Hazards Of Sulphuric Acid And Caustic Soda
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A factory will be extended and it will consist of sulphuric acid and caustic soda and these two substances are hazardous substances which will be stored with propane which is a flammable substance and storage of these chemicals can pose various hazards to people and properties both on site and off site but theses hazards can be prevented or reduced as low as reasonably practical.
Sulphuric acid in concentrated form is highly irritating, toxic and corrosive to the tissue. Contact with this acid during leakage or spillage can rapidly destroy the tissue, and can cause severe burns, shock, collapse and other symptoms related to those of severe thermal burns, causing onsite hazard to the workers. The material used to construct the tank can cause hazard, according to HSE (2007), Sulphuric acid comes in contact with iron and some steel, hydrogen can be produced and trap quantities of these hydrogen can cause explosion resulting in onsite hazard. Leakages resulting from storage tank, tank truck can drain down the right way of embankment to the low grounds. If there is water flow, it can lead to water body containing acid causing off site hazard on the people that might drink from it, swim in the water, death or sickness off fishes and other water bodies. SCL (2002)
Caustic soda can cause both onsite and offsite hazard, if caustic soda reacts with atmospheric carbon di oxide, blockages can be formed as a result of sodium hydroxide clumping.HSE (2007). During unloading of caustic soda if the lid of the tanks, flanks connected to the pipeline, the valves are opened or defected; ejection of caustic soda from the openings can result in accidents. Leakages of the tanks can also flow into the environment causing off site hazard. If this alkali comes in contact with the eyes it could lead to lowering or loss of vision, dermatitis or chronic eczema can affect skin. If the concentration is very high it can rapidly decompose affected tissue. Inflammation of the mouth, throat, oesophagus and stomach may occur if come in contact with NAOH. Japan Soda industry association (2006). As seen in sulphuric acid, this alkali can cause unusual fire and explosion hazard. If it comes in contact with water, moist air and certain metals. OSHA. Spillage of sulphuric acid and caustic soda can also result in slip and trip of workers. HSE (2003)
To reduce the risk of sulphuric acid the tank which the acid is stored should be constructed to appropriate standard by a specialist. Acid resistant material should be used to bund the acid stores. HSE (2007). Sulphuric acid residue and vapour are usually retained in empty containers. For this reason labelled safeguards should be observed until they have been thoroughly cleaned. The storage area should be correctly sited and provided with warning notices. Storage tanks should be segregated from incompatible material. The flooring should be constructed by acid resistant to prevent accidents such as slips and trip. The storage area must be secured and regular inspection should be carried out for the container and ancillaries in case of defect to avoid leakages Carson and Mumford (1988).
The risk of sulphuric acid can be reduced by carrying out some precautions against exposure to the acid such as enclosing transfer, safety showers and eye wash facilities should be provided close to areas where exposure to the acid is possible. Employees and employers should be kitted up with personal protective equipment such as PVC plastic gloves with gauntlets, PVC plastic chemical suits, acid resistance boots, chemical goggles or face shield these personal protective equipment should be worn regularly especially when getting in contact with the acid and the whole body should be protected not wearing some and omitting others because contact of the acid with any part of the body can cause harm as seen above. Carson and Mumford (1988)
Sulco is a chemical company in one of its bulletin described how a storage tank for sulphuric acid can be constructed and thus explains that carbon steel should be used in the construction of tanks and piping for concentrated sulphuric acid over 70% while the pumps and valves should be constructed with 316 stainless steel to avoid iron contamination and alloy 20 for prolonged life since they are subjected to wear. Concrete footing should be used to support the storage tank. The storage tank should be surrounded by a dike, dike material can be concrete or earth lined with compacted clay or can be a synthetic liner. The design and operation stages should be done with care to avoid liquid full sections of pipe between closed valves of which the hydrogen produced by steel corrosion causes dangerous pressures most especially in warmer weathers. On delivery of the sulphuric acid the competent person should ensure that the tank is big enough to contain the amount of sulphuric acid that is being delivered to avoid over filing. The person receiving the sulphuric acid should check the unloading connections of the truck to ensure that the material is unloaded into the proper storage tank to avoid explosion. SCL (2002)
