Safety, Environment, and Health Issues of Iron and Steel Industry
Safety, Environment, and Health Issues of Iron and Steel Industry
The iron and steel industry is a heavy industry. In addition to the safety hazards normally present in giant plants, massive equipment, and movement of large masses of materials, employees are exposed to the heat of molten metal and slag at temperatures upto 1,800 deg C, toxic or corrosive substances, respirable air-borne contaminants, and noise. Spurred by economic pressures for greater efficiency and regulatory provisions, the industry has made great strides in the introduction of newer equipment and improved processes which afford greater safety and better control of physical and chemical hazards. Workplace fatalities and lost-time accidents have been significantly reduced, but are still a significant problem. Working in a steel plant continues to remain a dangerous occupation in which the potential hazards cannot always be designed out. Accordingly, this presents a formidable challenge to everyday plant management. It calls for ongoing studies, continuous monitoring, responsible supervision, and updated education and training of employees at all the levels.
In the iron and steel industry, large amounts of material are processed, transported, and conveyed by massive equipment. Iron and steel plants typically work under serious safety, environment, and health issues. An integrated approach is normally needed to cope with such situation. This includes combining of good engineering and maintenance practices, safe working procedures, employees’ training, and use of personal protective equipment (PPE).
Safety organization is of prime importance in the iron and steel plant, where safety depends so much on employees’ reaction to potential hazards. The first responsibility for management is to provide the safest possible physical conditions, but it is normally necessary to get everyone’s cooperation in safety procedures. Accident-prevention committees, employees’ safety representatives, safety incentives, competitions, suggestion schemes, slogans and warning notices can all play an important part in the implementation of safety in the plant. Involving all people in site hazard assessments, behaviour observation, and feedback exercises can promote positive safety attitudes and focus work groups working to prevent injuries and illnesses.
Accident statistics reveal danger areas and the need for additional physical protection as well as greater stress on housekeeping. The value of different types of protective clothing can be evaluated and the advantages can be communicated to the employees concerned.
Training in safety is to include information about hazards, safe methods of working, avoidance of risks, and the wearing of PPE. When new methods, technologies, or processes are introduced, it is even necessary to retrain even those employees with long experience on older types of methods, technologies, or processes. Training and refresher courses for all levels of employees are particularly valuable. Training and refresher courses are to familiarize people with safe working methods, unsafe acts to be prohibited, safety rules, and the regulatory provisions associated with accident prevention. Training is to be conducted by experts and is to make use of effective audio-visual aids. Safety meetings or contacts are to be held regularly for all persons to reinforce safety training and awareness.
Heat exposure is a problem throughout a steel plant, especially in plants located in hot climates. Recent studies have shown that, contrary to previous belief, the highest exposures occur in those areas, where employees are monitoring hot steel continuously, rather than during melting, when, although temperatures are higher, they are intermittent and their effects are limited by the intense heating of the exposed skin and by the use of eye protection. The danger of heat stress is reduced by adequate fluid intake, adequate ventilation, the use of heat shields and protective clothing and periodic breaks for rest or work at a cooler task.
All dangerous parts of machinery and equipment, including lifts, conveyors long travel shafts, and gearing on overhead cranes, are to be securely guarded. A regular system of inspection, examination, and maintenance is necessary for all machinery and equipment of the plant, particularly for cranes, lifting tackle, chains and hooks. Effective lockout / tag out procedures are to be implemented for maintenance and repair. Defective tackles ar to be scrapped. Safe working loads are to be clearly marked, and tackle not in use are to be stored neatly. Means of access to overhead cranes are to be, wherever possible, by staircase. If a vertical ladder is to be used, it is to be hooped at intervals. Effective arrangements are to be made to limit the travel of overhead cranes when people are at work in the vicinity. It can be necessary, as needed by regulatory provisions in certain countries, to install appropriate switchgear on overhead cranes to prevent collisions if two or more cranes travel on the same runway.
Potentially hazardous vibration is created by oscillating mechanical movements, more frequently (i) when machine movements have not been balanced, (ii) when operating shop floor machines, and (iii) when using such portable tools as pneumatic drills and hammers, saws, and grindstones. Damage to vertebral discs, low back pain, and degeneration of the spine has been attributed to whole body vibration in a number of studies of overhead crane operators.
Whole body vibration can cause a variety of symptoms (e.g., motion sickness, blurring and loss of visual acuity) which can lead to accidents. Hand-arm vibration has been associated with carpal tunnel syndrome, degenerative joint changes and Reynaud’s phenomenon in the finger tips (white finger disease), which can cause permanent disability. A study of chippers and grinders has shown that they are more than twice as likely to develop Dupuytren’s contracture as a comparison group of employees.
Lasers have a wide range of applications in a steel plant. They can cause retinal damage at power levels far below those needed to have effects on the skin. Laser operators can be protected by sharp focus of the beam and the use of protective goggles, but other employees can be injured when they unknowingly step into the beam area or when it is inadvertently reflected at them.
Radioactive nuclides are employed in many measuring devices. Exposures can normally be controlled by posting of warning signs and appropriate shielding. Much more dangerous, however, is the accidental or careless inclusion of radioactive materials in the scrap steel being recycled. To prevent this, many plants are using sensitive radiation detectors to monitor all scrap before it is introduced into the processing.
Locomotives, rails, wagons, buggies, and couplings are to be of good design and maintained in good condition. Also an effective system of signalling and warning is to be in operation. Riding on couplings or passing between wagons is to be prohibited. Where road and rail track is crossing, movement of the road traffic to be controlled preferably by drop gate. No maintenance is to be carried on the rail track unless measures have been taken to restrict the movement on the track.
Coke production, ironmaking, and steelmaking processes produce large quantities of gases. After the dust has been removed, these gases are used as fuel sources in the various units of the steel plant. These gases contain large amounts of carbon monoxide (blast-furnace gas, 22 % to 30 %, coke oven gas, 5 % to 10 %, and converter gas, 68 % to 70 %).
