HAZARDOUS MATERIALS
Sodium nitrate is an oxidizing, relatively stable, white-to-colorless, odorless, ionic crystalline solid of moderate toxicity with a salt-like, slightly bitter taste. It is a very popular and common chemical used in the manufacture of explosives (such as dynamite and black powder), fertilizers, food additives, glass, matches, meat preservatives, pharmaceuticals, pottery enamel, pyrotechnics, refrigerants, and other nitrates of sodium salts. Molten sodium nitrate also may be used as a salt bath as a quenching medium for metals.
PROPERTIES
Sodium nitrate is nonflammable but is a very powerful oxidizer, which means it enhances the combustion properties of anything that burns and makes highly flammable materials explosive. It has a specific gravity of 2.67, a molecular weight of 85, a melting point of 584°F, and a listed boiling point of 716°F (at which it decomposes) and is very soluble in water. Its chemical formula is NaNO
HAZARDS
Sodium nitrate’s major hazard is that it is an oxidizer or oxidizing agent (the terms are interchangeable)—that is, under the slightest urging, such as the application of heat or pressure (friction provides both), sodium nitrate releases its oxygen.
Combustion requires the presence of fuel, oxygen or oxidizer, and energy in the “proper” form and amount (the fire triangle theory of fire). If the sodium nitrate is mixed with or in contact with a fuel and the energy input is enough to release the oxygen contained in the nitrate ion. two legs of the fire triangle (fuel and oxygen or oxidizer) are present. If the energy source is great enough to raise the temperature of the fuel to its ignition temperature, an explosion or fire (or both) will occur. Also, if sodium nitrate is heated to 1,000°F, it will explode.
Sodium nitrate is a popular oxidizer because it is plentiful and therefore relatively inexpensive. It is used in commerce because it provides a dependable delivery of precise amounts of oxygen when and where it is needed in a chemical reaction. Problems occur only when this chemical reaction gets out of control, or when the hazardous material escapes from its container and contributes to an unwanted chemical reaction.
The chemical reaction sodium nitrate participates in is almost always an oxidation reaction; a rapid oxidation reaction (uncontrolled) is recognized as a fire at best and a violent explosion at worst.
Each time the fire triangle theory of fire has been mentioned above, the term oxygen or oxidizer has been used. It is very important for you to recognize this subtle change. Most firefighters have been taught that oxygen is one of the three legs of the triangle, and they, therefore, believe that atmospheric oxygen must be present for a fire to occur. While it is true that the majority of fires involve atmospheric oxygen, atmospheric oxygen need not be present for the fire to start. What must be present (in conjunction with the fuel and energy) is an oxidizer, which may contain oxygen within its chemical structure and will release it readily, or it may be an oxidizer like the halogens (fluorine, chlorine, bromine, or iodine), which contain no oxygen whatsoever but will support combustion. (In fact, fluorine is a more powerful oxidizing agent than oxygen and therefore will react more violently in a mixture with a fuel than oxygen. When any of the halogens are present in gaseous or vapor form, the effect is the same as it would be if more oxygen had been added to the atmosphere surrounding the fire or potential fire.)
The other change in the fire triangle concerns the notion that heat must be present; actually, the correct term is energy. While heat almost always is the form of energy present when a fire starts or an explosion occurs, you must realize that other forms of energy (chemical, electrical, or mechanical) may be sufficient to raise the temperature of the fuel to its ignition temperature and start the oxidation reaction. Even though heat may be the form of energy that manifests itself, heat may not be present just before the fire or explosion occurs. It is very important for the concept of energy to be accepted as the third leg of the triangle for a safer analysis of a potential disaster.
Sodium nitrate is a very efficient carrier and deliverer of oxygen and therefore never should be allowed to come in contact with or. worse, intimately mix with anything that will burn. This must be carried even further in industrial or storage scenarios—sodium nitrate or any other oxidizer never must be stored with or near anything that will burn. It is extremely important that this rule be enforced by anyone inspecting the premises, particularly firefighters carrying out a preplanning inspection. SARA Title III has provided the means of communicating the presence of this and other hazardous materials on the premises where they are stored and/or used. Knowing of the presence of such a hazardous oxidizer w ill help you determine your actions.
Sodium nitrate reacts dangerously with many chemicals. It reacts explosively with aluminum, antimony (powdered), aluminum oxide, barium thiocyanate, boron phosphide, sodium, sodium hyposulfite, sodium phosphinate, sodium thiosulfate, and mixtures of sulfur and charcoal (which form gunpowder). It reacts violently with most organic matter and nonmetals as well as with acetic anhydride, calcium-silicon alloys, magnesium chloride, magnesium chloride plus jute, sodamide, wood, and such classes of chemicals as acetates, amidosulfates, cyanides, hydrophosphites, and thiocyanates. While the literature lists these as “violent” reactions, there is no reference to the fact that these reactions may be explosive in nature. So. w henever you encounter a list of combinations of chemicals that produce a violent reaction, you should expect an explosion or a chemical reaction that resembles an explosion. You also should not overlook the possibility of the release of dangerous by-products, including toxic compounds.