Unloading must be done by two people to reduce the possibility of accident and also in case of emergency the other can be of assistance and the facilities required for unloading should also be designed to reduce accidents location of the overflowing vent should be of interest, the vent should be directed away from buildings, isolation valves and air shut off valves into the dike. In cases of ruptured unloading hose, liquid isolation valve and air shut off valve should be far from the loading area so that the leak can be stopped quickly and safely. The truck driver should ensure that all equipment on his truck such as unloading hose is in good order. He and the person receiving should wear personal protective equipment and should be trained on proper actions to be carried out in case of spillage. During unloading of the acid, the truck should be wedged by wheel chocks to prevent movement while offloading. The ignition should also be off unless tractor air is needed. There should be post warning signs, the operators should route traffic away from off loading areas. In an event of spill, ensure that the unloading area are covered or sealed for containment. The regulated air supply should be at normal of 30psi and maximum of 35psi. SCL (2002)
From above it can be deduced that leakage can result in water body containing acid. To prevent this, steps should be taken to construct earth dikes downstream to contain the acid and water. If it is a frozen ground, back-hoe and front end loader will be necessary if a dam is needed, but if there is a high rate of flow through the area, damming may not be feasible, then a place farther downstream will be located where the contaminated water can be contained for neutralization before it reaches the main water course. The ph of the effluent liquid should be between 6.0-9.0 and the local regulation must be met before being sent for disposal. The tank truck should be made of 316 stainless steel, to prevent iron contamination. SCL (2002)
Preventive measures should be carried out to avoid onsite and offsite hazard due to splash, leakage, outflow or penetration of caustic soda to the external environment. Due to its corrosive properties to avoid harm during working hours, a competent person should be employed to handle the alkali. He should be trained on the properties of caustic soda and various precautions on handling it. To avoid leakage of caustic soda, the competent person should be in charge in checking pipe opening and closing of valves, checking of the commencement and termination of the receiving and checking of the quantities received. Care should be carried out during loading and unloading of this alkali to the tanker to avoid mistake in transferring the alkali to the wrong tank to avoid exothermic reaction or explosion. The competent person should always wear personal protective equipment such as rubber gloves, rubber apron, work cap, protective goggle, cotton or synthetic fibre work, rubber boots and dust mask. Shower and face washing facilities should be provided close to where the caustic soda is being handled in case of any accident such as spillage or leakage. Japan Soda industry association (2006). Skin cream are also necessary for protecting the skin, they help wash contamination from skin and after work cream aids replacement of skin oil and this can also be carried out when working with propane and sulphuric acid.HSE (2006).
To prevent leakages of caustic soda from flowing out of storage tank a spare tank should be installed to receive the alkali before emergency action is being carried out. Liquid bank such as earth fill, concrete, pit-like structure, pond and depression can also be constructed to accumulate the leaked caustic soda. These facilities tend to prevent harm from happening and the accumulated leaked caustic soda is then recovered and disposed. The alkali is disposed by neutralizing it with acid then wash it away it away with large quantity of water. The caustic soda water solution (water used for washing) should be neutralized before disposal to the river or sewage system to prevent polluting the river. Large quantity of leakage can be reduced by surrounding the leaked alkali with sand before disposing it as described above, small quantity of leaked liquid can be flushed with water or wiped off, and solid caustic soda can be recovered by scraping it together with sand or soda ash. The equipment that is being used to handle the caustic soda should be inspected periodically and the record should be retained. Erroneous operations can be prevented by taking certain measures like indicating name and directions of flow of the liquid, colour-coding and indication of the opening or closing direction of major valves and cocks. Checklist should be done during inspection of operating facilities and procedures. Japan Soda industry association (2006).
