Investigation of induced recirculation during planned ventilation system maintenance.

The Office of Mine Safety and Health Research (OMSHR) investigated ways to increase mine airflow to underground metal/nonmetal (M/NM) mine working areas to improve miners' health and safety. One of those areas is controlled recirculation. Because the quantity of mine air often cannot be increased, reusing part of the ventilating air can be an effective alternative, if implemented properly, until the capacity of the present system is improved. The additional airflow can be used to provide effective dilution of contaminants and higher flow velocities in the underground mine environment. Most applications of controlled recirculation involve taking a portion of the return air and passing it back into the intake to increase the air volume delivered to the desired work areas. OMSHR investigated a Nevada gold mine where shaft rehabilitation was in progress and one of the two main fans was shut down to allow reduced air velocity for safe shaft work. Underground booster fan operating pressures were kept constant to maintain airflow to work areas, inducing controlled recirculation in one work zone. Investigation into system behavior and the effects of recirculation on the working area during times of reduced primary ventilation system airflow would provide additional information on implementation of controlled recirculation into the system and how these events affect M/NM ventilation systems. The National Institute for Occupational Safety and Health monitored the ventilation district when both main fans were operating and another scenario with one of the units turned off for maintenance. Airflow and contaminants were measured to determine the exposure effects of induced recirculation on miner health. Surveys showed that 19% controlled recirculation created no change in the overall district airflow distribution and a small reduction in district fresh air intake. Total dust levels increased only modestly and respirable dust levels were also low. Diesel particulate matter (DPM) levels showed a high increase in district intake mass flow, but minor increases in exposure levels related to the recirculation percentage. Utilization of DPM mass flow rates allows input into ventilation modeling programs to better understand and plan for ventilation changes and district recirculation effects on miners' health.

Effect of thimerosal and other sulfhydryl reagents on calcium permeability in thymus lymphocytes.

We have studied the effects of thimerosal, a mercurial compound extensively used as a preservative, as well as other sulfhydryl reagents (e.g. p-hydroxymercurybenzoate, hydrogen peroxide, bromophenacyl bromide, and mercuric chloride) on Ca2+ homeostasis and the redox status of sulfhydryl groups in thymus lymphocytes. They all induced an increase in [Ca2+]i which was blocked with dithiothreitol, suggesting that they act via the oxidation or blockade of sulfhydryl groups. [Ca2+]i increase could be directly related to the effect of the different reagents on cellular protein sulfhydryl content. Experiments with ethidium bromide indicate that the observed rise in [Ca2+]i was not due to a non-specific increase in membrane permeability. Thimerosal differs from the other agents studied in its oxidative properties, which is probably linked to the production of a potent reductor molecule, thiosalicylic acid, which may modulate its oxidative capacity.

Calcium release induced by inositol 1,4,5-trisphosphate in thymocyte microsomes. Inhibition by barium and strontium.

The properties of calcium transport in microsomes and the effect of inositol 1,4,5-trisphosphate (IP3) on accumulated calcium were studied in rat thymocytes. Active calcium transport shows an apparent affinity constant for calcium of 0.2 +/- 0.01 microM and a maximal velocity of 2.3 +/- 0.6 nmol/mg/30 min (mean +/- SD). IP3 was able to induce release of calcium only in the absence of oxalate. At 6 microM ambient free calcium, half-maximal effect of IP3 was attained at 2 microM and maximal calcium release was produced by IP3 concentrations over 5 microM. Barium and strontium did not modify calcium uptake by microsomes but markedly inhibited the action of IP3.