Strict regulations and principles apply when mine blasting is to be conducted within half a kilometre of buildings or areas with any significant human activity to avoid injury and damage to property.
Nico Pienaar, director of surface mining industry organisation ASPASA, says the requirements of the relevant Mine Health and Safety Act Explosives Regulations, 2018 – Regulation 4.16(2) are clear and should provide a minimum base-line for procedures to ensure safe blasting.
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The regulation covers all aspects of the requirement and in addition to providing safe blasting, compliance with the regulation mitigates legal action in the event of a mishap.
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“In order to understand the regulation it is best to break it down to basics and it is important to note that it needs to be applied wherever blasting operations are to be carried out within a horizontal distance of 500 m from structures and places which may be necessary to protect to prevent any significant risk; and to provide some guidelines regarding the application to be submitted to the Principal Inspector of Mines (PI) for written approval.
“The employer must also take reasonable measures to ensure that no blasting operations are carried out within a horizontal distance of 500 meters of any public building, public throughfare, railway line, power line, any place where people congregate or any other structure, which it may be necessary to protect in order to prevent any significant risk.
“This is unless a risk assessment has identified a lesser safe distance and any restrictions and conditions to be complied with or a written application is submitted to the PI accompanied by the following documents for approval- (i) a sketch plan indicating the distance from the blasting area to the affected structures; (ii) the risk assessment; (iii) a proof of consultation with the owners of the affected structures; and (iv) restrictions and conditions. (c) a written approval has been granted by the Principal Inspector of Mines; and (d) any restrictions and conditions determined by the Principal Inspector of Mines are complied with.”
“The Regulation provides clear requirements for the Application to be submitted to the PI for decision – Reg. 4.16(2) (a) and (b) The Application must provide the following safety, technical and legal aspects:
- Risk assessment in consultation with the explosives supplier and other subject matter experts Identify structures and places to be protected
- Determine the minimum distance blasting to be carried out
- Specify and Articulate Measures to limit blast induced hazards including recommended restrictions and conditions
- The application must prove consultation with the owners of the affected structures and how any concerns will be addressed
- Monitor blast hazards
“Limiting and measuring of blasting-related hazards is an interesting and complex field, which can fill an entire book.
“But if we limit the discussion to a high-level overview relevant to air-blast and ground vibration it is clear to see the complexity. Although numerous regulations place the onus on the mine owner to ensure that the blasting operations do not cause damage to private property, there are no statutory limits for air-blast and/or ground vibration, laid down in South African law.
“The mine owner, in turn, relies on advice from experts such as engineers employed by the major suppliers of explosives or independent consultants.
“The South African Bureau of Standards (SABS) adopted the International Organization for Standardization (ISO) standard ISO4866 (2nd edition in 2010) which provides guidelines for the measurement of vibrations and evaluation of their effects on fixed structures, not safe limits of vibration for structures.
“Explosive manufacturers and suppliers in South Africa generally play a key role and make recommendations based on the USBM RI 8507 limits tables: Maximum PPVs at frequencies below 50 Hz are recommended for a variety of building types; Maximum charge sizes (per delay) for a range of distances to ‘typical’ and ‘sensitive’ structures. Compilation of vibration limits for civil and engineering structures such as power lines, roads, pipelines, and conveyors.
“Where to measure? Field Practice Guidelines for Blasting Seismographs, published by the International Society of Explosives Engineers (ISEE, 2015), is the industry standard for the correct monitoring of blast vibrations. Monitoring equipment: All monitoring equipment must be calibrated at least annually and operated by trained persons.”
“To effectively address community complaints, demands and subsequent production losses, it is critical to determine the actual limits for a specific blasting operation, before designing a solution.
“Although International acceptable standards like the US Bureau of Mines (USBM) and The US Office of Surface Mining Reclamation and Enforcement (OSMRE) study publications are well known and applied in South Africa, it is important to acknowledge site specific factors.
“To address these challenges, it is sometimes more important to understand and address the reasons for the community complaints, rather than the possibility of actual blasting-related hazards.
“More often than not, it may be necessary to distinguish between fear of actual blast damage and blast nuisance or irritation”.
“Therefore the strategy to design at much lower limits than International acceptable limits. The type and quality of structures are also important factors to determine actual acceptable limits, rather than international acceptable limits tables.
“To prevent damage numerous strategies can be applied such as the accurate control of mass explosives per delay and the management of ground vibration and air-blast.
“It is important that the mine understands the initiation point and timing and applies suitable electronic blasting systems.”
A risk assessment is also required to prevent hazards and should be conducted in consultation with the explosives supplier to identify a lesser safe distance, restrictions, and conditions to be complied with.
A rock engineering consultant should also be consulted to for a risk assessment in support of applications to blast to 50 m of railway line and the 11 kV power line beyond. Consulting engineers should compile a report of risk compliance to blast within a 500 m radius from the identified structures.
A drill and blast procedure are required when blasting is to be carried out within 500 m to ensure drilling and blasting is executed as designed. A sketch plan is also required to indicate the distance from the blasting area to the affected structures.