Comparison of MERV 16 and HEPA filters for cab filtration of underground mining equipment.

Significant strides have been made in optimizing the design of filtration and pressurization systems used on the enclosed cabs of mobile mining equipment to reduce respirable dust and provide the best air quality to the equipment operators. Considering all of the advances made in this area, one aspect that still needed to be evaluated was a comparison of the efficiencies of the different filters used in these systems. As high-efficiency particulate arrestance (HEPA) filters provide the highest filtering efficiency, the general assumption would be that they would also provide the greatest level of protection to workers. Researchers for the U.S. National Institute for Occupational Safety and Health (NIOSH) speculated, based upon a previous laboratory study, that filters with minimum efficiency reporting value, or MERV rating, of 16 may be a more appropriate choice than HEPA filters in most cases for the mining industry. A study was therefore performed comparing HEPA and MERV 16 filters on two kinds of underground limestone mining equipment, a roof bolter and a face drill, to evaluate this theory. Testing showed that, at the 95-percent confidence level, there was no statistical difference between the efficiencies of the two types of filters on the two kinds of mining equipment. As the MERV 16 filters were less restrictive, provided greater airflow and cab pressurization, cost less and required less-frequent replacement than the HEPA filters, the MERV 16 filters were concluded to be the optimal choice for both the roof bolter and the face drill in this comparative-analysis case study. Another key finding of this study is the substantial improvement in the effectiveness of filtration and pressurization systems when using a final filter design.

Air cleaning performance of a new environmentally controlled primary crusher operator booth.

The National Institute for Occupational Safety and Health (NIOSH) cooperated with 3M Company in the design and testing of a new environmentally controlled primary crusher operator booth at the company's Wausau granite quarry near Wausau, WI. This quarry had an older crusher booth without a central heating, ventilation and air conditioning (HVAC) system, and without an air filtration and pressurization system. A new replacement operator booth was designed and installed by 3M based on design considerations from past NIOSH research on enclosed cab filtration systems. NIOSH conducted pre-testing of the old booth and post-testing of the new booth to assess the new filtration and pressurization system's effectiveness in controlling airborne dusts and particulates. The booth's dust and particulate control effectiveness is described by its protection factor, expressed as a ratio of the outside to inside concentrations measured during testing. Results indicate that the old booth provided negligible airborne respirable dust protection and low particulate protection from the outside environment. The newly installed booth provided average respirable dust protection factors from 2 to 25 over five shifts of dust sampling with occasional worker ingress and egress from the booth, allowing some unfiltered contaminants to enter the enclosure. Shorter-term particle count testing outside and inside the booth under near-steady-state conditions, with no workers entering or exiting the booth, resulted in protection factors from 35 to 127 on 0.3- to 1.0-µm respirable size particulates under various HVAC airflow operating conditions.

ACTH and alpha-melanotropin in central temperature control.

Adrenocorticotropin (ACTH) and alpha-melanotropin (alpha-MSH) occur in brain tissue known to be important to temperature control. These peptides cause hypothermia if they are injected centrally in sufficient doses, but they do not act on the central set point of temperature control. Instead they appear to inhibit central pathways for heat conservation and production. In addition to their hypothermic capability, these peptides are antipyretic when given centrally in doses that have no effect on normal body temperature. ACTH has previously been associated with fever reduction in both clinical and experimental studies, and it may be that endogenous central ACTH is important for limitation of maximal fever. The hypothermic and antipyretic effects of ACTH do not depend on stimulation of the adrenal cortex because they are also observed in adrenalectomized rabbits. Nor is the antipyretic effect limited to the rabbit inasmuch as a comparable effect has been demonstrated in the squirrel monkey. The two peptides may be involved in central mediation of normal thermoregulation and fever, perhaps limiting the febrile response and other rises in body temperature by acting as neurotransmitters or neuromodulators in central thermoregulatory pathways.

The effect of fever on central alpha-MSH concentrations in the rabbit.

The recent demonstration of the ability of centrally administered alpha-MSH to reduce pyrogen-induced fever in rabbits suggested a role for the peptide in central temperature control. Using a sensitive radioimmunoassay we have established the presence of immunoreactive alpha-MSH (ir alpha-MSH) in discrete CNS sites of the rabbit and have demonstrated a distribution of this activity similar to that seen in other species. Pyrogen-induced fever did not alter concentrations of ir alpha-MSH in tissue extracted from the paraventricular region of the hypothalamus, median eminence, midbrain central grey, preoptic/anterior hypothalamic region, pineal or pituitary. A decrease in arcuate nucleus ir alpha-MSH content was seen in febrile animals, although this change was not statistically significant. Significantly higher levels of ir alpha-MSH were detected in septal extracts of febrile rabbits (0.81/+-0.10 pg/micrograms protein, n=9) than in extracts from afebrile controls (0.54/+-0.04, n=17). This finding suggests the septum to be the central site of action of alpha-MSH to inhibit fever and further implies a modulatory role of the peptide in the central control of thermoregulation.

Central and peripheral injections of ACTH (1-24) reduce fever in adrenalectomized rabbits.

Central administration of ACTH (1-24) reduces fever in normal rabbits in doses that have no effect on afebrile body temperature. Previous experimental and clinical reports indicate that peripheral administration of both ACTH and corticosteroids reduces fever, and since central injection of corticosteroids can also lower fever it might be that the antipyretic effect of intracerebroventricular (ICV) ACTH (1-24) is due to adrenal stimulation. To learn whether this endogenous central peptide can produce antipyresis independently, ACTH (1-24) was injected ICV in bilaterally adrenalectomized (ADX) rabbits made febrile by IV injections of leukocytic pyrogen (LP). ACTH (250 ng) given ICV reduced fever in these animals and had a slight hypothermic effect when given to the same rabbits when they were afebrile. Doses of 25-75 ng reduced fever without influencing normal body temperature. Intravenous injections of ACTH (2.5 micrograms) also lowered fever caused by IV LP in ADX rabbits. The present findings raise the possibility that release of endogenous central ACTH, and perhaps entry into the brain of circulating ACTH, the release of which is known to increase in fever, limits the magnitude of the febrile response by influencing central temperature controls.

Insulin-induced renin release: blockade by indomethacin in the rat.

1. Since prostaglandins appear to mediate adrenergically stimulated renin release, the effect of indomethacin was examined on insulin-induced renin and catecholamine release in conscious rats. Insulin (10 units/kg subcutaneously) increased plasma renin activity from 2.8 +/- 0.5 to 9.0 +/- 1.1 pmol h-1 ml-1 (P less than 0.001) while also increasing plasma adrenaline, noradrenaline and the urinary excretion of prostaglandin E2 and F2 alpha. Plasma potassium and glucose were reduced by 16 and 54% respectively. 2. Indomethacin (14 mumol/kg subcutaneously) reduced the urinary excretion of prostaglandin E2 and F2 alpha by 67 and 54% respectively, without altering the other parameters. 3. Indomethacin inhibited insulin-induced renin release by 67% (P less than 0.02) and blocked the insulin-induced increases in urinary prostaglandin E2 and F2 alpha. The insulin-induced changes in plasma catecholamines, potassium and glucose were unaltered by indomethacin. 4. These findings suggest that renal prostaglandins mediate this form of adrenergically stimulated renin release by acting at a side distal to the beta-adrenoreceptor.