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Red Dog Operations Update

Red Dog Mine Sulfur Dioxide Update

Sulfur Dioxide (SO2) emissions are naturally present at Red Dog due to the natural characteristics of the ore. In late 2025, increased iron sulfide in the material being mined has led to higher emission levels.

Teck actively manages Sulfur Dioxide (SO2) at Red Dog Operations. The health and safety of our personnel is our top value. Red Dog has since made significant progress to lower the SO2 risk at site through intensive mitigation efforts including successfully cooling and rehandling reactive material, expanding monitoring capacity, enhancing facility air handling systems, and implementing additional protocols for the safety of personnel on site. Monitoring and Mine Safety and Health Administration (MSHA) inspections show that emission levels are within federal mine safety and health standards for SO2 exposures and there are no community health concerns related to SO2 at Red Dog.

Red Dog is working closely with NANA, external experts and the federal Mine Safety and Health Administration (MSHA), to monitor emission levels and take actions to reduce emissions and protect continued health and safety for workers. This work includes:

  • Cooling reactive ore using water and snow trucks to reduce the SO2-generating reaction
  • Relocating highly reactive waste rock to permanent underwater storage to stop and/or prevent the SO2-generating reaction.
  • Expanded SO2 monitoring capabilities including both indoor and outdoor stationary monitors, SO2 alarm systems, and monitoring programs that send regular reports and alerts for SO2 level awareness.
  • Raising fresh air intakes for buildings to higher elevation
  • Installing activated carbon air filters and automatic shut off controls triggered by SO2 thresholds in building HVAC systems

Monitoring is being conducted to confirm emission levels are within federal mine safety and health standards for SO2 exposures. No citations related to SO2 were issued.

Early stages of our response focused on reducing the number of personnel on site. Where possible, personnel were transitioned to remote work from their homes or other Teck offices. Staff whose jobs required them to remain on site were relocated to different living and/or working areas or placed on paid administrative leave if their personal health was at greater risk of SO2 exposure. As of January 2026, all mitigation criteria were met and personnel returned to site following their regular schedules.

Red Dog Operations formed the Self Heating Reactive Rock (SHRR) SO2 technical work group to develop an integrated SHRR management plan that supports safe, reliable production and aligns with other key Red Dog initiatives including evaluating risks with the upcoming spring freshet, support for Red Dog Mine Life Extension (MLE), and SO2 mitigations through closure. The SHRR group meets weekly and includes a representative from NANA.

For any questions or concerns, please contact us at rd-ca@teck.com or 907-754-5168

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  • SO2 is a colorless gas that is heavier than air and has a pungent odor. It is not flammable. SO2 is generated when oxygen in air reacts with iron-rich rock (oxidation).
  • Normally this would not be an issue while in the ground, however when the rock is mined and exposed to air, it heats up and can release SO2 gas.
  • A similar reaction occurs with packet-style hand warmers, which contain iron. When opened, they are exposed to oxygen in the air, which reacts with the iron and creates heat.
  • Sulfur Dioxide (SO2) is naturally present at Red Dog due to the metallurgical characteristics of the ore and associated waste rock. As these materials are excavated and exposed to air, oxygen can react with these sulfur- and iron-rich materials in a process known as oxidization.
  • At Red Dog, the safety and health of personnel on site is our top value. To protect the continued health and safety of personnel, Red Dog works closely with the federal Mine Safety and Health Administration (MSHA), as well as external experts, to monitor emission levels and take action to reduce SO2 emissions at site.
  • We have strengthened our monitoring systems, raised fresh air intakes to higher elevations, and installed carbon air filters on air handling units in buildings to reduce emissions in facilities.
  • We have a robust program for assessing when respirators are required on site and dedicated subject matter experts who administer the respiratory protection program.
  • Monitoring is being conducted to confirm emission levels are within federal mine safety and health standards for SO2 exposures. Monitoring data and mitigation plans were reviewed with MSHA during recent inspections. No citations related to SO2 were issued.
  • In the event SO2 levels exceed mine safety and health standards, emergency response personnel have protocols in place to move personnel from an area of higher concentration to safe muster areas of low concentration until the SO2 levels reduce sufficiently.
  • Personnel who are required to work onsite but have concern for potential health risks will be evaluated by medics to determine whether they have elevated risks to exposure.
    • If the medic finds the employee has an elevated risk from exposure, they will be put on Administrative Leave with Pay until the human health risk to employees is sufficiently resolved.
    • If the medic finds the employee does not have an elevated risk of exposure, they have the option to be put on unpaid leave.
  • Red Dog adheres to the NIOSH exposure limits of 10 hours TWA (Time Weighted Average) at 2ppm and 15 minutes STEL (Short Term Exposure Limit) at 5ppm. This is a stricter (more conservative) exposure limit than federal standards require.
  • Red Dog works closely with NANA, external experts, and the federal Mine Safety and Health Administration (MSHA), to monitor emission levels and take actions to reduce emissions and ensure the continued health and safety for workers.
  • Red Dog Operations formed the Self Heating Reactive Rock (SHRR) SO2 technical work group to develop an integrated SHRR management plan that supports safe, reliable production and aligns with other key Red Dog initiatives including evaluating risks with the upcoming spring freshet, support for Red Dog Mine Life Extension (MLE), and SO2 mitigations through closure. The SHRR group meets weekly and includes a representative from NANA.
  • Waste rock stockpiles Main Pit Dump #4 (MPD4) were identified as hot spots for SO2 emissions. To mitigate these emissions, we are cooling hot spots with water and snow, and excavating and transferring reactive material to the Main Pit Water Reservoir (MPWR) for permanent underwater storage.
  • All air handlers have been moved to recirculation mode with only the minimal make up air being drawn to maintain positive pressure in the facilities.
  • Air intakes for the Personnel Accommodation Complex (PAC) were relocated to reduce ingress of SO2 into living accommodations.
  • Activated carbon filters have been installed in the air handler units in support of enhanced SO2 removal.

