Managing dust risks at quarries!

In this article, Josh Thomas from instrumentation specialist Ashtead Technology, discusses the risks associated with dust at quarries, and highlights the vital role of monitoring.

Josh Thomas

Background
Almost all quarrying operations have the potential to create dust. Control measures should therefore be established to prevent the generation of levels that cause harm. These measures should be identified in the health and safety document, and measurements should be taken to monitor exposure and demonstrate the effectiveness of controls.

Many minerals contain high levels of silica, so quarrying activities of these materials generate silica dust known as respirable crystalline silica (RCS) and particular care must be taken to control exposure. Guidance is available from the British Health & Safety Executive (HSE); see document HS(G) 73 Respirable crystalline silica at quarries. Sandstone, gravel and flint typically contain over 70% crystalline silica, shale contains over 40% and granite can contain up to 30%. Inhaling RCS can lead to silicosis which is a serious and irreversible lung disease that can cause permanent disablement and early death. There is an increased risk of lung cancer in workers who have silicosis, and it can also be the cause of chronic obstructive pulmonary disease (COPD).

The British Control of Substances Hazardous to Health Regulations 2002 (COSHH) requires employers to ensure that exposure is prevented or, where this is not reasonably practicable, adequately controlled. The COSHH definition of a substance hazardous to health includes dust of any kind when present at a concentration in air equal to or greater than 10 mg/m³ 8-hour time-weighted average of inhalable dust, or 4 mg/m³ 8-hour TWA of respirable dust. This means that any dust will be subject to COSHH if people are exposed to dust above these levels. Some dusts have been assigned specific workplace exposure limits (WELs) and exposure to these must comply with the appropriate limits. For example, the WEL for RCS is 0.1 mg/m³ 8-hour TWA.

The Quarries Regulations 1999 (GB) cover all surface mineral workings, and include tips and stockpiles, as well as areas used for crushing, screening, washing, drying and bagging. Buildings and other structures are also included, as are common areas and prospecting sites. The Regulations were created to protect the health and safety of quarry staff, as well as others that may be affected by quarrying activities, such as those living, passing or working nearby, or visiting the site.

The role of monitoring
In order to assess the risks posed by dust, it is necessary to undertake both workplace monitoring – inside buildings, vehicle cabs etc., as well as environmental monitoring in and around the quarry. The technology for doing so is similar but different instruments are available for every application. Ashtead supplies personal air sampling pumps when it is necessary to conduct compliance monitoring, or when the identification and measurement (in a laboratory) of a specific dust type, such as RCS, is required.

Once the dust risks at a quarry have been assessed, ongoing monitoring is more often conducted with direct reading instruments that employ optical techniques to measure the different particulate fractions. Portable battery-powered instruments such as the TSI SidePak and the DustTrak are ideal for this purpose and feature heavily in Ashtead’s fleet of instruments for both sale and rental.

Installed TSI DTE

The same dust monitoring technology is employed by the TSI DustTrak Environmental (DTE), which has been developed specifically for applications such as dust monitoring at quarries. Fully compliant with stringent MCERTS performance requirements, the DTE employs a ‘cloud’ based data management system, which provides users with easy access to real-time data on dust levels, with the optional addition of other sensors. Alarm conditions can be set by users so that text and email alerts are issued when threshold levels arise. The DTE monitors PMTotal, PM₁₀, PM_2.5 and PM_1.0 mass fractions simultaneously, which provides detailed information on the type of dust present, and means that alarms can be set for specific fractions.

Clearly, dust monitors can perform a vital role in helping to protect safety at working quarries. However, a TSI DTE was recently hired from Ashtead Technology to perform monitoring prior to the commencement of quarrying operations, so that baseline dust levels could be established for comparison once the quarry is operational. Monitoring prior to operations is important, because airborne dust at a quarry is not necessarily derived from the quarry alone; local agricultural or industrial activities may also contribute to the particulate burden. This also highlights the advantages of 24/7 monitoring because dust pollution may be intermittent, so continuous monitors such as the DTE are able to identify peaks and thereby assist in the attribution of sources.

Ashtead Technology fitted the DTE mentioned above with a solar panel and rechargeable battery so that it could operate unattended for extended periods in a remote location. With web-based access to the data, site visits were minimised and costs lowered. This equipment was hired from Ashtead to avoid capital expenditure, and looking forward, the client is planning to add a Lufft wind monitor to the rental, because data on wind speed and direction helps with modelling and with the identification of dust pollution sources.

Summary
Ideally, quarry site monitoring should be undertaken prior to the commencement of operations to establish baseline levels for that site. Risk assessments can then be undertaken around the site and within buildings and vehicles/machinery. However, conditions can change significantly, so continuous monitoring is preferable. Changes in quarry practices and weather can affect environmental conditions, and workplace exposure can be affected by a wide range of factors such as broken filter bags, spillage, insufficient cleaning, filter blockage and dry (instead of wet) drilling or cutting.