Carbon monoxide sometimes leaks from the top or body of blast furnace or from the many gas pipelines inside the plant accidentally, causing acute carbon monoxide poisoning. Most cases of such poisoning occur during work around blast furnace, especially during maintenance work. Other cases occur during work around hot stoves, inspection visits around the furnace body, work near the furnace top or work near slag notches or the tapping holes. Carbon monoxide poisoning can also result from (i) gas released from water-seal valves or seal pots in the steelmaking area or rolling mills, (ii) from sudden shutdown of blowing equipment, boiler rooms or ventilation fans, (iii) from leakage, (iv) from failure to properly ventilate or purge process vessels, pipelines or equipment prior to work, and (v) during closing of pipe valves.
Good care is needed in storing oxygen. Supplies to different parts of the plant need to be piped and clearly identified. All lances are to be kept clean.
There is a never-ending need for good housekeeping. Falls and stumbles caused by obstructed floors or implements and tools left lying carelessly can not only cause injury but also can throw a person against hot or molten material. All materials are to be carefully stacked, and storage racks are to be suitably placed for tools. Spills of grease or oil are to be immediately cleaned. Lighting of all parts of the shops and machine guards is to be of a high standard.
Good general ventilation throughout the plant and local exhaust ventilation (LEV) wherever substantial quantities of dust and fumes are generated or gas can escape are necessary, together with the highest possible standards of cleanliness and housekeeping. Gas equipments are to be regularly inspected and well maintained so as to prevent any gas leakage. Whenever any work is to be done in an environment likely to contain gas, carbon monoxide gas detectors are to be used for ensuring safety. When working in a dangerous area is unavoidable, self-contained or supplied-air respirators are to be worn. Breathing-air cylinders are always to be kept in readiness, and the operatives are to be thoroughly trained in methods of operating them.
With a view to improving the work environment, induced ventilation is needed to be installed to supply cool air. Local blowers can be located to give individual relief, especially in hot working areas. Heat protection can be provided by installing heat shields between employees and radiant heat sources, such as furnaces or hot metal, by installing water screens or air curtains in front of furnaces or by installing heat-proof wire screens. A suit and hood of heat-resistant material with air-line breathing apparatus gives the best protection to the furnace operators. As work in the furnaces is extremely hot, cool-air lines can also be led into the suit. Fixed arrangements to allow cooling time before entry into the furnaces are also necessary.
Acclimatization leads to natural adjustment in the salt content of body sweat. The incidence of heat affections can be much lessened by adjustments of the workload and by well-spaced rest periods, especially if these are spent in a cool room, air- conditioned if necessary. As palliatives, a plentiful supply of water and other suitable drinks are to be provided and there are to be facilities available for taking light meals. The temperature of cold drinks is not to be too low and employees are to be trained not to swallow too much cold liquid at a time. Light meals are to be preferred during working hours. Salt replacement is needed for jobs involving profuse sweating and is best achieved by increasing salt intake with regular meals.
In cold climates, care is needed to prevent the ill-effects of prolonged exposure to cold or sudden and violent changes of temperature. Canteen, washing and sanitary facilities are preferably to be close at hand. Washing facilities are to include showers, changing rooms, and lockers are to be provided and maintained in a clean and sanitary condition.
Steel plant is one of the noisiest industries, although hearing conservation programmes are decreasing the risk of hearing loss. The major sources include fume extraction systems, vacuum systems using steam ejectors, electrical transformers and the arc process in electrical arc furnaces, rolling mills, and the large fans used for ventilation. At least half of noise-exposed employees are handicapped by noise-induced hearing loss after as little as 10 years or 15 years on the job. Hearing conservation measures include periodic noise and hearing assessments, noise control engineering, maintenance of machines and equipment, personal protection, and employee education and training. Causes of hearing loss other than noise include burns to the eardrum from particles of slag, scale, or molten metal, perforation of the drum from intense impulse noise and trauma from falling or moving objects.
Wherever possible, sources of noise are to be isolated. Remote central panels remove some operatives from the noisy areas. Hearing protection is needed in the worst areas. In addition to enclosing noisy machinery with sound-absorbing material or protecting the employees with sound-proofed shelters, hearing protection procedures have been found to be effective means of controlling noise-induced hearing loss.
Steel plant employees can be exposed to a wide range of pollutants depending on the particular process, the materials involved and the effectiveness of monitoring and control measures. Adverse effects are determined by the physical state and propensities of the involved pollutant, the intensity and duration of the exposure, the extent of accumulation in the body, and the sensitivity of the individual to its effects. Some effects are immediate while others can take years and even decades to develop. Changes in processes and equipment, along with improvement of measures to keep exposures below toxic levels, have reduced the risks to the employees. However, these have also introduced new combinations of pollutants and there is always the danger of accidents, fires, and explosions.
Dust and fumes are generated at several points during the production of iron and steel. Dust and fumes are found in the preparation processes, especially sintering, in front of the blast furnace and steel furnace. Dusts and fumes from iron ore or ferrous metals do not readily cause pulmonary fibrosis and pneumoconiosis is infrequent. Some lung cancers are thought to be connected with carcinogens found in coke-oven emissions. Dense fumes emitted can particularly affect crane operators.
Emissions of fumes and particulates are a major potential problem for employees working with liquid metals, making and handling of coke, and charging and tapping of furnaces. They are also troublesome to employees assigned to equipment maintenance, duct cleaning, and refractory dismantling operations. Health effects are related to the size of the particles (i.e., the proportion that are respirable) and the metals and aerosols which can be absorbed on their surfaces. There is evidence that exposure to irritant dust and fumes can also make steel plant employees more susceptible to reversible narrowing of the airways (asthma) which, over time, can become permanent.
Exposures to silica, with resultant silicosis, once quite common among employees in such jobs as furnace maintenance in steel melting shop and blast furnace, have been lowered through the use of other materials for furnace linings as well as automation, which has reduced the number of employees in these processes.
