Analysis and Countermeasures of blasting hazards i

2022-08-11
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Analysis and Countermeasures of blasting hazards in water conservancy and hydropower projects

blasting is widely used in the construction of water conservancy and hydropower projects, and plays an important role in facilitating construction production, accelerating construction progress, saving costs, etc. However, blasting safety is also a problem that cannot be ignored. Blasting operation is a dangerous construction process, which has the characteristics of high technical content, many unforeseen factors and complex working environment. Although with the progress of blasting technology and the continuous accumulation of blasting experience, the construction blasting accidents of water conservancy and hydropower projects have been greatly reduced than before, they still occur from time to time, causing certain casualties, property losses and environmental damage, with a great negative impact. To put an end to blasting accidents, we must carefully and comprehensively analyze the root causes of blasting accidents, and take measures to eliminate the root causes of blasting accidents, so as to complement each other, engage in post-processing, and change it into beforehand control, so as to give priority to prevention and nip in the bud. Therefore, this paper starts with the dangerous sources of blasting operation in water conservancy and hydropower projects, analyzes the dangerous sources that may cause blasting accidents, and puts forward corresponding countermeasures to avoid and reduce the occurrence of blasting accidents by effectively controlling the dangerous sources of blasting.

analysis of dangerous sources of construction blasting

common dangerous sources of construction blasting in water conservancy and hydropower projects include blasting flying stones, blasting seismic effect, air shock wave, water shock wave, lightning, high-voltage electromagnetic field, stray current, toxic gas, blind blasting, expired pyrotechnic material treatment, etc., but different types of blasting operations and blasting environment have different dangerous sources, It needs to be analyzed in combination with specific blasting operations. Blasting operations in special types or special environments will also produce uncommon hazards, such as water hammer waves and swells caused by blasting operations underwater or near water areas. With the development of technology and the accumulation of blasting experience, the analysis and understanding of blasting hazards in the construction of water conservancy and hydropower projects are gradually going deep and comprehensive

    1. Blasting flying stones

in the construction of water conservancy and hydropower projects, the accidents caused by blasting flying stones account for the largest proportion of blasting accidents. There are many factors that cause blasting flying stones, such as blasting type, blasting environment, blasting scale, blasting medium, etc., but in general, the accidents caused by blasting flying stones mainly have the following three reasons

first, the blasting parameters such as the amount of blasting charge and unit consumption exceed the design value, resulting in blasting flying stones exceeding the safety range. For example, when a unit demolished a concrete base by blasting in the foundation pit of a construction site, a large number of concrete blocks flew out of the blasting hit the crane about 200m away from the blasting area, causing damage to the crane's boom members, silencers, outrigger cylinders, etc., and a direct economic loss of about 100000 yuan. Through investigation and analysis, the main reason is that the unit consumption of blasting operation is too large. The designed unit consumption of blasting is 0.3 ~ 0.4kg/m3, while the actual unit consumption of blasting is 0.6kg/m3, which is nearly twice the design value

second, necessary covering and protection measures were not taken for the artillery area according to the design requirements. When the blasting part is close to buildings or equipment and facilities, in order to block blasting flying stones, protective measures such as covering sandbags and steel wires at the blast hole are generally taken to reduce blasting energy and blasting flying stones. For example, when a unit carried out blasting operations in the 23 # dam section of the dam foundation pit of a construction site, the blasting flying stones smashed two drilling rigs and bent frames about 60m away from the blasting area, the drilling rigs were smashed and scrapped, and the bent frames were smashed. After checking the site and investigation and analysis, the measures to control blasting flying stones have been taken into account in the blasting design. In addition to the control of blasting parameters, the design also requires that the blast hole be covered with two layers of sandbags, and then a layer of steel wire. However, during the implementation process, the protective measures were not strictly based on the two force columns, and the dial gauge measuring grid was used to implement the design requirements. Only a layer of sandbags were covered on the blasting part, causing the blasting flying stones to smash the drilling rig and bent

third, the blasting warning work is not in place. Before blasting operation, safety warning is an important link to ensure safety. If the warning work is not in place, during the blasting process, personnel and vehicles enter the blasting area by mistake, or personnel and equipment in the blasting warning area are not evacuated in time, the consequences will be very serious. For example, when a unit was carrying out the demolition blasting of the water retaining wall of 23 # ~ 24 # units at a construction site, due to the insufficient warning work, the equipment and personnel in the warning area did not withdraw to the safety zone before the blasting, a manned bus stopped less than 100m away from the blasting area, and a person in the bus was killed by a broken flying stone on the head

