CHEMICAL DATA NOTEBOOK SERIES #105: SODIUM HYDROSULFIDE
BY FRANK L. FIRE
Sodium hydrosulfide is a water-reactive, toxic, corrosive, irritating, colorless-to-lemon-colored, flammable solid with an odor of rotten eggs. Its common uses include bleaching; chemical milling solutions; the dehairing of animal hides; glassmaking; ore flotation; paper pulping; the processing of dyestuffs; and the manufacture of cellophane, rayon, and many chemicals.
Water solutions and one solid form of sodium hydrosulfide are classified as corrosive materials. The product is fully soluble in water and reacts with it, slowly evolving toxic hydrogen sulfide gas that is also flammable and potentially explosive if ignited while confined. The hydrogen sulfide gives the odor of rotten eggs to the sodium hydrosulfide.
PROPERTIES
Sodium hydrosulfide is known principally as a flammable solid. It spontaneously ignites but has no known flash point. Any explosive (flammable) range reported is that of hydrogen sulfide, which is from 4.3 percent to 46.0 percent in air. The boiling point of sodium hydrosulfide is not reported. Various references list its melting point as 131°F, 328°F, and 650°F. One reference states that sodium hydrosulfide decomposes at its boiling point, listed at 131°F. Its specific gravity is 1.79, and its molecular weight is 56; it is soluble in water in all proportions. Its chemical formula is NaSH.
HAZARDS
Sodium hydrosulfide`s main hazards are that it is a flammable solid and a water-reactive material. As it is exposed to the atmosphere, it begins to react with the moisture present, producing hydrogen sulfide and generating heat. Eventually, the heat buildup is great enough to accelerate the generation of hydrogen sulfide and then to ignite the gas. If the buildup of the heat is slow, a large amount of the gas may be formed over time. If there is no air disturbance, the buildup of gas might be sufficient to produce a devastating explosion on ignition.
If the hydrogen sulfide is not ignited, it can be fatal to anyone exposed to it without proper respiratory protection. The first effect this toxic and flammable gas has on humans is the deadening of the olfactory nerve, killing the sense of smell and leading to a deadly exposure to a gas the exposed person believes is no longer present. The STEL (short-term exposure limit) for hydrogen sulfide is 15 ppm for 15 minutes; the TLV-TWA (threshold limit value-time weighted average) is 10 ppm over each eight hours of a 40-hour workweek.
Sodium hydrosulfide is considered to be stable during normal transportation. Solutions containing 45 percent of this product are slightly corrosive to iron and steel and very corrosive to aluminum, zinc, and copper. The pH of such a solution is between 9.5 and 10. (A pH in the range of 7.1 to 14.0 is alkaline, or caustic; a pH of 7.0 is neutral; and one of 6.9 or below is acidic.) Contact with acids may result in the evolution of large quantities of hydrogen sulfide gas. Reactions of the solid product with diazonium salts may be violent or explosive. Sodium hydrosulfide is highly toxic, irritating, and corrosive to body tissue. Its decomposition under fire conditions produces additional hydrogen sulfide. Products of combustion are likely to include other toxic sulfur compounds.
Contact with solid sodium hydrosulfide or strong solutions thereof can cause slow-healing burns of the skin with some scar formation. Dilute solutions, mists, or hydrogen sulfide gas may only irritate the skin.
Eye contact with sodium hydrosulfide or strong solutions containing it may result in pain, tearing, sensitivity to light, conjunctival edema, and possible irreversible damage to the cornea. Sodium hydrosulfide dusts are extremely corrosive to the eyes.
Inhaling hydrogen sulfide may result in breathing difficulty, choking, coughing, dizziness, headache, irritation, weakness, and eventually death–if the concentration is high enough. Chest tightness, cyanosis, and pulmonary edema may be delayed six to eight hours or longer. Severe nonfatal exposures can cause brain damage and permanent loss of the sense of smell.
Ingesting sodium hydrosulfide can cause burns of the mouth, tongue, esophagus, and gastrointestinal tract; diarrhea; nausea; and vomiting. Collapse, unconsciousness, and death due to respiratory paralysis can occur if large quantities are ingested. Hydrogen sulfide will be generated when the swallowed product contacts the hydrochloric acid in the stomach.
NONFIRE RELEASE
The release of any appreciable quantity of sodium hydrosulfide must be considered dangerous because of the material`s hazards and the different manners in which they may manifest themselves. The release should trigger the community`s emergency re-sponse plan, providing the incident commander with all the resources needed to mitigate the emergency.
If sodium hydrosulfide is leaking but not on fire, it is possible that it will generate large amounts of hydrogen sulfide gas. Therefore, downwind evacuation from the immediate spill area should be considered until properly equipped responders have evaluated the hazard. This decision must be made on a case-by-case basis according to all the circumstances of the individual incident.
Even though sodium hydrosulfide is a solid material, the release must still be approached from upwind and uphill because the product may be reacting with the moisture in the air and release toxic and flammable hydrogen sulfide. If the release is of the product in solution, the corrosive properties of that solution must be considered, as must the possibility that hydrogen sulfide may also be released.
Spilled sodium hydrosulfide may be covered by a plastic sheet or another impervious material, to protect it from moisture and contain any hydrogen sulfide being released. The product may be shoveled into secure containers; the shovels must not be made of a metal with which the product will react such as aluminum, zinc, or copper. This salvage activity should be performed by professional members of a salvage firm, since they have been properly educated, equipped, and trained in such activities.
If the product cannot be covered, a water spray can be used to sweep hydrogen sulfide gas or sodium hydrosulfide dust from the air; the water must not be allowed to contact the released solid sodium hydrosulfide.