Asbestos, once used extensively for thermal and noise insulation, is now encountered only in maintenance and construction activities when formerly installed asbestos materials are disturbed and generate airborne fibres. The long term effects of asbestos exposure include asbestosis, mesothelioma and other cancers. A recent cross-sectional study found pleural pathology in 20 out of 900 steel plant employees (around 2 %), much of which is diagnosed as restrictive lung disease characteristic of asbestosis.
The predominant source of sulphur emissions in steel plant is the use of high-sulphur fossil fuels and blast furnace slag. Hydrogen sulphide has a characteristic unpleasant odour and short-term effects of relatively low-level exposures include dryness and irritation of nasal passages and the upper respiratory tract, coughing, shortness of breath and pneumonia. Longer exposures to low levels can cause eye irritation, while permanent eye damage can be produced by higher levels of exposure. At higher levels, there can also be a temporary loss of smell which can delude workers into believing that they are no longer being exposed.
Over 1,000 chemicals are used or encountered in steel plant mainly (i) as raw materials. (ii) as contaminants in scrap and / or in fuels, (iii) as additives in special processes, (iv) as refractories, and (v) as hydraulic fluids and solvents used in plant operation and maintenance. Coke making produces by-products such as tar, benzene and ammonia while some others are generated in the different areas of the steel plant. All can be potentially be toxic, depending on the nature of the chemicals, the type, the level and duration of the exposures, their reactivity with other chemicals, and the susceptibility of the exposed employee. Accidental heavy exposures to fumes containing sulphur oxides and nitrogen oxides have caused cases of chemical pneumonitis. Carbon monoxide, which is released in all combustion processes, can be hazardous when maintenance of equipment and its controls are substandard. Benzene, along with toluene and xylene, is present in coke-oven gas and causes respiratory and central nervous system symptoms on acute exposure. Long-term exposures can lead to bone marrow damage, aplastic anaemia and leukaemia.
Bench and top-side operations in coke production, cast house operations in the blast furnace, furnace front operation and continuous-casting operations in steel making, all involve strenuous activities in a hot environment. Heat rated illness prevention procedures are needed to be implemented.
High levels of work stress are found in the steel plant. Exposures to radiant heat and noise are compounded by the need for constant vigilance to avoid accidents and potentially hazardous exposures. Since several processes are in continuous operation, shift work is a necessity. There is the potent stressor of potential job loss resulting from automation and changes in processes, plant relocation and downsizing of the employees.
All parts of the body are at risk in most operations, but the type of protective wear needed vary according to the location. Those working at furnaces need spats, boots, gloves, helmets with face shields or goggles against flying sparks and also against glare, and clothing which protects against burns such as overalls of fire-resisting material. Safety boots, safety glasses and helmets are imperative in almost all places and gloves are widely necessary. The protective clothing needs to take account of the risks to health and comfort from excessive heat. For example a fire-resisting hood with wire mesh visor gives good protection against sparks and is resistant to heat. Different synthetic fibres have also proved efficient in heat resistance. Strict supervision and continuous promotional campaigns are necessary to ensure that PPEs are worn and correctly maintained.
The ergonomic approach (i.e. investigation of the employee-machine-environment relationship) is of particular importance at certain operations in the iron and steel plant. An appropriate ergonomic study is necessary not only to investigate conditions while an employee is carrying out various operations, but also to explore the impact of the environment on the employee and the functional design of the machinery used.
Musculoskeletal injuries are common in steel plant. Despite the introduction of mechanization and assistive devices, manual handling of large, bulky and / or heavy objects remains a frequent necessity. Constant attention to housekeeping is necessary to reduce the number of slips and falls. Furnace brick-layers have been shown to be at highest risk of work-related upper arm and low back problems. The introduction of ergonomics into the design of equipment and controls (e.g., crane drivers’ cabs) based on study of the physical and mental requirements of the job, coupled with such innovations as job rotation and team working, are recent developments aimed at enhancing the safety, well-being and performance of steel plant employees.
Pre-placement medical examinations are of great importance in selecting persons suitable for the arduous work in the iron and steel plant. For most work, a good physique is needed. Hypertension, heart diseases, obesity and chronic gastroenteritis disqualify individuals from work in hot surroundings. Special care is needed in the selection of crane drivers, both for physical and mental capacities. Medical supervision is to pay particular attention to those exposed to heat stress. Periodic chest examinations are to be provided for those exposed to dust, and audiometric examinations for those exposed to noise. Mobile equipment operators are also to receive periodic medical examinations to ensure their continued fitness for the job.
Constant supervision of all resuscitative appliances is necessary, as is training of employees in first-aid revival procedure. A central first-aid station with the requisite medical equipment for emergency assistance is to be provided. If possible, there is to be an ambulance available at the first aid station for the transport of severely injured persons to the nearest hospital under the care of a qualified ambulance attendant. In larger plants first-aid stations or boxes are to be located at several central points.
Protecting steel plant employees against potential toxicity needs allocation of adequate resources for a continuing, comprehensive and coordinated programme which is to include the following elements.
- Assessment of all raw materials and fuels and, when possible, substitution of safer products for those known to be hazardous.
- Effective controls for the storage and safe handling of raw materials, products, by-products and wastes.
- Continuous monitoring of employees’ personal occupational environment and ambient air quality, with biological monitoring when required, and periodic medical surveillance of employees to detect more subtle health effects and verify fitness for their jobs.
- Engineering systems to control potential exposures (e.g., equipment enclosures and adequate exhaust and ventilation systems) supplemented by personal protective equipment (e.g., shields, gloves, safety glasses and goggles, hearing protectors, respirators, foot and body protection, etc.) when engineering controls do not suffice.
- Application of ergonomic principles to design of equipment, machine controls and tools and analysis of job structure and content as a guide to interventions which can prevent injury and enhance employees’ well-being.
- Maintenance of readily available, up-to-date information about potential hazards, which is to be disseminated among employees and line managers as part of an ongoing employee education and training programme.
