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Mitigating airborne contaminants in tunnel construction
Workers’ exposure to airborne contaminants is a fundamental health and safety issue in tunnel construction, and the importance of taking it seriously cannot be reiterated enough. With rapid advancements in DPM monitoring and dust collection technologies, however, the industry has the necessary tools to adequately monitor and control workers’ exposure to diesel fumes and dust. By Munesu Shoko
Tunnels are created using tunnel boring machines (TBMs), sprayed concrete lining (SCL) processes and other tunnelling methods such as load & haul, supported by diesel plant operations. Each of these processes has the potential to expose workers to airborne contaminants that, if not adequately controlled, can lead to significant harm.
Lisa Andrews, Marketing and International Business Development at Grydale, an original equipment manufacturer (OEM) of a range of fixed and mobile industrial dust collection equipment, agrees, saying that tunnelling development produces high volumes of dust through different excavation processes such as roadheaders, drill & blast and spoil transition from TBMs. A critical aspect of any tunnel construction, she says, is ventilation design and dust control so that workers’ exposure to diesel fumes and dust is reduced to safe, acceptable levels.Silica or silicon dioxide, she adds, is a naturally occurring and widely abundant mineral that forms a major component of most rocks and soils. “New health and safety regulations specifically relating to the control of respirable crystalline silica (RCS) have been introduced to classify silica in the same bracket as asbestos. Many countries are now halving the workplace exposure limit (WEL) for RCS for an 8-hour time weighted average from 0,1 mg/m³ to 0,05 mg/m³,” explains Andrews. The risk of dust-related diseases, she adds, increases with exposure levels. Due to the high production volumes and enclosed workspaces, workers in underground operations have a higher risk of dust exposure. Management of dust within tunnel construction usually requires a hierarchy of control measures to be implemented, including the use of a dust scrubber (dust collector) and providing ventilation at the face through brattice wings or ducting. “Direct dust extraction of the large amount of dust created in rock excavated at the tunnel face is the single most important process for controlling the risks from both respirable dust and RCS. Reducing the dust at the face through the use of a dust collector allows respiratory protection, effectively controlling the residual dust risks to workers,” she says. There are many types of ventilation design and dust control system and as each tunnel is unique, so is each ventilation design and dust control solution. Each ventilation system, says Andrews, has limitations in terms of dust control, with the selection of the system being dependent on geology, climate, tunnel dimensions, location/site access, construction method and sequence, targets to be achieved, cost of materials and ease of maintenance. “The three main factors that affect the typical volume of air flow required within the tunnel during construction works are airflow, diesel plant (type & kW) and people,” she says. “These factors all combine to determine what capacity of the ventilation/dust extraction system is required.”
DPM to the fore
With regards to DPM (diesel particulate matter), the new gold standard for regulator support is coming out of the UK following the release of the British Standards (BS 6164) that clearly state the dangers of diesel particulate matter. According to Stephen Griffiths, EMEA product champion for Occupational Health with the UK’s BSI national standards body, “construction has the largest burden of cancer among all industrial sectors”. In 2012, Francois Velge, Managing Director at Pinssar, an Australian company that developed the world’s first real-time DPM monitoring system, the World Health Organisation declared diesel engine exhaust a Group 1 carcinogen. This is the same group as tobacco and asbestos. “Currently, diesel is still the main source of energy in all UK tunnel construction and fit-out projects and the industry does not see this changing dramatically in the near future,” he says. “Whatever the future may hold for diesel/electric powered equipment, workplaces need to be cognisant of protecting their workers against DPM exhaust today.” DPM – also referred to as diesel engine exhaust emissions or DEEE – is so fine that it can penetrate all natural human defenses such as the nose, throat and lungs, and enter the blood stream, and has the potential to cause life threatening illness and long-term health problems such as lung cancer, bladder cancer and heart conditions. A healthy workforce is an efficient workforce, Velge reiterates. “The construction industry is already spending a significant amount of money to reduce its DPM exhaust emissions (e.g. by means of diesel particle filters), without necessarily understanding the size of the problem,” he says. “You can’t manage what you don’t monitor. Now, with the latest innovative technology, construction companies can deploy continuous real-time monitoring of diesel particulate matter to enable management of emission controls. This will protect the well-being of construction workers in the underground environment as well as the progress of any tunnelling project.” In addition to protecting workers, says Velge, an improved diesel management system can reduce the environmental impact, help achieve positive ESG (Environmental, Social and Governance) outcomes and protect the community through building a healthier project.
