MINEARC TECH TOPIC: AIR TIGHT ENVIRONMENTS
This MineARC Tech Topic explains the importance, components and procedures necessary to ensure refuge chambers maintain an air tight environment.
The primary control over the internal environment of a refuge chamber to ensure it can preserve life is that it is hermetically sealed, or air tight.
In the harsh environments of heavy industry, refuge chambers provide workers with the confidence that in the event of an emergency taking refuge inside a chamber will keep them protected and alive. It is essential that a refuge chamber is air tight in order to control the internal environment and maintain a habitable atmosphere by preventing contaminants, noxious fumes and other undesirable substances from entering the occupied chamber and poisoning the breathable air. A number of critical high-quality components and processes guarantee a chamber’s air tightness.
For more information on the standards of breathable air, please view the MineARC Tech Topic: Breathable Air article.
Not only is it the largest opening, but the door seal will face the most wear and tear of any sealing surface of the chamber. Every time the door is opened and closed the seal will expand and compress. The seal is further mechanically compressed when the door handles are engaged. This ensures a seal under both positive and negative pressure.
In addition to this, parts of the door seal are exposed to the harsh external environment of the mine. They are exposed to accidental damage on entering the chamber, floor rocks, mud and water build up resulting in corrosion, wear and tear, and aging of the rubber, leading to an imperfect seal.
As it is a critical spare part and a high-use perishable consumable of the chamber, door seals are replaced every four months during a service.
Check valves are one-way valves that play an integral role in the safety of the refuge chamber. As compressed air is added to the refuge chamber, a means for this air to escape to avoid over pressurisation is required. These openings also need to re-close automatically when the internal chamber pressure is back equal to, or lower than the external pressure to maintain a sealed air environment within the chamber.
Like door seals, all check valves require changing every four months. Corrosion in humid and salty underground environments occurs frequently, potentially damaging check valves and their moving parts, and rendering them inoperable; compromising the overall safety of the refuge chamber.
For more information on positive pressure, please view the MineARC Tech Topic: Internal Positive Pressure article.
For more information on temperature control and air conditioning, please view the MineARC Tech Topic: Temperature Control article.
In order for refuge chambers to maintain positive pressure and prevent the ingress of gas, smoke, fumes and other airborne contaminants, it is necessary that the door seal, check valves, compression glands, emergency hatch seals and any other leak points remain air tight. To ensure and confirm the integrity of these components and their ability to maintain an air tight internal environment, a field vacuum test is performed.
To perform a vacuum test, mine air is turned off, the chamber door closed and the air inside the refuge chamber is heated. This causes the chamber to expand, and some air will bleed out through the check valves. The air conditioning is then turned to cool. Cooling the internal air causes the chamber to contract. This allows a vacuum to form inside the refuge chamber. This vacuum can be quite strong; preventing the chamber door from opening. Any leaks would be easily audible and are therefore easily located.
A vacuum test is performed on every refuge chamber during manufacture, and should also be performed as part of every four monthly chamber service and regular inspections.
Genuine Parts & Servicing
The vital importance of the aforementioned refuge chamber components should not be understated. In order to ensure the integrity of the refuge chamber, conducting regular vacuum tests is imperative. For a refuge chamber to function optimally, and as part of essential preventative maintenance to guarantee their efficacy in an emergency situation, MineARC recommends a comprehensive service be undertaken every four months.
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