With a variety of applications for dust monitoring, it is important that appropriate technology is employed, so the Ashtead Technology instrument fleet has been developed to meet almost every need, and technical advice is available to help consultants and quarry operators ensure that dust hazards and effectively managed.

#Environment @ashteadtech @_Enviro_News

Methane detection in mines.

Mining is big business, with the world’s 50 largest mining companies worth a total of 1 trillion dollars (€0.81 trillion). Worldwide, the mining industry is responsible for the direct employment of 3.7 million people, with over 150 million indirectly supported by small-scale mining operations.  Many other sectors, such as high-tech industry, are also entirely dependent on mined supplies of materials.

Guardian NG detects methane

There is inherent danger in creating and operating within subterranean tunnels which results in a high mining date rate, over 5 deaths per day due to mining accidents recorded in China alone. This is a worldwide problem, with high-profile incidents in the last 10 years occurring in New Zealand, Russia and the US among others.

The most common source of mining accidents, particularly in coals mines, is an explosion of methane gas. Methane is a colourless, odourless gas which is trapped in mines as part of the coal formation process. As coal is formed from compressed plant matter methane is produced as a by-product then, when rocks are excavated, methane is released into the local atmosphere with potential deadly consequences.

Methane Explosions in Mines
Methane explosions in mines are the result of the concentration of a methane leak in a closed environment. If methane reaches a critical concentration in the air, which is between 5 to 15 % it can react with the oxygen to form carbon dioxide, water and heat. This reaction needs a source of ignition to begin. This doesn’t necessarily have to be an open flame, sparks from mining processes, or a high localised temperature (over 600 °C) on hot equipment, can be enough to cause an explosion.

The pressure wave created by a methane explosion is often more dangerous than the initial explosion. The waves can displace large amounts of coal dust, spreading highly flammable particles throughout the air. The dust can ignite as part of a chain reaction, spreading flames along the mining shaft, consuming any available oxygen to further fuel the fire and generating large amounts of toxic gases.

Safety Measures to Avoid Methane Explosions
Methane release is unavoidable in coal mines as it is always present. The problem with methane explosions is not just restricted to active mining sites either. Many abandoned also leak methane gas, potentially into residential areas where it can still reach high enough concentrations to be at risk of explosion.

The risk of methane gas accumulation in mines means that gas sensing is an essential part of any mining safety network. To reduce the risk of methane build up, ventilation equipment is used in mines to keep methane concentrations below the explosion limit.

Sensors can be placed at ventilation exits to mine, measuring the outgassing of methane to determine that the methane concentration in the mine itself is not close to critical methods. External sensors are also important to monitor the release of methane to the environment surrounding the mine.

In order for gas sensing to be an effective safety measure, the gas sensors used must be able to detect low methane concentrations at a high reliability.

The Guardian NG for Methane Detection
One sensor range that is suited to the critical safety issue of detecting methane outgassed from mines is the Guardian NG series from Edinburgh Sensors. Capable of detecting methane concentrations between 0-1%, these infra-red based sensors are sensitive enough to detect even the smallest of leaks.

The Guardian NG series is designed as an easy-to-use, standalone gas sensor that can continually monitor and log methane concentrations in conditions where the gas is present between 0 – 100 % volume, with the most sensitive sensor being able to detect between 0-1%. The sensor has an impressively rapid 1.5 minute warm-up time and is capable of operating in a range of conditions varying from 0 – 95 % relative humidity and 0 – 45 °C.

What makes the Guardian NG series particularly well-suited to mining applications is they can be easily integrated in to existing ventilation equipment. As the sensor itself is electronic and could generate sparks, it should be situated on the surface of the mine measuring gas concentrations released from the mine vents. This provides a guarantee that ventilation systems are working and can also be used to monitoring the off-gassing of old mining sites.

Infra-red sensors offer some advantages over the traditional heat of combustion sensors that are typically used for mining applications and are commonly used in other areas where methane detection is required as methane absorbs infra-red light very strongly at characteristic wavelengths. They also offer faster response times and potentially have longer service lives than heat of combustion sensor alternatives.

One huge advantage of IR sensors in safety applications is the fail-safe nature of the technology. If the IR lamp, and therefore the sensor, fails then no signal is received by the detector, which is an equivalent effect to the sensor detecting a high methane concentration. As a result, a full alarm would sound, notifying staff that the sensor has failed and there is a potentially dangerous situation.

With its sensitivity and accuracy for methane detection and short response time of less than 30 seconds from sample injection, the Guardian NG series offers one answer to the critical safety issue of explosion prevention in mining.

