What are the fundamental differences between free pour and cartridge chemical scrubbing for refuge chambers?

This MineARC Tech Topic explains the importance of equal and even pressure to the efficiency of chemical reaction to ensure the performance characteristics of the refuge chamber are optimised.

Chemical scrubbing is the process of removing undesired gases from the air using chemical reactions to change the composition of the gas to water and heat as they pass through the system.

Scrubbing systems work in conjunction with active chemicals to ‘scrub’ the build-up of harmful gases such as carbon monoxide (CO) and carbon dioxide (CO2) from the air inside the refuge chamber. During entrapment, occupants consume oxygen and expire CO2 and CO as part of their normal respiration. CO can also enter the chamber during occupant entry and if the compressed air intake is compromised. CO2 can build up and poison the air causing a number of symptoms including visual and hearing dysfunction, unconsciousness and eventually, death. Removal of these harmful gases is therefore a vital necessity for any refuge chamber, especially if mains air fails or becomes compromised.

For more information on the colourless, odourless and deadly gasses, carbon monoxide and carbon dioxide, please view the MineARC Tech Topic: Carbon Monoxide & Carbon Dioxide article.

MineARC Scrubbing – The Past

MineARC originally utilised what is referred to as ‘Free Pour Chemicals’ to scrub the air of harmful gases. This consisted of three different chemical types that would be opened and poured into blue and white trays in varying quantities. This system was fitted as standard to all HRM Series I, II, and III Refuge Chambers.

The three types of free pour chemicals included a CO2 chemical often referred to as Medisorb, Sofnolime or Sodalime, a CO chemical often called Sofnocat, and a moisture removal chemical. Each refuge chamber required twelve 10kg tubs of moisture removal chemical, six 1kg tubs of CO chemical and depending on the occupancy, the following amount of 4.5kg CO2 chemical containers:
8-Person = 18
12-Person = 26
16-Person = 32
20-Person = 44

MineARC Scrubbing – The Present

The current MineARC Series IV and ELV/ELVP Scrubbing Systems use pre-packaged MARCISORB chemical absorber cartridges, an improved alternative to the traditional free pour chemicals found in earlier scrubbing system models.

MineARC’s MARCISORB CO2 and MARCISORB CO cartridges provide superior scrubbing capacity, are easy to load, safe to handle, and can store for long periods. The use of chemical cartridges also translates to noticeable cost savings over the life of the chamber when compared to free pour methods. Each refuge chamber requires just one 15kg MARCISORB CO chemical cartridge and the following quantities of 15kg MARCISORB CO2 cartridges:
8-Person = 8
12-Person = 10
16-Person = 14
20-Person = 16

The Science

All MineARC scrubbing equipment including plenum trays, are designed so that pressure and flow is evenly distributed throughout the scrubbing material to ensure the performance characteristics of the chemical are optimised. This allows for a standard duration of 36 hours (required by the 2013 WA DMP Guidelines: Refuge Chambers in Underground Mines) and any variant of these characteristics will result in a shortened duration.

Equal and even pressure will result in an efficient rate of chemical reaction. If there are high pressure pockets in the plenum tray or defects in the chemical bed, the chemical will ‘channel’. This is where the airflow follows the path of least resistance and will drastically reduce the efficiency and effectiveness of the material, ultimately reducing duration. In some cases this reduction can be as high as 60% (14.4 hours).

The scrubbing material itself is also very important. It’s size and shape create a packing density matrix that requires a specific flow and pressure differential to ensure it is effective. Variants of this density will impact the efficiency and ultimate duration of this breathing source. Any changes to the chemical or the equipment would require calculations to ensure, as a life support system, it is able to remove CO2 and CO in the chamber over the full duration of entrapment.

Non-MineARC chemical is usually a different shape, most commonly a diver-grade spherical granule. MineARC’s material is a crushed triangle that has a greater efficiency and allows for more material to be stored within the same volume. This tightly packed volume then requires a specific pressure and flow to achieve the appropriate rate of reaction. Any variants in this will reduce efficiency and therefore duration. As you can see below a triangle granule allows more material to be consumed before exhaustion. The area of the triangle is less than the circle with the same wall thickness. Using the circular material immediately reduces the amount of chemical you have available to you in that volume, which means less duration.

Packed together, the circles have more space between them than the triangles. Triangular particles are packed down in a way that inhibits channelling – where air flows through gaps as a path of least resistance and doesn’t use the chemicals around it.

For more information on Scrubbing Systems, please view the MineARC Tech Topic: Scrubbing Systems article.

The Benefits of Chemical Cartridges

Less units of chemical required, more room in chamber

Unlike earlier free pour methods that require three separate chemicals, MARCISORB Chemical Cartridges feature an in built moisture removal capability. This means that the overall quantity of chemical required by the chamber is significantly reduced.

Less manual handling, no direct chemical handling

As less chemical quantities are required, there will be a reduced need of manual handling to transfer chemical to the scrubber trays. The cartridge chemical is contained in spill-proof and compact plastic cartridges, with no need for workers to come into direct contact with the chemical itself.

Less uncertainty, no room for user error

Reduced uncertainty with how much chemical should be used, with accurate chemical amounts efficiently distributed inside each of the pre-packaged cartridges.

Conformity across refuge chamber fleet

All of MineARC’s refuge chambers now come with MARCISORB cartridge chemical as standard. Using the one type of chemical scrubbing system assists in streamlined training and purchasing processes.

DID YOU KNOW? MineARC can upgrade all Series I, II and III free pour chemical refuge chambers to the pre-packaged MARCISORB Chemical Cartridges by using a ‘Plenum Tray’. A Plenum Tray is a pre-fabricated steel tray that acts as an adaptor on existing scrubber frames, converting the scrubber system from using free pour chemical, to using the more efficient cartridge chemical.

For further information regarding MineARC’s Scrubbing System and MARCISORB Chemical Cartridges, please email to speak to a MineARC representative.