The safeguarding of health and life is the number one priority for underground infrastructure projects. While culture and approach are critically important, the industry has also seen the development of innovative tools and technologies that assist in making the underground environment and working places more safe and secure, both on an everyday basis, and in the event of an unexpected occurrence.
This article explores four technologies that are finding a place in the North American tunneling industry:
- Refuge chambers.
- Proximity detection and collision avoidance.
- Gas detection and environmental monitoring.
- Automated conveyor health monitoring.
These technologies are either new or new to the North American tunneling industry. The benefits and applicability of each will be reviewed as well as identifying evolving features that improve on past capabilities or practices. Some of these technologies also deliver productivity benefits in addition to their primary safety purpose.
Technology innovation or introduction into an industry typically takes one of three forms:
- Adaptation of benchmark technologies from other industries.
- Adaptation of technology from other geographical sectors in the same industry.
- Grassroots innovation.
In the case of the technologies explored in this article, the channels are primarily adaptational, although there is an element of building-block innovation with conveyor monitoring.
While the motivators for this technology introduction are overwhelmingly safety driven, there are also synergistic productivity benefits to the development of the technology itself. These factor into the decisionmaking process of the tunnel constructing entity as to when and how to deploy them. In some cases, the technology is an ingrained part of the tunneling culture in other jurisdictions while relatively new or lesser known in North America. In other cases, the technology is cutting edge, and just beginning to have its potential explored.
This article reviews the benefits and applicability of each of the four technologies presented as well as identifying evolving features that improve on past capabilities or practices.
Refuge chambers are used worldwide in the underground mining industry. They are designed to provide a suitable safety haven as a temporary environment for a specific number of occupants and a specific timeframe when an incident has caused a hostile environment in the underground workings. Their purpose is to safeguard human life for a reasonable duration until the occupants can be safely evacuated.
Similarly, refuge chambers are deployed in tunneling projects. Drill-and-blast or sequential excavation method (SEM) projects of greater length with limited egress options will almost always include refuge chambers in their safety strategy. The presence and judicious use of refuge chambers may also benefit tunnel design and construction by reducing egress requirements.
Most mechanically driven projects over a certain diameter will have a refuge chamber incorporated into the tunnel boring machine (TBM) structure. This may also be supplemented with a refuge chamber in the tunnel behind the TBM for those projects where significant work will be taking place once the supported excavation has been created.
Rigid rescue chambers. The most commonly used type of chamber, a rigid, steel-supported structure is shown in Fig. 1.
In many sectors overseas, the refuge chambers are ingrained in the culture and specified in bid documents. In North America, the historical trend has left the use of refuge chambers up to project discretion.
The International Tunnelling Association’s (ITA) Working Group 5 (WG5), whose mission is “Health and Safety in Works” published in 2018 the revised “Guidelines for the Provision of Refuge Chambers in Tunnels Under Construction.” This is a comprehensive guideline that the authors have used as an indispensable reference in designing refuge chambers. In a nutshell, the key factors to consider as represented in Fig. 2 are:
- 24-hour duration requirements.
- Space, volume and seating requirements.
- A manual or automated positive-pressure system.
- Lighting, noise level, signal and electrical requirements
- Extended-life CO2 components, remote monitoring systems (temperature, humidity, power, external air supply, voice communication and maintenance reminders).
Inflatable refuge chambers. Inflatable, air-powered refuge chambers designed specifically for the U.S. underground coal mining industry occupy a high share of the market. They are designed to be mobile, for placement relocation, with a low profile, are easily handled compared to rigid refuge chambers and are easily deployed in a matter of minutes when circumstances dictate. Figure 3 shows them in predeployment and deployed modes.
While relatively unknown to North American tunnelers, the features and benefits of this technology, custom-designed to ITA requirements and to specific project capacity needs, can make them an economical and attractive option for project builders to safeguard the workforce. Inflatable chambers with capacities up to 48 residents have been designed (4.7 m (15.5 ft) long × 2.1 m (6.8 ft) wide × 1.15 m (3.8 ft) high prior to deployment and 18.6 m (61 ft) long × 3.6 m (12 ft) wide × 121 cm (48 in.) high deployed). A typical inflatable chamber for 18 people has a representative dimension of 4.1 m (13.5 ft) long × 1.5 m (4.9 ft) wide × 0.9 m (2.9 ft) high, prior to deployment and 9.6 m (31.7 ft) long × 3.6 m (12 ft) wide × 122 cm (48 in.) high deployed).
Proximity detection and collision avoidance
Equipment-to-personnel and equipment-toequipment collisions are real risks in underground work environments. Confined quarters, reduced visibility, less-than-ideal sightlines, noise, driver distraction and complacency may all be factors that contribute to collisions and pose injury or loss-of-life scenarios.
Proximity detection and collision avoidance (PD/ CA) systems take portions of control away from humans in a manner similar to today’s systems in state-of-theart automobiles and provide measures that contribute to incident avoidance or mitigation. As a result, these systems are accepted and ingrained in many tunneling markets just as they are in mining. Per the authors’ experience, they are newer to the North American tunneling industry and have been left to project discretion, as opposed to making up part of the bid documents as they do elsewhere.