The tunnel construction industry’s focus on the health and safety of its workers makes it well placed to adopt real-time DPM monitoring technology. Pinssar offers the world’s first (and only) continuous, real-time DPM monitoring system for harsh environments such as tunnelling construction. The low-maintenance, plug-and-play diesel monitoring system was specifically developed to provide diesel emissions data on a continuous, 24/7 basis. “Our innovative solution provides the missing piece of the puzzle when it comes to monitoring DPM. It complements the existing point-in-time methods (tail-pipe, personal and hand-held) but provides more granular insights to enable timely action and prompt management of mitigating controls,” explains Velge. The solution comprises a ruggedised, fixed, particle monitor called the Pinssar DPR which works continuously to collect DPM samples and send data in real time, and the Pinssar Dashboard, a configurable interface which records and displays samples from the Pinssar DPR, as well as internal diagnostics. Additionally, the data captured by this flexible solution is compatible with the company’s control system architecture. This technology is said to be the world’s only enabling solution for integration with ventilation simulation software. On the dust collection front, Grydale designs and manufactures a comprehensive range of mobile dust collection systems, available in diesel, electric or hybrid systems. A full range of mobility options is available, including the internationally patented Track Mounted units, Hydraulic Stepping Systems, Drag Skids, Trailer Mounted and Castor Wheel (towable) units. Grydale JMS M-Series dust collectors, explains Andrews, are complete dust collection systems that feature a centrifugal exhaust fan; dirty air intake; patented drop out box; high efficiency filters; reverse pulse filter cleaning system; dust discharge system; clean air exhaust and a fan silencer. All components are mounted on a single mobile base to create 6 m³/s to 60 m³/s (12 000 CFM – 125 000 CFM) of airflow. Mobility, combined with compact integrated design, provides significant advantages on construction sites. Grydale holds international patents for manufacturing the only self-propelled (track mounted) mobile dust collector on the market. “These units can be transported easily and be operational in a short space of time with limited set up requirements,” explains Andrews. “Units don’t require long, expensive ducting to be constructed/installed. They can also be relocated easily during operation and be moved alongside dust generating equipment with ease. The single mobile base and compact footprint mean units take up less room on construction sites.” “The fact that our mobile dust collectors are complete dust extraction systems mounted on a single mobile skid is a key differentiator,” says Andrews. “It means that units can be quickly mobilised alongside the excavation equipment being utilised.” Meanwhile, electric and hybrid powered units feature a variable speed drive (VSD) which is used in conjunction with a velocity probe to regulate power consumption and achieve the air volume required. “We have seen savings of up to 60 kW per machine,” says Andrews. A key benefit of Grydale’s diesel powered units is that they eliminate the need for an external power supply such as a mains connection or auxiliary power units, and feature variable air flow control to minimise fuel consumption. “Independent, certified air flow performance and filtration testing has been conducted both above and below ground as part of rigorous performance verification and certification processes. Results show a filtration collection efficiency of 99,99% at 0,067 micron to meet workplace health and safety regulations in a wide range of industries,” says Andrews.
Due to the innovative design, says Velge, the Pinssar system is the only solution worldwide which supports the requirements of the updated BS 6164 (2019). “The Pinssar particulate monitor was developed specifically to detect sub-800 nanometre particles which evolved into our patented diesel emission technology with 23 unique innovations recognised globally,” he says. The benefits of the Pinssar solution include an ability to influence and reduce worker exposure to acceptable levels of DPM and enabling tunnel construction companies to understand and make informed choices regarding ‘unseen’ air quality hazards. Reliability is a key attribute of this solution. It is a proven, ultra-low maintenance solution designed specifically for harsh environments. Its simplicity reduces the complexity of identifying the source of dangerous DPM levels. “With this solution, tunnelling contractors are able to establish and acknowledge DPM baseline trends for their environment and to establish long-term strategies for management. They are also able to prevent project downtime and substantiate DPM mitigation costs (filters, ventilation, and others),” he says. Connectivity is another big benefit of the Pinssar solution. Companies can collect configurable 24/7 data for approved users to enable smarter decisions and to move more tonnes safely. This data can be accessed by approved users on a number of different platforms, including mobile phones, desktop and laptop, SCADA systems etc. The secure nature of the system means that customers can protect their competitive advantage as all data remains proprietary to the owner. “The system is compatible with control system architecture and all ventilation simulation software/VoD (ventilation on demand). Meanwhile, real-time detection of changing DPM levels enables operations to rapidly manage controls and responses,” says Velge. While Pinssar acknowledges the dangers of dust, the company has identified the need to focus specifically on diesel particulate matter, and is now deemed the leading expert when it comes to continuous monitoring of diesel emissions for harsh environments. Pinssar’s internationally respected views have been the catalyst for a much needed change in the industry and the advancement of DPM monitoring strategies. “As a trusted advisor, Pinssar assists when requested by customers to review and analyse the data and provide guidance for continuous improvement. We also have a global reach, with our product deployed across six continents,” says Velge. Pinssar’s solution was recognised with a “Highly Commended” rating in the category Innovation in Instrumentation and Monitoring during a London industry award ceremony.
