Safety in Cement Plants and Technology: Cement is one of the most widely used materials in the globe. Each man, woman, and child in the world consumes about 3 tons of concrete every year, which contains about 10-15% of cement (WBCSD, 2013). The cement industry is a heavy industry employing a large number of people, and huge machines such as kilns, mills, crushers, silos, large-capacity motors, and industrial fans. According to the Bureau of Labor Statistics (BLS) (2017), cement, concrete, lime, and gypsum product manufacturers in the US employed 149,000 persons over 16 years of age in 2016, out of the total 151,436,000 persons employed in the US in all the industrial sectors. The cement industry is known for generating dust and gaseous pollution. Cement manufacturing processes like crushing, milling, clinkering, cooling, and cement grinding generate dust and gases that pollute the environment. Green (2005) states that the cement industry is linked to dust, explosions, road transport accidents, high ambient temperatures, high noise levels, diseases, and wide variations in macro-climatic and micro-climatic conditions.
10 most frequently cited safety and health violations
According to Galassi (2016), the director of enforcement programs of the Department of Labor’s Occupational Safety and Health Administration (OSHA), a preliminary list of the 10 most frequently cited safety and health violations for the fiscal year 2016, compiled from nearly 32,000 inspections of workplaces of the industrial sectors in the United States by federal OSHA staff are:
- Fall protection
- Hazard communication
- Scaffolds
- Respiratory protection
- Lockout/Tagout
- Powered industrial trucks
- Ladders
- Machine Guarding
- Electrical wiring
- Electrical, general requirements
Falls are among the leading causes of worker deaths. It is observed that too many workers are killed or gruesomely injured when machinery starts up suddenly while being repaired, or hands and fingers are exposed to moving parts. Lockout/tagout and machine guarding violations are often the cause of the accidents.
The high number of fatalities associated with forklifts, and a high number of violations for powered industrial truck safety, indicate a need for an appropriate solution besides the administrative and regulatory safety directions. Galassi (2016) reports that more than 4,500 workers are killed on the job every year, and approximately 3 million are injured in industrial sectors, even though by law, employers are responsible for providing safe and healthful workplaces for their workers.
Health Hazards in the Cement Industry
The cement industry is faced with two main categories of hazards: the hazards from accidents and hazards from dust and gases emitted in the plant (Fig. 1).
Fig.1: Two areas of hazards in cement plants
1. Hazards due to accidents
The cement industry is not free from safety violations in plant operations and has a history of many fatal accidents involving serious injuries and even loss of human life. The data on the total number of fatal accidents in the US, the manufacturing sector, and cement, and concrete products in 2015 is shown in Table 1. There were 353 fatal injuries in manufacturing sectors in the US in 2015. The cement and concrete product manufacturing sector has 26 fatal injuries, 7.36% of all the manufacturing sectors in the US. The number of fatal injuries in transportation incidents was 15 against the total incidents of 94 with a 15.96% share of all the manufacturing sectors in the US. The fatal incidents in cement and concrete products due to contact with objects and equipment alone were 7 out of 102 incidents in manufacturing sectors, a 6.86% share.
High-temperature workplaces, heavy and moving machines, dusty environments, and violation of safety measures are some of the key factors causing health hazards to the workmen, damage to the costly machines, and loss of materials. Although the list of accidents in cement plants is very long, 10 accidents occurred in recent times in different countries including China, USA, Australia, India, Pakistan, Egypt
Table 1: Fatal occupational injuries by industry and event or exposure, all United States, 2015
| Industry | Total fatal injuries (Number) | Event or exposure | |||||
| Violence and other injuries by persons or animals | Transportation incidents1 | Fires and explosions | Fall, slips, trips | Exposure to harmful substances or environments | Contact with objects and equipment | ||
| Total in USA | 4,836 | 703 | 2054 | 121 | 800 | 424 | 722 |
| Manufacturing Sectors | 353 | 37 | 94 | 19 | 63 | 38 | 102 |
| Cement and concrete product manufacturing | 26 | Nil | 15 | Nil | Nil | Nil | 7 |
| 1 includes roadway, non-roadway, air, rail fatal injuries and fatal occupational injuries resulting from being struck | |||||||
and Mallawi are compiled in Table 2, which are based on the data reported by Global Cement News (2017). The causes of these accidents include cylinder explosion, roof collapse, fall from the height, silo collapse, getting trapped in between the machines in operations, trapping of workers during belt cleaning, fire, and burns from hot clinker. There are many more reasons of accidents in cement plants such as back firing at the kiln plateform, explosion of ESP due to excessive CO, electrical flash over, toppling of forklift trucks, jumping of motors from foundations, breakage of rollers and tire of kilns etc.
