from eight to 48 hours later. The victim may feel fine until symptoms resembling 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, causing a shortage of oxygen to the heart. This produces all the symptoms of a heart attack and usually ends in death.
Nitric oxide is a very reactive and oxidizing chemical. The long list of chemicals with which nitric oxide reacts includes all organic materials— nitric oxide will react with any material that will burn, by supporting its combustion. If the material burns very slowly, contact with nitric oxide will cause it to burn readily (assuming sufficient energy is present to provide an ignition source); if the material burns readily, contact with nitric oxide will make it explosive. All flammable gases and liquids, many combustible liquids, and any metallic or organic dusts fall into this explosive category. The rule, of course, is never to allow any oxidizer to come in contact with (or even to be stored next to) any fuel (anything that will burn). Nitric oxide also reacts with bromine, chlorine (in the presence of oxygen), fluorine, fluorine oxides, halides, oxygen, and all other strong oxidizing agents.
Nitric oxide is considered corrosive because it rapidly converts to nitrogen dioxide and nitrogen tetroxide and forms nitric acid by nitrogen dioxide dissolving in moisture. Thus, nitric oxide always will be corrosive to eyes and skin and to many metals in the presence of sufficient moisture.
Nitric oxide is an irritant in only very low’ concentrations, where irritation of the eyes, skin, and throat may become noticeable. However, tests on animals indicate that concentrations below 100 ppm will cause eye irritation over several hours. Remember that this concentration is considerably higher than levels permitted for exposed workers.
If the nitric oxide has been liquefied (the major reason for doing this is to save money by putting more material into a container of the same size), at least two additional hazards will be present. Nitric oxide’s boiling point of — 241.6 means that any liquid nitric oxide will be at least that cold. Contact with materials at temperatures that low will cause immediate (and probably irreversible) tissue damage.
The second hazard is the tremendously high vapor-to-liquid ratio. There is no published information, but it is likely that at least 600 cubic feet of vapor will be produced by one cubic foot of the liquid. This means that any release of the cryogenic nitric oxide will be extremely dangerous. Contact of the liquid with any organic material (including asphalt used for paving) can create a very explosive mixture.
NONFIRE RELEASE
Any release of nitric oxide requires evacuation of at least one-half mile around the point of release and one to two miles downwind. As the nitric oxide converts to nitrogen dioxide, whose specific gravity is 1.59, the danger downwind becomes greater. At this density, the nitrogen dioxide “hangs together” longer and flows downhill, seeking low spots and confined areas. A moderate breeze or high-pressure water spray or fog will readily disperse the gas. Contain all runoff water, as it will contain dissolved nitrogen dioxide and, therefore, nitric acid.
Eliminate all ignition sources, since anything that will burn will do so in an accelerated manner when mixed with nitrogen dioxide. The effect of mixing anything that will burn with nitric oxide will resemble adding oxygen to a fire.
Liquefied nitric oxide is more rare than the compressed form, but should there be a release of the liquefied form, the evolution of gas will be highest as the first liquid contacts the ground. As the ground quickly cools, the evolution of gas will slow. There will be a very great danger of fire and/ or explosion anywhere these gases flow, as well as a more immediate danger of poisoning any unprotected humans exposed to the gas.
Contain liquids by building containment ponds or digging pits, and cover the liquefied nitric oxide with a compatible material, if possible. It is questionable whether applying foam w ill slow the evolution of gases; contact foam manufacturers for advice. Do not come in direct contact with the liquid or gas.
Prevent all liquids from entering sewers and waterways. Liquefied nitric oxide entering a sewer creates a potentially explosive situation. The liquid nitric oxide w ill generate large quantities of gaseous oxidizing agent, requiring only the proper ignition source to produce a fire or explosion. Fuel is present in all sewers as decomposing organic matter. Also, keep runoff water contaminated with nitric oxide (now converted to nitric acid, another oxidizer) out of sewers. In case of entry, immediately warn all sewage treatment facilities.
Runoff water entering a lake, pond, stream, or river will be diluted fairly quickly, depending on the volume of water present and how quickly it is moving. Liquefied nitric oxide that enters a waterway will begin to boil rapidly as the water heats it up. Very little gaseous nitric oxide w ill dissolve in the water, but notify all downstream users immediately in any circumstances.
Runoff water, once contained, will be acidic. Conventional neutralization agents such as calcium carbonate (ground limestone), sodium carbonate (soda ash or baking soda), and sodium bicarbonate (baking soda) may be used to neutralize the liquid. Always test neutralization techniques on small samples of the product. If violent reactions occur, of course, do not use the procedure on a large amount of product. Do not attempt any neutralization techniques on pure liquefied nitric oxide.
More likely, the release will be in gaseous form. After evacuating and securing the area, determine whether attempts should be made to plug the leak, if at all possible. If the leak is small and can be plugged by conventional methods of driving plugs or using straps to hold a plug secure, an attempt may be possible, but personnel doing the plugging must be properly protected and, preferably, professionally educated, trained, and equipped employees of a salvage firm or of the product’s manufacturer. Emergency responders should not be involved in these procedures unless they are properly protected and human life is immediately threatened.
If the leaking gas can be directed, the nitric oxide can be neutralized by leading it through a solution of sodium hydroxide (caustic soda) and calcium hydroxide (slaked lime).