- Installation and maintenance of systems for the storage and retrieval of the voluminous health and safety data, as well as for the analysis and reporting of records of inspection findings, accidents and worker injury and disease.
Coal, coke, and chemical plant
Coal is the most important raw material in the production of metallurgical coke. The coal-handling operations consist of unloading from rail wagons or trucks, blending of different qualities of coal, proportioning, pulverizing, bulk-density control using oil, and conveying to the coke oven battery bunkers. The coking of the coal is carried out by-product or heat recovery coke ovens. In most of the cases, by-product coke ovens are used which are designed and operated to collect the volatile material from the coal. The by-product coke ovens consist of three main parts namely (i) the coking chambers, the heating flues, and the regenerative chamber.
The reactions during the carbonization of coal for the production of coke are complex. Coal decomposition products initially include water, oxides of carbon, hydrogen sulphide, hydro-aromatic compounds, paraffins, olefins, phenolic and nitrogen-containing compounds. Synthesis and degradation occur among the primary products which produce large amounts of hydrogen, methane, and aromatic hydrocarbons. Further decomposition of the complex nitrogen containing compounds produces ammonia, hydrogen cyanide, pyridine bases and nitrogen. The continual removal of hydrogen from the residue in the oven produces hard coke. The by-product coke ovens have facilities for recovering and processing coal chemicals, and coke oven gas.
During the coal unloading, preparation, and handling operations, thousands of tons of coal are processed, producing dust, noise, and vibrations. The presence of large quantities of accumulated dust can produce an explosion hazard in addition to the inhalation hazard. During the process of coking, ambient and radiant heat are the major physical concerns, particularly on the top of the coke oven batteries, where a large number of the workmen are deployed. Noise can be a problem in mobile equipment, primarily from drive mechanism and vibrating components which are not adequately maintained. Ionizing radiation and / or laser producing devices can be used for mobile equipment alignment purposes.
Mineral oil is typically used for operation purposes for bulk density control and dust suppression. Materials can be applied to the coal prior to being taken to the coal bunker to minimize the accumulation and to facilitate the disposal of hazardous waste from the by-products operations. The major health concern associated with coking operations is emissions from the ovens during charging of the coal, coking, and pushing of the coke. The emissions contain numerous polycyclic aromatic hydrocarbons (PAHs), some of which are carcinogenic. Materials utilized for sealing leaks in lids and doors can also be a concern during mixing and when lids and doors are removed. Asbestos and refracting ceramic filters can also be present in the form of insulating materials and gaskets, although suitable replacements have been used for products which earlier contained asbestos.
The coal-related hazards which are associated with rail wagons, and vehicular traffic as well as conveyor belt movement are present. The majority of accidents occurs when workmen are struck by, caught between, fall from, are entrained and entrapped in, or fails to lockout such equipment (including electrically).
The mechanical hazards of greatest concern are associated with the mobile equipment on the pusher side, coke side and the charging car on top of the battery. These equipments are in operation practically the entire work period and little space is provided between it and the operations. Caught-between and struck-by accidents associated with mobile rail-type equipment account for the highest number of fatal coke-oven production incidents. Skin surface burns from hot materials and surfaces and eye irritation from dust particles are responsible for more numerous, less severe occurrences.
PAHs are produced in the majority of the combustion processes. In steel plant, coke production is the major source. When coal is partially burnt to produce coke, a large number of volatile compounds are distilled off as coal tar pitch volatiles, including PAHs. These can be present as vapours, aerosols, or adsorbates on fine particulates. Short-term exposures can cause irritation of the skin and mucous membranes, dizziness, headache and nausea, while long-term exposure has been associated with carcinogenesis. Studies have shown that coke-oven operators have a lung cancer mortality rate twice that of the general population. Those most exposed to coal tar pitch volatiles are at the highest risk. These include employees working on the oven topside and working with the longest period of exposure. Engineering controls have reduced the numbers of employees at risk.
To maintain dust concentrations during coal production at acceptable levels, containment and enclosure of screening, crushing and conveying systems are needed. Low emission cars are also needed in addition to wetting agents applied to the coal. Adequate maintenance procedures, belt procedures, and clean-up procedures are needed for the minimizing of the spillage and keeping of the passageways alongside process and conveying equipment clear of the coal. The conveyor system is to use only those components which are known to be effective in reducing spillage and maintaining containment, such as belt cleaners, skirt boards, proper belt tension and so on.
Due to the health hazards associated with the PAHs released during the coking operations, it is important to contain and collect these emissions. This is best accomplished by a combination of engineering controls, work practices, and maintenance practices. It is also necessary to have an effective respirator programme. The controls are to include the following.
- A charging procedure designed and operated to eliminate emissions by controlling the volume of coal being charged, properly aligning the car over the oven, tightly fitting drop sleeves, and charging the coal in a sequence which allows an adequate channel on top of the coal to be maintained for flow of emissions to the collector mains and re-lidding immediately after the charging.
- Drafting from two or more points in the oven being charged and an aspiration system designed and operated to maintain sufficient negative pressure and flow.
- Providing air seals on the pusher machine level bars to control infiltration during charging and carbon cutters to remove carbon build-up.
- Keeping of uniform collector-main pressure adequate to convey the emissions.
- Changing of door and gaskets as needed to maintain a tight seal and adequately cleaned and maintained pusher side and coke side sealing edges.
- Luting of lids and doors and maintaining door seals as necessary to control emissions after charging.
- Minimizing of green pushes by heating the coal uniformly for an adequate period.
- Installation of large enclosures over the entire coke side area to control emissions during the pushing of coke or use of travelling hoods to be moved to the individual ovens being pushed.
- Routine inspection, maintenance, and repair for proper containment of emissions.
- Positive-pressure and temperature controlled operator cabins on mobile equipment to control workmen exposure levels. To achieve the positive-pressure cabin, structural integration is imperative, with tight fitting doors and windows and the elimination of separations in structural work.
