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There has been a spill of concentrated sulphuric acid at the chemical plant where I work at as the Safety Engineer. In this report, I will explain what Sulfuric Acid is, the health risks and hazards associated with it, the safety precautions that should be taken and how the spill should be handled.
Sulfuric Acid, H2SO4, also commonly known as battery acid or vitriol, is one of the top products in the chemical industry, with 40 million tons produced annually in the U.S. It is a colourless, odourless and oily mineral acid that is soluble in water at all concentrations. Sulfuric acid is extremely hazardous; it reacts with water violently and exothermically and as a result, is highly corrosive.
Safety Risks & HazardsExposure routes of sulfuric acid: Inhalation, ingestion, skin/eye contactTarget organs: Eyes, skin, respiratory system, teethSkin contactSulfuric acid is a very strong acid that is extremely corrosive. When mixed with water, it is highly exothermic and will boil and spit dangerously. Sulfuric acid is also a strong dehydrating agent that will suck the water out of carbohydrates and other organic compounds that contain oxygen and hydrogen. Due to its exothermic and dehydrating properties, burns caused by sulfuric acid are more serious than other strong acids such as hydrochloric acid. Additional tissue damage might occur due to dehydration and secondary thermal damage.
IngestionIngestion of sulfuric acid can be fatal. When swallowed, the victim will suffer from painful burns in the mouth and throat due to its exothermic properties, abdominal pain, rapid development of low blood pressure and in some cases, shock or collapse.
InhalationInhalation of sulfuric acid will cause a burning sensation, sore throat, laboured breathing, shortness of breath, tightness in the chest, dizziness and coughing. Some of these symptoms may be delayed. When exposed to heat, sulfuric acid will disperse toxic fumes, acid aerosols and sulfur dioxide gas. Inhalation of these gases will cause severe and immediate irritation of the eyes, respiratory tract and mucous membranes, and potentially, lung oedema.
Chronic ExposureExposure to sulfuric acid for long periods of time will increase the risk of lung damage and potentially cancer. Chronic exposure to sulfuric acid aerosols will also lead to erosion of the teeth. Strong inorganic acid mists containing sulfuric acid are carcinogenic to humans.
Safety Measures and PrecautionsSulfuric acid should be kept in a well-ventilated area with a corrosion-resistant concrete floor. It should be stored in a stainless steel container, away from water, metals, organic materials, strong reducing agents, combustible materials, bases and oxidising agents.
When working with sulfuric acid, workers should always wear protective clothing, acid-resistant gloves, face shield, eye protection, and breathing protection. Workers should never eat, drink or smoke in the working area. The working area must be well-ventilated.
During a spillage, workers must immediately evacuate the danger area. Only those dressed in complete protective clothing, including a self-contained breathing apparatus with proper cartridges or a positive pressure, air-supplied respirator should be allowed in the spill area. Sulfuric acid cannot be allowed to enter the environment.
When cleaning up the spill, workers must take extra precautions because they will be handling large amounts of concentrated sulfuric acid. The area has to be very well-ventilated and workers must be dressed in the protective clothing mentioned above. First aid procedures will have to be in place in case of any contact with the acid.
First Aid ProceduresExposureProcedure (Refer for medical attention in all cases!)InhalationFresh air and rest. Place the victim in a half-upright position and give aritificial respiration if needed.
SkinRemove any contaminated clothing and irrigate the underlying skin with large amounts of water. Continue for 10 to 15 minutes to cool the tissue surrounding the acid burn in order to prevent secondary damage to the skin.
EyesRemove any contact lenses. Rinse with large amounts of water for several minutes, see a doctor.
IngestionRinse mouth, do not induce vomiting.
When diluting sulfuric acid, add the acid slowly and carefully to water and not the reverse. This is to take advantage of the high heat capacity of water and to prevent the dispersal of a sulfuric acid aerosol.
Workers must be careful not to let the sulfuric acid come into contact with any metals as it will cause a very violent and rapid reaction, leading to the generation of hydrogen gas. Hydrogen gas is extremely flammable and will pose a fire and explosion hazard.
To prevent a fire, remove all ignition sources (No smoking, flames, sparks etc.) and ground all equipment.
In case of a fire, do NOT use water. Use powder, foam or carbon dioxide instead to extinguish the flames.
Possible Risks to the Surrounding EnvironmentIf the spillage of sulfuric dioxide is not contained within the plant, and is allowed to enter the environment, the atmosphere, waterways and land will be adversely affected. Direct spillage from the chemical plant will have a corrosive effect on land organisms – causing serious burns on plants, birds and animals. The acid will also enter the surrounding waterways, lowering the pH of aquatic systems, lakes, rivers etc. This, along with the corrosive and toxic effects of sulfuric acid, will be extremely harmful to aquatic organisms and also to the animals that feed/drink from the water source. The contaminated water source will take a long time to recover from the sulfuric-acid-induced pH stress.