 

@Edinst #PAuto

Robust and reliable data communications support in Czech mining enterprise.

In times of increasing digitisation of industrial processes, the importance of robust and reliable data communications is becoming more evident. The communication network is often critical to operations and failure to get data from A to B can have serious impact on production. Data networks supporting monitoring and control systems within mining applications require a special kind of robustness. Not only do the operating conditions include fluctuating temperatures, dust and dirt, but there is also constant vibration, which is extremely tough on network devices and cables.

The Vršany Lom brown coal surface quarry is using Westermo Lynx Switches and Wolverine Ethernet extenders to make up its entire data communications network.

The sheer size of an open-pit mine makes it difficult to maintain a data network and the need to constantly move mining equipment puts a considerable stress on the network cables.

Monitoring from the control room.

At Vršany Lom, one of the largest mines in the Czech Republic, all of these challenges have been overcome with the implementation of robust industrial networking technology from Westermo. Vršany Lom is a brown coal surface quarry located in the North Bohemian coal basin near the town of Most. The site is mined by Vršanská uhelná a.s., which is a part of the Sev.en group, a major European mining company responsible for the largest coal reserves in the Czech Republic.

Over the course of an eight-year period, Marek Hudský, chief technical engineer at Vršanská uhelná a.s., has strived to create the perfect monitoring and control system and supporting data communications network.

“The communications network is my responsibility and something I have designed, built and improved over many years,” explains Marek. “The continuous improvements have made a massive impact to overall production. The average time to transport the coal from the mine to the collection site has been reduced from 25 minutes to less than four minutes. On an annual basis this adds up to an extra month’s worth of production.

Control of the bucket wheel excavator is performed by the operator, but the communications network enables operation to be monitored from the central control room.

“This significant improvement has been achieved by reducing network downtime, which previously was very common and required many hours of maintenance. Today, interruptions to production due to network issues are rare.”

The Vršany Lom open-pit quarry covers an enormous area and mining takes place at several locations simultaneously. The coal is extracted using large bucket wheel excavators and loaded onto kilometer long conveyor belts that transport it to the collection site. Some sections of the conveyors are permanently positioned, whilst others are moved as the digging location changes.

Conveyor belts stretching out over many kilometers transport coal to a central collection point. The data communication cables are installed along the conveyors, connecting monitoring and control equipment for the excavators and conveyors to the control room.

The entire network is now running entirely on Westermo WeOS-powered devices, consisting of 60 Westermo Lynx switches and 40 Wolverine Ethernet extenders. The data communication equipment and cabling are installed along the conveyor belts. This connects several hundred sensors that provide critical operational data to the central SCADA system, which helps to ensure safe and effective mining. Fibre optic cables are located inside the permanent conveyors, with the Lynx switches installed in substations at set points along the conveyor belts. The fibre network is configured in a ring topology with Westermo’s FRNT super-fast ring reconfiguration protocol providing network reconfiguration times of less than 20 ms.

“The fibre network works flawlessly. The switches and cables have been in operation for quite a while now and have required very little maintenance,” explains Marek. “The real challenge is the data communication closer to the actual mining. This is where operating conditions are really tough due to continuous vibration and electromagnetic interference from the machines. Also, because the equipment needs to be constantly moved this exposes the cabling to constant wear and tear.

“We have been familiar with Westermo technology since the days of short haul modems. We knew they produced high quality products and when first introduced to the Wolverine Ethernet Extender we were immediately interested. At that point we were using a custom-made communication device, which was not really suitable for a tough mining environment. It caused regular network downtime, maintenance and production standstills, which was a completely unsustainable situation.”

“The first thing that appealed to me about the Wolverine was that was able to provide reliable data communication over regular twisted pair copper cables,” said Marek. “We use copper cables because they can withstand a lot more abuse than fibre before failing, however, when the digging location changes cabling is often bent, cut and sliced, which can reduce the quality of signal. . Despite this we are still able to achieve reliable data communication thanks to the Wolverine device which enables reliable communication even if the copper cabling is not in pristine condition. Secondly, the device had the robust characteristics that are needed to operate reliably in this type of environment. Finally, the Wolverine offered a lot of functionality, such as super-fast ring reconfiguration, LLDP and SNMP that enabled both a very technically advanced and very robust network solution.

“It has been quite a long process of continued improvement to get to where we are right now with the network in terms of functionality and reliability. Last year, I replaced the remaining legacy devices. We are now running the network entirely using Westermo WeOS-powered products and I am very pleased with the overall performance.

“We have always looked for that next improvement that will further strengthen the resilience of the monitoring and control system. By selecting Westermo products and utilising the WeOS operating system to its full capacity, Vršanská uhelná will now see many years of robust and trouble-free data communications.”

@Westermo #PAuto