Mark J. Schultz, P.E.

Chief, Environmental Assessment and Contaminant Control Branch

Dust Division

Mine Safety and Health Administration

Pittsburgh Safety and Health Technology Center

Pittsburgh, Pennsylvania, USA

“Field Group”

Health Effects of Utilizing Belt Air in Underground Coal Mines

• Effects on Dust Concentrations when utilizing belt air to ventilate the working face.

Current Standard

• 71.100 – Each operator shall continuously maintain the average concentration of respirable dust in the mine atmosphere during each shift to which each miner in the active workings is exposed at or below 2.0 mg/m3 of respirable dust.

Mine Ventilation is used to Dilute and Render Harmless

• All Noxious Gases

• Dusts!!!!

Dust Concentrations are Inversely Proportional to Air Quantity

Double the Air Quantity, Concentration is Cut in Half!!!

N X Air Quantity = 1/N Concentration

• N=2• 2 Quantity = ½ Concentration

Dilution is a very powerful tool used in Dust Control!

Background History

• Early 1990’s, Robert Haney gave a presentation to the belt air advisory committee on the same topic.

• He issued a paper titled “Effect of Belt Air On Dust Levels In Underground Coal Mines”

In this paper, Mr. Haney states that the Belt Air Advisory

Committee concluded that the use of belt air could increase or decrease dust levels; however, the change would not have a

significant impact on face worker dust exposures.

The committee further recommended that a designated

area with a 1.0 mg/m3 standard be established when belt air is used to

ventilate the face.

• This designated area would be in the belt entry just outby the section tailpiece

This designated area would enforce the same intake standard

mandated in 70.100(b)

• 70.100(b) Each operator shall continuously maintain the average concentration of respirable dust within 200 feet outby the working faces of each section in the intake airways at or below 1.0 mg/m3 ….

• Belt tailpieces are generally located more than 200 feet outby the working face.

Advisory Committee Addressed 3 Specific Health Related Concerns

• The effect on intake dust levels when belt air is used at the face;

• The effect on worker exposure when belt air is used at the face; and,

• The potential entrainment of dust in the belt entry.

SIP Spot Inspection Program

• From August thru September, 1991, MSHA conducted the SIP Program

• Purpose of the SIP was to assess actual dust levels and the extent of dust controls in the coal mining industry.

• What Effect does Belt Air have on Intake Dust levels when Belt Air is Used to Ventilate the Face?

Results of the SIP When Utilizing Belt Air

• Intake dust concentrations– Intake dust concentrations were 0.18 mg/m3

higher on continuous miner sections when using belt air to ventilate the faces

– Intake dust concentrations were 0.12 mg/m3 higher on longwall sections when using belt air to ventilate the faces

Longwall Intake Dust Concentrations(6 Longwalls surveyed)

all used belt air to ventilate the face

• Intake Dust concentrations ranged from 0.1 to 0.4 mg/m3

• Belt Intake Air concentrations ranged from 0.4 to 1.2 mg/m3

• Combined Intake concentrations ranged form 0.1 to 0.5 mg/m3

• Belt Air contributed 0.1 to 0.3 mg/m3 to face dust levels.– Belt Air Quantities were significantly lower than

Intake Entry Air Quantities

Longwall Face Dust Concentrations Sources

6 mines surveyed

• Intake Air 0.1 to 0.4 mg/m3

• Belt Air 0.1 to 0.3 mg/m3

• Combined Intake 0.1 to 0.5 mg/m3

• Crusher/Stageloader 0.5 to 1.3 mg/m3

• Face Contributions 1.8 to 11.3 mg/m3

– Committee’s conclusion – belt air was not a significant dust source on the longwall compared to other face dust sources

Recent NIOSH PublicationDust Control on Longwalls –

assessment of the state-of-the-artJ.P. Rider & J.F. Colinett

• Studied 8 longwalls– 4 used belt air as intake air and 4 ventilated

belt air to the return

Results

• Survey Results showed– Intake Belt Air Intake 0.18 mg/m3

Belt 0.40 mg/m3

- Return Belt Air Highest 0.34 mg/m3

Most below 0.20 mg/m3

• Paper concluded – “Although the average dust levels in the belt entry are relatively low, the belt entry has the potential to add to face dust levels. However, according to past research studies (Potts and Jankowski, 1992) potential increases in face dust levels seemed to be negated by the potential for increased dilution with the additional air reaching the face.’

