Mining FAQ’s


Welcome to our “Mining Safety” Frequently Asked Questions. Understanding Your Needs and Looking for Customized Solutions!

Please do not hesitate to Contact Us for additional information.

ON2 builds, supplies, and services our mobile mine refuge chamber, the TommyKnocker. It is easy to move and can include a Refuge One Air Centre making it a complete Mine Refuge System. The ON2 TommyKnocker Sales Brochure explains the function, sizes and uses of the TommyKnocker Refuge Chamber and outlines all of the standard and optional equipment.

You need to install an ON2 mine refuge chamber when:

  • There is no escape-way or secondary means of exit from the mine
  • Miners are working in remote areas of the mine, away from the normal access route into the mine
  • Developing new levels
  • Developing a new mine
  • Re-entering an old mine

When initial mine development is underway, interim safety procedures are necessary until refuge chambers are established underground. The use of portable ON2 refuge chambers or the provision of oxygen self-rescuers are alternatives if a permanent refuge chamber is not practical.

The number of chambers and their size depend on the maximum number of workers expected to use the chamber at one time. Be prepared for contingencies, such as when additional individuals could be present at any location (e.g. geologists, visitors, inspectors, trainees, managers, etc.). Always have enough ON2 Refuge One Air Centres on hand to provide breathable air for the maximum capacity of the chamber.

Locate a refuge chamber at these points in your mine:

  • Main or normal travel routes
  • As close as possible to the greatest number of working places
  • A safe distance from hazardous areas

The chamber should be within a maximum 15-minute walk for any crew member.

This will depend on the number of miners and other workers within a 15-minute walk of the chamber. Be prepared for contingencies, such as when there could be additional individuals at any location (e.g. geologists, visitors, inspectors, trainees, managers, etc.).

A mine’s rescue plan should include the maximum time it will take to rescue trapped miners. This is the mining company’s responsibility to prepare and train for. ON2 builds Air Centres and Refuge Chambers that provide up to 96 hours of breathable air. 

There are three main sources of breathable air in a refuge chamber:

1. Dead air space within the refuge chamber

2. The Mine’s compressed air pipelines

3. ON2’s Refuge One Air Centre

No, these systems do not address the proper control of carbon dioxide, which can quickly build up and contaminate your occupants’ air supply.

In a sealed refuge chamber without ventilation, falling oxygen and rising carbon dioxide concentrations pose varying degrees of discomfort and potentially life threatening circumstances to the occupants. The size of the chamber and how long occupants will be contained will impact the air quality (see Performance Data Sheet). Safe values must be determined by your mine’s Industrial Hygienist.

  • 350 ppm: Normal carbon dioxide concentrations
  • 5000 ppm: The Time-Weighted Threshold Limit Value (TLV-TWA), where occupants would experience increased breathing rates
  • 10,000 ppm: Headaches occur
  • 30, 000 ppm: The Short-Term Exposure Limit (TLV-STEL); no more than 15 minutes at this level
  • 50,000 ppm: Causes panting and discomfort; intoxication will occur within 30 minutes
  • 100,000 ppm: Unconsciousness occurs
  • over 100,000 ppm: Unconsciousness followed by death within one minute
  • 20.9% Oxygen: The normal atmospheric oxygen concentration
  • 19.5% Oxygen: The minimal acceptable level of oxygen
  • 18% Oxygen: Occupants will require additional effort to breathe
  • 16% Oxygen: Flames are extinguished and the occupants’ pulse and breathing rate will increase
  • 14% Oxygen: Occupants experience fatigue upon exertion, emotional upset, impaired judgment, and faulty coordination
  • 12% Oxygen: Occupants’ respiration is impaired, causing heart damage, poor judgment, discomfort, vomiting, and nausea
  • Below 10% Oxygen: Unconsciousness and death occur

Depending on the size of the chamber and the number of occupants, studies have shown likely levels of 5000 ppm carbon dioxide, the Time-Weighted Threshold Limit Value (TLV-TWA), will be reached in less than one hour and dangerous levels (20,000 ppm) are reached within four hours.

Furthermore, depletion to 18% oxygen, which causes increased breathing rate, could be reached in less than five hours and dangerous levels (less than 16% oxygen) in less than eight hours.

The maximum safe time within a refuge chamber depends on the size of the chamber, the number of occupants, the expected time of occupancy in a worst case scenario, the acceptable levels of CO2 and O2 and the source (if any) of breathable air.

ON2 suggests designing and equipping your chamber to keep the occupants alive for at least 48 hours and ON2 has redesigned their Refuge Systems to provide up to 96 Hours of breathable air.

Our Refuge One Air Centre is manufactured to field-testing standards. There are currently no CSA standards for this type of unit, so the unit itself is not CSA approved. However, the 120-volt charger is CSA approved, as are all other components in the unit.

ON2’s Refuge One Air Centre is designed to use a particular size of carbon dioxide absorbent to obtain maximum efficiency. Please CONTACT US for more information about the type of carbon dioxide absorbent we recommend.

5 years, from the date of manufacture which is stamped on both the Battery case and the Sodalime Keg.

The standard 14 ft. (4267mm) chamber accommodates 10 occupants; for every additional 2 ft in length, the chamber can hold another 2 people. The maximum number of people that an ON2 TommyKnocker can accommodate is 20.

The TommyKnocker (and the Refuge One Air Centre) require 120V AC and 60 Hz charger inputs and 12V DC outputs. The optional Air Conditioning unit is wired for 230V AC, with inverted battery power as backup. We can also supply 220V and 50 Hz units (other voltages and frequencies are available).

Refuge One Air Centre provides breathable air to both permanent refuge stations and mobile refuge chambers such as our ON2 TommyKnocker. The Air Centre scrubs the carbon dioxide from the internal chamber air and replenishes oxygen at a metered rate from the high pressure oxygen cylinders. The ON2 Refuge One Air Centre Sales Brochure explains the function, sizes and uses of the Air Centre and outlines all of the standard and optional equipment.

The Refuge One Air Centre works independently, regardless of the supply of external electricity and/or mine compressed air.

The TommyKnocker can be quoted with or without the Refuge One Air Centre.

Contact ON2 for more information and prices on these additional features available for the TommyKnocker:

  • Compressed air system
  • Carbon monoxide scrubber
  • Communication Centre
  • Portable gas monitor
  • Air conditioner
  • Entertainment unit