Training of workmen is also necessary so that proper work practices are used and the importance of proper procedures to minimize emissions is understood. Routine workmen exposure monitoring is also to be used to determine that levels are acceptable. Gas monitoring and rescue programmes are to be in place, primarily due to the presence of carbon monoxide in coke-gas ovens. A medical surveillance programme is also to be implemented.
Ironmaking and steelmaking
Fig 1 shows overall flow diagram of coke production, ironmaking, and steelmaking.
Fig 1 Flow diagram of coke production, ironmaking and steelmaking
For iron making, the essential feature is the blast furnace, where iron ore is reduced to produce hot metal (liquid iron). The furnace is charged from the top with sinter and iron ore, coke, and flux. Hot air enriched with oxygen is blown in from the bottom. The carbon monoxide produced from the coke reduces the iron oxides into hot metal containing carbon. The furnace produce hot metal at a temperature of around 1,550 deg C. Both hot metal and slag collect at the bottom of the furnace. The furnace is tapped periodically, and the hot metal is then be poured into pig iron for later use, or into ladles where it is transferred in liquid condition for steelmaking. The iron ore fines are normally subjected to sintering or pelletizing before charging into blast furnace. The liquid slag is either granulated at the cast house or cooled in slag pit.
Hot metal contains large amounts of carbon as well as other impurities. It is refined by oxidizing the impurities for making steel. The steelmaking process is carried out either in the basic oxygen furnace (converter) or the electric arc furnace. Some mini steel plants of smaller capacity use induction furnace for steelmaking. Both electric arc furnaces and induction furnaces use scrap and direct reduced iron for making steel. The liquid steel made is further refined using ladle metallurgy and vacuum degassing. The liquid steel is the cast into slab, blooms, or billets in conventional continuous casting machines. For hot strip production, thin slab casting and rolling process is used in some plants.
During the ironmaking and steelmaking processes, large amounts of material are processed, transported and conveyed by massive equipments. Ironmaking and steelmaking processes are full of hazards and need wide-ranging safety and health procedures to address hazards in an environment which can be unforgiving. An integrated approach combining good engineering and maintenance practices, safe job procedures, employees’ training and use of PPEs is normally needed to control the hazards.
Burns can occur at many points in the ironmaking and steelmaking processes. These points can be at the front of the furnace during tapping from molten metal or slag, from spills, spatters or eruptions of liquid metal from ladles or vessels during processing, teeming (pouring) or transporting, and from contact with liquid metal as it is being formed into a final product. Water entrapped by liquid metal or slag can generate explosive forces which spills liquid metal or hot material over a wide area. Water leakage or inserting a damp implement into molten metal can cause violent eruptions.
Mechanical transport is essential in iron and steel production processes which exposes employees to get potential struck-by and caught- between hazards. Overhead travelling cranes are found in almost all areas of ironmaking and steelmaking. Bigger plants also rely heavily on the use of fixed-rail equipment and large industrial tractors for the transportation of materials.
Safety procedures for crane use need training for (i) enduring proper and safe operation of the crane and rigging of loads to prevent dropped loads, (ii) good communication and use of standard hand signals between crane drivers and slingers to prevent injuries from unexpected crane movement, (iii) inspection and maintenance of crane parts, lifting tackle, slings and hooks to prevent dropped loads, and (iv) safe means of access to cranes to avoid falls and accidents on crane transverse ways.
Safety procedures for rail movements also need good communication, especially during shifting and coupling of rail cars, to avoid catching people between rail car couplings.
Maintaining proper clearance for passage of large industrial vehicles and other equipment and preventing unexpected start-up and movement are necessary to eliminate struck-by, struck-against and caught-between hazards to equipment operators, pedestrians and other vehicle operators. Procedures are also essential for inspection and maintenance of equipment safety appliances and passage ways.
Good housekeeping is the foundation of safety in the areas of ironmaking and steelmaking. Floors and passage ways can quickly become obstructed with material and implements which pose a tripping hazard. Large quantities of greases, oils and lubricants are used and if spilled can easily become a slipping hazard on walking or working surfaces.
Tools are subject to heavy wear and soon become compromised and perhaps dangerous to use. Although mechanization has greatly lessened the amount of manual handling in the industry, ergonomic strains still can occur on many occasions.
Sharp edges or burrs on steel products or metal bands pose cut and puncture hazards to the employees involved in finishing, shipping, and scrap-handling operations. Cut-resistant gloves and wrist guards are frequently used to eliminate injuries.
Protective eye-wear procedures are particularly important. Foreign-body eye hazards are prevalent in most areas, especially in raw material handling and steel finishing, where grinding, welding, and burning are conducted.
Planned maintenance is particularly important for accident prevention. Its purpose is to ensure the efficiency of the equipment and maintain fully operative guards, since failure can cause accidents. Adhering to safe operating practices and safety rules is also very important because of the complexity, size and speed of process equipment and machinery.
Emissions generated in steelmaking can contain heavy metals (e.g., lead, chromium, zinc, nickel and manganese) in the form of fumes, particulates, and adsorbates on inert dust particles. They are frequently present in scrap steel streams and are also introduced in the manufacture of special types of steel products. Studies carried out on employees melting manganese alloys has shown impaired physical and mental performance and other symptoms of manganism at exposure levels significantly below the limits currently allowable in most countries. Short-term exposure to high levels of zinc and other vapourized metals can cause ‘metal fume fever’, which is characterized by fever, chills, nausea, respiratory difficulty and fatigue.
Exposure to silica is a risk to employees engaged in lining, relining and repairing furnaces and vessels with refractory materials, which can contain high silica. Ladles are lined with fire-brick or bonded crushed silica and this lining requires frequent repair. The silica contained in refractory materials is partly in the form of silicates, which do not cause silicosis but rather pneumoconiosis. Employees are rarely exposed to heavy clouds of dust.