PD/CA systems either come as part of the package from original equipment manufacturers (OEM) or are system add-ons. Representative types include:
Each have their strengths and drawbacks, and the authors have chosen to focus on electromagnetic systems, believing that they offer the greatest benefits from a safety perspective.
Electromagnetic PD/CA. Electromagnetic systems are typically OEM agnostic and can be easily deployed across a contractor’s entire fleet of equipment, including surface gear (such as cranes) and conveyor belts and other fixed equipment. They offer secure 360° stable field coverage (including the capability of customprogramming “hazard” and “critical” zones) and are typically unaffected by visibility and penetrate almost any material, allowing them to “see” around corners and obstacles. This is particularly beneficial in complex workings such as caverns or SEM excavations.
Some electromagnetic systems also offer an attractive feature: the ability to automatically slow or stop a piece of equipment to avoid an incident without relying on human response times. Electromagnetic PD/CA has the unique capability of differentiating between pedestrians and other machinery and allows the operator to have awareness of which hazard is nearby in real time.
Safe working conditions promote productivity. Stable PD/CA systems help to mitigate the workforce learning curve and dramatically reduce nuisance alarms, which have proven to be a downfall of earlier PD/CA types whereby personnel began to ignore the warnings in a “boy who cried wolf” manner.
A representative electromagnetic system is shown in Fig. 4.
Gas detection and environmental monitoring
The need to monitor one’s environment underground and detect gases is certainly not new to North American tunneling. This has existed for a long time as a requirement with demand varying from project-toproject.
Today, however, with the progression of digitalization and the development of new technologies, new approaches can be taken to calibrating equipment, collect data, manage data and pursue downstream automation in the form of such benefits as ventilationon- demand.
Both fixed/wired and battery-powered wireless sensor technology is now available (see Fig. 5) that gives users the capability to monitor multiple atmospheric variables as well as up to 64 types of gases. E-module sensor technology now permits easy changing and reprogramming of detection units, as well as an attractive feature of being able to quickly exchange sensors for calibration at the surface. This negates the need to bring calibration gas samples underground, a tedious process for those responsible for the monitoring system.
Today’s sensors are facilitated by two-way communication allowing remote control and command, permitting on/off toggling, threshold manipulation and alarm activation/deactivation. Data from the sensors is transmitted to a site server. From that server, corresponding manipulation of underground ventilation may be automatically controlled as a function of varying numbers of personnel or equipment underground or other programmable factors.
The wireless sensor technology enables versatile functionality, such as emplacement on project multiservice vehicles (MSV), so that monitoring is managed along the length of the tunnel rather than simply at fixed points.
Progress with gas detection and environmental monitoring technology gives tunnel builders new tools and approaches to meet the specification demand, to safeguard the workforce, to respond to events and to benefit from the data generated to potentially operate more efficiently.
Conveyor health monitoring
In North American tunneling, conveyor health monitoring has largely fallen under the purview of the “walking boss,” an individual with potentially many more pressing duties who is charged with visually and auditorily checking the conveyor belt over the course of a shift, looking for potential problem areas. Conveyor downtime means excavation downtime — an expensive proposition. The task is even more challenging if extraneous noise, diminished lighting or an elevated belt installation is involved.
A new technology is emerging from the mining industry that permits high-tech monitoring of a conveyor system’s rollers on a continuous, real-time basis using a single fiberoptic cable retrofitted along the length of the system. This technology was introduced at the Underground Construction Association (UCA) Cutting Edge Conference in November 2021 and has been adapted for application to tunneling based on interest demonstrated by industry leaders.
In this system, the fiber-optic cable detects acoustic changes along the conveyor and categorizes them into known parameters. Data is transmitted to and processed in the cloud with certain thresholds programmed to preemptively alert operators. Operational conveyor system aberrations, such as broken balls or cracked cages in a ball race, worn idler bearings or imminent bearing seizures are identified and thus the operator can prioritize roller replacements during planned maintenance shutdowns rather than due to an emergency breakdown event. This is accomplished with technology in a way that no human can match. In addition to avoiding downtime, the risk of heat generation from bearing or roller failure that may lead to a fire can be avoided. In this case, problems are avoided rather than cured. This technology is in its infancy in tunneling.
Culture and attitude are critically important to safety success. At the same time, technology, training and reinforcement are also important.
Technology evolves … just think where the tunneling industry was safety-wise a century, a half-century or even a decade ago. Now tunnelers can be kept safe for a prescribed period in a hostile atmosphere underground. Avoidance of collisions is no longer solely reliant on human ability, and conveyors can be monitored far more effectively. Gas sensors can also be calibrated on surface.
The technology discussed in this article shows that the continuum moves onward, and that safety and productivity can be intertwined.
ITA—Working Group N°5 Health and Safety In Works—ITA Report N° 14. 2014. Guidelines for the Provision of Refuge Chambers in Tunnels Under Construction. https://about.ita-aites.org/publications/wg -publications/1051/guidelines-for-the -provision-of-refuge-chambers-in-tunnels- under-construction. Michaud, T. 2021. Conveyor System Health Monitoring & Failure Prediction Using Fiber Optics & Artificial Intelligence: A Case Study from South Africa. UCA Cutting Edge Conference, 2021.