Training should be carried on individuals involved in handling or working with the alkali, to prevent accident, they should be trained on proper usage of the personal protective equipment and first aid kit. HSE (2006)
Caustic soda should be isolated from metals such as aluminium, tin, zinc because it corrodes them and hydrogen can be formed from this process and this can cause explosion. Caustic soda should be kept far from other chemicals, organic peroxides etc. From the above it can be deduced that not any material can be used to construct the storage tank for caustic soda. Steel can be used but it is safer to use a tank lined with rubber or alkali resistant synthetic resins. Defects and openings in the lid of the tanks, the body of the tanks, the flank connected to the pipeline and valves should be checked for by a competent person before injection of caustic soda into the tank. Japan Soda industry association (2006).
Health monitoring should be carried on the workers working with propane, sulphuric acid and caustic soda. They should be asked to check their skin every six months for dryness and soreness and if these symptoms appears, the proper use of hand cream and PPE by the workers should be investigated HSE (2006).
According to Carson and Mumford (1988) leakages of propane can results hazard. Even small leakages can cause harm resulting in large volume of potential flammable gas. Propane is known to have anaesthetic properties; it is also known to cause depression of the central nervous system and can also be nauseating when inhaled. The density of propane is such that when released it can accumulate at low levels, filling valleys, sumps, ditches pits hugging contours of the ground, pipe-trenches, and propane is known to travel considerable distance causing offsite hazard when it comes in contact with a source of ignition can cause fire and explosion risk. Loss of liquid propane at temperature of 15oc causes vaporization of propane this is usually seen in nearly all propane released to the atmosphere this results in flammable vapour air cloud. This can cause onsite and offsite hazard. The propane can disperse harmlessly or it can ignite immediately in the factory (onsite hazard) if it comes in contact with an ignition source it can also drift until it reaches an ignition source then ignites, the cloud may burn with or without explosion, if the clouds is too rich to explode it may form a mobile fire ball. This can cause off site hazard. The radiant heat from this can cause burns on people and destroy properties and probably ignite combustible material depending on their distance to the fire ball. Debris can also be drawn in to the fireball by convection currents.
Carson and Mumford (1988) explain that onsite and offsite hazards can also result from boiling liquid expanding vapour explosion (BLEVE). This result from failure of LPG vessel exposed to fire and mechanical damage this can be due to corrosion or by impact or due to over filling. The failure can result from either combination of weakening of part of the vessels exposed to fire and or excess pressure due to the effects of heat on the vessel content damages from BLEVEs arises from blast wave due to release of internal pressure, thermal radiation as a result of fire ball from massive burning of the contents of the vessels in the air which is preceded by ground flash, projection of fragments scattered over considerable distances due to violent rupture of the tank. Carson and Mumford (1988) explains that missiles usually travel alongside the direction which the end of the container is facing, but in some cases deviation can occur this can result in both onsite and offsite hazard. BLEVE can affect people and equipment onsite, passersby, onlookers, emergency services; road tankers can also be affected. BLEVEs can also affect road tankers during delivery if the tank suddenly rupture and blast and the blast are usually then followed by fireball. During transportation of hazardous material BLEVEs is the more severe and two types are known to affect tankers which is fired BLEVEs which has been discussed above and the cold BLEVE which can result from violent impact on the tank during traffic accident and other causes as seen in the storage tank. Accidental spill which can occur during delivery of propane can result to severe fire and explosion causing injuries and fatalities amongst off-road population resulting in off side hazard. Paltrinier, Gabriele, Menson et al (2009).
