Pre-incident planning of fires in underground hard rock mines: old and new risks
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Fires in underground mines may pose a challenge to fire and rescue personnel where the complex environment and multiple influences of a fire are poorly considered during pre-incident planning.
*CTIF Editorial Note: This research paper is specifically on fires in underground hard rock mines, but many of the conclusions can be adapted towards pre-planning of any underground area or other space which is confined and / or has limited access, ventilation and evacuation routes.
Fires in underground mines pose challenges that include the 3-dimensional feature of the mine, long distances filled with smoke and the limited number of routes to access the fire. Existing risks include smoke spread, falling rocks and fires affecting the ventilation flow.
New risks may include the introduction of battery-powered mine vehicles with different fire behaviour, emission of toxic substances and the changing conditions that fire and rescue personnel will face.
This study on pre-incident planning in underground mines applied data from experiments, inventories and design fire studies. A number of questions were considered related to information sources, fire modelling, capturing complexity and using fire scenarios. When performing fire modelling, empirical models could be used to complement other modelling tools.
The study found that for modelling of spatially extensive mine sections, the use of ventilation network-based mine fire simulations could be a better option. Using an analytical toolbox, an iterative testing of plans and an ongoing planning process, the pre-planning challenges for a mine can be mitigated.
A key tool during fire and rescue operations is pre-incident planning, which assists personnel in the decision-making process and can remedy the initial lack of information. The main issues with pre-incident planning in underground mines are the complex mining environment, the ever-changing layout of the mine and the highly transient and numerous ways a fire will behave.
This paper studies pre-incident planning in underground hard rock mines and proposes information sources, modelling tools and contents of these plans. Questions considered are: What information sources to use? How to use fire modelling? How to capture the complexity of the mine? Data and findings from fire experiments, inventories and design fire studies were applied in this study.
In order to investigate pre-incident planning of fires in underground mines, data was applied from fire experiments, inventories and design fire studies. It is recommended that empirical models focusing on specific phenomena be used to complement other modelling tools.
The use of empirical models may be cumbersome and using ventilation network-based mine fire simulation software is an alternative. Design fire scenarios and modelling results are a key tool when analysing fire behaviour and testing the plan and act as a checkpoint during the planning process. Mine ventilation systems should have instructions on how to manage the system and how to test it against design fire scenarios for mine sections and backup actions.
By using analytical tools, iterative testing of plans and ongoing planning process, the high risks of fire in an underground mine can be mitigated.
Some examples from the research paper are listed below:
(For the full paper, please download the pdf at the top of this post.)
A fire underground can spread beyond the start object and fire gases can affect installations further away. The ignition of adjacent fuel or the smoke spread may initiate further risks. These cascading effects need to be identified and analysed and included in the plan. When analysing cascading effects, input data from risk analysis of mine sections, descriptions of the production process and range of effects from a fire are valuable assets. Cascading effects could be identified and described in the plan, enabling fire and rescue personnel to break the chain of events and mitigate the consequences.
Alternative chains of events
One of the key parts of pre-incident planning is alternative chains of events, which increase the number of tactical options available and provide room for manoeuvre. The planning covers the different directions that an incident can take and developing backup plans and actions. The planning includes analysing possible scenarios and preparing tactical options to counter the sequence of events. Preparing tactical options includes obtaining or prepositioning specialised equipment and training of personnel for specific situations.
Underground mines with limited access routes and ventilation options increase the need for planning. The sensitivity and vulnerability in case of a system failure increases the need for a backup plan.
Access routes must be carefully planned as the number of access routes may be limited and will need to serve as attack routes and as evacuation routes. Preferably, the routes should be divided into primary and alternate attack and evacuation routes to limit the risk of the 2 operations interfering with each other. When determining access routes, parameters such as the position of the fire and existing fire and smoke barriers should be considered. The selection of access routes should be synchronised with the management of the mine ventilation during a fire. The choice of access routes will not be static but will vary from fire to fire and during a fire.
When planning the evacuation by vehicle, the aim is to prevent traffic jams and ensure a steady traffic flow. There is also the possibility of vehicles driving through smoke with limited visibility. Designated access routes for specialised equipment and vehicles should be verified to ensure accessibility and the possibility of turning the vehicle around. Positions deemed critical could be identified in the plan and actions to facilitate the turnaround (such as lighting) should be considered. The inclination of the decline could be included if it affects the accessibility. The transportation time to reach positions underground could be included in the plan.
Fire protection systems
Plans should list existing automatic fire suppression systems as well as contain information on the design of the system. Information should be specific: is the suppression system designed to extinguish the fire or is it designed to contain the fire? A fire suppression system in a parking drift with large mine vehicles may be designed to contain the fire. This information is required when additional fire suppression resources are sent to the site and a prolonged smoke production could be expected.
The general lack of fire doors or barriers in a decline and the high frequency of vehicles makes a design fire scenario applicable (Hansen 2010a). The result will be helpful when planning for evacuation, alternative chains of events and the management of the mine ventilation.
Pre-planning involving the ventilation system should include instructions on how to manage the ventilation system in case of a fire in a mine section. The instructions would specify what fans should be running or not and doors that should be open. The plan should also contain positions of fans, shafts, refuge chambers and places where fresh air can be found. The plan should be verified against design fire scenarios for the mine section. Backup actions should be planned in case of a loss of power or closed fire barriers. Sites critical with respect to the mine ventilation should be identified and monitored, and backup plan actions initiated if a barrier malfunctions or the smoke spreads in an undesired direction.
Heat Release and Fire Growth Rate
The fire growth rate and heat release rate of vehicle fires can be very high due to the fuel load on vehicles. A high heat release rate will cause backlayering and severe smoke production and a high fire growth rate may initiate a throttle effect that seriously affects mine ventilation (Hansen 2020). Figure 2 shows the heat release rate of a loader in an underground mine (Hansen & Ingason 2013). The initial fire growth and heat release rates are very high and cause problems to the mine ventilation. A second peak in the heat release rate can be seen after approximately 50 minutes. This is due to the fuel igniting or being engulfed at later stages. Therefore, periods of peak heat release rates can be expected at later stages.