Minimising the adverse impacts of blasting

Maxam views the identification and proactive management of risk as fundamental in its business. We must assist our customers with environmental risks due to blasting operations, which is a challenge, as we are often dealing with the emotions of community members, not facts.

Management of environmental effects of blasting is time-consuming to most operators as it continually changes. Blasting can be straightforward if handled in a risk adverse manner; however, changes in blasting methods due to environmental challenges is evident in a growing number of operations in Australia.

Traditionally, operational efficiency drives changes in blasting methods, but in the present environment community responsibility is the main cause for change.

Near neighbours at Australian quarries is not new, but it is an everyday risk that must be managed proactively in every blast. It is difficult in some operations to conduct blasting that is cost-effective for production due to the need to meet environmental restrictions.

Maxam is regularly enlisted by its clients to assist with vibration, air overpressure, flyrock minimisation and dust reduction. Customers increasingly request advice on specialised blasting techniques for rehabilitation and visual aspects of quarry operations. This is not all due to urban encroachment, as the quarry industry realises its corporate responsibility to actively minimise its impact on communities.

Urban encroachment has led to increased vigilance of current licence conditions by neighbours and legislative authorities. It also creates increased difficulty in obtaining renewals or extensions of current operations, adding significant expenses to operators. These increased costs can be divided into three categories:
1. Increased detail in preparation of development applications and/or ?extra? studies to justify extraction licences.
2. Increased costs due to inefficiencies of current operations where development and/or new mining leases are delayed.
3. Increased costs due to changed methods that enable the site to continue operating and meet environmental licence limits.

Maxam assists its customers in minimising the impacts of these drivers. It works with customers to develop blasting impact studies that highlight the methodologies and costs that must change if housing or industrial developments adjacent to sites are approved.

It is often the case that substantial increases in costs of production would need to occur if developments went ahead unchanged. These cost increases are evident in some Australian sites where new or extensions of leases have been delayed due to community concerns.

Concerns with blasting are at the heart of these hold-ups due to their widespread and event-focused nature. Unfortunately, forward planning of extraction of the site resource suffers and inefficiencies in the process occur. This can take the form of stalled development of benches, smaller blasts, etc. Maxam works with its customers to alleviate these challenges.

In all blasts where customers use Maxam Technical Services, a process of pre-blast planning occurs. Maxam personnel propose designs that are appropriate to the risk environment presented, be it vibration control, airblast minimisation or a combination of both.

It must be remembered that in blast design timing and/or weather conditions when firing is critical, eg when there is no low cloud cover, wind directions are favourable and there has been sufficient time since the last major rain event (otherwise vibration levels increase due to decreased attenuation of vibrations through the ground mass). These factors, in addition to other methodologies such as laser profiling, borehole tracking and electronic detonators, all assist with sites with particular challenges.

Much has been written about environmental aspects of blasting and there are guidelines to minimise impact on neighbours. Legislative limits have been set at levels below which any actual damage will not occur and are realistically and significantly below any damage onset. They are aimed not primarily at eliminating damage to structures, but rather at minimising human discomfort.

Initial human discomfort levels occur at levels significantly lower than damage levels of structures. Human discomfort is a significant community responsibility for quarry operators to consider. However, whatever the level at which damage to sensitive sites actually occurs, the limits must be met in order for quarries to continue operating.

Maxam is involved in several sites where customers have decided to set limits for blasting lower than the legislative limits to avoid community complaints. These levels are based more on human discomfort.

The impact on sensitive sites must be considered because not all quarry operators? sites can economically extract material if the methodology of no complaints is applied. If vibration or airblast are near upper permissible limits, then damage is unlikely and, in fact, levels well above the limits will not lead to damage. This ?buffer? zone, or difference between human discomfort and actual damage, is what requires emphasis when dealing with near neighbours. Maxam can demonstrate these differences to neighbours.

Maxam?s experience of blasting in quarries in Australia over the last 21 years has shown that most neighbours are receptive to explanations about vibration levels and airblast required to cause damage and how the site is monitoring the blasting impact on the community.

A demonstration for neighbours is a valuable tool for community education. In a demonstration, an environmental monitor is set up at a house and we ask the people involved – children are great for this! – to jump up and down next to the monitor. This often shows a reading over the limit for the site that surprises the people involved and demonstrates the relativity of the impact of vibrations.

The other effective monitoring demonstration is for air overpressure which also shows participants that the usual levels from blasting are commonly exceeded by everyday gusty winds. Most people do not realise that a wind gust of 18km/hr can result in air overpressure levels over 115 dB. Showing neighbours air overpressure levels fluctuating from below 90 dB to over 120 dB in gusting winds without blasting indicates to them that the levels produced by blasting will not affect their properties. In practice, air overpressure occurs over a wider frequency range which neighbours perceive in two ways: above 20Hz the air overpressure is audible, while below 20 Hz, the air overpressure wave is inaudible, but can cause objects to shake, eg rattling of loose windows and crockery.

Maxam believes that the benefits of best practice environmental management to minimise noise and blast impacts are vital to the Australian quarry industry. Maxam has the resources required for its customers and the quarry industry as a whole to meet this goal and is proactive with its current customers in this process.

Provision of correctly focused technical services is essential to successful resolution of neighbours? concerns and/or changes in blasting methods to allow sites to meet the legislative targets. These services consist of laser profiling, borehole tracking, blast design, analysis of environmental blasting records, videos of blasts and records of complaints.

Unless this is carried out, stopgap fixes that provide short-term fixes will at best be enacted rather than long-term solutions. Maxam has taken this latter approach with all its customers when dealing with environmental challenges.

Additionally, if we as an industry sector take a proactive attitude to this issue, it will benefit all sector businesses in the short term economically as well as improved community acceptance and attitudes towards quarrying and allow sustained economical growth in the extraction industry to occur.

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