Risk assessment should be carried out to prevent off site and on site hazard as seen above and this should meet up with the standard of DSEAR. HSE (2009)
As seen from above one main hazard that can affect both onsite and offsite is human error and this can be prevented by employing a trained and competent person who understands the job and the characteristics of the chemicals they are working with. During filling of vessels with propane, it is the duty of the competent person to ensure that the required free space is left in the vessels after addition of propane. He should also ensure that the storage vessels of propane should not be manifolded together and if manifolding is unavoidable then suitable non return valves should be fitted. Carson and Mumford (1988)
Another hazard could result from the type of vessels in which the propane is stored. According to Carson and Mumford (1988) propane can be stored in any common metal (since its non corrosive) except from aluminium and external corrosion must be prevented. Non-metallic materials like rubber and certain plastics should be avoided. To ensure a good tank that will not give problem, advice on the type of materials to construct the storage vessels, valves, pipes, joints, seals etc. Should be given by the supplier and the plant should be designed, installed and maintained by a competent engineer using appropriate standard or codes. The storage vessels should be designed to endure the highest vapour pressure to be encountered during use; this can be due to highest temperature of exposure usually solar. The tank should be inspected for soundness, crack detection and weld integrity and this should be every five years.
The positioning of the tank should also be considered, from above it can be deduced that some tanks are usually position below the ground level and other above the ground. Neither of the two ways can cause risk. To prevent the storage of propane below the ground level the tanks must be securely fixed and external protective coating should be provided to resist soil corrosion. If the tank is situated above the ground, the tank vessels should be elevated above the ground. It can be placed on the cement floor and the floor should be sloped away from the tank to prevent accumulation of propane in case of leakage or spillage. Installation are usually fitted with water drench systems to discharge water onto the vessels, this should be done in such a way that the water discharged onto the vessels gets to all the part of the vessels in case the vessels is threatened by direct flame impingement or radiant heat. This also prevents unnecessary discharge of vapour. This appliated could be from fixed points such as drencher heads and monitors or mobile units spray nozzles. From above it can be deduced that BLEVEs occurs almost immediately hence these water spray stem should be automatic and should be less or equal to 600mm from the vessel surface to negate wind effects. Continuity of water supply should be at designed stage since the water discharge needs to be sustained for a prolonged period Carson and Mumford (1988).
According to Landucci et al (2009) fired BLEVE on LPG road tankers during loading and unloading operations are the main cause of societal risk. Paltrinier, Gabriele, Menson et al (2009) explains that from previous studies it can be deduced that 85% of BLEVEs are thermally induced; hence prevention of fired BLEVEs may lead to reduction of risk related to LPG transportation. They further said that passive protection such as pressure relief valves and thermal coating can avoid fired BLEVE. The presence of thermal coating increases time to failure allowing time for effective mitigation actions by fire brigades. The employer or supervisors should ensure that the tank used in transporting the propane should have thermal coating. According to activities involving transportation of hazardous material (hazmat) is the main contributors to overall risk; hence reduction of risk can be achieved acting on hazardous material transport.
A study carried out by Landucci et al (2009) also agrees with Paltrinier, Gabriele, Menson et al (2009) saying that coating produces effective protection of the tanks, it also increases the expected time for the tank to fail. They also concluded that introduction of fire protection coating may be a possible route to improve the safety of LPG distribution by road.
The factory should be extended in such a way that the location of the storage tank will be far from the population in case of missiles and explosions hazard may not be formed. The end of the tank should be positioned from the population and the main building of the factory in case of missiles since missiles follows the direction of the end of the tank. Carson and Mumford (1988).
According to HSE (1999) there are five steps to be considered when working with flammable substances, firstly ventilation: the area should be properly ventilated to enhance dispersal of liquids or gases in case of leaks, spills or release from any process. Secondly the storage and handling area should be free from ignition sources such as electrical equipment, smoking materials hot surfaces, open flames from heating equipment. Thirdly the chemical should be properly contained with the fourth step being elimination and this is not an option the fifth step by separating the chemical from other chemicals. These chemicals can be separated by physical barrier, wall or partition. If these steps above are carried out effectively where ever possible, the risk that can result the chemical will reduce especially that of propane. This can be summarised as ventilation, ignition, containment, exchange and separation (VICES), this five principle helps to ensure safe working conditions with flammable substance such as propane.
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