Alloy additions to furnaces making special steels sometimes bring potential exposure risks from chromium, manganese, lead and cadmium. Vanadium and other alloy additions can cause chemical pneumonitis.
Furnaces can cause glare which can injure eyes unless suitable eye protection is provided and worn. Manual operations, such as furnace bricklaying, and hand-arm vibration in chippers and grinders can cause ergonomic problems.
Blower plants, oxygen plants, gas-discharge blowers and high-power electric arc furnaces can cause hearing damage. Furnace operators are to be protected by enclosing the source of noise with sound-deadening material or by providing sound-proofed shelters. Reducing exposure time can also prove effective. Hearing protectors (earmuffs or earplugs) are frequently needed in high-noise areas because of the unfeasibility of obtaining adequate noise reduction by other means.
Hot slabs, blooms, and billets are rolled in hot rolling mills into steel products. Part production of the hot rolled strips is further processed in cold rolling mills. Part production of the cold rolled strips is further processed in the coating lines. Fig 2 shows overall flow diagram of rolling of steel products.
Fig 2 Overall flow diagram of rolling of steel products
Rolling mills can be of several types. They normally contain roller conveyor to convey, heated slab / bloom / billet from a reheating furnace to the rolling mill stand. Surface scale is removed from the heated slab / bloom / billet, which is then rolled in different roll stands of the rolling mill. In modern continuous mills, the rolling speed can be very high.
The hot-rolled sheet steel is normally cleaned or pickled in a bath of sulphuric or hydrochloric acid to remove surface oxide (scale) formed during hot rolling. A modern pickling line operates continuously. Coils of cleaned, hot-rolled sheet steel are cold rolled to make a product thinner and smoother. The cold-rolling process hardens sheet steel so that it is to be annealed in an annealing furnace to make it more formable. After the steel has been softened in the annealing process, a temper mill is used to give the steel the desired flatness, metallurgical properties, and surface finish. The product can be shipped to consumers as coils or further side-trimmed or sheared into cut lengths.
Mechanization at the rolling mills has reduced the number of trapping points at machinery but they still exist, especially in cold rolling mills and in finishing departments. In cold rolling, there is a risk of trapping between the rolls, especially if cleaning in motion is attempted. Nips of rolls are to be efficiently guarded and strict supervision exercised to prevent cleaning in motion. Severe injuries can be caused by shearing, cropping, trimming and guillotine shears unless the dangerous parts are securely guarded. An effective lockout / tag out procedure is necessary for maintenance and repair.
Severe injuries can take place especially in hot rolling, if employees attempt to cross roller conveyors at unauthorized points. An adequate number of cross over bridges are to be provided and their use enforced. Looping and cobble can cause extensive injuries and burns, even severing of lower limbs. Where full mechanization has not eliminated this hazard, protective posts or other devices are necessary.
Special attention is to be paid to the hazard of cuts to employees in strip and sheet rolling mills. Such injuries are not only caused by the thin rolled metal, but also by the metal straps used on the rolled products, which can break during handling and constitute a serious hazard.
The use of large quantities of oils, rust inhibitors and so on, which are normally applied by spraying, is another hazard normally encountered in sheet rolling mills. Despite the protective measures taken to confine the sprayed products, they frequently collect on the floor and on communication ways, where they can cause slips and falls. Gratings, absorbent materials and boots with non-slip soles are hence to be used, in addition to regular cleaning of the floor.
Oil mists generated in the cold rolling of steel can produce irritation of skin, mucous membranes and upper respiratory tract, nausea, vomiting and headache. One study reported cases of lipoid pneumonia in rolling mill employees who have longer exposures.
Even in automated rolling mills, accidents occur while changing of heavy rolls in the stands. Good planning frequently reduces the number of roll changes needed. It is important that the roll changing operation is not done under pressure of time and that suitable tools are to be provided.
The automation of modern rolling mills is associated with number of minor breakdowns, which are frequently repaired by the mill crew without stopping the mill or parts of it. In such cases it can happen that it is forgotten to make use of necessary mechanical safeguards, and severe accidents can take place. The fire hazard involved in repairs of hydraulic systems is frequently neglected. Fire protection is to be planned and organized with particular care in mills having hydraulic equipment.
Tongs used to grip hot material can knock together. The square spanners used to move heavy rolled sections by hand can cause serious injuries to the head or upper torso by backlash. All hand tools are to be well designed, frequently inspected and well maintained. The tongs used at the rolling mills need to have their rivets renewed frequently. Ring spanners and impact wrenches are to be provided for roll changing crews. Bent-out, open-ended spanners are not to be used. Employees are to receive adequate training in the use of all hand tools. Proper storage arrangements are to be made for all hand tools.
Several accidents can be caused by faulty lifting and handling and by defects in cranes and lifting tackle. All cranes and lifting tackle are to be under a regular system of examination and inspection with particular care is needed in the storage and use of slings. Crane drivers and slingers are to be specially selected and trained.
There is always a risk of accidents from mechanical transport. Locomotives, wagons, and bogies are to be well maintained and a well-understood system of warning and signalling is to be enforced. Clear passage ways are to be provided for the fork-lifts and other trucks.
Several accidents are caused through falls and stumbles or badly maintained floors, by badly stacked material, by protruding billet ends and cribbing rolls and so on. Hazards can be eliminated by good maintenance of all floor surfaces and means of access, clearly defined walkways, proper stacking of material and regular clearance of debris. Good housekeeping is necessary in all parts of the plant including the yards. A good standard of illumination is to be kept throughout the plant.
In hot rolling, burns and eye injuries can be caused by flying mill scale, splash guards can effectively reduce the ejection of scale and hot water. Eye injuries can be caused by dust particles or by whipping of cable slings. Eyes can also be affected by glare.
PPE is of big importance in the prevention of rolling mill accidents. Helmets, safety shoes, gaiters, arm protection, gloves, eye shields, and goggles are to be worn to meet the appropriate risk. It is essential to secure the cooperation of employees in the use of protective devices and the wearing of protective clothing. Training, as well as an effective accident prevention organization in which employees or their representatives participate, is important.
