MINEARC TECH TOPIC: FIRE PROTECTION
This MineARC Tech Topic explains what fire rated materials are used to construct passive fire rated MineARC refuge chambers.
Did you know? MineARC refuge chambers are designed for a minimum duration of 36 hours. This is the burn time of the rubber tyres and fuel load of a large mining vehicle.
Fire dangers exist in underground mining and tunnelling operations. The current MineARC refuge chambers are designed for a minimum duration of uninterruptible power supply (UPS) and breathing contaminant scrubbing of 36 hours. This figure is based on the burn time of the rubber tyres and fuel load of a large mining vehicle. These types of fires are accepted examples of mining operation risks.
The heat transfer properties of these fires into refuge chambers in underground mines depends greatly on the position of both the fire and the chamber. It is difficult to give a fire rating to a chamber due to the changing environment of its position and the mobile nature of the fire risk. Refuge chambers are therefore currently designed to protect against breathing contaminants and lack of oxygen, but not excessive heat load over a long duration.
The positioning of a chamber is very important. A standard MineARC Refuge Chamber (Standard Design or Compact Design) will not be able to sustain life within the chamber if ambient conditions exceed 47°C. Calculations on how the chambers are position depend almost solely on the ambient conditions. Upgrades for higher ambient conditions are available.
MineARC are unable to produce a guideline for positioning distance of chambers as the heat loads on it would be incredibly difficult to establish. Current recommendations from the Department of Mines and Petroleum are that chambers must be within 750m any underground personnel (1500m apart). Distances of this nature would likely produce conditions favourable for refuge chamber positioning.
MineARC has constructed a number of passive fire rated refuge chambers where insulation and protection against fires of short duration and high intensity were used.
MineARC can provide a passive insulated chamber that is:
A key consideration is heat removal from the chamber’s occupied space. A refuge chamber can become uninhabitable without the use of an air conditioner to protect from the latent heat and humidity protected by insulation, the exterior condenser of the air conditioner can be exposed to extreme heat, causing it to fail.
MineARC’s current passive protection for this includes insulated shielding at the rear of the chamber including the UPS cabinet which houses the batteries required to power the refuge chamber’s life support systems (scrubbing units, air conditioning and lighting), in the event of a loss of mains power. The battery cabinet doors also include intumescent grill blocks that allow ventilation of the cabinet. These blocks expand to shut when exposed to elevated temperatures and a fire’s naked flame, forming an incombustible barrier to the spread of fire and hot smoke.
Battery Box and Air Conditioner Compartment Protection.
To comply with all the current refuge chamber guidelines, the chamber also must include a portal window as well as a secondary means of egress (an escape hatch). The passive protection solutions for these includes a portal window cover and an external opening “kick out” escape hatch that is able to be caulk-filled and insulated. The internal occupied space of a passive fire rated chamber is almost identical to a standard MineARC refuge chamber.
Reviewing the curve, it is clear that while passive protection can be developed for the occupied space, the current air conditioning system, which is rated to an external temperature of 50 degrees, will need to be suspended for much of the fire duration. As such alternative cooling would be required to meet the curve above.
MineARC also have misting systems that emit water vapour into the surrounding atmosphere. This effectively reduces the ambient conditions and increases the ambient operating temperatures to as high as 60°C. Fire suppression devices have also been fitted to chambers in areas that are likely to experience some heat loading that can be extinguished from the chamber.
Secondary cooling methods are a critical component to meeting any tunnelling time/temperature curve. This ensures there is an ability to continue to cool the occupied space when the primary air conditioning is suspended.
Currently MineARC are able to provide a MARCiS liquid carbon dioxide (CO2) cooling as a secondary cooling method. However, the CO2 bottles are required to be kept below 40 degrees within an insulated section of the chamber. This part of the chamber is cooled by the air conditioner during its operation, and once the MARCiS is activated the bottles cool their own insulated room. The exhaust gas, CO2, is then plumbed to the battery cabinet and air conditioner bay to eliminate the oxygen and reduce the risk of fire spread. This cooling method however is large, and at times impractical. Thermal storage methods and continued research and development into secondary intrinsically safe cooling continue at MineARC.
Did you know? The exact level of protection from a potential threat such as a fire, the positioning of the refuge chambers, and the possible methods that could be utilised for operating in higher ambient conditions are all factors being continually developed at MineARC.
For further information regarding MineARC’s range of Refuge Chambers, please email firstname.lastname@example.org to speak to a MineARC representative.