The air around the incident and dow nw ind constantly must be monitored by health officials, to offer warnings of deadly or harmful concentrations. Such monitoring must take place until well after the incident has ended. Never assume that the danger has passed because no reddish-colored gases are visible.
IDENTIFICATION NUMBERS AND RATINGS
CAS
(Chemical Abstract Services)
10102-43-9; 63907-41-5 when mixed with nitrogen tetroxide
STCC
(Standard Transportation Commodity Code)
4920330
RTECS
(Registry of Toxic Effects of Chemical Substances) QX0525000; QX0700000 when mixed with nitrogen tetroxide
UN/NA
(United Nations/North America)
1660; 1975 when mixed with nitrogen tetroxide
CHRIS
(Chemical Hazard Response Information System)
NTX
RCRA
(Resource Conservation and Recovery Act)
P076
DOT
(U.S. Department of Transportation)
Poison Gas
IMG
(International Maritime Organization)
2.3, poison gas
FIRE SCENARIO
Some controversy surrounds the use of extinguishing agents on a fire involving nitric oxide. One source suggests that only water spray or fog be used, since there might be some reaction with any gases propelling dry chemicals. There is also concern that halons possibly could cause reactions. Other sources recommend using any fire extinguishing agent that can be effective on the burning material.
Since nitric oxide is shipped in pressurized containers, the threat of a BLEVE (boiling-liquid, expanding-vapor explosion) always is possible when the containers are threatened by radiated heat from a fire or impinging flames. The hazard is worse with nitric oxide than with most other compressed gases, since containers of nitric oxide (and some other poison gases) have no safety relief device protecting the container. The theory behind this is that there is more danger to human life from the deliberate release of poison gas from an overpressurized container than from the possibility that the container will BLEVE. And, with no safety relief device, a constant exposure to radiated heat or impinging flame certainly will cause the container to fail catastrophically.
All containers, therefore, must be cooled with water applied with unmanned appliances from as far aw ay as possible. Never approach containers of nitric oxide that have been heated. Leave salvage of containers after a fire (and even if there is no fire) to the owners of the product, the manufacturer, or a professional salvage team. Do not become involved in salvage.
Remember that all released nitric oxide is extremely toxic, corrosive, and a powerful oxidizing agent. Do not let the “poison gas” placard keep you from protecting yourself from these other hazards.
PROTECTIVE CLOTHING AND EQUIPMENT
Choose protective clothing and equipment to prevent nitric oxide in liquefied or gaseous form from contacting the eyes, respiratory system, or skin. You may have to wear chemical-resistant goggles under full face shields to protect the eyes from splashes; only positive-pressure, selfcontained breathing apparatus will protect the respiratory system from the gas. Rubber gloves, boots, and aprons and normal turnout gear that is impervious to liquid may offer very short-term protection. Remember that the presence of nitric oxide makes anything that burns very combustible. Some encapsulating suits and some turnout gear rated as flameresistant may burn readily in the presence of high concentrations of nitric oxide or nitrogen dioxide. Also, no material contacted by the cryogenic liquid will offer much protection. The material will be so cold that it will shatter at the first impact or use.
Some manufacturers claim that encapsulating suits made of butyl rubber, chlorinated polyethylene, and polyvinyl chloride will offer protection against nitric oxide. Chlorinated polyethylene, chlorobutyl rubber, and polyethylene are claimed to be effective against nitrogen tetroxide. Another source says that only Saranex™ offers adequate protection against nitrogen dioxide, while no material is recommended for very long against nitrogen tetroxide. Remember, protection is relative. A material’s ability to protect the wearer depends on its thickness and lack of holes, the integrity of its seams and zipper closings, its general condition (has it been exposed to “powerful” chemicals before?), the concentration of the product it is to protect against, and the length of exposure time. Contact the suit manufacturers to check their products’ ability to withstand nitric oxide, and ask nitric oxide manufacturers for their recommendations on suitable protective material.
FIRST AID
Inhalation. If the victim has inhaled the fumes of nitric oxide, nitrogen dioxide, and nitrogen tetroxide or the vapors of acids formed by the reactions of nitric oxide, move him/ her to fresh air and keep warm and quiet. Administer mouth-to-mouth resuscitation if the victim has difficulty breathing or has stopped breathing altogether, being aware that such action may expose the first-aid giver to the chemical in the victim’s vomit or lungs. One reference calls for the administration of oxygen. Summon medical attention immediately. There is a danger of immediate and delayed effects, for 48 hours or longer.
SYNONYMS
mononitrogen monoxide nitrogen monoxide nitrogen oxide nitrogen(II) oxide
Eye contact. In the case of vapors, flush the eyes immediately for at least 15 minutes, lifting the eyelids occasionally. Summon immediate medical attention.
Skin contact. In the case of contact with the gas, remove contaminated clothing and wash affected body areas with large amounts of water. Should the liquefied gas contact the skin, gently apply tepid (not hot) water to affected body areas. Remove clothing carefully so that damaged frostbitten skin will not be aggravated. Seek immediate medical attention.
Ingestion. Ingesting liquefied gas is highly unlikely. Severe frostbite damage will occur to the mouth and esophagus. Seek immediate medical attention.
