Unit 2 part B Question 7 Ans

UNIT 2

INDUSTRIAL SAFETY

DANGEROUS AND HIGHLY TOXIC MATERIALS

The effect of chemical substances on human body and safety precautions are closely related.

 Chemicals substances affect the body by ingestion, inhalation and absorption through skin contact.

INGESTION:

                        It occurs accidentally during handling of chemicals. Contaminated hands and dirty vessels used for eating and drinking are most common routes of ingestion. Accidental swallowing of chemicals in the laboratory is also possible. If it is in light dose, then the detoxicating effect the liver exerts, has a protective effect in such cases. When massive doses are taken, it can lead to fatalities in case of absence of immediate medical action.

INHALATION:

                       It is a common route for entry of dangerous chemicals. The air we breathe may contain dusts, fumes, gases or vapours. These impurities affect the lung directly while others are absorbed in the blood stream through lungs.

                DUSTS:

                               Consists of finely divided solids which may settle down only with great difficulty. During inhalation, a large amount of larger dust particles are entrapped in the nose and bronchial tubes and the rest go up to lungs. This causes respiratory diseases on continued exposure.

                 FUMES:

                                 Strictly consist of condensed solid particles in air, though the term is used loosely for condensed vapours or sublimated vapours too.

             

    GASES:

                                 Remain gaseous at ambient temperature in the atmosphere in the atmosphere. Gases of different types are miscible and enter chemical reactions too.

ABSORPTION:

                      This can be a source of entry of harmful solids and liquids into the body. This is by absorption through the skin into the vital parts of the body.

DUSTS AND FUMES:

                      

                      INERT DUSTS: Carbon dust is present in plants manufacturing and using carbon black and graphite products. Carbon dust causes blackening of lung tissues.

                                                    Silicate powder is widely used as fillers in chemical industries. Fuller’s earth is also widely used in refining operations. Both these dusts causes discomfort. Good ventilation and handling in closed systems can be useful in controlling these dusts.

                       HARMFUL DUSTS: Silica dust is used in rubber, refractories and in abrasives. On breathing, it stimulates the production of fibrous tissues in lungs, which in course of time interfere the passage of air to lungs, causing shortness of breath and leading to tuberculosis. In cases, where the usage of silica dust is unavoidable, proper ventilation and protection for respiratory systems should be followed.

                                                            Vanadium dust is present as catalysts and also in fuel oils and is also used in alloys, pigments and electroplating. Uranium is a vital raw material in nuclear industries. All these cause inflammation of the lungs.

                                                            Chromate dusts are used in chromate industries and are associated with lung cancer.

GASES AND VAPOUR:

                    SIMPLE ASPHYXIANTS: These gases cause reduction of oxygen by displacing it to a level where it does not support life and cause suffocation. (eg)N2, CO2, OH4, C2H6, C9H8, C4H10, C2H4, C9H6  and C2H2. In such cases, we have to make use of respiratory protective systems and good ventilation is important.

                   CHEMICAL ASPHYXIANTS: CO damages the oxygen carrying capacity of the blood causing permanent brain damage or even death. Cyanides (Hydro cyanic acid, organic and inorganic cyanide compounds.) damage the mechanism of transmission of oxygen from hemoglobin to the cell. Though death is rapid, the victim does not show asphyxiation.

                    PULMONARY IRRITANTS:  This affect the lungs in addition to cause irritation to upper respiratory. (eg) chlorine, phosgene, nitrous oxides, sulphur trioxide, ozone, bromine, fluorine and dimethyl sulphate.

                    UPPER RESPIRATORY IRRITANTS: These irritate the upper respiratory passages and the eyes. Lungs may not affected if the victim is able to escape quickly as the irritation is severe even at low concentrations. (eg) Ammonia, Formaldehyde, SO2, aldehydes, styrene, methyl acetate formate and furfural.

 TOXIC CHEMICALS:

LEAD, MANGANESE AND MERCURY DUSTS:

Lead is one of the oldest known poisons whose effect is exerted on blood, bowels and nervous system. It causes anemia, colic and constipation and by entering the nervous system paralyses muscles of the hand and foot. In severe cases it leads to depression.