    2. Blasting seismic effect

during the blasting process, a large part of the explosion energy will spread around in the form of seismic waves, causing ground vibration, and causing the ground near the blasting area and objects on the ground to bump and shake, resulting in blasting seismic effect. If the blasting charge is large and the blasting area is close to the building, the building will be damaged to a certain extent. For example, during the excavation peak of a project, the blasting charge is large, usually more than 30 tons per blasting charge, and during the segmentation, the single section detonating charge is more than the single section design charge. Therefore, the seismic effect caused by blasting is quite obvious, which will crack the roof and walls of houses about 300m away from the blast area. Therefore, before carrying out relatively large blasting operations, the blasting seismic effect should be fully considered to reduce and avoid the damage to buildings caused by blasting seismic effect

    3. Lightning causes early explosion accident

due to the extremely high energy of lightning, extremely strong electromagnetic fields will be generated at the moment of lightning. If the electric explosion circuit is directly struck by lightning or strongly induced by the high-strength magnetic field of lightning, early explosion accident is very likely to occur. For example, a unit uses electric detonating to carry out blasting. After completing the charging and connection, the personnel are evacuating outside the blast area. Suddenly, lightning strikes the blast area, and four blast holes explode, resulting in two deaths and one serious injury among the personnel evacuating outside the blast area. Another example is that a unit was excavating the road under the 110kV high-voltage line at a construction site when it was raining. After completing the non electric blasting charging and network connection, a unit was ready to connect and detonate the electric detonator. Due to the effect of the high-voltage strong magnetic field, the detonating electric detonator exploded. Fortunately, the detonating network has not been connected, otherwise the consequences would be unimaginable. It can be seen that in thunderstorm weather or in the environment of high-voltage electromagnetic field, it is very dangerous to use electric blasting for blasting operation

    4. Disposal of expired initiating explosive materials

expired initiating explosive materials are still very dangerous. When destroying expired initiating explosive materials, it is necessary to complete the corresponding approval procedures, develop a reliable destruction treatment plan, and destroy them according to the specified procedures and requirements when there are safety assurance measures, otherwise it may cause casualties. If 6200 non electric millisecond detonators of a certain unit have expired, it is planned to install the expired detonators into the blast holes ready for blasting, and destroy the expired detonators during blasting. In the process of loading expired detonators into blast holes, due to impact and extrusion, 110 expired detonators that have been loaded into four blast holes detonated, and two Gunners died on the spot and four others were injured

    5. Swell during blasting

when rock and soil blasting is carried out near the water area, the blasting rock and soil will be dumped into the water body to produce swell, which is very harmful. If the hazard source of surge is not carefully analyzed before blasting, or the correct installation method is to screw the sensor to the bottom first and take reliable control measures, serious consequences will be caused. For example, when a unit was blasting the left abutment of the dam, the charging amount was 3.5t, and the blasting volume was about 8000m3. More than 5000 m3 of ballast produced after blasting instantly poured into Hanoi, which was more than 70 meters away from the left abutment of the dam, and their measurement range and utilization range were also different. Hanoi immediately produced a huge surge nearly 8m high, and the surge was transmitted upstream along the river at a very fast speed, involving five evacuees 300m away in the river, resulting in three deaths, Two people were seriously injured. After analysis, the main reason for the accident is that the surge was not considered in the blasting design, which reflects the lack of relevant knowledge and experience of blasting designers. During the construction blasting of water conservancy and hydropower projects, the reason for such a huge surge is that the river is relatively narrow. The ballast produced by several small explosions in this part has blocked the river and formed a dam. A pond with a depth of about 5m and a width of about 10m has been formed in front of the dam, and the water has passed through the diversion tunnel. The blasting volume was large, and more than 5000 m3 of earth and rock poured down from high places, producing a huge impact force. Because the river had been intercepted, the huge impact force could only be transmitted to the upstream, resulting in a huge surge. The accident also shows that blasting operation in special working environment may produce uncommon hazard sources, which should be paid enough attention to.  

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