Red Dog has strengthened our SO2 monitoring capabilities to support early detection and response. As of April 2026, over 28 stationary indoor monitors and 10 outdoor stationary monitors were installed throughout site and 30 SO2 detectors were installed in air handlers intakes with automatic shut off controls.

To improve real‑time data access, a new dashboard was developed to provide shift-level reports and alerts for elevated SO2 levels. These reports are displayed throughout site for personnel to view.

  • Monitoring and MSHA inspections show that emission levels are within federal mine safety and health standards for SO2 exposures.
  • Additionally, the MSHA inspector reviewed Red Dog’s risk assessment for the mitigation plan to cool the material reacting in Main Pit Dump 4 (MPD4). The inspector was satisfied with the methodology and risk controls proposed to mitigate the hazards and protect the miners while performing mitigation activities.
  • Additional monitoring systems, including new stationary and HVAC-integrated units, further support ongoing regulatory compliance and safe operations across the site.
  • Yes. The Food and Drug Administration (FDA) allows SO2 and other sulfites as food preservatives but requires mandatory labeling if food items contain greater than 10 parts per million (ppm). No readings in the food preparation and distribution areas have exceeded 10 ppm.
  • Out of an abundance of caution, NMS has engaged the Alaska Department of Environmental Conservation (ADEC) and is following best practices recommended by ADEC.
  • Impacts of SO2 may be determined by several factors including the dose (amount) and method of contact (for example, by breathing, eating, drinking, or touching). Other considerations include your age, sex, diet, family history, lifestyle, and health.
  • Under low concentrations (<5ppm), inhaling SO2 can cause irritation to the nose, eyes, throat, and lungs. Those with preexisting respiratory conditions may experience symptoms at concentrations as low as 0.25ppm.
  • Unprotected exposure to high concentrations of SO2 can cause permanent damage to the lungs.
  • Symptoms can be worsened by preexisting health conditions like asthma.
  • Health effects can be prevented or mitigated with respiratory protection equipment with appropriate cartridges.
  • Monitoring and MSHA inspections show that emission levels are within federal mine safety and health standards for SO2 exposures.
  • SO2 is a colorless gas that is heavier than air and has a pungent odor. It is not flammable. SO2 is generated when oxygen in air reacts with iron-rich rock (oxidation).
  • Normally this would not be an issue while in the ground, however when the rock is mined and exposed to air, it heats up and can release SO2 gas.
  • A similar reaction occurs with packet-style hand warmers, which contain iron. When opened, they are exposed to oxygen in the air, which reacts with the iron and creates heat.
  • Sulfur Dioxide (SO2) is naturally present at Red Dog due to the metallurgical characteristics of the ore and associated waste rock. As these materials are excavated and exposed to air, oxygen can react with these sulfur- and iron-rich materials in a process known as oxidization.
  • At Red Dog, the safety and health of personnel on site is our top value. To protect the continued health and safety of personnel, Red Dog works closely with the federal Mine Safety and Health Administration (MSHA), as well as external experts, to monitor emission levels and take action to reduce SO2 emissions at site.
  • We have strengthened our monitoring systems, raised fresh air intakes to higher elevations, and installed carbon air filters on air handling units in buildings to reduce emissions in facilities.
  • We have a robust program for assessing when respirators are required on site and dedicated subject matter experts who administer the respiratory protection program.
  • Monitoring is being conducted to confirm emission levels are within federal mine safety and health standards for SO2 exposures. Monitoring data and mitigation plans were reviewed with MSHA during recent inspections. No citations related to SO2 were issued.
  • In the event SO2 levels exceed mine safety and health standards, emergency response personnel have protocols in place to move personnel from an area of higher concentration to safe muster areas of low concentration until the SO2 levels reduce sufficiently.
  • Personnel who are required to work onsite but have concern for potential health risks will be evaluated by medics to determine whether they have elevated risks to exposure.
    • If the medic finds the employee has an elevated risk from exposure, they will be put on Administrative Leave with Pay until the human health risk to employees is sufficiently resolved.
    • If the medic finds the employee does not have an elevated risk of exposure, they have the option to be put on unpaid leave.
  • Red Dog adheres to the NIOSH exposure limits of 10 hours TWA (Time Weighted Average) at 2ppm and 15 minutes STEL (Short Term Exposure Limit) at 5ppm. This is a stricter (more conservative) exposure limit than federal standards require.
  • Red Dog works closely with NANA, external experts, and the federal Mine Safety and Health Administration (MSHA), to monitor emission levels and take actions to reduce emissions and ensure the continued health and safety for workers.
  • Red Dog Operations formed the Self Heating Reactive Rock (SHRR) SO2 technical work group to develop an integrated SHRR management plan that supports safe, reliable production and aligns with other key Red Dog initiatives including evaluating risks with the upcoming spring freshet, support for Red Dog Mine Life Extension (MLE), and SO2 mitigations through closure. The SHRR group meets weekly and includes a representative from NANA.
  • Waste rock stockpiles Main Pit Dump #4 (MPD4) were identified as hot spots for SO2 emissions. To mitigate these emissions, we are cooling hot spots with water and snow, and excavating and transferring reactive material to the Main Pit Water Reservoir (MPWR) for permanent underwater storage.
  • All air handlers have been moved to recirculation mode with only the minimal make up air being drawn to maintain positive pressure in the facilities.
  • Air intakes for the Personnel Accommodation Complex (PAC) were relocated to reduce ingress of SO2 into living accommodations.
  • Activated carbon filters have been installed in the air handler units in support of enhanced SO2 removal.

