CHEMICAL DATA NOTEBOOK SERIES #99: PHOSPHORUS PENTASULFIDE
HAZARDOUS MATERIALS
Phosphorus pentasulfide is a highly reactive, flammable, water-reactive, toxic, hygroscopic, light green to greenish-gray solid with an odor of rotten eggs. It is used to manufacture asphalt, flotation agents, insecticides, oil additives, and safety matches.
Phosphorus pentasulfide is a solid that has no flash point. It has an ignition temperature of 287 ’F, and the lower explosive limit (EEL) of its dust is 0.5 ounce per cubic foot. There is no determined upper explosive limit (UEL). It has a specific gravity of 2.03 and a molecular weight of 222. It melts at 527°F. boils at 955°F, and is soluble in caustic solutions such as sodium and potassium hydroxide. Phosphorus pentasulfide reacts slowly with water to liberate hydrogen sulfide, a very toxic and flammable gas. Phosphorus pentasulfide’s chemical formula is P.
HAZARDS
Phosphorus pentasulfide is classified as a flammable solid, which is an extremely hazardous property. A flammable solid is any solid material, other than an explosive, that is liable to cause fires through friction or through retained heat from manufacturing or processing or that can be ignited readily and when ignited burns so vigorously and persistently as to create a serious transportation hazard.
The combustion products evolved when phosphorus pentasulfide burns include sulfur dioxide, phosphorus pentoxide. phosphoric acid, and hydrogen sulfide. Sulfur dioxide is a toxic, corrosive, irritating, colorless gas with a sharp, choking odor and a wide range of uses. Some skin irritation could result at low concentrations due to the formation of sulfurous acid as the sulfur dioxide dissolves in the moisture on the skin.
Phosphorus pentasulfide’s ignition temperature, listed in some references as its autoignition temperature, is 287°F. This temperature is extremely low and can be reached not only by all common ignition sources but also by simple friction. Thus phosphorus pentasulfide is extremely hazardous because it can be ignited at such very low temperatures.
The use of the term “autoignition” is gaining popularity, as it is more descriptive of the way substances ignite. The term “ignition” in “ignition temperature.” defined as the temperature to which a substance must be raised before it will ignite, may convey that there has to be an ignition source before the fire will occur. “Autoignition” should convey that all that is needed is some input of energy that will cause some small part of the material to reach the specified temperature and ignite. The input of energy could come from an ignition source such as an open flame or a spark, but it could also come from radiant heat, the heat of a chemical reaction, friction, or any other source that would cause the ambient temperature to rise to that level.
Reactivity is another hazard of phosphorus pentasulfide. The chemical reacts slowly with water to form phosphoric acid and hydrogen sulfide. Phosphoric acid is a corrosive, toxic, irritating, nonflammable, colorless, odorless liquid or crystalline solid. Since one of phosphoric acid’s major uses is in soft drinks and other beverages, emergency responders might mistake it for a nonhazardous material. However, concentrated phosphoric acid is a very corrosive material.
Hydrogen sulfide is a toxic, flammable, irritating, colorless gas with a distinctive, offensive odor. Its major hazard is that it is a very toxic gas. Another hazard is that it can hide the biggest clue to its existence: its powerful and disagreeable odor. It is considered a stable chemical: but since it is flammable, it also presents an explosion hazard. And since phosphorus pentasulfide’s reaction with moisture also generates heat, the reaction itself might be the cause for the ignition of the hydrogen sulfide.
Phosphorus pentasulfide is considered toxic. Its TLV-TWA (threshold limit valuetime weighted average—the amount of material to which a worker may be exposed in a normal w’orkweek with no adverse effects) is 1 mg/m (1 milligram per cubic meter of air). Its STEL (short-term exposure limit—the amount of material to which a worker may be exposed in a very short time, usually 15 minutes, with no adverse effects) is 3 mg/m’.
Symptoms of exposure to phosphorus pentasulfide include mild to moderate skin irritation. If inhaled, symptoms include apnea, conjunctivitis pain, coughing, dizziness, fatigue, headache, insomnia, irritability. lacrimation (tearing of the eyes), and respiratory irritation. Inhaling high concentrations can cause severe breathing difficulties. pulmonary edema, respiratory failure, and death.
Phosphorus pentasulfide is hygroscopic, which means that it has such an affinity for water that it will absorb any moisture in the air or any of its surroundings. The reaction will liberate hydrogen sulfide.
Phosphorus pentasulfide also reacts with acids, alcohols, oxidizing agents, and many other chemicals. These reactions may be very violent, evolving toxic gases, corrosive liquids, and other hazardous reaction products.
