Daily Question on Hazardous Chemicals [Daily Question 090420]

1. Materials such as reactive metals and alloys, metal hydrides, borohydrides, and metal powders react violently upon contact with moisture, releasing H2 and a large amount of heat, which causes the H2 to burn and explode； 2. Metal carbides and organometallic compounds such as K4C, Na4C, Ca2C, Al4C3, etc., release substances like C2H2 and CH4 that are highly flammable and explosive when exposed to heat ； 3. Metal phosphides react with water to produce the flammable, explosive, and toxic PH3 ； 4. Metal sulfides produce toxic and flammable H2S gas when exposed to moisture ； 5. Calcium oxide, anhydrous aluminum chloride, sodium peroxide, sodium hydroxide, fuming sulfuric acid, chlorosulfonic acid, phosphorus trichloride, etc., release large amounts of heat when in contact with water, which can ignite nearby flammable materials.

I read in a literature source that, based on the danger posed by the substances produced when hazardous chemicals react with water, such chemicals can be divided into the following three categories: (1) Those that release large amounts of heat when in contact with water or humid air: acids, bases, and oxides. (2) React with water to produce flammable gases and release a large amount of heat: metals, hydrides, carbides. (3) {I don’t know; it’s not visible below the reference.]

From a fire safety perspective, hazardous chemicals that react upon contact with water can be mainly divided into three categories. First, it causes combustion upon contact with water, but does not produce large amounts of toxic or harmful gases ； Second, it causes combustion upon contact with water, producing large amounts of toxic and harmful gases ； Third, it does not cause combustion after reacting with water, but it can produce large amounts of toxic and harmful gases.

Hazardous chemicals that react with water are mainly divided into three categories. First, it causes combustion upon contact with water, but does not produce large amounts of toxic or harmful gases ； There are two specific scenarios: in one case, a reaction with water produces flammable gases, releasing a large amount of heat that directly causes the flammable gases to ignite ； Second, upon reaction with water, no flammable gases are released, but a large amount of heat is generated, sufficient to ignite the surrounding flammable materials. Second, it causes combustion upon contact with water, producing large amounts of toxic and harmful gases ； The main ones include potassium phosphide, sodium phosphide, magnesium phosphide, strontium phosphide, aluminum magnesium phosphide, aluminum phosphide, calcium phosphide, etc. When they react with water, heat is released and toxic phosphine gas is generated, thereby causing combustion. Third, it does not cause combustion after reacting with water, but it can produce large amounts of toxic and harmful gases. These mainly include acetyl chloride, aluminum trichloride, antimony pentachloride, chromyl chloride, dibenzoyl chloride, methyl dichlorosilane, methyl trichlorosilane, phosphorus oxychloride, n-propyltrichlorosilane, tin chloride, sulfur monochloride, thionyl chloride, dichlorosulfoxide, titanium tetrachloride, trichlorosilane, trichloro cyanuric acid, sulfonyl chloride, zirconium tetrachloride, antimony pentafluoride, bromine pentafluoride, bromine trifluoride, chlorine trifluoride, and diphenyl phosphine pentasulfide. When these substances come into contact with water, they react to produce toxic and harmful gases such as hydrogen chloride, chlorine gas, hydrogen fluoride, hydrogen sulfide, sulfur dioxide, nitrogen trichloride, and phosgene.

Light metals, such as sodium, potassium, calcium, etc. Alkali metal peroxides, such as K2O2, Na2O2. Alkali metal oxides, such as K2O, Na2O. Carbides, such as CaC2

1. Materials such as reactive metals and alloys, metal hydrides, borohydrides, and metal powders react violently upon contact with moisture, releasing H2 and a large amount of heat, which causes the H2 to burn and explode； 2. Metal carbides and organometallic compounds such as K4C, Na4C, Ca2C, Al4C3, etc., release substances like C2H2 and CH4 that are highly flammable and explosive when exposed to heat ； 3. Metal phosphides react with water to produce the flammable, explosive, and toxic PH3 ； 4. Metal sulfides produce toxic and flammable H2S gas when exposed to moisture ； 5. Calcium oxide, anhydrous aluminum chloride, sodium peroxide, sodium hydroxide, fuming sulfuric acid, chlorosulfonic acid, phosphorus trichloride, etc., release large amounts of heat when in contact with water, which can ignite nearby flammable materials.