Radiant heat levels of upto 1,000 kcal/sqm have been measured at work points in rolling mills. Heat stress diseases are a concern, but employees in modern mills normally are protected through the use of air-conditioned pulpits.
Considerable noise develops in the entire rolling zone from the gearbox of the rolls and straightening machines, from pressure water pumps, from shears and saws, from throwing finished products into a pit and from stopping movements of the material with metal plates. The general level of operating noises can be around 84 dBA to 90dBA, and peaks up to 115 dBA or more are not unusual. The unit ‘dBA’ is an expression of the relative loudness of sounds in air as perceived by the human ear. In the A-weighted system, the decibel values of sounds at low frequencies are reduced compared with unweighted decibels, in which no correction is made for audio frequency.
Cleaning of the finished products with high-speed percussion tools can lead to arthritic changes of the elbows, shoulders, collarbone, distal ulna and radius joint, as well as lesions of the navicular and lunatum bone. Joint defects in the hand and arm system can be sustained by rolling mill employees, owing to the recoiling and rebounding effect of the material introduced into the gap between the rolls.
When lead-alloyed steel is rolled or cutting-off discs containing lead are used, toxic particles can be inhaled. It is hence necessary constantly to monitor lead concentrations at the workplace, and employees liable to be exposed are regularly to undergo medical examination. Lead can also be inhaled by flame scarfers and gas cutters, who can at the same time be exposed to nitrogen oxides (NOx), chromium, nickel and iron oxide.
Butt welding is associated with the formation of ozone, which can cause, when inhaled, irritation similar to that due to NOx. Employees working at the reheating-furnace can be exposed to harmful gases, the composition of which depends on the fuel used (blast furnace gas, coke oven gas, coal, or oil) and normally includes carbon monoxide and sulphur dioxide. LEV or respiratory protection may be needed.
Employees lubricating rolling-mill equipment with oil mist can suffer health impairment due to the oils used and to the additives they contain. When oils or emulsions are used for cooling and lubricating, it is to be ensured that the proportions of oil and additives are correct in order to preclude not only irritation of the mucosae but also acute dermatitis in exposed employees.
Large amounts of degreasing agents are used for the finishing operations. These agents evaporate and can be inhaled. Their action is not only toxic, but also causes deterioration of the skin, which can be degreased when solvents are not handled properly. LEV is to be provided and gloves are to be worn.
Strong acids in pickling shops are corrosive to skin and mucous membranes. Appropriate LEV and PPE are to be used. Acid mists from pickling areas can cause skin, eye and respiratory irritation. Exposures to hydrochloric and sulphuric acid mists from pickling baths have also been associated with a nearly two fold increase in laryngeal cancer as per one study.
X rays and other ionizing radiation equipment can be used for gauging and examination. Strict precautions in accordance with the regulatory provisions are needed
Environment and health relates issues
The iron and steel plant, because of the large volume and complexity of its operations and its extensive use of energy and raw materials, has the potential of having a considerable impact on the environment and the health of the people. Fig 3 shows the pollutants and waste generated in a steel plant. These can be classified in three primary categories namely (i) air pollutants, (ii) waste water contaminants, and (iii) solid wastes.
Fig 3 Pollutants and waste generated in a steel plant
Air pollutants from the iron steel plant are one of the major environmental concerns. These pollutants include gaseous substances such as oxides of sulphur and nitrogen, and carbon monoxide. In addition, particulates such as soot and dust, which can contain iron oxides, have been the focus of controls. Emissions from coke ovens and from by-product plants have been a concern, but the continuous improvements in the technology of emissions control during the past few decades, coupled with more stringent statutory regulations, have considerably reduced such emissions.
Total pollution control costs, over half of which relate to air emissions, have been estimated to range from 1 % to 3 % of total production costs. In a modern steel plant, air- pollution control installations represent around 10 % to 20 % of total plant investments.
Air pollutants vary (i) with the particular process, (ii) the engineering and construction of the plant, (iii) the raw materials used, (iv) the sources and amounts of the energy needed, (v) the extent to which waste products are recycled into the process, and (vi) the efficiency of the pollution control measures. For example, the introduction of basic oxygen steelmaking has permitted the collection and recycling of waste gases in a controlled manner, reducing the amounts to be exhausted, while the use of the continuous-casting process has reduced the consumption of energy, resulting in a reduction of emissions. This has increased product yield and improved quality.
Sulphur oxides – The quantity of sulphur oxides, formed largely in the combustion processes, depends primarily on the sulphur content of the fossil fuel used. Both coke and coke oven gas used as fuels is major sources of sulphur oxides. In the atmosphere, sulphur oxides can react with oxygen radicals and water to form a sulphuric acid aerosol and, in combination with ammonia, can form an ammonium sulphate aerosol. The health effects attributed to sulphur oxides are not only due to the sulphur oxides but also because of its tendency to form such respirable aerosols. In addition, sulphur oxides can be adsorbed onto particulates, many of which are in the respirable range. Such potential exposures can be reduced not only by use of fuels with low sulphur content but also by reduction of the concentration of the particulates. Use of electric arc furnace decreases the emission of sulphur oxides by eliminating the need for coke, but this passes on this pollution control burden to the power generating plant. Desulphurization of coke oven gas is achieved by the removal of reduced sulphur compounds, primarily hydrogen sulphide, prior to combustion.
Nitrogen oxides – Like the sulphur oxides, oxides of nitrogen, primarily nitrogen oxide and nitrogen dioxide, are formed in fuel combustion processes. They react with oxygen and volatile organic compounds (VOCs) in the presence of ultra-violet (UV) radiation to form ozone. They also combine with water to form nitric acid, which, in turn, combines with ammonia to form ammonium nitrate. These can also form respirable aerosols which can be removed from the atmosphere through wet or dry deposition.
