The use of compressed air BA in mines is not exactly a new concept, the apparatus designed and manufactured by the Frenchmen Rouquerol and Denayrouze in 1870 relied on a single small compressed air cylinder (30 bar – 440psi, pressure), and simple demand valve that lasted around 15 minutes.
However, in order to get a reasonable duration with this type of equipment it was necessary until recently to carry cylinder (s) that weighed around 30 – 40 kg, quite impossible.
Around 10 years ago, with the advent of "carbon fibre composite cylinders", an apparatus with a duration of around 1 ½ hours weighs in at 15 – 18 kg., a lot more manageable.
So far, several countries have begun using CABA after trailing successfully, then amending current legislation that would normally only permit Closed Circuit (oxygen) BA.
Poland has now legislated to use CABA for any rescue or firefighting operations in mines, Australia’s coal mines are able to use it for what they term "self and aided" rescue, where single or twin cylinder CABA are kept below ground in the gate roads of longwall or pillar & stall workings, and the UK are closed to legislation permitting it also for general mines rescue & firefighting.
Fig 1
Member of a German mines rescue team in Drager PSS single cylinder (46 minute total) duration CABA (photo, Drager)
Advantages
There are many advantages in using CABA;
- Less initial cost per set, typically US$2000 – 3000 compared with US$5000 – 6000 for closed circuit sets.
- Less maintenance cost, air is cheaper to pump in, with no shipping in of O² storage cylinders
- No CO² absorbent cost
- Turn around time quicker, with only the facemask to disinfect
- Far less parts to wear out or change
- Cool breathing temperature
- Inside of visor does not suffer from misting up, no wiper required
- Duration can be extended underground with use of "quick-fill" from storage cylinders if required
- Ease and speed of donning and checking
- No dangers of O² ignition or enrichment
Disadvantages
Everything has to have its drawbacks;
- Maximum duration around 1½ hours
- This does depend on the wearers breathing rate, and not on a constant flow
- "Entrapped" procedure is impossible, only slowing the breathing down
- Wearer trials have shown little advantage over closed circuit sets in hot and humid atmospheres, even with the cooler temperature
- Slightly heavier than a closed circuit set, especially if compared with a similar duration.
For a great deal of operations then, especially ones limited to 1 hour or so, this type of equipment is ideal. Obviously, all of this has to be decided before hand, its no good going for a casualty rescue if the travel time in apparatus is 45 minutes each way.
At least most European manufacturers are offering twin cylinder CABA, or as they term it "Extended Duration CABA", and currently, the main trend is towards using twin cylinder configuration with 2 X 6.8ltr X 300 bar cylinders. This gives a theoretical air capacity of 3672 litres, and again a theoretical total duration of 92 minutes. Take off the allotted safety margin of 18 minutes (for a twin cylinder), this giving a working duration of some 74 minutes at the average breathing rate of 40 ltr/min.
Now we all know what happens when you walk faster, or have to carry a heavy casualty, your breathing rate increases! Therefore, it is important to keep an eye carefully on the pressure gauge and work out turn around times etc., using the "safety margin" exactly as it should be, as safety, and not part of the work time. Isn’t this what we have a team captain for?
fig 2
Here we can see the profile of the cylinders is certainly higher than a closed circuit set, but generally is not a problem. This application is by a rescue team in a long tunnel in the Republic of Ireland, using the Drager PA94 set (photo, B. Robinson)
Proof
In some recent research that was compiled for a project of mine, we came up with the following figures for a three-man team using the twin cylinder configuration sets.
- The shortest duration to whistle (safety margin point) was 58 minutes, the member had walked (briskly) some 5600 m.
- Next was after 72 minutes and 6600 m
- Final member was 75 minutes and 6900m
- This works out at a walking pace of 5.52 kph (3.43 mph) on level ground, carrying no casualty, but each person carrying an SCSR and caplamp battery on their belt.
Other research carried out in both Poland and Germany has shown that there is little, sometimes no benefit in wearing CABA versus Closed circuit BA in hot and humid atmospheres, depending on the temperature and humidity. This is partly due to the high oxygen concentration of a closed circuit set giving the wearer an advantage, and certainly the pulse rate is far higher using CABA in these conditions, generally the pulse frequency being 15 – 20 bpm. more with the CABA wearer (Auswahlkriterien fűrAtemschutzgeräte , Antekeuer, Lottner, Maldener & Roder, 1999)
fig 3. 2 members of the mines rescue team from Bytom, Poland using the Faser APS4080 to great effect during an underground coal mine roadway fire. (photo, Zygmunt Goldstein)
Conclusions
So there you have it, a brief overview of current world trends with regards to CABA use in mines rescue, now its up to you to decide if it has good application in your type of operation. Certainly, for a small (geographic distance) operation this is ideal, and keeps costs down, maybe allowing the funds to be spent on other beneficial equipment for your teams. In Australia, Britain and Poland however, it is being used as a supplement to closed circuit sets, not a replacement.
Brian Robinson, August 02’
Mines rescue consultant,
Great Britain
Email: Rescue1UK@aol.com