From a fire safety perspective, hazardous chemicals that react upon contact with water can be mainly divided into three categories. First, it causes combustion upon contact with water, but does not produce large amounts of toxic or harmful gases ； Second, it causes combustion upon contact with water, producing large amounts of toxic and harmful gases ； Third, it does not cause combustion after reacting with water, but it can produce large amounts of toxic and harmful gases. 1. It causes combustion upon contact with water, but no large amounts of toxic or harmful gases are produced. There are two specific scenarios in which combustion occurs as a result of a reaction with water: one is that the reaction generates flammable gases along with a large amount of heat, which directly leads to the combustion of those flammable gases ； Second, upon reaction with water, no flammable gases are released, but a large amount of heat is generated, sufficient to ignite the surrounding flammable materials. No large amounts of toxic and harmful gases are produced as a result of the reaction with water; in other words, no significant quantities of such gases are generated during the chemical reaction when water is involved. However, this does not mean that no safety measures against toxins are required throughout the disposal process. For example, combustion products can be toxic, some liquids become volatile when heated, and their vapors can be toxic; likewise, solid dusts and liquids themselves may be toxic, so enhanced safety precautions are still necessary. Alkali metals mainly include lithium, sodium, potassium, etc., and their chemical reaction equations are as follows: 2Li + 2H2O → 2LiOH + H2↑ ； 2Na+2H2O+2NaOH+H2↑ ； 2K+2H2O→2KOH+H2↑ ； These alkali metals react with water in a highly exothermic reaction, and the heat released is sufficient to cause hydrogen to burn. At the same time, carbon dioxide cannot be used as a fire extinguishing agent for alkali metal fires; it reacts chemically with sodium metal. The chemical equation for this reaction is as follows: 4Na + CO2 → 2Na2O + C. The carbon atoms are displaced, allowing further combustion to occur. Metal powders, primarily those of magnesium, zirconium, titanium, aluminum, and zinc in powder form, pose a serious risk of explosion and fire. When exposed to air, an oxide layer forms on their surface; this oxide layer acts as a protective coating. However, when it comes into contact with moisture in the air, a chemical reaction occurs that releases hydrogen gas and heat, and this initial combustion can trigger the spontaneous ignition of these metal powders. Metal-organic compounds mainly include trimethylaluminum, dimethylcadmium, triisobutylaluminum, diethylzinc, ethan sodium, and others. Some of these substances can catch fire on their own in air; reacting with water intensifies the burning, and explosions may even occur. Hydrides mainly include the hydrides of alkali metals such as lithium hydride and sodium hydride. The reaction equations with water are: LiH + H2O → LiOH + H2↑; NaH + H2O → NaOH + H2↑. These reactions produce hydrogen gas, which releases heat and can cause combustion. Boron-based and silicon-based molecular hydrogen compounds, such as diborane and silanes, undergo vigorous chemical reactions with the moisture in air; this releases heat and generates hydrogen, which can cause combustion. The reaction equations for diborane and disilane with water are: B2H6 + 6H2O → 2H3BO3 + 6H2↑ and SiH6 + 4H2O → 2SiO2 + 7H2↑. Saline-type carbides mainly include calcium carbide (acetylene), aluminum carbide, magnesium carbide, etc. When these substances react with water, they undergo hydrolysis, producing flammable hydrocarbons along with heat, enough to ignite the gases generated. Alkaline corrosives such as sodium hydroxide, potassium hydroxide, and sodium hypochlorite solutions (with more than 5% available chlorine) release large amounts of heat when in contact with water or humid air, which can cause the surrounding flammable materials to catch fire. Peroxides such as potassium peroxide and sodium peroxide react violently when in contact with water; exposure to a large amount of water can lead to an explosion, while even a small amount of water can cause ignition. Strontium peroxide also catches fire easily upon contact with just a small amount of water. 