Sodium hydrosulfide–solid and in solutions–must be prevented from entering the sewer system or waterways. This can be done by using catch basins, damming waterway entries, building containment ponds, or digging containment pits. Appropriate hoses, pumps, and storage containers or vacuum trucks may be used to recover accumulated liquid pools. Equipment must be compatible with the spilled product. Remaining spilled liquid may be controlled by absorbing it with cement powder, clay, earth, fly ash, sand, commercial sorbents, or other compatible substances. The used sorbent materials–which add to the overall volume of contaminated material–pose the same hazards as the spilled product and must be handled in the same safe manner. All contaminated soil must be removed and disposed of in accordance with all federal, state, and local regulations.
Any entry of sodium hydrosulfide into a pond or lake could be fatal to aquatic life near the point of entry. The product will dissolve in the water and slowly spread away from the point of entry. If the entry is into a river or stream, the contamination will be carried away and mixed throughout the water at a rate proportional to the speed of the moving water. If the volume of moving water is great, the material will dissolve and dilute faster. All possible downstream users of the water must be notified immediately if the product enters a waterway. The environmental authorities will have to determine the extent of contamination and when the water will be safe to use once again.
According to one reference, the product can be neutralized by applying a suitable neutralization agent to the contaminated water, which may reduce environmental hazards. Neutralization is defined as the chemical reaction in which an acid and a base are reacted, bringing the resulting solution to a pH of 7.0 (neutral). Neutralization is also any reaction caused by the reaction of two or more chemicals that results in a neutral solution. It is not clear whether the reference is referring to a water solution of sodium hydrosulfide in addition to any water contaminated by it. In any event, the pH of typical sodium hydrosulfide solutions is between 9.5 and 10. Although adding an acid to the solution will begin the neutralization process, keep in mind that since contact of solid sodium hydrosulfide with acids may result in the evolution of large quantities of hydrogen sulfide gas, this same reaction could take place in a concentrated solution. As always, a small amount of the solution should be used first to see if adding an acid will cause such a release. Don`t forget: Acids are hazardous materials also and can cause great harm if handled or used in an improper manner.
FIRE SCENARIO
Should the released material be exposed to fire, keep in mind that excess heat can cause the product to decompose and release hydrogen sulfide. If the exposure is to the heat of a fire, the product may seem to burst into flame as the hydrogen sulfide is ignited. If enough hydrogen sulfide accumulates before ignition, an explosion may occur.
Containers of sodium hydrosulfide exposed to heat or flame should be cooled with water from unmanned appliances positioned as far away as possible unless there`s a chance that the containers may be breached by the water, which would result in the contamination of the surrounding area.
However, if it is possible to contain large volumes of water, adding flooding amounts of water may be a viable mitigation technique as long as it is always kept in mind that the resulting solution will be corrosive and some hydrogen sulfide may be released from the solution. This technique might prevent large quantities of hydrogen sulfide from being released rapidly, but it will create large volumes of corrosive liquid, which will have to be neutralized or removed as a hazardous material in itself.
In any event, if hydrogen sulfide is being released in quantities that could endanger human life, deliberate ignition of the released gas may be a possible solution. Deliberate ignition of any gas should not be done unless the possibility of an explosion is negligible. This decision can be made only by the incident commander–only after consultation with all available resources.
At least one reference lists dry chemical, foam, and water spray as appropriate extinguishing agents. The use of water in the small amounts present in foams and sprays is questionable, since contact with moisture may cause more material to burn. It may be best to evacuate the area and let the product burn to consume any hydrogen sulfide or other organic sulfur compounds formed, while you protect exposures.
PROTECTIVE CLOTHING AND EQUIPMENT
All protective clothing and equipment must be selected to provide the emergency responder with the maximum respiratory, eye, and skin protection against sodium hydrosulfide. Regular turnout gear impervious to penetration by powdered solids and corrosive liquids may protect skin against contact with the powder or alkaline solution. Protection may involve using methods that prevent powder from entering through sleeves and pants cuffs. Rubber boots, gloves, aprons, coveralls, and hoods may offer protection. Fire department standard operating procedures should call for the use of total encapsulating suits. The manufacturers of the department`s suits and of the sodium hydrosulfide can help departments determine the level of protection the suits provide against sodium hydrosulfide. Their opinions should include the levels of protection for both the powdered solid and the alkaline solutions.
Chemical-resistant goggles that will not permit powder to pass through must be worn under a face shield. Positive-pressure, self-contained breathing apparatus is required.
FIRST AID
Inhalation. Move the victim to fresh air; keep him warm and at rest. If breathing stops or becomes difficult, administer artificial respiration. (Avoid mouth-to-mouth contact, since the first aid giver may be exposed to the chemical in the victim`s lungs or vomit.) Obtain immediate medical attention.
Some references may advocate the use of amyl nitrite as an antidote for hydrogen sulfide exposure. The use of amyl nitrite is controversial in this application and should be used only on a physician`s advice.
Eye contact. Immediately flush eyes with lukewarm water, gently flowing water for 20 minutes while holding the eyelid open. Do not rinse contaminated water into the nonaffected eye. If irritation persists, repeat flushing. Obtain immediate medical attention.
Skin contact. Remove all contaminated clothing at once. Wash the affected body areas with large amounts of water. Get immediate medical attention.
Ingestion. If the victim is conscious, administer large quantities of milk or water immediately. Do not attempt to make the victim vomit. Get medical attention immediately. At least one reference advises that fluids be given again if vomiting occurs naturally. n
 |
 |
FRANK L. FIRE is the vice president of marketing for Americhem Inc. in Cuyahoga Falls, Ohio. He is 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.