Inhalation of mercury vapour or absorption of mercury through the skin gives rise to skin irritation. It’s effects are excessive salivation, gum inflammation and loss of teeth. The nervous system is also affects leading depressions, irritation and loss of confidence.

Manganese poisoning develops slowly and affects the brain causing tremor of hands, salivation etc.

CENTRAL NERVOUS SYSTEM POISONS: Vapour of certain chemicals produce a narcotic effect on the body and also produce other side effects. Alcohols have a narcotic effect which is maximum with methyl alcohol and decreases with decreased volatility of succeeding alcohols. Petroleum hydrocarbons are mostly aliphatic compounds, produce narcotic effects which are more pronounced in the case of lower boiling fractions. Toluene and xylene are known to have narcotic effects.

  Halogenated hydrocarbons are an important class of toxic substances. The following are:

(1)   CHLOROFORM: cause narcotic action, also liver damage and bad effects on the lungs.

(2)   CARBON TETRA CHLORIDE: dangerous narcotic, can damage liver and kidney. On heating it gives rise to phosgene, which can affect the lungs.

(3)   TETRA CHLORO ETHANE: damages the liver producing all characteristics of jaundice. Kidneys may also be damaged.

(4)   CHLORINATED AROMATICS: These are poisonous for nervous systems.

(5)   CARBON-DI-SULPHIDE: : in production of rayon and is a narcotic poison causing harm when inhaled in some small doses for a longer periods. The effect on the brain is to cause excitement, depression, fatigue, loss of memory, insanitary, muscular weakness and loss of vision.

(6)    HYDROGEN SULFIDE: causes headache, dizziness, and excitement.

BLOOD POISONING:

Benzene is an important raw material and a popular solvent in several applications. It has a narcotic effect. If absorbed in small concentrations over a long period, it causes damage to the bone marrow. In early stages, it shoes symptoms of fatigue, insomnia and weakness, while in advanced cases it leads to hemorrhage from gums and under the skin.

Aniline, nitro benzene, toluidines and xylidines. On absorption tend to combine with hemoglobin and reduce the oxygen carrying capacity in the blood leading to deprivation of oxygen. Chloro compounds of toluidines are known to cause bleeding from the bladder.

Phenol on absorption causes head ache, dizziness and respiratory paralysis in the initial stages, while in advanced stages can cause diarrhea, kidney, liver damage and loss of apetite

Dinitro phenol and dinitro ortho cresol can cause jaundice like effects as well as cataract on continued absorption.

Dyestuff intermediates such as benzidine, alpha and beta naphthyl amines enter through the skin and cause bladder cancer over a long period of exposure to small doses.

CONTROL OF DISEASES DUE TO CHEMICAL EFFECTS:

1.      Educating the workers of hazards and keeping managers and supervisory staff informed of upto date developments.

2.      Informing the medical profession about the hazards of the industrial process to help them diagnose the worker’s ailment and detect the onset of poisoning early enough.

3.      Replacement of dangerous chemicals by less dangerous ones.

4.      Changing the process to enable elimination of a dangerous raw material or intermediate.

5.      Automatic and fully enclosed handling to avoid spillage, dusts in handling, transport, packing etc. 

6.       Providing effective ventilation to avoid hazards of dusts, fumes, vapours etc. besides natural ventilation, artificial ventilation and exhaust ventilation are used effectively.

7.      Using wet methods to avoid dusts in handling and grinding.

8.      Implementing housekeeping and cleanliness.

9.      Instituting work permit systems to enable work to be done with full precautions against anticipated hazards.

10.  Providing means of personal protection with appropriate equipment for specific precautions for head, eyes, face, body, hands, feet etc. as well as respiratory protection for carrying out work involving chemical hazards due to handling acids, alkalis etc.

11.  Providing wasing and first aid facilities to suit the specific chemicals handled.

12.  Having a schedule of medical check of the blood, urine, stools, lungs, skin etc. to detect onset of symptoms of poisoning.