2. Reaction with water causes combustion and the release of toxic and harmful gases. It should be noted that for solids, liquids, and dusts alike, their toxicity and pathways of harm must be fully considered in order to enhance safety measures during handling. Salt-type phosphides mainly include potassium phosphide, sodium phosphide, magnesium phosphide, strontium phosphide, aluminum magnesium phosphide, aluminum phosphide, calcium phosphide, etc. When they react with water, heat is released and toxic phosphine gas is generated, thereby causing combustion. Aluminum phosphide and calcium phosphide are fumigants used in grain and tobacco warehouses. In warehouse fumigation, if the reactor is not properly installed, excessive droplet reactions occur, generating a lot of heat; coupled with the low auto-ignition temperature of phosphine, this can easily lead to fires, and there have been many incidents that serve as lessons in this regard. Organometallic compounds such as potassium amalgam and sodium amalgam can undergo exothermic chemical reactions with humid air and water to produce hydrogen, which can cause combustion and the release of highly toxic mercury vapor. Acidic corrosives such as sulfuric acid, nitric acid, perchloric acid, chlorosulfonic acid, nitrosous sulfuric acid, sulfur trioxide, chromium oxychloride, phosphorus pentoxide, phosphorus pentachloride, anhydrous aluminum chloride, iodine monochloride, etc., when their liquids spill and come into contact with humid air or surrounding flammable materials, absorb moisture and release large amounts of heat. The heat generated by 1 kilogram of sulfuric acid reacting with water is sufficient to boil 8 kilograms of water. The flammable materials are quickly carbonized and ignited, while large quantities of toxic gases are produced. As the fire progresses, the flammable packaging materials catch fire as well, the containers break, causing more liquid to spill, thereby intensifying this vicious cycle and expanding the scale of the disaster. For example, in 1971, blind discharge of water from a sulfuric acid warehouse at a chemical plant caused 29 soldiers to be poisoned and their hair to turn white, serving as a profound lesson. Salts such as sodium dithionite (commonly known as safety powder) and sodium hydrosulfite generate heat when exposed to water or moist air, which causes them to burn while emitting yellow smoke and toxic, flammable sulfur dioxide. Other types, such as diethylzinc and lithium aluminate, react with water to cause combustion and produce highly corrosive vapors such as zinc oxide and lithium hydroxide. 3. When in contact with water, it does not cause combustion, but it can produce toxic and harmful gases. These include acetyl chloride, aluminum trichloride, antimony pentachloride, chromyl chloride, dibenzoyl chloride, methyl dichlorosilane, methyl trichlorosilane, phosphorus oxychloride, n-propyltrichlorosilane, tin chloride, sulfur monochloride, thionyl chloride, dichlorosulfoxide, titanium tetrachloride, trichlorosilane, trichlorocyanuric acid, sulfone tetrachloride, zirconium tetrachloride, antimony pentafluoride, bromine pentafluoride, bromine trifluoride, chlorine trifluoride, and phosphorus pentasulfide. When these substances react with water, they produce toxic and harmful gases such as hydrogen chloride, chlorine gas, hydrogen fluoride, hydrogen sulfide, sulfur dioxide, nitrogen trichloride, and phosgene. At the same time, it is essential to fully understand the toxicity level and routes of harm associated with these substances in order to carry out proper handling and protection measures. This post was last edited by lyhh9024 on 2009-4-20 01:37.]

