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Air Quality 

 
Author: Maurie Phifer (Montana Tech)

Revised: August 2012

Summary

Air quality management in both surface and underground mines is the focus of this review. Air quality is an issue at every mine and is something that must be monitored and controlled. This review will cover the pertinent regulations regarding air quality in both metal and nonmetal surface and underground mines, technical papers on this subject, consultants and suppliers related to air quality, and the types of software that are used in industry to monitor air quality. This review will also cover the TLV's (threshold limit values) that have been set for various gases that are encountered in underground mines.

INTRODUCTION

Air quality management in mining is a complex task, mainly due to the wide range of source types, the fact that most are diffuse and highly variable in nature, difficult to measure, and site-specific in terms of silt and moisture contents. Air quality management issues related to mining are mainly centered around particulate impacts. Dust is a major concern for surface mines, and many surface mines employ a variety of techniques to combat and manage dust. Measurements play a vital role in assuring the quality of workplace air. Tailpipe measurements allow diagnosis and correction of engine emissions; workplace contaminant measurements are made to ensure that ventilation is adequate or help determine the problem if it isn't. Contaminant concentrations in the workplace air are the result of three components:

  • Contaminant concentrations of the air source
  • Tailpipe emissions of the equipment in that area
  • The local air quantity and distribution

Whether a surface or underground mine, dust and other particulates are a constant hazard for those working in the mining industry. Dust and other particulates cause a wide range of damage to the lungs. If the dust settles in the nose, it may lead to rhinitis, an inflammation of the mucous membrane. If the particle attacks the larger air passages, inflammation of the trachea (tracheitis) or the bronchi (bronchitis) may be seen. The size and heaviness of the particulates that enter the lungs is important because large, heavy particles settle more rapidly. Some substances, when in particle form, can destroy the cilia that the lungs use to remove the particles. When some particles dissolve in the bloodstream, they are carried by the blood around the body, where they may affect the brain, kidneys, and other organs.

Below are some of the regulations around air quality management both in Canada and the US. A threshold limit value is defined as a time-weighted average concentration of an air pollutant at the workplace for a conventional 8-hour workday and a 40-hour workweek, to which nearly all workers may be repeatedly exposed without adverse health effects.

REGULATIONS

SURFACE MINES

The regulations regarding surface mines differ from coal surface mines to metal surface mines. Both types of regulations will be covered in this review. The industry has long been aware of the danger of coal dust to individuals' health and there is extensive literature covering the hazards of coal dust and methods to prevent or inhibit dust and other contaminants. Mines are not static and have continually changing footprints, and environmental factors such as temperature, weather, and humidity compound emissions uncertainty. For both coal and metal surface mines in the US, MSHA (Mine Safety and Health Administration) limits the exposure of airborne contaminants to the threshold limit values adopted by the American Conference of Governmental Industrial Hygienists. These TLV's are set forth and explained in the 1973 publication "TLV's Threshold Limit Values for Chemical Substances in Workroom Air Adopted by ACGIH for 1973," and can be found by writing to the Conference or at http://www.acgih.org/.

In addition to these TLV's, MSHA has additional regulations for surface coal mines. Since methane is a major concern in every coal mine, surface coal mines must do additional testing to ensure that the methane content in the air must be less than 1.0 volume per centum.


UNDERGROUND MINES

Air quality is an even greater concern in underground mines, especially coal mines. For all underground mines, the air quality must have a minimum oxygen content of 19.5% and a maximum CO2 content of 0.5%. As well MSHA regulates that the following gases cannot be permitted to accumulate in excess of the concentrations below:

  • Carbon Monoxide (CO) - 2.5%
  • Hydrogen (H) - .8%
  • Hydrogen Sulfide (H2S) - .8%
  • Acetylene (C2H2) - .4%
  • Propane (C3H8) - .4%
  • Sulfur Dioxide (S02) - 5 ppm
  • Methane (CH4) - 1.0%

In Canada, the regulations for underground and surface mines fall under the Occupational Health and Safety Act. Each province has a ministry set up that is responsible for monitoring mines and ensuring compliance of the rules regarding air quality. In BC, mines fall under the jurisdiction of the Ministry of Energy and Mines, and mine inspections for acceptable air quality conditions are conducted through this office. The Mines Act states that dust or other airborne contaminants must "be removed by suitable means such as vacuuming, wet sweeping, or wet shoveling, or be suppressed." The TLV's for airborne concentrations of chemical agents are set to the same levels as adopted by the previously mentioned American Conference of Governmental Industrial Hygienists. The Department of Justice has additional regulations regarding ventilation and levels of respirable dust for underground coal mines.