Pinssar’s DPM monitoring solution has established itself within the underground mining industry throughout the world and has been adopted as the preferred solution by some of the largest mining companies globally. “The tunnel industry’s leading projects are now prescribing continuous, real-time DPM monitoring as a requirement to keep their workforces safe and healthy. A typical flagship project includes the early uptake by the progressive SMP4 joint venture for the TELT project, one of the most significant European tunnelling projects,” says Velge.
Grydales’s JMS M-Series dust collectors have been deployed on some flagship tunnelling projects around the world with great success. At the Rozelle Interchange, a group of underground tunnels connecting the M4 – M5 Link with adjacent roads in Sydney, NSW, a total of 31 JMS M-Series dust collectors was deployed for general ventilation and dust extraction at source during construction. Several JMS M-Series dust collectors were also deployed at the Sydney Metro, Australia’s largest public transport project. In 2024, Sydney will have 31 metro stations and more than 66 km of new metro rail, revolutionising the way Australia’s biggest city travels. By the end of the decade, the network will be expanded to include 46 stations and more than 113 km of world-class metro for Sydney. Elsewhere, Grydale has provided its dust collection solutions to the Metro Tunnel, a key rail infrastructure project currently under construction in Melbourne, Australia, that includes the construction of twin 9 km rail tunnels between South Kensington station and South Yarra with five new underground stations. While TBMs are being used to build most of the Metro Tunnel, station box excavation and tunnelling between the two CBD stations are being undertaken by roadheaders. The use of Grydale ventilation and dust control systems has resulted in a clean and safe work environment during construction, which has been monitored and approved by regulators to meet unionised working orders. Grydale has conducted independent air flow performance and filtration testing on all units both above and below ground as part of rigorous performance verification and certification processes. Testing undertaken has been certified by the National Association of Testing Authorities (NATA) and units have shown a collection efficiency of 99,99% at 0,067 micron.
Commenting on some of the new trends in DPM monitoring, Velge notes that all around the world, governments and industry are reviewing their existing guidelines, which have been described as too broad. Those guidelines were established with a mix of theory and the technologies available at the time. “However, those previous technologies are unable to monitor DPM continuously within the dynamic work environment. They only take random, point-in-time samples which generally provide some pieces to the puzzle but never the full picture. The new technology addresses these shortfalls by providing a picture of the continuously changing underground environment in real time,” he says.
From a dust collection perspective, Andrews notes that there is a strong trend towards ‘dust extraction at source’ and the use of mobile dust collection units, located either within the main tunnel excavation area or mounted on the surface. Another notable trend in this field are the changes in dust discharge. To avoid secondary dusting, she says, dust is no longer simply discharged to the tunnel floor. To utilise ‘wet discharge’ (slurry augers), it is collected in bulker bags via side incline augers for removal from site. “There is also a big move towards ‘hybrid’ solutions to allow the most efficient use of power,” says Andrews. “We have also seen a big trend towards the use of VSDs to allow units to be more efficient – only generating the power required for that stage of construction.” On short tunnels and station excavations, she adds, large volume (40 – 60 m³/s) units can be located on the surface, with ducting erected to the excavation area for space proofing in the excavation area (reduction of plant in the excavation area).
Given their successes in many flagship tunnel projects, Andrews predicts a strong future for mobile dust collectors, especially given the increasing regulations around the management of dust within tunnel construction. Velge is of the view that Pinssar’s DPM monitoring technology will enable jurisdictions around the world to follow on from the industry-leading BS 6164 standard. “World leading progressive companies are relying more and more on making timely data-driven decisions in their drive for continuous improvement in health and safety, and their ESG strategy for carbon reduction,” concludes Velge.