Page 102 - Advances In Productive, Safe, and Responsible Coal Mining

86 Advances in Productive, Safe, and Responsible Coal Mining

for metal and nonmetal mines and most other countries have similar requirements.
Limits in the parts per million (ppm) range are established for most toxic gases,
including carbon monoxide (CO), nitrous oxides (NO and NO 2 , which are both com-
monly referred to as NO x ), hydrogen sulfide (H 2 S), and sulfuric oxides (SO 2 and SO 3 ).
In the US, limits for these gases are typically established by the National Institute for
Occupational Safety and Health (NIOSH) and the American Council of Government
Industrial Hygienists (ACGIH). Many countries have their own standards, while
others accept and incorporate US or European limits.
For flammable and explosive gases, such as methane (CH 4 ), the limit is typically
1.0% or about 20% of the lower explosibility limit (LEL). Some countries permit a
limit at 1.5% CH 4 . In the US, exemptions may be granted up to 1.5% in certain return
airways per 30 CFR §75.321(d), if additional precautions, including a minimum air-
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flow quantity of 12.7m /s (27,000cfm) and atmospheric monitoring systems (AMS)
with audible and visible alarms, are in place. In bleeder airways, up to 2.0% CH 4 is
permitted per 30 CFR §75.321(e).
The average respirable mine dust concentration in US coal mines must not exceed
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1.5mg/m (per 30 CFR §70.100, as of August 1, 2016). Dust concentrations beyond
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60m (200ft) outby the working face are limited to 0.5mg/m . Stricter requirements
are provided if the mine dust contains quartz. Monitoring for dust, diesel particulate
matter (DPM), and exposure to radioactive substances is conducted at regular inter-
vals both by the mine operator and by government inspectors. For DPM, the personal
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exposure limit (PEL) for US metal and nonmetal mines is 160μg/m total carbon (TC)
per 30 CFR §57.5060, while an equivalent rule does not exist for coal mines.
Quantity and quality of mine air are typically monitored by ventilation engineers
and technicians, mine foremen, equipment operators, mechanics, and certified mine
examiners. Unless preparing for special work, mine examiners test air quality and
quantity at regular intervals ranging, in the US, between 20min in face areas to daily
or weekly in more remote airways. Unlike other countries, the US has no general
requirement for installing AMS or other methods to continuously monitor air quality
or quantity in key areas of mines. Technologies exist for such, from online air quality
monitoring for single or multiple gases, air quantities, and oxygen deficiency; to sim-
ple, passive gas sampling tube bundle systems that continuously draw air quality
samples from multiple locations throughout the mine to be analyzed with online appa-
ratus at the surface.

6.4 Ventilation of continuous miner faces and sections
in coal mines

In the US, underground coal mining is frequently carried out using the room-and-pillar
mining method where coal is cut and loaded with a continuous miner. Longwall gate
road development in US and Australian coal mines is also done with continuous
miners, cutting two to four parallel roadways separated by pillars. European mines
use road headers cutting single-entry gate roads with large, arched cross sections
and standing support while continuous miner headings are primarily supported with
roof bolts.