         

                  HIGHLY RADIO-ACTIVE MATEIALS.

ACTIONS TO BE TAKEN INCASE OF FIRES:  

           Fire fighting equipments should be used. Avoid contacts with leaking or damaged packages. Move undamaged packages if any without risk. In small fires, use carbon-di-oxide or dry chemicals. On large fires, flooding amounts of water should be used.

ACTIONS TO BE TAKEN INCASE OF SPILLS:

            Avoid contact with leaking or damaged packages and placing them in metal containers. Shut off liquid leak or use absorbent materials for containing leakage. Entries to the hazardous area should be stopped for a minimum possible time. In case of radio-active corrosive materials, dilute the spill with large amounts of water.

            In case of radioactive pyrophoric materials, gather the spilled material using shovel and place under water or mineral oil in metal containers as soon as possible to prevent self-ignition.

    In case of corrosive radioactive materials, attempt to plug releases from container opening using wooden plugs or freeze leakage by cooling with water stream at point of opening or pressurized co2  can also be used for freezing the leakage. Use water spray to reduce vapours.

                                                              HIGH PRESSURE OPERATIONS

The term pressure is taken to be any pressure above atmospheric pressure. Application of high pressure in industries has become common feature. Pressures upto 1000 atmospheres are now in large scale use in chemical industries.

  Uses of high pressure in industries are classified under the following heads.

1.      Production or maintenance of a liquid phase. (eg) liquefaction of air, oxygen, liquid phase cracking of petroleum hydrocarbons.

2.      Storage of gases. Transportation and use of gases in high pressure cylinders.

3.      Compaction of powers, briquettes, extrusions and related pressing operation of solids.

4.      Separation of liquids from solids.(eg) pressing of vegetable oils from seeds.

5.      Increasing gas solubility in liquids.(eg) scrubbing of gases like CO, CO₂ by liquids.

6.      Increase of chemical reaction rates. (eg) petroleum refining operations.

7.      Shifting chemical equilibrium.(eg) synthesis of ammonia, methyl alcohol.

High pressure reaction vessels are called autoclaves. They permit storage and reactions of gases and liquids or both. Autoclaves are operated only in places such that nobody can be injured if something go wrong with the equipment. The qeuipment is equipped with safety valves, pressure gauges, safety vent and inspection holes well sealed during operation. Personnel concerned with the operation should be familiar with the contents. Pressure and temperature at which the equipment is operated and tested, maximum admissible pressure and temperature, material of construction of the vessel and its working volume.

Gas cylinders are generally used for storing gases under pressure. These cylinders should be distinguished clearly by coloured band or paints and name of the gas clearly written. The pressure regulator is also painted in the same colour. They are handled always vertically and stored in a cool place. The metal cap is placed in position to prevent injury to the pin valve, whn the cylinder is not in use.

Cylinders with poisonous gases or flammable gases should be kept in specified places and should be checked for any possible leaks with soap solution. The cylinder should always be operated through the pressure regulator. The valve should be opened gradually and slowly.

Important safety rules to prevent high pressure hazards:

1.      Pressure gauges should be free of air inside the tube. The gauges should be installed above eye level. They should not be allowed to corrode.

2.      Flammable gases at high pressures on rubbing against the wall of metallic pipes cause static electricity discharge. Good earthing is essential.

3.      Direct fired vessels should not be emptied suddenly. They are cooled by the fluid running in slow velocities.

4.      Two safety valves should be provided with one of them operating at slightly lower pressures.

5.      Bursting of ruptured disc vessels cause sudden high temperatures and may ignite flammable gases. Sufficient venting is necessary.

6.      High pressure equipments should be confined in special rooms having thick walls. The high pressure gases must be quickly ventilated to the topmost point of the buildings when any pressure release takes place.

7.      Any leak developed may cause explosion or fire. Hence they must be repaired quickly by slow release of pressure first and then carry out repair works.