Effect on Worker Dust Exposure when Belt Air is used to Ventilate

the Face• SIP - Designated Occupations

– Designated occupation dust concentration on continuous miner sections were 0.64 mg/m3 lower.

– Designated occupation dust concentrations on longwall sections were 0.33 mg/m3 lower.

• Although the intake dust concentrations increased when using belt air to ventilate the faces, the additional air helped to dilute the Designated Operator’s dust exposures!

Entrainment and Reentrainment of Dust in Belt Entries

• Entrainment of dust occurs during the cutting, crushing and breaking of material.

• Reentrainment occurs when dust that has initially been suspended settles and then becomes airborne dust again.

• Longwall belt was chosen to look at this because it represents a worse case scenario. – Higher tonnages and higher belt speeds!

Entrainment/ Reentrainment StudySIP - 2 longwall belts studied

• Looked at inby and outby dust concentrations along a belt line

• Belts were approximately 2000 feet long

• Relative velocities of 750 to 940 ft/min– Belt speed (825 fpm) added to air velocities

(127-317 fpm)

Results Concluded

• 0.1 to 0.2 mg/m3 increase in dust • Outby dust sources were much higher

contributors to dust 0.8 to 1.0 mg/m3

– Belt Transfer

Studies indicated that belt air dust sources were primarily due to outby transfer points

Reentrainment was not significant dust source

Advisory Summary

• The use of belt air will generally cause the combined intake dust level to increase. If the belt air concentration is greater than the intake air concentration, the combined intake will increase. This increase , however, should not have a significant impact on a mine’s ability to meet the 1.0 mg/m3 dust standard.

Advisory Summary - continued

• The use of belt air could increase or decrease the exposure at the face depending on the specific section's dust control and ventilation configuration. Any increase would not exceed the increase in the combined intake dust concentration.

Advisory Summary - continued

• The air velocities that will result when belt air is used to ventilate the face will typically not be high enough to cause entrainment of dust in the belt entry. Additionally, the removal of box checks would remove restrictions that cause localized high velocities. This should reduce the amount of dust entrainment taking place in the belt entry.

Advisory Summary - continued

• If increased entry velocity is caused by restriction, dust levels as a result of entrainment can increase. If increased entry velocity results from an increase in air quantity, dilution compensates for entrainment and dust levels will not significantly change. The added air flow could then provide additional dilution of dust generated in the face area.

Any Changes since these Summaries?

• Higher Tonnages– Belt are hauling more coal

• Belt Speeds have increased

• Belt Lines are longer

• Higher Air Quantities in belts– Increased panel lengths – Controlling methane

Recent Field Experience

• Field group looks mostly at mines experiencing dust problems– Most of the mines have experienced repeated

non-complinace

• 22 mines have reports– 2 mines used belt air at the face

• (1 LW & 1CM)

Results

• Mines that do not use belt air (20 Mines)– Avg. DO Conc. 1.08 mg/m3

– Avg. Intake Conc. 0.08 mg/m3

Results – Using Belt AirMines using Belt Air (2 Mines)

• 1 Longwall – LW DO Conc. 1.92 mg/m3

– LW Intake Conc. 0.03 mg/m3

– LW Belt Conc. 0.14 mg/m3

– LW Combined Intake 0.06 mg/m3

• 1 CM Section (Reverse Scrubber)– CM DO Conc. 1.31 mg/m3

– CM Intake Conc. 0.63 mg/m3

– CM Belt Conc. 0.65 mg/m3

– CM Combined Intake 0.63 mg/m3

SummaryAgree with Previous Advisory’s

Findings• Belt dust control technologies exist that

can control and reduce dust concentrations in belt entries

• Additional air to a working face can help to dilute dust that is generated and to lower personal dust exposures

• Designated Area helps to assure belt line dust concentrations are controlled