Page 341 - Advanced Mine Ventilation

318 Advanced Mine Ventilation

Exposure to excessive concentrations of radon and radon daughters has been linked
with a high incidence of lung cancer. The maximum exposure limit for radon daughters
has been set at 1.0 working level (WL), with a yearly cumulative exposure of 4 work-
ing level months (WLM). A working level is defined as that concentration of short-
5
lived radon daughter products in a liter of air that will yield 1.3 10 million electron
volts of alpha energy in decaying through radium C’. WLM is a cumulative measure of
exposure that is calculated by multiplying the average WL of exposure during a given
timed period by the time of exposure and dividing by 173 (the number of working level
hours per WLM) [4].
An example calculation is as follows:
Given the following exposures during a shift:

4 h 0.4 WL
2 h 0.2 WL
2 h 0.1 WL

Find the WLMs of exposure.
Solution:

4 0:4 þ 2 0:2 þ 2 0:1
Average WL ¼
8
¼ 0:275 WL

WLM ¼ð0:275 WLÞð8hÞ=ð173Þ
¼ 0:013 WLM

19.2 Monitoring of Mine Gas

In the United States, CO monitoring in the belt entry is required by law for fire detection.
This was the beginning of mine monitoring. It slowly developed into atmospheric moni-
toring system (AMS). While the CO-monitoring system monitors only CO concentra-
tions in strategic locations, the AMS monitors many other parameters and locations.
Parameters that are monitored comprise CO, CH 4 ,O 2 ,NO, H 2 concentrations, smoke,
air velocity, and air temperature. The locations that are monitored comprise mine airway,
battery charging station, fans, fan houses, electric equipment, pumps, and coal storage.
A monitoring system, as defined by the Mine Safety and Health Administration, is a
network of hardware and software meeting the requirements of 30CFR 75.301 and
capable of performing the following functions:

1. Measure the required atmospheric parameters.
2. Transmit the data to a surface location.
3. Provide alert and alarm signals.
4. Process and store measured data.
5. Create reports by analyzing the data.