In Vietnam, stone mining and processing belong to the group of occupation required to carry out risk assessments to have better measures for preventing occupational accidents and occupational diseases. The need for a method, risk assessment process and OSH management system is urgent. To meet that demand of production reality, VNNIOSH has selected and established the method and process for assessing and controlling OSH risks at stone mining and processing facilities.
Risk assessment methods
*For OSH risks: Employ quanlitative risk assessment method with 5x5 risk assessment matrix (Fig.1).
Fig1: Risk assessment matrix
* Against health risks: Using the semi-quantitative assessment method of VNNIOSH based on Russian method and Vietnam’s current standards on OSH. The risk is determined based on results of categorizing working conditions (Fig. 2).
Fig 2: Categotizing working conditions and corresponding occupational health risks
Results of risk assessment
The results of VNNIOSH’s risk assessment at 03 facilities showed that stone mining and processing in general have a high level of OSH risks, of which, the quarrying stage generally has higher risk level than the stone processing stage. Many hazards during extraction range from high, very high to extremely high levels such as landslides/rock displacement, mines explosion due to out of control, combustion of explosives, extreme microclimate, falling from height, vehicle accidents, collision with the moving part of machines (saw plates), noises and vibrations.
Landslide/rock displacement; mines explosion due to out of control, combustion of explosives: These are characteristic hazards needing to be mentioned first because of their particularly serious consequences. Landslides androck displacement are determined to be due to the instability of the rock mass at the slope. Impacts on the rock layer during extraction (such as blasting, loading and unloading rock) or sudden changes in the rock layer structure due to prolonged heavy rains could be the final direct cause of landslide/rock displacement. In the process of storing, transporting and using explosives, there is also the explosion hazard due to uncontrolled explosion and combustion of explosive materials. Risk assessment results showed that at facilities using blasting as mining technology, the chance of creating hazards such as landslides/rock displacement, combustion of explosives materials and uncontrolled blasting are always extremely high. Meanwhile, in facilities using diamond wire cutting technology, these hazards are eliminated as explosives are not in use.
Microclimate: The level of risk caused by the microclimate is determined on the basis of the Wet Buld Global Temperature (WBGT), taking into account the simultaneous impact of the microclimate parameters, including temperature, humidity, wind speed. and solar radiant heat, to the heat stress workers are exposed to. The risk assessment results showed that in hot days of summer-autumn, microclimate is also an extremely high and very high level risk. Heat can cause a number of health conditions such as cramps, dehydration (or heatstroke) exhaustion, at worse can cause heat shock, leading to death. The result of this assessment is a necessary warning to help stone mining and processing facilities identify and proactively apply corresponding control measures to minimize health risks to workers during hot days.
Falling from height: The risk of falling from height can occur to workers operating hand drills, self-propelled drills, crusher and screener composition, diamond wire cutters, and machine maintenance/repair. There are no guardrails and seat belts at these overhead work positions.Workers operating hand drills, working in steep terrain, narrow ground face higher probability of falling and a very high level of risk; Meanwhile, operators of self-propelled drilling machines, screener and crusher composition, diamond wire cutters, machine/equipment repair are exposed to high risks.
Vehicle-caused accidents: Many vehicles such as trucks, forklifts, bucket excavators, loaders, and hydraulic hammers are likely to cause accidents to their own operator and to other people working around during working and traveling. Workers are warned to keep a safe distance from the working vehicle. However, steep terrains, sharp curves, sight obstructions, etc., may be the cause of the accident. The level of risk is assessed at a high level for trucks that transport rocks from the mountains, while for the rest of the vehicles, it is moderate.
Collision with machine moving parts: The danger of collision with the moving part of the machine (saw plate) arises in both the stone slitting machine and the stone cutting machine, but the levels of risk are different. The worker operating the cutting machine is exposed to a high risk of having to push the stone plate towards the cutting plate with his hand during the cutting process, easily losing momentum and putting his hand into the saw plate. Meanwhile, with the sawing machine, the worker uses the winch to position the block, fix the block, then push the sawing machine control button, the saw plate automatically moves towards the block and slits the stone, so take only medium risk.
Noise: Most of the machines/equipment used in both quarrying and processing (sawn stone processing and screening-crushing) generate noise. Workers operating hydraulic hammer, stone cutting, stone cutting, stone chipping are exposed to a high level of risk (noise levels 96-105 dBA equivalent); Meanwhile, workers operating bucket excavators, wheel loaders, rotary kilns, stone grinders, stone shavings, manual stone grinders, and truck drivers are only exposed to moderate risks (noise levels 91 to 95 dBA equivalent ). In some other working positions such as operating diamond wire cutting machines, driving forklifts, repairing machine/equipment, the risk of noise caused is only low.