Phosphorus pentasulfide is not corrosive when dry; however, as it reacts with water and forms phosphoric acid, the solution becomes corrosive to living tissue, metals, and some minerals.
NONFIRE SCENARIO
Any release of any appreciable amount of phosphorus pentasulfide should trigger the community’s emergency response plan. It is not always possible to protect spilled material from moisture, so the first hazard is the generation of highly toxic and flammable (explosive) hydrogen sulfide. If the spill has occurred on damp ground, the generation of hydrogen sulfide will begin. Confinement of the heat generated by the pile of material may allow the hydrogen sulfide to be ignited.
If the release is on dry ground, there is still concern about the moisture in the air. As hydrogen sulfide is generated, there will be a distinct odor of rotten eggs. However, those who are exposed to the gas may think the odor has disappeared, since the gas deadens the sense of smell. Thus, those exposed may be overcome by the gas quickly. This is the main reason that anyone handling a release of phosphorus pentasulfide must wear respiratory protection at all times.
For any release of phosphorus pentasulfide, evacuate everyone near the release and consider evacuation for a minimum of onehalf mile downwind. Approach the release site from upwind to avoid igniting the hydrogen sulfide. Hydrogen sulfide’s vapor density is 1.1. Since the vapor density of air is 1.0, any gas with a vapor density higher than 1.0 will sink to the ground and flow along low spots in the terrain. However, 1.1 is just slightly higher, and any breeze will quickly disperse the gas. If the day (or night) is calm, responders may want to disperse any generated gas by using a highpressure spray or fog in the direction the gas is moving, being extremely careful not to allow water to contact the solid material.
Protect the solid material from the wind and air by covering it with a plastic sheet or other compatible material, making sure no water is introduced with the cover. Properly protected, equipped, educated, and trained salvage teams can remove the product. Firefighters should not be involved in salvage operations.
Surround the released phosphorus pentasulfide with dikes of dry earth, sand, or other materials. Prevent entry of the material into sewers or waterways.
Any entry of phosphorus pentasulfide into a sewer system presents a toxic and explosive danger throughout the sewer system. There almost always is water present in such systems, and contact of the water with the material will generate large amounts of hydrogen sulfide in a somewhat confined space. The gas will follow the pipes downhill and uphill and spread as far as the continued generation of gas forces it. The gas will travel slowly throughout the system, and there will be an explosion anywhere the gas exists within its flammable range (4.3 to 46 percent in air) and finds an ignition source producing enough energy to raise a small part of the gas to its ignition temperature (5()0°F). Warn all sewage treatment facilities of any entry into the system and eliminate all possible ignition sites.
Any entry of phosphorus pentasulfide into any water will begin the generation of hydrogen sulfide. If the material enters a stationary body of water, such as a pond or lake, the generation of gas and contamination of the water will be localized. In this case, you can use water spray or fog directly over the source of the gas to disperse it, since it already is in water. After the incident has run its course, the environmental experts who responded as part of the emergency response plan should determine which neutralizing agents (if any) should be used to counter the generation of phosphoric acid. The size of the body of water and the amount of material entering it will determine the degree of concentration of the contamination. If all the material has reacted and the body of water is large enough, no action may lx* necessary to return the water to a safe condition after some time has passed. Aeration of the water may be necessary to remove any hydrogen sulfide dissolved in the water. There probably will be damage to aquatic life in the area of the spill.
If the release is into a stream or river, it will be more widespread and difficult to control. If the water is moving rapidly, the reaction of the material will be faster, and the hydrogen sulfide will be released more rapidly and over a larger area. The phosphoric acid generated will be carried farther, but it also will be diluted more rapidly and may cause little harm.
If the water is slow moving, the contamination by the acid and the generation of the gas will be more concentrated. In some cases, it may be possible to divert the contaminated water into a low-lying area, where it may be treated and purified before being returned to its natural flow. All activity during water diversion and treatment must be carried out by personnel protected from the toxic effects of the gas and w ith no possible ignition sources present that could cause the gas to explode.
Immediately notify all downstream users of the water of any contamination. Any intake of contaminated water by an industrial end user (or any user) could cause damage to equipment at best and could poison personnel and/or cause an explosion and fire at worst.
FIRE SCENARIO
If any released phosphorus pentasulfide or any containers of phosphorus pentasulfide are threatened by fire, prevent the fire and its radiant heat from reaching the material or heating the containers. If any of the material reaches 287°F. it will ignite and begin to decompose. The products of combustion include phosphorus pentoxide, phosphoric acid, sulfur dioxide, and hydrogen sulfide, which might be ignited by the heat of the reaction. Water may be used to fight the fire, but it must not contact the phosphorus pentasulfide.