Table 2: Accidents in Cement Plants – 10 Case Studies
(Source: Global Cement News, 2017)
| Case No. | Country | Year | Brief Description | Details of Accident |
| 1 | China | 2017 | Four workers died at Zhongda cement plant. | On March 21, 2017, four workers died when the roof of a shed collapsed at the Zhongda cement plant in Zhangzhou, Fujian Province. Three workers died at the scene and another died in hospital, according to the Xinhua News Agency. |
| 2 | US | 2016 | Worker killed in fall at Midlothian Ash Grove Cement plant | A worker died from a fall at the Midlothian Ash Grove Cement plant in Texas on 10 May 2016. The worker, a maintenance mechanic at the plant, was working on the top of a concrete mixing tower. The Mine Safety and Health Administration and Ash Grove Cement are investigating the cause of the accident. |
| 3 | US | 2016 | Maintenance worker died from a fall from the top of slurry tank at Midlothian cement plant | A maintenance worker aged 46 years, died in May, 2016 from a fall from the top of a slurry tank in Midlothian cement plant. In its report on the incident, the Mine Safety and Health Administration (MSHA) said that the cement producer failed to provide protection around openings through which workers could fall and that it failed to use fall prevention and protection devices. |
| 4 | India | 2016 | A cylinder in the fine coal crusher plant exploded at an ACC cement plant in Sindri, Jharkhand, India | A cylinder in the fine coal crusher plant exploded, probably due to extra pressure generated by the hot air generator attached to the crusher. ACC stopped production at the plant to conduct an internal inquiry into the incident. |
| 5 | India | 2014 | Worker dies in freak accident in cement factory in Chhijwar, Madhya Pradesh, India | A worker was killed on 10 May 2014 while cleaning the belt of a crusher in Jaypee’s cement plant in Chhijwar, Madhya Pradesh. The incident took place when the worker was cleaning the crusher belt, got trapped in the machine. The victim was rushed to Hospital but he died on the way. The plant management agreed to pay compensation of US$16,753, provide a job to a family member and also provide free training to the son of the deceased. |
| 6 | India | 2013 | Fire at Jammu & Kashmir Cement plant, India | A fire broke out at the government run Jammu & Kashmir Cement plant in the Pulwama district of south Kashmir on 3 December 2013. No one was hurt and damage was caused to a few machines like motors, diesel oil tank, hot air generator and coal mill. |
| 7 | Pakistan | 2016 | Silo collapses at Fauji Cement plant in Pakistan. | A raw meal silo has collapsed at the Fauji Cement Company plant at Tehsil Fateh Jang, Punjab. The structure containing 25,000t of raw material collapsed on 29 May 2016 also causing damage to the coal mill area of second production line. The company reported no casualties |
| 8 | Australia | 2009 | Worker died due to fatal injury when crushed between two hydraulic rams at Cement Australia | A worker was fatally injured when he was crushed between two hydraulic rams while working at the factory on 13 September 2009. The North South Wales (NSW) Industrial Relations Commission found that CA Kandos and Cement Australia had breached the Occupational Health and Safety Act 2000, by failing to install fixed guarding along the entire length of a feeder and conveyor system as required by Australian safety standards and failing to provide adequate supervision and instruction to the worker. The Commissioner noted that the systems in place at the time of worker’s death were comprehensive but defective in a number of respects. The company was fined a total sum of US$ 172,843. |
| 9 | Egypt | 2014 | Four killed in scaffold collapse at Sinai Cement Plant, Egypt | Four workers were killed and at least 35 others were injured on 27 December 2014 when a scaffold collapsed in the Sinai Cement plant. Four workers were killed and at least 35 others were injured on 27 December 2014, when a scaffold collapsed in the Sinai Cement plant in central Sinai. Sinai Cement denied that it had a connection with the accident in a statement. |