8.      Oils should never be used as lubricants when oxygen is stored.

9.      Regulator inspection, hydraulic testing at 1.5 times the working pressure should be carried out..

10.  Too rapid rise in pressure should be avoided.

11.  Joints should not be tightened under pressure.

12.  All high pressure areas should be marked clearly and any unauthorized entry should be prohibited.

PLANT  LAYOUT:

Processing units are the real backbone of the plant. Also processing units are the most hazardous areas. So these should be removed from the boundaries of the plant and these should be consolidated rather than be scattered. The processing units should be kept downwind from both, the major ignition sources and the major concentration of the people. It’s well to maintain these units from major tankage areas since these are hazardous to each other. Even though we are speaking about consolidating the processing units, we should have some separation between them since they are mutually hazardous to each other. This is true in the case where the units are not integrated process wise. One unit may be in full production as the other may be under shutdown or major maintenance presenting an increased potential for trouble.

      Spacing is a matter of good judgement. The factors which should be considered while making such judgements are:

      1. Operating pressure,

      2. operating temperature,   

      3. types of materials present in the units,

      4. quantities of materials present in the units,

      5. types of structures present in the units,

      6. relative value of the units and

      7. space required for fire fighting or other emergency operations.

       Every plant will need some administrative buildings. These main offices should be located on the periphery of the plant and as isolated as possible from the hazardous areas of the plant. The reason is, most of the sales people and suppliers used to visit these units and they may not be unaware of the nature and location of the hazards in the plant and may cause any serious hazardous problems. Another reason is, the isolated buildings will permit smoking without much danger to the plant. This also permits a very clear marking between the areas where smoking is permitted and where it is not permitted. Another one reason is, the offices will house a large number of people and separation of these people from the hazardous areas units improve the odds in favor of safety.    

            We should keep the laboratory buildings separate from the main office buildings, since we may keep small amounts of flammables and also toxic gas may be present.

            Boiler plants are major ignition sources.  The maintenance shops are also ignition sources as well as a concentration of people. The shops should be upwind and separated by distance.

            Warehouses will be normally located adjacent to the shops and both must be accessible by the railroads. Good plant layout will avoid routing railroads throughout the plant, thus avoiding the coincident hazards. The tank car and tank truck loading and unloading facilities should also have their own traffics and these should not pass through the plant.

            Waste water treating facilities may turn out to be the ultimate point of collection of flammables spilled anywhere in the plant and so a downwind and a remote location is necessary.

            Cooling towers have the similar characteristics of collecting toxics or flammables which may leak into the water side of the coolers in the operating units. So these should also have a downwind direction. The cooling water tower fog can block visibility on roadways, units etc.

            Tanks are the major storage units for toxic materials. Its wise to keep the people, operating units and tankage as far apart as possible.

            Plant layout includes the problem of roadways which are very important to safety. The layout should plan to minimize the road crossings by ground level pipe alleys and the pipe alleys should be looped in certain services. A looped system is one so arranged and valved that a failure at any point in the system can be isolated by closing the valves. Since in emergency cases, the piping for these services should be looped. (a) Fire water and (b) steam for power and heat.

            We should keep the electrical power lines also under the ground level of the plant. In view of safety, the location for first aid stations should be remote and it should be kept within reach from the hazardous areas since from these areas only major part of the people come for treatment.

            If we need to construct a plant in slopy or hilly site, we should keep the sources of flammables, liquid or vapour uphill from the points of ignition. Also the sources of toxics and flammable liquids should be downhill from points of concentration of people. The site may be subjected to flooding also. In such cases, it is wise to construct the boiler houses, electric power station and pumping stations on higher ground. Tanks are also equally important since any empty tank may be floating on little amount of water. This can cause the lines to these tanks be ruptured, resulting in large spills, to further aggravate the emergency.

                HIGH TEMPERATURE OPERATIONS

            Commercial chemical production of useful products  results from the conversion of one substance into another. Some conversions are simple and subjected to little hazard but some are most complex and sometimes dangerous paths which the substances may take under only slight variations in pressure or temperature or composition. The kinetics of various steps are rarely known and difficult to for see.