IDENTIFICATION NUMBERS AND RATINGS
CAS
(Chemical Abstracts Services) 1314-80-3
STCC
(Standard Transportation Commodity Code) 4916320
RTECS
(Registry of Toxic Effects of Chemical Substances) TH4375000
UN/NA
(United Nations/North America) 1340
CHRIS
(Chemical Hazard Response Information System) PPP
RCRA
(Resource Conservation and Recovery Act) U189
DOT
(U.S. Department of Transportation) flammable solid
NFPA 704 Rating
(National Fire Protection Association) 3-1-2–W-
IMO
(International Maritime Organization) 4.1, flammable solid
If the phosphorus pentasulfide itself begins to bum. carbon dioxide, dry chemical, and dry sand may be used as extinguishers. However, they will be effective only if the amount of product burning is small and the proper amount of extinguishing agent is available and may be applied safely. If water must be used on a large fire, be aware that the released hydrogen sulfide may make the fire worse or it may make the incident ground more dangerous because of its toxicity. If water is used, all of it must be contained, since it will be highly contaminated. The immediate danger to everyone exposed near the fire is exposure to hazardous combustion products. The hydrogen sulfide generated during combustion should be consumed by the fire. The sulfur dioxide generated is not combustible, and its relatively high vapor density of 2.2 means that, after initially rising on the thermal column, it will cool and fall back to earth fairly rapidly. This might occur over a rather large area, or it could cause problems downwind to anyone without respiratory protection. The phosphoric acid generated is corrosive, and that hazard will be spread with the smoke and the thermal column. The phosphorus pentoxide is really the anhydride (no water present) form of phosphoric acid, and its presence doubles the hazards presented by phosphoric acid.
Fires involving phosphorus pentasulfide must be fought with great care and with the proper personal protective equipment. The hazards are not gone when the fire has been extinguished. Exposed metal probably will have been heated above the ignition temperature of phosphorus pentasulfide, and reignition is very probable. This is true unless all of the material has been soaked with water and the reaction with water is completed or all the material has been consumed in the fire. Still, the residue is acidic and corrosive.
Any material not consumed by the fire or totally reacted with water undoubtedly is evolving hydrogen sulfide. This poses toxic and explosion hazards, and the incident scene may be very hazardous until it is cleaned up by experts.
PROTECTIVE CLOTHING AND EQUIPMENT
Select protective clothing and equipment that provide the maximum respiratory, eye, and skin protection against phosphoric acid, sulfur dioxide, and hydrogen sulfide. Regular turnout gear may temporarily provide skin protection against dilute phosphoric acid, but wear acid-resistant clothing whenever you encounter phosphoric acid. Emergency responders who might contact the acid must wear total encapsulating suits. Suits may be constructed of natural rubber, neoprene, nitrile-butadiene rubber, nitrile rubber, polyethylene, polyvinyl chloride (PVC), or Saranex®. Contact the manufacturers of phosphoric acid and the encapsulating suits regarding the best protection. Responders must use SCBA in phosphoric acid releases; it also will protect them from the hazards of hydrogen sulfide (the toxic hazard) and sulfur dioxide.
Protection is relative. It may be defined as thickness of the suit material: integrity of the seams, zippers, and other closures; concentration of the acid; time elapsed since contact; material used in the suit; and the overall condition of the suit.
FIRST AID
Inhalation. For inhalation of phosphoric acid mist, hydrogen sulfide gas, or sulfur dioxide gas. move the victim to fresh air and keep him calm and warm. If the victim’s breathing has stopped or becomes labored, administer artificial respiration, being aware that you might be exposed to material in the victim’s lungs or vomit. Seek immediate medical attention.
Eye contact. Flush the eyes immediately for at least 20 minutes, lifting the eyelids occasionally. Be careful not to wash the product into the clean eye. Immediate medical attention is required.
SYNONYMS
phosphoric sulfide
phosphorus persulfide
sulfur phosphide
thiophosphoric anhydride
Skin contact. Wash the affected body areas with large amounts of water. Medical attention is necessary for all phosphoric acid burns.
Ingestion. For phosphoric acid ingestion, if the victim is conscious, administer large quantities of milk, milk of magnesia, or water immediately. There is disagreement about whether to induce vomiting. Usually vomiting is not induced when a corrosive is ingested. Never try to force an unconscious person to drink anything or to vomit. Immediate medical attention is mandatory, and medical authorities should decide whether to induce vomiting. Ingestion of liquid hydrogen sulfide or sulfur dioxide is highly unlikely.