| 10 | Malawi | 2014 | Worker dies due to hot clinker covering them at Shayona Cement plant in Malawi | One worker died and three others injured at the Shayona Cement Factory in Kasungu. Hot clinker caused the injuries due to an open door at the plant. “When they switched on the furnace, the cement stone busted from the clinker and produced hot ashes which covered them. One died in the process of receiving treatment, while the other three are in critical condition,” said local police. |
2. Hazards due to dust and gaseous emissions
The cement industry, by nature of its processes, emits hazardous dust and gases. The cement industry alone produces 5% of the total greenhouse gasses in the atmosphere and is the second largest emitter of CO2 globally (Trudeau, N; et al., 2011). It contributes significantly to the imbalances of the environment, especially to the air quality (Zimwara, D., et al. 2012). The key environmental emissions are nitrogen oxides(NOX), Sulphur dioxide (SO2), and grey dust (Albeanu et al, 2004). Green (2005) cites several hazards in the cement industry, which include:
- Workers are exposed to hazards of climatic conditions, dusts produced during drilling and crushing, explosions, and falling rocks and earth. Accidents in the haulage of materials to the cement works are one of the important hazards. Dust is the main hazard in cement processing.
- High ambient temperatures, especially near furnace doors and kiln platforms, and radiant heat.
- High noise levels of about 120 dB in the vicinity of ball mills, which is much higher than the 60 dB in normal conversations.
- Carbon monoxide concentration ranging from traces to 50 ppm near the rotary kilns.
- Workers affected with diseases of respiratory system, digestive disorders, skin diseases, rheumatic and nervous conditions, hearing and visual disorders. Chronic bronchitis, often associated with emphysema is reported as the most frequent respiratory problems.
- Acid-resistant cement, used for refractory plates, bricks and dust contain high amounts of free silica and exposure to them involves a definite risk of silicosis. Some cases of severe pneumoconiosis have been found – most likely as a result of exposure to materials other than clay and Portland cement.
- Skin diseases account for about 25% or more of all the occupational diseases. ‘Cement eczema’ might be due to the presence of hexavalent chromium in the cement. Possible sources of the chromium in cement include:
- volcanic rock (tuff)
- the abrasion of the refractory lining of the cement kiln
- the steel balls used in the grinding mills
- different tools used for crushing and grinding the raw materials and the clinker
- The wide variations in macro-climatic and micro-climatic conditions found in the cement industry can lead to various disorders of the locomotor system (arthritis, rheumatism, spondylitis and various muscular pains) and the peripheral and nervous system (back pain, neuralgia, radiculitis of the sciatic nerves).
Risk Control in cement plants
Risk control from the accidents and emission of dust and gasses are the main concerns in cement plants. Three important elements of risk control are to eliminate risks, combat risks and minimize risks (Fig. 2).
Eliminate risks
Eliminate risks by substituting the dangerous by the inherently less dangerous items, for example, use of less hazardous substances; substituting a type of machine which is better guarded to make the same product and avoiding the use of certain processes.
Combat risks
Combat risks at source by engineering controls and giving collective protective measures priority, for example, separate the operator from the risk of exposure to a known hazardous substance by enclosing the process; protect the dangerous parts of a machine by guarding; design process machinery and work activities to minimize the release of, suppress or contain, airborne hazards; design machinery which is remotely operated and to which materials are fed automatically, thereby separating the operator from danger areas.
