Laboratory results of foam application testing for longwall shield dust control in a simulated environment

There were 37 longwall faces operating in mines in the United States in 2019.The average panel width for these longwalls was approximately 368.5 m(1209 ft).This translates to a range of approximately 170-240 shields per longwall,depending upon the width of shield.The movement of longwall shields is a significant contributor to respirable dust overexposures to longwall operators.Foam is expected to have the potential to reduce this shield dust generation.The foam is applied to the area on the roof between the coal face and the shield tip after the shearer passes.In this study,the longwall shield dust simulator was used to test three foam agents for their ability to control dust from longwall shield movements.Results showed that at low-velocity ventilation(≈3.0 m/s(600 fpm))all foam agents were able to produce dust reduction levels of at least 45%.At high-velocity ventilation(≈5.1 m/s(1000 fpm)),the reductions were lower and more variable,ranging from being undeterminable for one foam agent to having 46%-63%reductions for the other two foam agents,with one instance of an increase in dust concentration.Overall,the use of foam agents can provide longwall shield dust control.Important factors are roof coverage and the ability of foam to remain on the roof for extended time periods.

Retinal nerve fiber layer thickness and retinal vascular caliber alterations in coal miners in northern China:a community-based observational study

AIM:To evaluate retinal nerve fiber layer thickness and retinal vascular caliber alterations in coal mine workers.METHODS:The community-based observational crosssectional study included 4004 participants of a subpopulation of the Kailuan Study.All the study participants underwent structured interviews with a standardized questionnaire,fundus photography and spectral-domain optical coherence tomography(OCT)examinations performed by trained doctors.RESULTS:The retinal nerve fiber layer thickness was significantly higher(P=0.006)and the central macular thickness was lower in coal miners(n=659,51.0±7.8 y)as compared to the control(working above the ground;n=477,51.8±7.5 y;P=0.032).Additionally,the downhole workers showed a significantly thicker retinal artery(P=0.012)and vein diameters(P<0.001).In multivariable regression,a thicker retinal nerve fiber layer was associated with a higher cumulative silica dust exposure(P=0.005)after adjusting for younger age and larger spherical equivalent.In a reverse pattern,a higher cumulative silica dust exposure(P=0.004)was significantly associated with a thicker retinal nerve fiber layer after adjusting for age,high-density lipoproteins and uric acid.Wider retinal vein diameters were associated with higher cumulative silica dust exposure(P=0.036)after adjusting for younger age and larger spherical equivalent.CONCLUSION:The retinal vessels diameters and retinal nerve fiber layer thickness are significantly thicker in long term of coal mining.The results of our study indicate that underground working environment may lead to retinal vessel dilation and inflammation.Thus,ocular examination might be needed within coal miners in order to monitor the occupational eye health as well as the incidence and progression of eye diseases.