African Mining February 2021 | Page 21

OPERATIONS • 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 .

Community relations 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 . Often 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 , for example , 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 .

Other requirements A risk assessment is also required in order to prevent hazards and should be conducted in consultation with the explosives supplier

Strict regulations and principles apply when mine blasting is to be conducted within half a kilometre ( 500m ) of buildings or areas with any significant human activity .

to identify a lesser safe distance , restrictions and conditions to be complied with .

A rock engineering consultant should also be consulted for a risk assessment in support of applications to blast to 50m of railway line and the 11kV power line beyond . Consulting engineers should compile a report of risk compliance to blast within a 500m radius from the identified structures .

A drill and blast procedure is required when blasting is to be carried out within 500m 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 . •

All photos : Leon Louw ©

Limiting and measuring of drilling and blasting-related hazards is an interesting and complex field .