What are the main categories of hazardous chemicals that react when in contact with water? I. Hazardous chemicals that react when in contact with water can be mainly classified into those that release large amounts of heat when exposed to water or humid air. (1) Acids: Primarily fuming sulfuric acid; when sulfuric acid dissolves in water, it releases a large amount of heat, which can cause splashes that injure people or lead to explosions. (2) Bases mainly include sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, etc. When they come into contact with water or humid air, they release a large amount of heat, which can cause the surrounding flammable materials to catch fire. (3) Oxides: Acidic oxides such as sulfur trioxide, phosphorus trioxide, and phosphorus pentoxide react with water to produce acids, releasing a large amount of heat in the process. Alkaline oxides such as sodium oxide and potassium oxide react with water to produce alkalis, releasing a large amount of heat. 2. When in contact with water, they react to produce flammable gases and release a large amount of heat. (1) Metals such as lithium, sodium, potassium, calcium, cesium, strontium, barium, as well as magnesium powder, aluminum powder, and zinc powder, undergo chemical reactions with water to produce hydrogen gas while releasing a significant amount of heat. (2) Hydrides mainly include calcium hydride, lithium hydride, titanium hydride, zirconium hydride, diborane, lithium borohydride, sodium borohydride, potassium borohydride, etc. They react violently with water, releasing hydrogen gas and generating heat that causes combustion. (3) Carbides mainly include calcium carbide (acetylene) and aluminum carbide; these substances react with water to produce flammable acetylene gas along with a large amount of heat. (4) Peroxides are mainly metal peroxides, such as sodium peroxide, potassium peroxide, zinc peroxide, magnesium peroxide, etc.; they react violently with water to produce oxygen and release a large amount of heat. (5) Organometallic compounds mainly include diethyl zinc, trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, triethyl antimony, sodium methoxide, etc. These substances react violently with water to produce flammable hydrocarbons, causing combustion and even detonations. (6) Silicon compounds – mainly magnesium silicide and calcium silicide – produce flammable **silicon hydride gases when exposed to moisture or water. 3. Produce toxic fumes or gases when exposed to water or humid air. (1) Non-metal halides: Non-metals such as boron, silicon, nitrogen, phosphorus, and sulfur can all form various corresponding halides with halogens. These halides emit fumes in humid air and react violently with water to produce toxic and harmful gases. For example: boron trichloride, boron trifluoride, boron bromide, phosphorus trifluoride, phosphorus trichloride, phosphorus tribromide, phosphorus pentachloride, phosphorus pentabromide, sulfur tetrafluoride, silicon tetrafluoride, chlorosilane, iodine trichloride, silicon tetrachloride, etc. (2) Metal halides: Halides of metals such as barium, aluminum, arsenic, antimony, bismuth, tin, zirconium, germanium, titanium, and iron emit fumes in humid air, and react violently with water to produce toxic and harmful gases. For example: aluminum trichloride, arsenic trichloride, arsenic tribromide, arsenic triiodide, antimony trichloride, antimony tribromide, antimony triiodide, tin tetrachloride, tin tetraiodide, titanium tetrachloride, zirconium tetrachloride, tellurium tetrachloride, germanium tetrachloride, molybdenum pentachloride, antimony pentachloride, iron trichloride, chromium fluoride, zinc chloride, copper chloride, etc. (3) Inorganic acids, mainly chlorosulfonic acid and fluorosulfonic acid, react violently with water to release toxic and irritating white fumes. (4) Sulfides mainly include phosphorus trisulfide, phosphorus tetrasulfide, phosphorus tetrasulfide heptasulfide, sodium sulfide, potassium sulfide, sodium hydrosulfide, barium sulfide, calcium hydrosulfide, ammonium polysulfide solutions, lime sulfur (calcium polysulfide), and barium sulfur compounds (barium polysulfide), etc. When exposed to water or humid air, they decompose to produce hydrogen sulfide gas, which is corrosive and irritating. (5) Phosphides mainly include compounds such as sodium phosphide, potassium phosphide, calcium phosphide, magnesium phosphide, zinc phosphide, tin phosphide, and aluminum phosphide. They decompose when exposed to water or humid air, releasing the flammable and highly toxic phosphine gas. (6) Cyanides: Metal cyanides such as sodium cyanide, potassium cyanide, zinc cyanide, silver cyanide, and calcium cyanamide (calcium carbide), as well as nitriles, produce highly toxic and flammable hydrogen cyanide gas when in contact with water. (7) Dithionites: Sodium dithionite, potassium dithionite, calcium dithionite, zinc dithionite and other such dithionites release heat when exposed to water or absorb humid air, which causes them to burn while emitting yellow smoke as well as toxic and flammable sulfur dioxide. (8) Organic compounds a. Halogenated hydrocarbons mainly include dichloromethane, carbon tetrachloride, bromoethane, and iodoethane; they can undergo hydrolysis in the presence of water or humid air to produce toxic gases or fumes. b. Esters mainly include methyl isocyanate, isobutyl chloroformate, phenyl isothiocyanate, ethyl chloroacetate, hexamethylenediisocyanate, toluene-1,2,4-diisocyanate, etc., which produce toxic fumes or gases. c. Acyl halides mainly include acetyl bromide, propionyl bromide, bromoacetyl bromide, acetyl iodide, valeroyl chloride, fumaroyl chloride, and benzoyl chloride; they react when exposed to humid air or water, releasing toxic gases or toxic fumes. (9) Amalgams mainly include alkali metal amalgams, alkaline earth metal amalgams, zinc amalgams, and lead amalgams. In contact with humid air or water, it can undergo an exothermic reaction that produces hydrogen, leading to combustion and the generation of highly toxic mercury vapor.