People living near the acid spill will also be seriously affected. They will be at risk from all the hazards mentioned earlier in the report, along with the risk of using contaminated water from polluted waterways.
Sulfuric acid will also enter the air and dissolve in the water in air to form SO3. It will remain suspended for some time until it is removed from the air through wet acid deposition (acid rain). Acid rain will cause the corrosion of buildings and structures.
Testing the Surrounding Environment for ContaminationA spillage of any chemical, including sulfuric acid, which is not contained within the chemical plant, will inevitably end up in the waterways surrounding the site of the spill. Thus, the extent of the acid contamination in the surrounding environment can be determined by measuring the concentration of sulfuric acid in the surrounding waterways. This can be done using volumetric analysis.
Titration, a type of volumetric analysis, is an accurate method for testing the surrounding environment for any contamination of Sulfuric acid. Acid-base titration, in this case, is used to find out the concentration of sulfuric acid in the surrounding waterways. It involves adding a progressive volume of one reactant from a burette to another reactant of known volume in a conical flask. The solution in the conical flask contains an indicator which will undergo a colour change when neutralisation of the two reactants is complete.
Using this method, a water sample is collected from a water source (lake, creek, ground water etc.) in the surrounding environment of the acid spill to be tested for Sulfuric acid. The water sample is then titrated against a standard solution, that is, a base of known concentration such as Sodium hydroxide. A change in colour of the indicator indicates that the neutralisation of the sodium hydroxide and the water sample containing sulfuric acid is complete. From the volume of the water sample needed to neutralise the sodium hydroxide, the concentration of sulfuric acid in the water sample can be calculated.
To calculate the concentration of sulfuric acid in the water sample, the chemical equation of the neutralisation reaction between sulfuric acid and sodium hydroxide is written out to determine the molar ratio of the reactants and products. The number of moles of sodium hydroxide is then calculated. The number of moles of sulfuric acid in the volume of water sample used is also calculated using the mole ratio derived from the equation. The concentration of sulfuric acid can then be found using the formulaConcentration of sulfuric acid (M) = Number of moles of sulfuric acid in water sample (mol)Volume of water sample (L)Additionally, the pH of the contaminated water can also be found and compared against the original pH of the water.
The Bronsted-Lowry TheoryThe Bronsted-Lowry Theory defines an acid as a substance that has the ability to donate a proton. The proton is actually a hydrogen ion that has lost its electron. So when an acid reacts, it donates a proton to the other substance. The substance which accepts the proton is a base. Thus, acids and bases come in conjugate pairs.
acid + base conjugate base + conjugate acid.
Sulfuric acid is an acid because it is able to donate protons.
H2SO4 (aq) + H2O (l) H3O+ (aq) + HSO4- (aq)As seen in the above equation, sulfuric acid donates a proton while water accepts the proton. This makes sulfuric acid the acid and the water the base. A hydronium ion and a hydrogensulfate ion are formed as products. The hydronium ion is a conjugate acid as it now has the ability to act as a proton donor while the hydrogensulfate ion is a conjugate base because it now has the ability to act as a proton acceptor.
Sulfuric acid is considered a strong acid because it has a strong ability to donate protons. H2SO4 is a better proton donor than H3O+ and H2O is a stronger proton acceptor than HSO4-.
The Arrhenius TheoryAcids and bases are electrolytes – that is, they conduct electricity. This means that they form ions when dissolved in water. Arrhenius focused on what was formed when acids and bases dissociate into ions. The fact that acids react with many metals to form hydrogen gas led Arrhenius to believe that acid solutions contained hydrogen ions. He came up with the theory that acids dissociate in water to form hydrogen ions while bases dissociate in water to form hydroxide ions.
Sulfuric acid is therefore an acid because it ionises in water to form hydrogen ions and hydrogensulfate ions.
H2SO4 (aq) H+(aq) + HSO4- (aq)Sulfuric acid is a strong acid because virtually all the molecules ionise to form H+ ions in aqueous solution. It is also a diprotic acid, which means that it contains two ionisable hydrogen atoms per molecule of acid. Sulfuric acid will ionise in two steps with water:H2SO4 (aq) H+(aq) + HSO4- (aq)HSO4- (aq) H+(aq) + SO4- (aq)HSO4- is a weak acid so only a small amount of it will be further ionised into H+ ions and SO4- ions.
Arrhenius also proposed that acids and bases neutralised each other because H+ ions and OH- ions combine to form water.