AIR QUALITY PERMITS

Mining companies must apply for air quality permits before operations can commence. The permits are based on federal, state, and local laws and regulations. The federal Environmental Protection Agency, the Department of Ecology (Ecology), and local clean air agencies, all regulate air quality. Here is an example of the Rosemont Copper Mine's mine air quality permit application.


MONITORING EQUIPMENT

Air monitoring instruments detect and monitor a variety of gases, chemicals, and particulates in ambient air. Ambient air monitoring equipment includes photoionization detectors (PIDs), flame ionization detectors (FIDs), single-gas meters, and multi-gas detectors. Air quality monitors can be hand-held or sensors that upload data in real time to a computer system that sets off alarms if concentrations of gases and/or dust rise to dangerous levels.

Some air sampling systems are worn by a worker during the work shift to determine exposure to ambient particulates, gases, or vapors. The pump draws a carefully controlled volume of air and airborne contaminants through collection media during the sampling period. The media is then sent to a laboratory for analysis resulting in an accurate and representative level of exposure. This is just one example of an air monitoring system. There are many different types of instruments available for use in the workplace and each mine must determine what contaminants they are measuring for and what device would work best in that environment.


SOFTWARE

An EPA website notes that the following are the most commonly used air quality models:

Dispersion Modeling - These models are typically used in the permitting process to estimate the concentration of pollutants at specified ground-level receptors surrounding an emissions source.

Photochemical Modeling - These models are typically used in regulatory or policy assessments to simulate the impacts from all sources by estimating pollutant concentrations and deposition of both inert and chemically reactive pollutants over large spatial scales.

Receptor Modeling - These models are observational techniques which use the chemical and physical characteristics of gases and particles measured at source and receptor to both identify the presence of and to quantify source contributions to receptor concentrations.

To list all the air quality related software out there would take pages. So I note only that the Breeze site provides a good overview. But see also see Scientific Software Group; MPAssociates; Agilaire; and the California Air Resources Board.


CONSULTANTS

The InfoMine Consultants database lists several consultants ready to assist you with air quality issue at your mine. Services range from site characterizations, through modeling, site measurement, laboratory testing, emission control equipment, and regulatory compliance.

Broadbent and Associates Inc. is one company that provides a wide array of air quality services to the mining industry and other industries. Their website states that, "BAI can assist owners and operators with all air quality permitting requirements whether constructing a new industrial facility, modifying existing equipment, or altering operating practices. BAI has experience with permitting programs and associated technical requirements such as control technology evaluations, emissions quantification, emissions trading, air quality analysis (including regulatory dispersion modeling), permit negotiations, and compliance determination methodology development." In addition to the permitting process, BAI provides emissions testing services and continuous monitoring and measurement of CO2, NO2, NO, SO2, CO.

Altus Environmental is another company that provides consultation to mining operations. Some of the air quality services that Altus offers are:
  • Feasibility and planning analyses
  • Regulatory and permitting evaluations
  • Source and emissions inventories
  • Control technology evaluations
  • Air impact analyses

TECHNICAL PAPERS

There are many papers and theses in the InfoMine library on air quality at surface mines. Some of the best are:


SUPPLIERS

The InfoMine Suppliers database uses the category Air Pollution Control Services. Sixteen suppliers of equipment are listed. Also try the category Dust & Fume Control which is subdivided into subcategories (1) Equipment; and (2)Reagents.

Many mines use American Ecotech technology to monitor the air and environment around the mine. Their website states "From remote, single ambient analyzers to complex industrial CEMs monitoring systems, American Ecotech can provide the right system for your project. All of our systems incorporate energy efficient designs, reducing operating costs and ensuring a lower carbon footprint."


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