When sodium nitrate is heated to decomposition, it liberates sodium oxide and a family of gases known as the nitrogen oxides, referred to in shorthand by the general formula NO. Many nitrogen oxides are oxidizing agents and/or toxic. This group of reddish-brownish gases includes nitrous oxide (N0), which is not particularly toxic; nitrogen oxide (NO); nitrogen trioxide, also known as nitrogen sesquioxide (NO0; nitrogen peroxide, also known an dinitrogen tetroxide (N); nitrogen dioxide (NO); dinitrogen pentoxide (N); and trinitrogen tetroxide (N3O4). The nitrogen oxides are particularly hazardous because they may produce symptoms similar to those of a heart attack, sometimes up to 48 hours after exposure. Nitrogen oxide poisoning, especially when accompanied by delayed symptoms, usually is fatal.
Sodium nitrate is toxic by ingestion. Although no TLV-TWA (threshold limit value-time weighted average) or STEL (short-term exposure limit) values are available, at least one reference lists sodium nitrate as an experimental tumorigen and as moderately toxic by ingestion and a poison if injected intravenously. One reference lists sodium nitrate as having an LD of 5 to 15 grams per kilogram.
Sodium nitrate (molten, not as a water solution) has been used in salt baths, which are used in tempering metals. Tempering involves hardening a metal by heating it to red-hot or white-hot temperatures and then cooling it suddenly. This cooling is done by immersing the metal part in a liquid after the metal part has been heated to the proper temperature. However, cooling the part rapidly down to the temperature of water (less than 212°F) drops the temperature of the part too far and may cause crystallization of the metal. Therefore, a molten material that has a temperature more suitable for the cooling process is necessary, and molten sodium nitrate is in that range. Its melting point of 584°F is a convenient one, since it is close to 600°F, the proper cooling temperature to impart the proper hardness to some metals.
Molten sodium nitrate salt baths present problems of which you must be aware. If the temperature controls allow the molten sodium nitrate to reach its boiling point of 7l6°F, the sodium nitrate will decompose and begin to liberate the toxic nitrogen oxides. If the molten liquid below the boiling point escapes its container, an extremely dangerous situation will occur. The molten sodium nitrate will flow along the low spots in the floor of the operation, mixing with any organic material present and producing a potentially explosive mixture. If it reaches a drain and enters a sewer line, the organic material usually found in sewers will provide the fuel side of the fire triangle, and all that is needed to produce a fire is a source of energy. Such a fire may be almost impossible to extinguish because the mixture w ill contain its own source of oxygen (the sodium nitrate) and will burn even if submerged in water.
NONFIRE RELEASE
Often in the case of the release of solid hazardous materials such as sodium nitrate, the danger is not recognized by the first responders, and the area’s emergency response plan may not be implemented. Certainly, if any appreciable quantity of sodium nitrate is released, you must implement the plan, alerting all safety forces, governmental agencies, and the proper environmental authorities.
As with any release of sodium nitrate or other inorganic oxidizing agents, the major concern is to keep it from contacting organic material or anything else that will burn. Since sodium nitrate is usually shipped as a free-flowing powder, if it is accidentally released, it will be easier to handle and salvage than a liquid material.
In any accidental release of any hazardous material, some organic material almost always is contacted. Soil contains organic material, the asphalt on a highway is organic (and a “good” fuel), and the wood in railroad ties (not to mention the organic materials used to treat them) is also a good fuel source. The important thing to remember in such a release is not to perform any act that will produce heat through friction, such as scooping sodium nitrate from the ground with a shovel. Salvage or cleanup of any spill of hazardous materials should be left to professional salvage firms, w hich provide properly educated, trained, and equipped workers to
perform this dangerous job. If possible, cover the released sodium nitrate powder with sheets of compatible material to keep it from blowing around and to prevent rain or other water from reaching it.
If sodium nitrate reaches a waterway in the solid form (as in an accident where a truck or rail car spills its load directly into a river, stream, lake, or pond), the solid material will sink to the bottom and dissolve fairly quickly. If the release is into a contained body of water, consult the manufacturer of the sodium nitrate for proper treatment of the water. If the spill is into a moving waterway, immediately alert all downstream water users and processors. All industrial intakes must be closed immediately,
and the contaminated water must be prevented from entering any drinking water system. The faster the movement and the larger the volume of the water, the more the sodium nitratewall be diluted anti the quicker the emergency will pass. The environmental experts will test the water to determine if it is safe to use.