Handling the SpillThere are three options for handling the sulfuric acid spill:1)Neutralise it2)Dilute it3)Absorb/ Soak it upNeutralising the Sulfuric AcidThe sulfuric acid spill needs to be contained and controlled before neutralisation can be carried out. Any run-off must be contained to prevent the contamination of water sources. To limit the contamination area, form dikes with non-combustible, inert, DRY materials like sand and earth.
Sulfuric acid is an acid so it needs to be neutralised using a base. Common neutralising bases include sodium hydroxide, sodium carbonate, calcium hydroxide etc. Sodium hydroxide, also known as caustic, is the most widely used alkaline neutralising chemical in industries. It is effective, inexpensive and easy to handle due to its high solubility. To neutralise the sulfuric acid, add NaOH slowly and carefully to the acid until the endpoint is reached. Aqueous sodium sulphate, a relatively safe salt will be formed as a product. The neutralised acid should then be collected in a plastic container and disposed of in accordance with local regulations.
Advantages: Neutralising agents are very effective in turning the very strong and hazardous acid into something that is much less harmful. The effect is almost immediate and the products are of manageable pH’s that can be disposed of safely and easily.
Disadvantages: Neutralisation is a highly exothermic reaction because of the large amounts of energy involved in breaking and forming bonds. The increase in temperature will make any un-neutralised acid extra corrosive and dangerous.
It is also difficult to measure the amount of neutralising agent needed as the exact amount of acid spilled, especially a large spill, is not known. Hazard zones cannot be well-defined and therefore the amount of base needed cannot be planned on the basis of calculations. It is sometimes desirable to add an excess of reagent to ensure that the spill is completely neutralised. However, sulfuric acid is an extremely strong acid so any excess base added will cause extreme changes in pH. To ensure that the neutralisation process is carried out smoothly, the spill would have to be tracked and contained to give a more accurate estimate of the amount of neutralising agent needed. This would take awhile and the delay will allow the acid to do more harm to the affected area.
Diluting the Sulfuric AcidDiluting sulfuric acid involves reducing the concentration of the acid by the addition of water. The dissolution of sulfuric acid in water is an extremely exothermic reaction, which means that a huge amount of heat is released, enough for the water to boil. When diluting sulfuric acid, the acid has to be added to water, and not the reverse. This is because water is less dense than sulfuric acid, so it will float on the surface of sulfuric acid. Sulfuric acid is also a fuming agent, so adding water to the acid will cause the fumes to repel the water and this may cause an accident. Adding water to sulfuric acid will result in a violent and dangerous boiling and spitting reaction.
When diluting the acid, constant stirring has to be carried out to avoid a layer of concentrated acid forming at the bottom which will lead to a large temperature gradient where the acid and water meets.
Advantages: Very dilute sulfuric acid is not corrosive. Water is inexpensive and large amounts of it can be obtained on-site and easily. This means that the spill can be dealt with immediately, thus reducing the harmful consequences of the spill.
Disadvantages: The large dilution heat created in the process is the main disadvantage. The extra heat makes any undiluted acid, or even the freshly diluted acid even more corrosive than before. It is also difficult to add the acid to water, since this is a spill after all. Water would have to be added to the acid, and this will result in a very violent and dangerous reaction. Even if the acid could be added to water, it would have to be done very slowly and carefully to avoid any extreme heating. The solution would have to be stirred constantly to allow the heat to dissipate. This process will be very tedious and dangerous.
Covering the Sulfuric Acid in Absorbent MaterialThe extent of the sulfuric acid spill can be contained by covering it with an inert, absorbent material such as vermiculite, dry sand and dry earth. The material is then shovelled using tools made from inert materials such as glass, enamel or ceramic into disposal containers. The waste is then disposed of properly according to local regulations. Combustibles and organic materials such as sawdust and cloth CANNOT be used to soak up the acid.
Advantages: This method is effective because it converts the liquid spill into a manageable solid which can be readily handled and disposed of. The acid can also be reclaimed from the material. The solid collected can be neutralised to reduce its high acidity or it can be incorporated into a suitable landfill.
Disadvantages: A large amount of material will be needed to cover the spill – this may be difficult to obtain on short notice i.e. in an emergency. Also, the collected solid is not neutralised, which means that it is still hazardous and corrosive due to the high acidity of sulfuric acid. The acid will still be in its concentrated form, making it possible for it to react with the moisture in the air, or to form toxic fumes.
Final ChoiceI think the most effective method for handling the sulfuric acid spill is neutralisation. Sulfuric acid is a very corrosive and harmful substance which very readily forms toxic fumes that are detrimental to the health of workers and also the environment. Therefore it is vital that we convert the sulfuric acid into a form that is much less harmful. The neutralisation process is immediate. The products of neutralising sulfuric acid are water and a harmless salt which are easy and safe to handle and clean up. Although the reaction is exothermic, its reaction is not as violent as when diluting the acid with water.
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