Chemical Data Notebook Series #27 Potassium Nitrate
FEATURES
HAZARDOUS MATERIALS
Potassium nitrate (chemical symbol KNO3) is an oxidizing, moderately toxic, white or colorless, odorless, ionic crystalline solid with a pungent, salt-like taste. It’s used in the manufacture of explosives, fertilizers, matches, pharmaceuticals, and rocket propellants. It’s also used in the glass, tobacco, meat processing, and metallurgy industries. It’s shipped in the form of solid crystals or powder.
Properties
Potassium nitrate won’t burn, but it will supply oxygen to support a fire. If involved in a fire, it will liberate oxygen, potassium oxide, and nitrogen oxide, a very toxic, reddish-colored gas. The compound has a molecular weight of 101 and a specific gravity of 2.11. It melts at 633°F, decomposes at 752°F, and is very soluble in water.
It’s a stable material in normal storage and transportation. It’s not water-reactive, but it will react violently (explode) when mixed with any material that burns easily. It will also explode when mixed with many sodium esters, sodium phosphate, lead phosphite, lead nitrite, tin, and tin compounds.
Hazards
Potassium nitrate’s major hazard is that it’s an oxidizer or oxidizing agent. The classical definition of an oxidizer is a material containing oxygen that gives it up readily, or otherwise supports combustion.
Giving up oxygen readily means that the slightest input of energy — either as heat or pressure — will separate the oxygen from its chemical combination and release it as ready to support combustion. This combustion can be in the form of a fire, or it can be an explosion or detonation.
Many factors will determine the speed of the reaction: the nature of the potassium nitrate-fuel mixture (the fuel being anything that will burn, usually organic in nature); the chemical nature of the fuel itself, its moisture content, and its size (surface area); the temperature of the materials; the homogeneous nature of the mixture; and the mixture’s confinement, or lack of it.
‘There are some oxidizing agents, such as the halogens, that contain no oxvgen. Conversely, there are many materials that contain oxygen—water, sand, and carbon dioxide, for instance—but do not give it up readily. The latter will give up their oxygen only under extremely energy-filled circumstances. The water molecule can be torn apart by the tremendously high temperatures of the center of a coal pile fire, and metallic sodium will rip apart the molecule to get the oxygen. Water, sand, and carbon dioxide can all be broken apart by burning metals, particularly magnesium, but these instances where they give up their oxygen are rare indeed. In fact, these materials are mostly used as fire extinguishing agents.
Potassium nitrate is one of the most common oxidizing agents in use today. It’s used to make gunpowder and used by terrorists in the manufacture of black powder.
Noncommercial black powder is extremely hazardous because of its extreme sensitivity to heat. Just about any mixing action will produce enough frictional heat to cause the material to deflagrate or, if confined, explode. The simple act of pouring it from one container to another may cause a discharge of static electricity great enough to cause ignition. Black powder is so sensitive that one author claims the energy used by a fly in walking up a wall is sufficient to effect its ignition. This sensitivity is due to the ease with which potassium nitrate will liberate its oxygen.
The ease with which potassium nitrate liberates oxygen and its subsequent intimate contact with the fuel portion of the mixture makes ordinarily difficult-to-burn materials very flammable, and easy-to-burn materials explosive. Oxygen’s normal presence in our atmosphere is approximately 21%, but in a mixture where oxygen is being generated, the concentration of oxygen in the air may be 80% or higher. All materials burn hotter and faster when the concentration of oxygen is higher, and it’s this increased rate of combustion that can cause a deflagration or detonation of ordinary combustible materials.
Potassium nitrate itself won’t burn, but one authority has stated that there is a possibility of explosion if it is involved in a fire. The possibility of nitrogen oxide generation exists when potassium nitrate is exposed to fire, and this byproduct is very toxic.
Potassium nitrate is considered to be of moderate toxicity, but severe problems can develop if significant amounts are ingested. These problems include diarrhea, increased urination (potassium nitrate is also sold as a diuretic for some animals), muscular problems, nausea, and even death. Contact with the skin and/or eyes will cause irritation, and the inhalation of potassium nitrate dust can cause irritation of the mucous membranes. In spite of its rating as being moderately toxic, potassium nitrate is approved as a food additive for human consumption. Obviously, the amount of potassium nitrate ingested must be limited to very small amounts!
Non-fire spills
Potassium nitrate is shipped in trucks and rail cars and packed in boxes, bags, and cartons. Any release of the material will be in a granular or powder form. Care must be taken to keep the spilled dust or powder from blowing around, and this can be done by covering with a plastic or rubber sheet or other covering that will keep the material from being disturbed. l he covering will also prevent rain or other moisture from reaching the material, which is very soluble in water.
If the material can’t be covered and rain is imminent, a containment pond can be constructed by using sand, clay, or other inorganic material to dike around the product and contain the subsequent solution that will be created by the potassium nitrate dissolving in the rainfall.
Care should be taken to keep all organic material from contacting the potassium nitrate, because this mixture now constitutes two sides of the fire triangle. All that’s missing is the energy to provide the ignition of a now highly combustible mixture.
Synonyms
nitre
potassium salt
saltpeter
nitric acid
potash nitrate
vicknite
Identification Numbers and Ratings
UN/NA
(United Nations/North America)
1486
CAS
(Chemical Abstract Service)
7757-79-1
RTECS
(Registry of Toxic Effects of Chemical Substances)
TT3700000
STCC
(Standard Transportation Commodity Code)
4918741 — crude
4918737 – refined
IMO
(International Maritime Organization)
5.1, oxidizing substance
NFPA 704 rating
(National Fire Protection Association)
1-O-O-OXY
Once confined, the product can be salvaged by vacuuming the dry material into clean, secure containers. Potassium nitrate may be shoveled, but extreme care must be taken if the product has come into contact with soil, which contains organic material. The friction heat of the shovel passing through the granular potassium nitrate might provide enough energy to liberate oxygen and cause ignition of the organic material in the soil.