II. Characteristics of accidents involving hazardous chemicals that react with water Due to the hazardous properties of such chemicals and the formation of flammable, explosive, toxic, and harmful substances as a result of their reaction with water, leaks, fires, and explosions related to them have certain unique characteristics compared to other types of accidents. They are more sudden, complex, lead to a wider range of damages, and result in more severe casualties. In summary, the following points can be noted: 1. High degree of suddenness Accidents involving hazardous chemicals that react with water can be caused by natural disasters, violations of safety procedures during production, storage, or use, problems with equipment or technology, or accidents that occur during transportation. In short, the causes of accidents are complex and varied. However, regardless of the cause of an accident involving hazardous chemicals when exposed to water, there is one common feature: a vigorous exothermic chemical reaction occurs as a result of contact with water or moisture. In addition to the substances themselves catching fire, flammable packaging or surrounding flammable materials may also ignite, and mixing with incompatible substances can lead to combustion as well. Moreover, such accidents occur independently of people's will and are highly sudden. 2. High hazard: Accidents involving hazardous chemicals often result in severe casualties and huge economic losses. Hazardous chemicals that react upon contact with water are no exception, especially as they pose a severe threat to human health. In the event of an accident involving a hazardous chemical that reacts with water, the toxic gases or fumes generated can enter the human body. They can interact with important substances within cells such as enzymes, proteins, and nucleic acids, thereby altering the amounts and structures of these cellular components. This disrupts the normal metabolism of cells, leads to dysfunction in the body’s systems, and results in poisoning. Moreover, due to the different levels of harm caused by various toxic substances, the routes of poisoning also vary. For example, polluted air can cause poisoning through inhalation via the respiratory tract and absorption through the skin ； Poisons can cause poisoning through skin penetration ； Ingesting contaminated food or water by mistake can lead to poisoning through absorption in the digestive tract. Furthermore, due to the different physicochemical properties of various toxic substances, they can cause different symptoms of poisoning and lead to various harmful effects. 3. High pollution potential: Chemical accidents involving reactions with water often result in severe environmental pollution; sometimes the impact on the environment lasts for a long time, with even more serious potential hazards. In the event of an accident, the high temperatures and toxic substances released turn the soil into scorched land or even harmful soil, and it takes a long time to restore such soil to its natural state. Furthermore, these toxic and harmful substances affect the reproduction of animals, plants, and microorganisms. 4. Difficulties in handling the accident: Some hazardous chemicals undergo violent reactions when exposed to water or moisture, producing toxic, harmful, and flammable gases that quickly spread throughout the area affected by the accident, thereby increasing the difficulties in dealing with it. Some hazardous chemicals react violently when exposed to water or moisture; the flammable gases produced mix with air to form explosive mixtures, widening the explosion range. Exposure to sparks or high temperatures can trigger combustion and explosions, putting the lives of emergency response personnel at risk.