            Temperature is the most frequent cause of divergence from the expected reaction rates. The Arrhenius equation is more exact and expresses the effect of temperature on the reaction rate in the form

                                    K         =          A*e^-E/R.T

            Where              K         =          rate constant

                                    A         =          Constant

                                    E          =          energy of activation of the reaction

                                    R         =          gas constant

                                    T          =          absolute temperature

                                    E          =          natural base for log.

            A reaction whose rate changes with temperature in concordance with the above equation is generally thought of us a normal reaction. But many other types of reaction rate curves which can occur besides the simple Arrhenius are

            Almost every chemical reaction requires the transfer of heat. Where heat transfer is rapid and occurs at high temperature fouling leads to hot spots on the tube, softening and ultimately to the loss of the tube. Temperature and pressure measurements at the inlet and outlet connections generally give an adequate warning of reduced heat transfer capacity. The use of visible and audible alarms when dangerous limits are reached is desirable. More critical installations should include devices to automatically cut off fuel supply. Start auxiliary ventilating systems, introducing blanketing steam or other protective measures. Problems arise only in scale up because the volume of a reactor goes up as the  cube of it’s size whereas the area goes only as the square of the size. Larger reactors must include coils or other systems providing surface extended beyond that possible with a jacket. The rate of generation of exothermic reaction is commonly exponential in temperature whereas heat transfer names linearly with the difference in temperature between the jacket coolant and the reactants. Reactors for such reactions are extremely sensitive to small changes in reaction or jacket water temperature and are uncontrollable unless the temperature at which they run is near ambient.

            Several methods of controlling exothermic reactions are available.

1.      Use dilute solutions or suspensions

2.      Feed one component slowly enough to prevent heat raise to a dangerous value.

3.      Add around 10% of a volatile solvent to soak up heat by volatilization if temperature raises suddenly.

4.      Provide automatic controls to shift operative conditions if raise commences.

HANDLING OF DANGEROUS MATERIALS

            1. Dangerous chemicals should be handled and stored under the supervision of competent person who is familiar with the risks and precautions to be taken.

            2. In case of any doubt as to the nature of the risk or the precautions to be taken the necessary instructions should be obtained from a competent authority.

            3. When dangerous chemicals are to be stored or handles, the workers concerned should be given adequate information concerning their nature and the special precautions to be taken handling them.

            4. Special precautions should be taken to prevent breakage or damage to containers of dangerous chemicals.

            5. I containers of dangerous substancesare broken or damaged to a dangerous extent, work should be stopped and workers concerned removed to a safer place until the danger has been eliminated.

            6. When highly flammable material is being handled, special measures should be taken to ensure that an incidental fire can be controlled immediately.

            7. Where necessary, non spaking tools should be provided in explosive atmospheres.

            8. Where corrosive materials are stored and handled, special care should betaken to prevent damage to the containers and to render any spillage harmless.

            9. Workers handling harmful substances should thoroughly wash their hands and face with soap before they take any food or drink.

            Safety in material handling involves more than purchase and corrent use of good material handling devices. There are less obvious factors which must be considered thoroughly.

            1. FLOORS : Conditions of the floor such as slipperiness, absorptive qualities, colours, nonsparkling and durability will have a great effect on material handling. Clean floors are a necessity to any safety programme. If debris is left lying on the floor, it may cause falls, unhygienic conditions. The use of mechanical cleaning devices are more effective than conventional manual methods.

            The tendency is to permit cracks and potholes in the floors to remain unrepaired until a wide area becomes bad enough to warrant complete resurfacing.

            Lines marked on floors inside and outside the plant can do more good than almost any other precautionary measures to organize production activities in a plant so that they are efficient and safe. Lines specify areas for aisles, storage, raw material areas,parking etc.

            2. LIGHTING : Lighting may also be the primary cause for an accident.

            3. OBSTRUCTIONS : Even though pipes, conduits, drains are necessary parts of plant structures, they often cause hazards. In planning the plant, such parts should be placed in such a way that they will cause a minimum of interference with persons ormaterials.