Vibration: Full body vibration is also a hazard while using most machines/equipment in stone mining and processing. Workers operating forklifts, loaders, buckets, hydraulic hammers bear a high level of risk, meanwhile workers driving trucks, slashing machines, chipping, spinning chunks, grinding stones manually has medium risk and workers operating hand drills, self-driving drills, stone cutting, stone grinding, machine/equipment repair are at low risk. In some other positions such as operating hand drill, self-propelled drill, cutter, grinder, planer, machine/equipment repair, the risk is low.
Electric shock: The danger of electric shock arises mainly in the stone processing area (sawn stone processing and screening-crushing) where there are many machines/equipment using electricity. The risk of electric shock in stone cutting, stone sawing, stone cutting, stone rotary kilns, screen grinding, and machine/equipment maintenance repairs are moderate.
Winded, trapped inside or between machine parts: At the position of operating cutting machine, grinder, chopper, screen mill, machine/equipment maintenance, repair, workers are at risk of hair curl/jam between the pulley and belt of the belt due to the unsealed cover structure, the foot slipped between the grinding shafts of the jaw crusher… Risk is assessed as moderate.
Flying objects, shrapnels: Workers operating diamond wire cutters are in danger of being cut by torn diamond wire hitting their bodies. Workers operating the screen mill, driving the excavator in the screening area are at risk of being hit by stones from the jaw clamping machine. Risk is assessed as moderate.
Silica dust: The activities of mining and processing stone generate dust with the silicon content fluctuating in the range of 2.7-3.7%. The dust risk is assessed based on the concentration of free silicon in inhaled dust at workplace. Measurement results showed that the concentration of free silicon in inhaled dust at the dust-generating working positions of 10 surveyed facilities is 1.1 to 4 times higher than the permitted limit according to the standard QCVN 02:2019/BYT, and the corresponding level of risk is assessed from low to medium. Hand drill operator, truck driver, bucket excavator, wheel loader, screen mill and machine/equipment repair worker is at medium risk, meanwhile, operator of self-propelled drill machine, hydraulic hammers bear only a low risk.
Falling objects due to lifting and transporting: At locationssuch as: operating hand drill, cutter, grinder, stone chipper, planer, stone rotary kiln, manual stone grinding, machine maintenance/repair equipment, workers must lift/transport the machine or stones by hand, thus presenting the risk of falling objects. For workers operating hand drills, cutters, grinders, chippers, and manual stone grinders, the risk level is assessed as moderate; Meanwhile, for workers operating planer, stone rotary kiln, machine/equipment maintenance and repair, the level of risk is low. The reason is due to the difference in the severity of the accident.
Lifting equipment used at stone mining and processing facilities includes: Cranes/winch (sawmill area, machine/equipment maintenance and repair), bucket excavator (mining area, crushing screen), wheel loaders (crushing and screening area), forklift (sawn stone processing area). The risk of falling objects while using bucket excavator, truck (mining area), stone saw, forklift and machine/equipment maintenance and repair locations is assessed as moderate; meanwhile, for bucket excavators, wheel loaders (crushing and screening areas), the risk level is low. The reason is due to the difference in the severity of the accident.
Slippery, falling: In the machine/equipment repairing area, there are many obstructions and/or grease, thus the level of risk is defined as moderate; Meanwhile, at the locations where hand drills, self-propelled drills, stone cutters, stone grinders, stone chippers, stone rotary kilns and hand grinders are operating, the risk is low.
Cut/clamped by the tool: When operating the cutting machine, the worker uses the crowbar to elevate stones, uses a small piece of rock to support a large rock, thus there is a risk of finger/hand clamping. The risk level is assessed to be moderate, whereas at the machine/equipment maintenance site, the cut/clamp risk is low.
Heavy duty: Workers operating hand drills, self-propelled drills, bucket excavators, wheel loaders, hydraulic hammers, saws, cutters, grinders, chippers, manual rock grinders and load-bearing trucks face moderate level of risk; Meanwhile, workers operating stone rotary kilns, machine/equipment repair and maintenance are only exposed to low risks.
Stress level: Workers using mines are exposed to moderate risk, while workers operating crushing-screening composite machines, repairing and maintaining machines/equipment are only exposed to low risk.
Loi Nguyen, PhD