Minimize risks
Minimize risks by designing suitable systems of work; using personal protective clothing and equipment.
Fig.2: Risk control approaches
Application of Technology in the safety of cement plants
Instrumentation for operational safety
Safety in cement plants can be greatly improved by improving the systems design, developing and installing the new equipment, which are safe and easy to operate, maintain and repair. Technology is one of the most important solutions to manage the risks encountered in the plant. Instrumentation is the backbone of the automation and safe operating systems in the plant. Latest technological developments in instrumentation, tailored to specific process requirements of modern large size cement plants, has enabled high degree of automation and safe operations. Table 3 presents the various application areas of the cement plants, the measuring tasks and the type of instruments used by cement plants (VEGA, 2017).
Table 3: Instrumentation in cement plants for safety of operations
| S. No. | Application Area | Measuring Task | Types of instrument used |
| 1 | Crusher | Level measurement and point level detection | Non-contact level measurement with radar, Microwave barrier for point level detection. |
| 2 | Conveyor belt transfer station | Level measurement and point level detection | Non-contact level measurement with radar at the belt transfer station, Overfill protection with capacitive point level detection at the belt transfer station. |
| 3 | Raw meal Silo | Level measurement and point level detection | Level measurement with radar, Vibrating level switch as overfill protection. |
| 4 | Cyclone | Build up measurement | Radiometric measurement of buildup in cyclone, container for radiation radioactive source capsule. |
| 5 | Conveyor belt | Mass flow measurement | Radiometric mass flow measurement of solids, Source holder as receptacle for the radiation capsule. |
| 6 | Clinker cooler | Level and pressure measurement | Non-contact level measurement with radar, pressure transmitter for pressure monitoring. |
| 7 | Clinker silo | Level measurement and point level detection | Level measurement with radar, Capacitive point level detection. |
| 8 | Compressor | Pressure measurement | Pressure transmitter for monitoring pressure. |
| 9 | Cement silo | Level and pressure measurement and point level detection | Non-contact level measurement with radar, vibrating level switch as overflow protection, pressure transmitter for monitoring pressure in the pipe lines. |
| 10 | Silo for solid fuels | Level measurement and point level detection | Level measurement with radar in silos for solid fuels, Overfill protection with vibrating level switch in silos for solid fuels. |
| 11 | Tank for liquid fuels | Level measurement and point level detection | Level measurement with radar in the tank for liquid fuel, Vibrating level switch for protection against overfilling. |
| 12 | Truck loading | Point level detection. | Overfill protection with vibrating level switch. Position detection of vehicles with radar. |
Source: VEGA (2017)
Diagnostic Tools in effective maintenance of cement plants
Maintenance plays an important role in creating safe working conditions in the plant. Even a small accident in the plant can be disastrous. The impact of poor maintenance in case of large size plants, is still greater. With the technological developments, new diagnostic tools have been developed over the years that have improved the quality of maintenance in cement plants and thereby reducing the number of accidents as well as reducing the pollution of dust and gases in the plants. Good maintenance system makes a plant safe working place. The diagnostic tools detect the problem much in advance for taking corrective actions to avoid any damage to the men, machines and materials. A list of equipment used to measure different parameters under predictive maintenance program is attached in Table 4 (Saxena, 2009). Safety of men, machines and materials helps in reducing the operating costs, raising productivity and improving morale of the workers.