Slower-moving streams may be dammed and/or diverted into lowlying areas where the contaminated water may be held, treated (according to manufacturer’s specifications), and released back into the waterway. There will be some damage to wildlife and waterfowl, but it will not be as great as if a powerful poison had been released into the water.
The same care must be used to prevent sodium nitrate from entering a sewer system. If such an entry does occur, notify sewage treatment plants. Care to prevent an explosion must be taken throughout the system. Deliberate dilution by flushing with water may be the proper mitigation technique if the environmental authorities agree and a large volume of water can be used. Since the principal danger is the intimate mixing of an oxidizing agent with a fuel, the more diluted the solution is, the less the chance of a fire or explosion.
IDENTIFICATION NUMBERS AND RATINGS
CAS
(Chemical Abstract Services)
7631-99-4
STCC
(Standard Transportation Commodity Code)
4918746
RTECS
(Registry of Toxic Effects of Chemical Substances)
WC5600000
UN/NA
(United Nations/North America)
1498
CHRIS
(Chemical Hazard Response Information System)
SDN
DOT
(U.S. Department of Transportation)
oxidizer
NFPA 704 Rating
1 -O-O-OXY
IMO
(International Maritime Organization)
5.1; oxidizing substance
Indeed, one of the mitigation techniques that can be used to reduce the danger of a fire once the sodium nitrate has been released on ground is to add water to dissolve the solid oxidizer. This should be done only if there is imminent danger of a fire because of the dangerous mixture that has occurred, and only if the resulting solution can be contained.
A safer mitigation technique is to have the product’s manufacturer, shipper, or buyer mechanically salvage the material. In any case, after the material has been removed, the environmental experts will have to determine the amount of soil contamination that has occurred and oversee its removal and disposal.
FIRE SCENARIO
Sodium nitrate will not burn, but its greatest hazard is the evolution of oxygen, which will support a fire. An intimate mixture of sodium nitrate with anything that burns produces an extremely hot fire and, in some cases, a very dangerous explosive mixture. This intimate mixture also may produce a situation where even the application of water may not extinguish the fire. An example of such a mixture is a flare, which once ignited must be allowed to burn out. since even the act of placing the flare under water will not extinguish it.
However, if the fire must be extinguished, or at least cooled down, to effect life rescue or to protect exposures, applying flooding amounts of water may be the only mitigation technique available to firefighters. The water must be applied from as great a distance as possible using unmanned appliances. The risk that molten sodium nitrate might be splashed around the water, spreading the danger, is always present. This is highly probable in attacking a fire where sodium nitrate is used as a salt bath. Steam explosions are also likely. As always, attempt to control the runoff water.
Sodium nitrate’s secondary hazard is the evolution of the very hazardous nitrogen oxides, produced by the energy of the fire causing a breakdown of the nitrate portion of the compound. This hazard is greater in smaller fires; in larger fires, the products of combustion and decomposition are more likely to be carried upward on the thermal column and dispersed relatively safely higher in the atmosphere. The hazard of the nitrogen oxide generation also will be high where the sodium nitrate is stored in a metal container or in large piles (free of organic material), where radiated heat will affect the material and cause its decomposition. Any sighting of reddish-brownish gases in an incident involving sodium nitrate indicates the presence of these toxic gases and reinforces the need for respiratory protection even when fighting fires from outside a building.
As in any situation where a hazardous material, its combustion products, or its decomposition products are involved, if no life is threatened, the environment is not endangered, no systems (such as drinking water, communications, or transportation) are endangered, and no exposures must be protected, do not attempt to intervene in the incident other than to prevent innocent bystanders from being injured. Let the incident run its course safely, and then bring in the professionals for cleanup. The bill, of course, should be picked up by the party responsible for the incident.
PROTECTIVE CLOTHING AND EQUIPMENT
Choose protective clothing and equipment that prevent contact of the sodium nitrate powder with the eyes or skin. Normal rubber gloves, aprons, boots, safety’ goggles, and face shields should suffice. NIOSH-approved dust respirators may be used in nonfire scenarios. However, in a fire or wherever the sodium nitrate may be exposed to extreme heat, positive-pressure, self-contained breathing apparatus must be used. There is no material that will protect a firefighter from the extreme heat of a fire involving sodium nitrate and, of course, nothing but distance will protect anyone from the effects of an explosion.
FIRST AID
For inhalation of the sodium nitrate dust, 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 immediate medical attention.
For eye contact, flush the eyes immediately for at least 15 minutes, lifting the eyelids occasionally. Immediate medical attention is required.
For skin contact, wash the affected areas of the body with large amounts of soap and water. If irritation continues after w ashing, seek medical attention.
Very little information is available concerning the effects of ingestion of sodium nitrate, so immediate medical attention is mandatory.
Originally ran in Volume 144, Issue 12.