Water can be used deliberately to dissolve the product, but the solution must be contained. If the organic material comes into contact with a solution of potassium nitrate and water, and the water evaporates, it will be covered with a very fine coating of potassium nitrate. The intimate contact with this finely divided powder not only presents a severe fire hazard, but also an explosion hazard. Furthermore, the potassium nitratewater solution will percolate into the soil, spreading the contamination and causing intimate mixture of organic substances with an oxidizer as the material dries out.
If water has been used deliberately to dissolve the potassium nitrate, or the product has been dissolved by the falling rain (and in both cases, contained in a containment pond or pit), the contained solution can be pumped or vacuumed into secure containers by well-trained professional salvage teams.
In any event, all ignition sources should be eliminated when mitigating an incident involving any oxidizing agent. If mechanical devices such as graders and frontend loaders are used to build containment ponds or dig containment pits, or used to remove the product, care must be exercised to avoid producing enough frictional heat to cause ignition of the mixture of potassium nitrate and organic material.
Cleanup and removal of hazardous materials should be done by well-trained and well-equipped professionals. This may mean involving a private salvage firm to remove the product, unless emergency responders fit this description.
The proper environmental authorities should be notified of the spill of any hazardous material, and they’ll make the final determination of contamination spread and depth of removal of contaminated soil. These authorities may have experience with spills of this nature and will have to conduct several tests to determine when the area can be declared decontaminated and safe.
If the spill has occurred in a waterway, all downstream users must be notified immediately, and intake of water for human or animal use must be stopped until contamination levels are monitored and considered to be safe.
If possible, the contaminated water should be diverted from streams and waterways, and contained until purification treatment is completed. If the spilled product is in crystalline or powdered form, it will dissolve fairly quickly, especially in a rapidly moving waterway.
If the contaminated water can’t be diverted, it must be monitored continually as the dissolved product moves downstream. Eventually, the solution will be diluted to a point that even the most sophisticated testing equipment will not be able to detect its presence. This rate of dilution depends on the amount of potassium nitrate spilled, the amount of water in the waterway, and how fast it is moving.
A very hazardous situation will be created if the spilled product or a solution of the spilled product enters a sewer. Sewers generally contain a great deal of organic matter, and if potassium nitrate is allowed to mix with it, a potentially explosive situation will be created. Even a water solution entering the sewer is hazardous.
If the solid potassium nitrate or potassium nitrate solution enters a sewer, notify the sewer treatment facility at once. The manufacturer of the product should also be notified. Flushing the sewer to eliminate the explosion hazard may be recommended. Isolation of the solution by the sewage treatment facility may be a viable mitigation technique. The facility may choose to evaporate the contaminated water or dilute the isolated solution to the point that it is totally harmless.
Fire situation
If potassium nitrate is directly involved in a fire, there is the possibility of an explosion. If an approaching fire threatens the spilled product, it might melt and begin to flow. All water used on the fire may have to be contained, since it will contain dissolved potassium nitrate. Water may be deliberately used on the spilled product to dissolve it and protect it from the heat, thereby removing the possibility of the generation of oxygen. This water must also be contained.
Water contacting the molten material will flash into steam because of the temperature of the molten potassium nitrate, but it will rapidly cool the molten product and then dissolve it.
During the exposure of extreme heat, the potassium nitrate may decompose and liberate deadly nitrogen oxide. This is signalled by the appearance of a reddish-colored gas. Positive-pressure, selfcontained breathing apparatus is always required in a situation in which nitrogen oxide may be present.
First aid
For skin contact, remove all contaminated clothing and wash the affected body area with large amounts of water. If irritation persists after washing, medical attention may be necessary.
For eye contact, flush the eyes with water for fifteen minutes, occasionally lifting the eyelids. If irritation remains after flushing, or vision changes are noticed, seek immediate medical attention.
For inhalation, remove the victim to fresh air immediately. Apply artificial respiration if breathing becomes difficult or stops. Immediate medical attention should be sought.
For ingestion, medical attention should be sought immediately.
Protective clothing
All clothing and equipment used must prevent contact of the product with the skin and respiratory system. This includes rubber gloves and boots, face shields and goggles, and any other clothing impervious to the product. SCBA should be worn during all firefighting procedures. For normal handling (non-fire situations) and involvement with the powder or dust (again, non-fire situations), a NIOSH-approved dust mask may protect the respiratory system.
Totassium nitrate is a very strong oxidizing agent, and as 1 such, will provide oxygen to support combustion at the slightest addition of energy. It’s this ease of release of oxygen that makes it valuable to industry. Mixtures of potassium nitrate and organic materials should be prevented from occurring, but if they do occur, all ignition sources must be eliminated, and handling of the mixture should be avoided. Any frictional energy caused by handling could ignite the mixture explosively.
Potassium nitrate is a stable chemical, but can react violently with many materials. It’s very soluble in water, and because of this, might spread its contamination and danger beyond the original spill site.
Glossary
Halogen — Any member of Group VII of the Periodic Table of the Elements. The common halogens are fluorine, chlorine, bromine, and iodine.
Inorganic — All chemicals except hydrocarbons and their derivatives.
Ionic — Those chemicals whose structure is held together by an ionic bond. The ionic bond is the electrostatic attraction of oppositely charged ions.
Oxidizer — Also called oxidizing agents. It is a substance that contains oxygen and will give it up readily, or will otherwise support combustion. There are oxidizers, such as the halogens, that contain no oxygen.
Organic — Any chemical that is a hydrocarbon or hydrocarbon derivative.
