Mining Contract: Extending and Monitoring the Scrubber Performance in Escape and Rescue Mining Rebreathers
In the event of a mining emergency, SCSRs are used for escaping from an underground mine and long duration CCBAs are used in mine search, rescue and recovery operations. Carbon dioxide chemical absorbents, oxygen-generating chemicals through carbon dioxide absorption, and pure oxygen in a chemical or gaseous form are the consumables used in such re-breathing apparatus. The performance efficiency of such apparatus can be optimized by monitoring and/or controlling these consumables.
Contract Status & Impact
In the event of a mining emergency, Self-Contained Self-Rescuers (SCSR) are used for escaping from an underground mine and long duration Closed-Circuit Breathing Apparatus (CCBA) are used in mine search, rescue and recovery operations. Carbon dioxide chemical absorbents, oxygen generating chemicals through carbon dioxide absorption, and pure oxygen in a chemical or gaseous form are the consumables used in such re-breathing apparatus. The performance efficiency of such apparatus can be optimized by monitoring and/or controlling these consumables.
At present, there are no End-of-Service Life Indicator (ELSI) for the carbon dioxide absorber nor the oxygen generating chemicals. The user knows that the apparatus is at the end of its operational duration only when the oxygen supply is depleted. Therefore manufacturers tend to oversize the carbon dioxide absorber in apparatus design without utilizing the full capacity of these absorbents. On-line monitoring of the carbon dioxide chemical bed will allow the apparatus to be designed more efficiently in terms of size, weight and duration.
It is envisaged that in the future electronic gas monitoring and/or electronic control of the oxygen delivery may be necessary to improve the efficiency of mine escape and rescue rebreathers. The oxygen sensor would be a key element in such electronic monitoring and control systems. Determination of the most optimum oxygen sensor/sensors is necessary for use with these electronic systems.
II. SCOPE of WORK
Test three off-the-shelf rebreathers with compressed O2 supply for actual CO2 scrubber endurance times. Test at two temperatures and with two workloads. Find the three best absorbents from five to seven candidate CO2 absorbents.
Test the three rebreathers with the three best absorbents at three temperatures and with three workloads. Expand testing to include two rebreathers with chemically released O2. Each of the five rebreathers will have its CO2 scrubber instrumented for temperature at several sites. From these temperature recordings, develop an algorithm that will determine remaining CO2 absorbency . For one of these rebreathers, build a prototype and demonstrate its function in a manned demonstration test.
Determine available and emerging technologies for O2 sensing, specifically suitable for respiratory protective devices in mine applications.
II.1 Test parameters for absorbent testing
CO2 absorbent candidates
After discussions with the sponsor, six candidates were listed: granular LiOH, Micropore LiOH (sheets), Sofnolime 4-8 (course grain), Sofnolime 8-12 (fine grain), HP Sodasorb 4-8 and DrägerSorb 400. There may be other candidates as well, such as hospital grade absorbents. Six to seven candidate absorbents will be selected and tested.
Range of temperatures
Many mines have temperatures around 15 °C (60 °F) year round. However, should the apparatus be stored close to an air intake or an opening then the temperature may be closer to outside temperatures, such as close to freezing or summer temperatures, say 5 and 30 °C (38 and 86 °F). Three candidate temperatures.
Range of wearer workload
Scrubber endurance will be determined at workloads that may be experienced: from rest to a workload that can be sustained for the expected apparatus duration. The workload will follow those defined in the new rule 42 CFR part 84 Sub-part O which came into effect on April 9th 2012. Specifically, "Cap 1" and "Cap 3" in its Table 2 will apply to these tests, i.e. minute ventilations of 55 and 30 L/min.
It could also be argued that testing at higher workloads would be prudent to determine how an apparatus would tolerate such workloads. Since the apparatus will be severely stressed, such tests would be short, say testing at 105 L/min. Three candidate workloads.
The sponsor has recommended testing the following five rebreathers:
Biomarine Biopack 240 (multi-hour duration with O2 bottle)
Dräger BG4 (multi-hour duration with O2 bottle)
Ocenco EBA 6.5 (one-hour duration with O2 bottle)
Dräger Oxy K plus (one-hour duration with chemically released O2)
CSE SRLD (one-hour duration with chemically released O2).
Motivation for the limited, initial set of tests
Testing the three rebreathers with compressed O2 supply with every candidate absorbent at every workload and at every temperature would require (6 to 7) * 3 * 3 = 54 to 63 tests per rebreather, i.e. a total of 162 to 189 tests. With an average of 2 tests per day it would take 81 to 95 test days to complete such tests.
In a more realistic, reduced set of tests, the worst performing absorbents for each rebreather can be found and removed from further testing: tests at two temperatures and two workloads per rebreather. Thus, the number of tests would be (6 to 7) * 2 * 2 = 24 to 28 tests per rebreather, i.e. 72 to 84 tests (36 to 42 test days).
II.2 Equipment required
Breathing simulator which exhales temperature controlled, humidified gas enriched with CO2. Gas removal to simulate O2 consumption.
Temperature controlled environment.
Recording system of temperatures inside the scrubber.