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Open-cut mine blasting, temperature inversions, and broken windows

Yoska Hernandez, Saturday May 25, 2024 - 17:18 AEST


Australia is home to numerous significant open-cut mines spanning various regions and mineral resources. Mining operations are essential for resource extraction but often come with considerable environmental and social challenges. One lesser-known but highly impactful issue is the propagation of blasting noise, especially under atmospheric conditions involving a temperature inversion near the ground, a phenomenon commonly associated with high-pressure cells.


As mentioned earlier in our story here, high pressure will dominate the southeast of the country over the weekend and into mid-next week. This high-pressure system will bring stable atmospheric conditions, clearer skies, and light-to-calm winds, allowing for rapid radiative cooling at night, which favours the formation of a near-surface temperature inversion layer. A temperature inversion occurs when a layer of warmer air sits above a layer of cooler air near the ground. Normally, temperature decreases with altitude, but an inversion creates a stable layer that, as we will explain, can significantly amplify the impacts of some mining operations, such as open-cut mine blasts.


This phenomenon can amplify the noise and vibrations from mining blasts, causing substantial disturbances and damage to nearby communities. Some impacts on residents living near mines may include:


Increased noise levels: Amplified noise levels can cause significant disturbances, leading to sleep disruption, stress, and anxiety among residents.


Structural damage: Intensified sound waves can cause physical damage to buildings, such as broken windows, cracked walls, and displaced objects within homes.


How temperature inversions alter noise propagation


In the presence of a temperature inversion, the inversion layer acts as a refractive boundary that alters the trajectory of sound waves. Instead of refracting upward, sound waves encounter a zone of increasing temperature with altitude, causing them to bend downward toward the Earth's surface. This happens because the speed of sound increases with temperature, as described by the equation: 


c=331.3+0.6T 


This equation represents a simplified approximation of the speed of sound in air at a given temperature in degrees Celsius, where:


c represents the speed of sound in meters per second. 


T represents the temperature in degrees Celsius. 


Within an inversion layer, the speed of sound increases with altitude. This means that sound waves travel faster at higher altitudes. As a result, sound waves cover a longer distance at higher levels, causing them to bend downward toward the ground (see schematic figure below). This refraction focuses the sound in specific areas, amplifying noise levels in those regions. Additionally, sound waves may experience reflection within the inversion layer, further enhancing noise levels.





Figure 1. Schematic illustration: The impact of an inversion layer on noise propagation. 


This behaviour of sound within an inversion layer is generally more noticeable when the distance between the noise source and receiver is greater than 2 km and depends on the strength of the inversion. The strength of an inversion is explained by how acute the temperature increase with height is. For example, a temperature increase of about 4°C over 100 metres of height can increase sound levels by around 3-5 dB, while a strong inversion with a temperature increase of about 8°C with height may produce an enhancement of sound levels of up to about 20 dB (as reported in some arid areas of Australia).


In conclusion, understanding the impact of temperature inversions on noise propagation from open-cut mine blasting is crucial for mitigating disturbances to nearby residents. Weatherzone offers a range of weather products and services that can help mining operations and communities better anticipate and manage these atmospheric conditions. With accurate forecasts, Weatherzone empowers you to make informed decisions and minimise the environmental and social impacts of mining activities. For more information on our weather solutions, visit https://business.weatherzone.com.au/ 


Reference: https://acoustics.asn.au/conference_proceedings/AAS2015/papers/p8.pdf 


- Weatherzone

© Weatherzone 2024

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