Table 4: State-of-the-art predictive maintenance techniques used in cement plants
| Predictive Maintenance Techniques | Maintenance Problems | Application | |
| Vibration measurement and analysis meter | Imbalance, mechanical looseness, defective bearings, broken gear teeth, defective rotor blades, oil whirl and misalignment. | Rotating machines, e.g., fans, gear boxes, pumps, turbines, compressors, internal combustion engines. | |
| Equipment for thermal analysis | Leaky steam traps, boiler refractory cracks, deteriorated insulation, loose electrical connections, hot or cold firing cylinders. | Furnaces, boilers, rotary kilns, steam system components, electrical switchboards and distribution equipment, motor controllers, diesel engines, power electronics, bearings, insulation of air-conditioned buildings. | |
| Shock Pulse Meter for measuring shock pulse values. | Trends of deteriorating bearing condition, especially roller and ball bearings. | Rotating machines. | |
| Ferrographic techniques | Excessive wear of bearing surfaces, fluid contamination | Lubrication, cooling, hydraulic power systems. | |
| Ultrasonic Leak Detector | Leaking valves, system leaks, leakages from seals. | Steam, hydraulic and pneumatic system piping. | |
| V Belt Tension measuring tool | Damage to shaft, bearing, pulley and loss of power due to slippage from loose V Belts. | Pulley drives | |
| Oil analysis equipment | Excessive wear of bearing surfaces, oil contamination and loss of lubricating properties. | Lubrication, cooling, hydraulic power systems and internal combustion engines. | |
| Megger for measuring and testing electrical insulation, rotor impedance testing, DC high potential testing. | Trend studies of electrical insulation condition, turn-to-turn and phase-to-phase short, grounds, reversed coils or turns. | Motor and generator windings, electrical distribution equipment. | |
| Relays for protection testing and time travel analysis. | Deteriorating or unsafe performance. | Circuit breakers, transformers and other protective devices. | |
| Testing equipment for testing quality of insulating oil | Over-heating, accelerated deterioration trends, hostile dielectric conditions. | Circuit breakers, transformers and other protective devices. | |
| Stereoscope for stereoscopic analysis | Corrosion, fatigue-cracking trends, hull fouling trends. | Underwater hull. | |
| Non-destructive testing equipment for testing of materials, e.g., ultrasonic, eddy current, borescopic inspections. | Corrosion, erosion, fatigue cracking, de-laminations, wall thickness reduction. | Shipboard machinery and associated piping systems and mechanical components. | |
| Equipment to measure and analysis of wear and dimensional values | Excessive wear and proximity to minimum acceptable dimensions which affect performance. | Sliding, rotating and reciprocating elements. | |
| Performance trending. | Loss in efficiency, deteriorating performance trends due to faulty components. | Heat exchangers, internal combustion engines, pumps, refrigeration units and compressors. | |
Source: Saxena, J. P. (2009)
Lafarge (2015), one of the global leaders in cement industry, has reduced the Lost Time Injury Frequency Rate (LTIFR) for Employees and Onsite Contractors from 0.84 in 2010 to 0.49 in 2014 by adopting multi-pronged strategy (Fig. 3), technology being the central point.
| Lost Time Injury Frequency Rate (LTIFR) = Number of Fatalities and lost time injuries per Million of Working Hours |
Fig.3: Lost Time Injury Frequency Rate for Employees and On-Site Contractors
Latest communication technology to improve safety and productivity
Over the years, communication systems in cement plants has changed from the legacy communication hardware to modern integrated systems. Many cement plants have already adopted the integrated communication system while others are going to adopt the new system soon. The importance of a good and most modern integrated communication system has been realized by the cement plants for improving the safety and productivity of the plant, especially the super large size cement plant.
Motorola Solutions (2017) has published the results of its 2017 industry survey in which more than 500 respondents from US manufacturing units across 57 states responded. The respondents included a wide range of executives from operations, maintenance, plant management, engineering, warehousing and distribution, and quality and safety compliance background. Following are the salient features of the findings of the of survey:
- Two way radios are still the primary form of plant communication, but the norm is to have ‘On-the-job’, multiple-devices communication system. 78% of the respondents in the survey stated that most of the workers in their operations are using multiple devices to communicate with each other.
- Manufacturers overwhelmingly demand seamless integration between the devices and employees.
- Employers want to leverage data intelligence from the communication system, for example, text messages and alerting, real-time plant floor messaging between people and equipment and use of GPS location tracking.
- 49% of the respondents are using digital or a mix of digital and analog radios. A third of analog users plan to switch to digital in the next two years.
- Even with the rise of smartphones, two-way radios are still the main mode of plant communications. Use of multiple devices on the job has become a norm.