III. Countermeasures for Handling Accidents Involving Hazardous Chemicals That React with Water When dealing with disasters caused by hazardous chemicals that react with water, it is first necessary to evacuate people from the affected area to safe zones; unauthorized personnel are prohibited from entering the contaminated area. Emergency responders must use head-mounted isolating respirators, wear gas masks, and don chemical protective clothing. Then, based on the physical and chemical properties of these hazardous chemicals, their dangerous characteristics, as well as the conditions at the accident site such as the extent of the leakage and any fires, appropriate actions are taken in a safe, effective, and flexible manner. 1. Category 1: Water-reactive acidic substances and acidic oxides. In the event of a leak of acidic substances and acidic oxides, which belong to the category of water-reactive hazardous chemicals, ensure proper ventilation; do not come into direct contact with the leaked material, and prevent it from coming into contact with flammable materials such as wood, paper, oil, etc. Seal the leak only when it is safe to do so. Spraying mist slows down evaporation (or diffusion), but do not spray water directly on the spill or the leak site. Absorb with sand, vermiculite, or other inert materials, and then collect and transport to a waste disposal site for disposal. In case of a fire, it is advisable to use fogged water, dry sand, or carbon dioxide extinguishers to put it out. 2. Category 1: Alkali substances and basic oxides that react with water. In the event of a leak of alkali substances and basic oxides, which belong to the category of hazardous chemicals that react with water, sand should be spread evenly over the surface of the leaked material, using soil absorption as a method for handling the situation. In the event of a fire or explosion, use misted water or sand to extinguish the fire. 3. Hazardous chemicals that react with water in Category 2: In the event of a leak or fire involving such hazardous chemicals, cement powder should be used to cover the area completely. Meanwhile, several small holes should be made in this covering layer to ensure that the released flammable gases burn steadily, thereby preventing the accumulation of these gases inside the area. It cannot be extinguished with water or water-based foam; it is mainly extinguished using sand. 4. Third category: Water-reactive halides and sulfides. In the event of a leakage of halides, sulfides, phosphorus compounds, dithionites, and organic compounds, which are part of the water-reactive hazardous chemicals in the third category, these substances should be absorbed using a mixture of sand and lime. Once complete neutralization is confirmed, they should be placed in enamel drums or polyethylene plastic containers, and then collected for harmless disposal by environmental protection authorities. Clean the polluted surface with soap or detergent. Water curtains made of lime water should be installed downwind, at an angle downwind from the accident site, as well as in areas with a large number of people. Straight-water nozzles can also be used on the upwind side to spray lime water vertically, thereby creating a large area covered by mist that can dilute and absorb the toxic and harmful gases produced as a result of decomposition when exposed to water. 5. Third category: Cyanide compounds that react upon contact with water. Among the hazardous chemicals that react when exposed to water, in cases of leaks on rainy days or in conditions of high air humidity, multiple sodium hypochlorite water screens should be set up downwind, at an angle downwind from the accident site, as well as in areas where there are many people. This creates a dense network of water droplets in the air, which enables the hydrogen cyanide gas generated as a result of the reaction with water to be oxidized into non-toxic carbon dioxide gas. If cyanide compounds enter waterways, notify downstream users who may be affected by water pollution, as well as relevant authorities such as local health departments, fire services, and pollution control agencies. Shut off water flow in the heavily polluted areas upstream of the source of contamination to slow down the discharge of wastewater; sprinkle large amounts of bleaching powder into the polluted waters. Using bleaching powder to create barriers can help oxidize the unhydrolyzed cyanide ions into less toxic cyanate ions, which can then be further oxidized into non-toxic carbon dioxide and other substances. 6. Third category: Mercury compounds that react with water. In the event of a leakage of such hazardous chemicals, mercury with a particle diameter greater than 1 mm can be collected using suction or vacuum pumps equipped for mercury collection. The floor surface from which mercury has been removed can be sprinkled with calcium polysulfide, sulfur, or bleach, or sprayed with a 20% ferric chloride solution or a 1%–1.5% potassium iodide solution, so that the mercury forms insoluble, non-volatile salts, which can then be collected and taken to a waste disposal facility for treatment.

Hazardous chemicals that react with water are mainly divided into three categories. ①It catches fire upon contact with water, but does not produce large amounts of toxic or harmful gases ； ②Upon contact with water, it reacts and causes combustion, producing large amounts of toxic and harmful gases ； ③It does not cause combustion upon contact with water, but it can produce large amounts of toxic and harmful gases.