Red Dog has strengthened our SO2 monitoring capabilities to support early detection and response. As of April 2026, over 28 stationary indoor monitors and 10 outdoor stationary monitors were installed throughout site and 30 SO2 detectors were installed in air handlers intakes with automatic shut off controls.

To improve real‑time data access, a new dashboard was developed to provide shift-level reports and alerts for elevated SO2 levels. These reports are displayed throughout site for personnel to view.

  • Monitoring and MSHA inspections show that emission levels are within federal mine safety and health standards for SO2 exposures.
  • Additionally, the MSHA inspector reviewed Red Dog’s risk assessment for the mitigation plan to cool the material reacting in Main Pit Dump 4 (MPD4). The inspector was satisfied with the methodology and risk controls proposed to mitigate the hazards and protect the miners while performing mitigation activities.
  • Additional monitoring systems, including new stationary and HVAC-integrated units, further support ongoing regulatory compliance and safe operations across the site.
  • Yes. The Food and Drug Administration (FDA) allows SO2 and other sulfites as food preservatives but requires mandatory labeling if food items contain greater than 10 parts per million (ppm). No readings in the food preparation and distribution areas have exceeded 10 ppm.
  • Out of an abundance of caution, NMS has engaged the Alaska Department of Environmental Conservation (ADEC) and is following best practices recommended by ADEC.
  • Impacts of SO2 may be determined by several factors including the dose (amount) and method of contact (for example, by breathing, eating, drinking, or touching). Other considerations include your age, sex, diet, family history, lifestyle, and health.
  • Under low concentrations (<5ppm), inhaling SO2 can cause irritation to the nose, eyes, throat, and lungs. Those with preexisting respiratory conditions may experience symptoms at concentrations as low as 0.25ppm.
  • Unprotected exposure to high concentrations of SO2 can cause permanent damage to the lungs.
  • Symptoms can be worsened by preexisting health conditions like asthma.
  • Health effects can be prevented or mitigated with respiratory protection equipment with appropriate cartridges.
  • Monitoring and MSHA inspections show that emission levels are within federal mine safety and health standards for SO2 exposures.