- Manufacturers indicated the following as top priorities (very important/important) for their communication system (Table 5).
Table 5: Priorities for a communication system
| S. No. | Communication priorities | Percentage |
| 1 | Resolving problems quickly by instantly connecting the right people | 95% |
| 2 | Hearing clearly anywhere, even in noisy plant conditions | 93% |
| 3 | Helping to protect workers with safety features | 89% |
| 4 | Reaching workers in any location, on-site and off-site | 87% |
| 5 | Keeping communications secure to avoid IT threats and cybersecurity hacks | 83% |
| 6 | Being able to communicate from any device or network | 77% |
| 7 | Having integrated voice and data applications | 69% |
- According to manufacturers, the benefits of connecting all of their communication devices include resolving problems with greater speed and efficiency, seamless and instant communications from any location or device, rapid response to emergency situations for worker safety, integrated voice and data for real time visibility and merging of all the devices. Manufacturers want advance features and services from their communication systems.
Process monitoring and precipitator protection measurement at the preheater
The composition of the exhaust gas at the outlet of the preheater provides indications of an imminent risk of explosion for the downstream electrostatic precipitator. To acquire this information, changes in the concentration of the gas components CO, NO, O2, and, if applicable, SO2, are measured at the preheater. The presence of high CO peaks in the exhaust gas indicates a risk for the downstream electrostatic precipitator. The extractive analyzer system with the gas analyzer are used to measure high dust loading, the gas temperatures, and the space limitations. This system enables reliable process gas monitoring, thus providing an economical solution for increasing plant efficiency and safety
Monitoring exhaust gas dedusting down-stream from clinker cooler and the coal mill
Dedusting equipment is used in cement plants for maintaining compliance with the regulatory dust limit values in the exhaust gas in accordance to local regulations. Electrostatic Precipitators or fabric filers are used for dedusting. Any leak or malfunction of the filtering equipment can be serious threat to the safety in the plant. Suitable measuring device with mountable probe is used for fabric filters whereas transsiometer is used for electrostatic precipitators. In-situ gas analyzers and extractive gas analyzer systems are used here.
Monitoring the coal bunker
Coal bunkers present the risk of smoldering fires in which CO can accumulate to form explosive mixtures with the air. By performing continuous measurement of the CO concentration, smoldering fires can be identified at an early stage (due to the rise in CO) and handled in a timely manner (Sick, 2012). In addition, O2 measurement can be integrated in order to monitor inert gas. The gas analyzer system with a sampling probe is the ideal solution. Simultaneous measurement of CO and O2 can be done and the values can be adjusted using ambient air.
Conclusion
Cement plants operate round the clock throughout the year except for the period for scheduled stoppages. Large number of workmen work in the plant for operations and maintenance of the plant and machinery. Workers engaged in the operations are exposed to variety of risks and dust and gaseous emissions. Large number of accidents takes place in cement plants which create human sufferings, loss of materials and damage to machines.
Technology plays an important role in reducing the number of accidents and the impact of dust and gases on the health of the people working in cement plants and also those living in the neighborhood of the cement plants. Instrumentation is an essential part for the automation and in monitoring the plant operations. Any unsafe condition in any part of the plant is noticed by the instruments before the damage takes place. A large number of dedicated instruments and equipment, thanks to the technological developments, have now been developed, Number of diagnostic tools have also been developed to monitor the condition of operating machinery. Both online instruments and off-line diagnostic equipment help to protect the men, materials and machinery in the plant through control of process parameters resulting in safe operating conditions in the plant. Monitoring the process parameters, dust and gaseous emissions help cement plants to protect its plant and machinery, specifically the accident-prone areas such as ESPs, Coal mills and coal bunkers. Modern integrated communication system plays a very important role in controlling and monitoring the process parameters, any adverse situation noticed in the plant and provide prompt and on the spot help for the safety in the plant. Safety deserves the highest attention and adoption of the latest technology is the guiding principle.
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