Particulate matter – Particulate matter, the most visible form of pollution, is a varying, complex mixture of organic and inorganic materials. Dust can be blown from stockpiles of iron ore, coal, coke, and fluxes (limestone and dolomite) or it can enter the air during their loading and transport. Coarse materials generate dust when they are rubbed together or crushed under vehicles. Fine particles are generated in the sintering, smelting and melting processes, particularly when liquid iron comes in contact with air to form iron oxide. Coke ovens produce fine coal, coke, and tar emissions. Potential health effects depend on the number of particles in the respirable range, the chemical composition of the dust, and the duration and concentration of the exposure.
Sharp reductions in the levels of particulate pollution have been achieved. For example, by using electrostatic precipitators to clean dry waste gases of basic oxygen steelmaking, the steel plants have decreased the level of emitted dust to a large extent. This, however, has resulted into a marked rise in energy consumption. Other methods of particulate pollution control include the use of wet scrubbers, bag houses, and cyclones (which are effective only against large particles).
Heavy metals – Metals such as cadmium, lead, zinc, mercury, manganese, nickel and chromium can be emitted from a furnace as a dust, fume, or vapour, or they can be absorbed by the particulates. Health effects depend on the level and duration of exposure.
Organic emissions – Organic emissions from primary steel operations can include benzene, toluene, xylene, solvents, PAHs, dioxins and phenols. The scrap steel used as raw material can include a variety of these substances, depending on its source and the way it had been used (e.g., paint and other coatings, other metals, and lubricants). Not all of these organic pollutants are captured by the conventional gas cleaning systems.
Radioactivity – In recent years, there are reports of instances in which radioactive materials have inadvertently been included in the scrap steel. The physico-chemical properties of the nuclides (e.g., melting and boiling temperatures and affinity for oxygen) determine what happens to them in the steelmaking process. There can be possibility of an amount which is sufficient to contaminate the steel products, the by-products and the various types of wastes, and thus need a costly clean-up and disposal. There is also the potential contamination of the steelmaking equipment, with resultant potential exposure of the shop floor employees. However, many steel plants have installed sensitive radiation detectors to screen all purchased steel scrap.
Carbon dioxide – Although it has no effect on human health or ecosystems at the normal atmospheric levels, carbon dioxide is important pollutant because of its contribution to the ‘greenhouse effect’, which is associated with the global warming. The steel industry is a major generator of carbon dioxide, more because of the use of carbon as a reducing agent in the production of iron from iron ore than from its use as a source of energy. By 1990, through a variety of measures for blast furnace coke rate reduction, waste-heat recovery, and energy saving, carbon dioxide emissions by the iron and steel industry have reduced by a large percentage over the earlier years.
Ozone – Ozone, a major constituent of atmospheric smog near the surface of the earth, is a secondary pollutant formed in air by the photo-chemical reaction of sunlight on nitrogen oxides, facilitated to a varying degree, depending on their structure and reactivity, by a range of VOCs. The major source of ozone precursors is motor vehicle exhausts, but some are also generated by iron and steel plants. As a result of atmospheric and topographic conditions, the ozone reaction can take place at great distances from their source.
Waste water contaminants
Steel plant discharges large volumes of water to lakes, rivers and streams, with additional volumes being vapourized while cooling various processes and equipments. Waste water retained in unsealed or leaking holding ponds can seep through and can contaminate the local water table and underground streams. These can also be contaminated by the leaching of rainwater through piles of raw materials or accumulations of solid wastes. Contaminants include suspended solids, heavy metals, and oils and greases. Temperature changes in natural waters due to discharge of higher temperature process water (around 70 % of steel plant process water is used for cooling) can affect the eco-systems of these waters. As a result, cooling treatment prior to discharge is necessary and can be achieved through application of available technology.
Suspended solids – Suspended solids (SS) are the main waterborne pollutants discharged from the steel plant. They comprise mainly iron oxides from scale formation during processing with coal, biological sludge, metallic hydroxides, and other solids can also be present. These are largely non-toxic in aqueous environments at normal discharge levels. Their presence at higher levels can lead to discolouration of streams, de-oxygenation, and silting.
Heavy metals – Steel plant water can contain high levels of zinc and manganese, while discharges from cold-rolling and coatings areas can contain zinc, cadmium, aluminum, copper and chromium. These metals are naturally present in the aquatic environment; however, it is their presence at higher than normal concentrations which create concern about potential effects on humans and the ecosystems. These concerns are increased by the fact that, unlike many organic pollutants, these heavy metals do not bio-degrade to harmless end products and can become concentrated in sediments and in the tissues of fish and other aquatic life. Further, by being combined with other contaminants (e.g., ammonia, organic compounds, oils, cyanides, alkalis, solvents and acids), their potential toxicity can be increased.
Oils and greases – Oils and greases can be present in waste water in both soluble and insoluble forms. Most heavy oils and greases are insoluble and are relatively easily removed. They can become emulsified, however, by contact with detergents or alkalis or by being agitated. Emulsified oils are routinely used as part of the process in cold rolling mills. Except for causing discolouration of the water surface, small quantities of most aliphatic oil compounds are innocuous. Monohydric aromatic oil compounds, however, can be toxic. Further, oil components can contain such toxicants as PCBs (Polychlorinated biphenyls), lead and other heavy metals. In addition to the question of toxicity, the biological and chemical oxygen demand (BOD and COD) of oils and other organic compounds can decrease the oxygen content of the water, thus affecting the viability of aquatic life.
Most of the solid waste produced in the steel plant is reusable. The process of producing coke, for example, gives rise to coal by-products which are important raw materials for the chemical industry. Many by-products (e.g., coke dust) can be fed back into the production processes. Blast furnace slag can be used in a number of ways such as land fill for reclamation projects, in road building, and as raw material for cement production. Steel, regardless of grade, size, use or length of time in service, is completely recyclable and can be recycled repeatedly without any degradation of its mechanical, physical or metallurgical properties. The recycling rate is estimated to be 90 %.